Edmunds dealer partner, Bayway Leasing, is now offering transparent lease deals via these forums. Click here to see the latest vehicles!

Chevy S10 - GMC S15 and Sonoma Engine and Underhood Problems



  • sunfiregt34sunfiregt34 Member Posts: 2
    I have a 2002 gmc sonoma with a 2.2 with 90k miles on it whenever my truck starts the rpm is kinda jumping around and whenever I go foward it hestates to shift to second gear but after that the truck runs good any ideas?

  • mickeymouse2mickeymouse2 Member Posts: 161
    p0303 does indicate that the PCM sees a misfire on #3.

    The most common problem is ignition arcing because of no dialectric greese on the sparkplug boot. Bad spark plug, fualty injector for #3, engine compression problem on #3, ect. You got to do some troubleshooting and hope its one of the easy problems. If your due for a tune up, do one and see.
  • tomf8tomf8 Member Posts: 6
    i have 99 s10 2.2ltr. eng the engine does not come up temp. and also no heat at heater in cab. i have changed thermostate 2 times and will not come up temp, runs about 130degrees. thanks for your help.
  • mickeymouse2mickeymouse2 Member Posts: 161
    If you have an electric fan for the radiator, I would suspect that it is coming on to early and too long, probably a bad temp sensor for the fan, or if you have AC the radiator fan switch for that.

    If you have a manual driven fan. I would first want to know if any modifications have been made to the engine, or the AC condensor removed or something. Has an add on transmission cooler been added?

    If your positive that the engine is running cold itself and not a problem with the guage and a heater control valve not letting hot coolant enter the heater core. Please post more info about your vehicle.

    Electric fan or manual? If electric fan, how long until it comes on after start up?
    Automatic or manual transmission?
    Modifications or add ons?
    How are you determining engine temp?
    Factory AC, or after makrket or none?
  • flashman3000flashman3000 Member Posts: 24
    Thanks for the info. Can this problem still exist without a code coming up? I have an Auto Xray 1500 scanner and had the dealer scan it w/o any results as well. All tests on the Emmissions system comes back normal. They ruled out the injectors during the last visit. How common is the faulty fuel preasure issue with this mode? Could this be a vacum, or faulty compression issue? What should the mileage be on this type of truck....roughly? Lot's of experience with the v-8s not so much with the 4.3L. Thanks again for all of your help I'll get to checking these out this weekend just to be sure.
  • flashman3000flashman3000 Member Posts: 24
    Not yet...changed the plugs and found one gapped at .065. Changed them out and the P0300 "random missfire" code went off. Still have the gas issue though the idle stumble seems to be gone. Still seems to be missing at normal speeds but I can't tell as the truck rides so freaking stiff in the first place. So far i've logged 135 miles on a half tank....can't be running right but it pulls hard under a load and feels strong through the gears.
    From what I can tell from other postings is that it can be either plugged cat, bad crank sensor, poor fuel preasure, fouled EGR, vacum leak, or a new truck....i just don't know how common any of these issues are in this model to know where to really start. Guess I have to pick one and start ruling them out one by one. Any ideas?
  • flashman3000flashman3000 Member Posts: 24
    About 82K. The truck was purchased from a 68 year old woman who only drove in the texas hillcountry. Trucks in good shape except for the gas economy. I'm going to check the crank sensor and fuel preasure this weekend to rule them out. Sprayed carb cleaner all around block, intake manifold...side, back to front. No change in rpm or evidence of any leaks there. Will be using some soapy water spray on all the hoses this weekend to rule that out as well.
  • mickeymouse2mickeymouse2 Member Posts: 161
    Can this problem still exist without a code coming up? Yes. PCM's are not all knowing. They know only what the sensors send them, and sometimes sensor info is wrong.

    How common is the faulty fuel preasure issue? Rare but I have had fuel pumps briefly and intermitantly loose pressure causing random misfires. I actually had to see the failure while it happened. I even had a fuel pressure regulator fail intermitantly dropping the pressure.

    Could this be a vacum, or faulty compression issue? Not a vacum issue, vacum leaks cause a lean miss and your o2 sensor would have caught that and run the engine ritch. Compression can cause misfires but I doubt that is your problem. Compression problems are rarely intermitant and are usally isolated by cyclinder and can be identified as a specific problem with one or more cyclinders.

    No doubt, you got a tuffy, intermitant stuff always is. You basically have to keep trouble shooting until you find it. An intermitant coil failure or not enough output of kv spark could be it also. All the PCM knows, is that every once in a while the crank sensor is picking up a weird vibration and interpreting it as missfires. Hell, one car I finally found it, it was a loose mounting bolt for the crank sensor.

    Heres a suggestion. Start with one system and eliminate it as the problem. Test it until the po300 comes back and if what ever you were testing checks out ok, move on to the next thing. Clear codes and test something else.
  • flashman3000flashman3000 Member Posts: 24
    You are the mandango! I'll get to checking it out this weekend and let you know how it goes. Thanks again for all your help. Most of my gear head friends either moved out of state or are dead. Yikes!!!
  • tomf8tomf8 Member Posts: 6
    it does not have a/c temp on guage comes up to just above a 100 just a guess on actual temp. eater problem arose before clold eng. temp. problem. there ave been modifications or changes to truck.it has 2.2 enh. auto trans.no a/c. it takes a long time to get above 100 degrees(many miles5to10). heater is not controlled by heater control valve per-say . it has hot water a the time it is controlled by doors in heater box in cab.
  • tomf8tomf8 Member Posts: 6
    a couple correction to previous post. there has been no mods. or changes to the truck. the heater core get hot water all the time, heat is controlled buy door in heater box.
  • toneygtoneyg Member Posts: 19
    All the door does is open to let the fan blow through the heater core. there is also a vacume actuated control valve, which is controlled by your tempeture slide on your controls. The reason it might be running too cool is (a). no thermostat, or (b) thermostat is the wrong temp which should be either a 180 or 210 degree.
  • tomf8tomf8 Member Posts: 6
    thermostat is 195degree as per oem changed twice
  • mickeymouse2mickeymouse2 Member Posts: 161
    You still haven't stated what type of cooling fan you have. Most s10 use a manual driven fan off the water pump. Some have a fan clutch. The one's that have a fan clutch have one for a reason: A manual driven one would keep the vehicle too cold. If the clutch is stuck, it may be pulling too much air through the radiator fins all the time. If this is your type, with the engine off spin the fan. It should make a few revolutions before coming to a stop, no more than five. If it doen't even make one complete revolution, replace it.

    If you have a single or duel electric fan set up, check to see at what time the fan is coming on. A few models used a duel fan set up like on Honda's. One of the fans is controled by your AC being used.

    I don't remember who posted that your vehicle has no heater control valve but only a door. I really don't care. This isn't your problem, but your vehicle does have a heater control valve.

    You should be fine with a thermostat rated at 195, I would suggest not replacing it any more, this isn't your problem.

    If you need help in identifying the fan clutch, it is made of aluminum about 6.5 inches in diameter with very small fins on it. It is located on your fan, between your fan and water pump.
  • flashman3000flashman3000 Member Posts: 24
    So far I'v replaced the usual...plugs, wires, cap, rotor, fuel fitler, air filter, and just changed the crank position sensor this weekend. I test drove it a bit and ran it in 3rd gear at about 2500 rpm. The missfire or skip still seems to be there. I couldn't get on the highway due to too much traffic but will run it this weeek to see how it goes.

    If it's still misses and the mpg is still in the toilet I'm going to check the fuel preasure, EGR Valve and then maybe get to the CAT. Don't think its any of them as I believe a sensor light would have come on. Anyone got any other ideas? I could use the help.

  • tomf8tomf8 Member Posts: 6
    it has a clutch fan and seems to spin as per turning serveral revolutions before stopping when cold.
  • flashman3000flashman3000 Member Posts: 24
    Not sure if this is a fix or not but i found this link on another site, same symptoms almost to a tee and same fixes where done without any luck from these guys. I have the Sequential Fuel Injection system on my 99 Sonoma 8th digit on the vin code X=SFI, W=Central Port Fuel Injection (CPI), Z= Throttle Body Injection (TBI).
    Not sure if this lead holds true for the SFI system. The post below is copied from
    http://www.s10forum.com/forum/f107/if-your-having-a-mystery-running-like-crap-pr- oblem-268309/

    The trouble-prone Sequential Central Port Injector (SCPI) fuel system was installed on GM's popular SUVs, pickup trucks and vans with 4.3L, 5.0L, and 5.7 liter engines. The defective fuel injection systems can cause GM owners to experience a "Service Engine Soon" light, misfires, rough idle, and hard start problems due to deposit build-up that cause poppet valves to stick and fail

    CHECK THIS OUT here is the link to it http://www.arb.ca.gov/newsrel/nr021103.htm

    took a lot of diggin there is a tsb for it the number is 99066g most gm dealers will tell you there isnt one. this is the link that shows you the tsb that i finally got a dealership to say there was after going to 4 of them.
  • mickeymouse2mickeymouse2 Member Posts: 161
    Unlikely its the Cat. When they go and plug up you have a lack of power until the engine just wont run due to excessive back pressure exceeding 3psi. EGR will cause a lean condition and cause a running problem. Its possible that its the egr, but that code po300 is usually a fuel pressure issue, or coil issue. I still think a poor output of kv spark from the coil or a fuel pressure problem is your best thing to check.
  • flashman3000flashman3000 Member Posts: 24
    Changed the crank position sensor with no changes...I found this on another site though all research has found that GM is keeping it quiet and only honors it on CA vehicles. I think I'm going to purchase the MFI set up and swap it out myself for about $250.00

    As I read this I believe it applies to my VIN...8TH digit is X=CSEFI any thoughts? I posted the GM Policy Letter below..maybe it will help others save some time and money.


    CERTAIN 1996, 1997, 1998, 1999, 2000, 2001, 2002 S/T, M/L, C/K, G,
    (RPO L35 - VIN CODE W OR RPO LF6 - VIN CODE X), 5.0L (RPO L30

    This bulletin is being revised to add the 2002 and 2003 model years to the SCPI Special Policy on certain S/T, M/L, C/K, G, P and W4/NPR truck models. Please discard Special Policy Bulletin Number 99066E, dated February, 2003.


    Some customers of 1996, 1997, 1998, 1999, 2000, 2001, 2002 model year S/T, M/L, C/K, G, P, W4/NPR trucks and 2003 NPR trucks, that are registered in California, equipped with 4.3L (RPO L35 and VIN Code W, or RPO LF6 and VIN Code X), 5.0L (RPO L30 and VIN Code M) or 5.7L (RPO L31 and VIN Code R) engine, and California emissions (RPO YF5), may experience a "Service Engine Soon" light, misfire, rough idle or hard start due to a deposit build-up on the Sequential Central Port Fuel Injector (SCPI) poppet valve(s). The deposit build-up may cause injector poppets to stick closed. Certain fuels have been found to interact with the SCPI system to cause the deposits.


    This special policy covers the SCPI failure condition described above for a period of ten (10) years or 200,000 miles, whichever occurs first, from the date the vehicle was originally placed in service, regardless of ownership.

    The repairs will be made at no charge to the owner. This special policy applies ONLY to repairs requiring SCPI system servicing, injector cleaning and/or MFI assembly replacement of the SCPI system. The customer should not be charged for performing a system check when it is determined that the SCPI system is not the cause of a customer complaint (labor operation T5532 is provided to submit claims for such system checks). Any additional necessary diagnosis and repairs that are not related to the SCPI condition are not covered by this special policy. The customer should be informed that any further service that is not covered by new vehicle warranty will not be covered by this policy.


    Involved are certain 1996,1997,1998,1999, 2000, 2001, 2002 S/T, M/L, C/K, G, P, W4/NPR and 2003 NPR model vehicles, registered in California, equipped with 4.3L (RPO L35 - VIN Code W, or RPO LF6 - VIN Code X),5.0L (RPO L30 - VIN Code M) or 5.7L (RPO L31 - VIN Code R) engine; and California emissions (RPO YF5). This Special Policy covers all vehicles within these model years, with these engine and emissions RPO's.


    Parts required to complete this special policy are to be obtained from General Motors Service Parts Operations (GMSPO). Please refer to your "involved vehicles listing" prior to ordering parts. Normal orders should be placed on a DRO Daily Replenishment Order. In an emergency, parts should be ordered on a CSO = Customer Special Order.

    IMPORTANT :Isuzu Parts Ordering: In order to comply with the 10-digit Isuzu part numbering system, Isuzu dealers must add an "8" to the beginning and a "0" to the end of the listed 8-digit part numbers when ordering parts through AIPDN.


    Customers will be notified of this special policy on their vehicles by General Motors (see copy of typical customer letter included with this bulletin - actual divisional letter may vary slightly).


    System Check: Use strategy-based diagnoses listed in the front of the Driveability and Emissionssection of the service manual. If the SCPI system is operating properly, inform the customer that the vehicle does not have the condition listed in the owner letter. If poor driveability conditions persist, inform the customer that any further diagnosis and repairs will be at their expense if the vehicle is outside the parameters of the new vehicle warranty.

    SCPI Injector Cleaning Procedure: If diagnosis leads to sticking poppet nozzles, use the service procedure from Service Bulletin 00-06-04-003B to clean the SCPI poppet nozzles. Please note that the service bulletin term for SCPI is Central Sequential Fuel Injection (CSFI), but is referring to the same fuel system assembly. If the poppet nozzles have previously been cleaned and the sticking condition has reoccurred, refer to the correction paragraph below.

    SCPI Fuel Tank Fill Pipe Assembly for 1997-99 M/L Van and 1999 - some 2000 C/K Truck: with 4.3L, 5.0L, 5.7L engines and built prior to listed VIN/Production dates on Service Bulletin 00-06-04-018: If diagnosis leads to sticking poppet nozzles on these models, use the service procedure from Service Bulletin 00-06-04-018 to replace the fuel tank fill pipe assembly, if this procedure has not been performed previously. Previous service procedure can be verified by checking GMVIS for Labor Operation L1065 on "M/L" trucks with replacement part number 15050573; or Labor Operation L1065 on "C/K" trucks with replacement part numbers 15747585 or 15747588.

    Correction: If, after cleaning the SCPI poppet nozzles, the normal service manual diagnosis still indicates that the SCPI is the cause of the customer complaint, or if the injectors have previously been cleaned and the vehicle has again experienced sticking poppet nozzles, refer to Service Bulletin 00-06-04-003B and replace the SCPI fuel assembly with the MFI fuel assembly. Please note that the service bulletin term for SCPI is Central Sequential Fuel Injection (CSFI), but is referring to the same fuel system assembly.


    For vehicles repaired under this special policy, submit a claim with the information indicated.


    Customer requests for reimbursement are for any previously paid repairs to, or replacement of, the Sequential Central Port Fuel Injection (SCPI) system. Repairs must have occurred within 10 years of the date the vehicle was originally placed in service, or 200,000 miles, whichever occurs first. The requests are to be submitted within two (2) years of the date on which the repair was paid or within two (2) years of the date of this Special Policy Bulletin, whichever is greater.

    When a customer requests reimbursement, they must provide the following:

    -Proof of ownership at time of repair.

    -Original paid receipt confirming the amount of unreimbursed repair
  • mickeymouse2mickeymouse2 Member Posts: 161
    This isn't making sense. Lets back up a bit. Have you always had this vehicle and is this problem new? Or; Did you just buy this vehicle? Is there a chance that there is a double core radiator in it by mistake? You also didn't answer how you measured engine temp at 130. Did you use a thermometer or your guage? Are you sure the engine is not getting warm and you just have a problem with your heater?
  • flashman3000flashman3000 Member Posts: 24
    Maybe your right, I'm going backwards and forwards on this deal. I'll check the fuel preasure first and swap out the coil first since both are cheaper guesses than replacing the injector unit. Intresting bit of information though. Just thought I would pass on what I came across. I'll post more as I replace em. Thanks for getting back so fast.
  • mickeymouse2mickeymouse2 Member Posts: 161
    I saw that lengthy post on the faulty GM injectors. Let me explain something. When an internal poppet malfunctions on a fuel injector, it is that one fuel injector that is bad. That will set a specific code for what ever cylinder that injector feeds fuel to. The PCM will not know why there is a specific misfire on a cylinder due to the bad injector, it just knows that something is wrong with that cylinder. GM injectors rarely go bad. In 30 years I have come across 2 GM vehicles that had a faulty injector causing a miss. Remember, you have random misfires and no other codes to help explain it. The PCM does not know fuel pressure, amount of KV spark coming from the coil, or if the 12 volt power to the coil is being interrupted, or failing due to a power issue from your ignition switch. Heres what you can do. Borrow a fuel pressure gauge from Autozone and test drive your vehicle so you can see the gauge. You may have to leave the hood slightly prop open and strap it, but you need to start eliminating things as possible causes. Autozone also has a kv tester or measurer that plugs in inline. About $3.00. Cheep! Unscrew the gap to 30 KV and make sure you have at least that much between your coil wire and cap. I think the spec on your truck is 40KV but test at 30kv first. Also, on your coil look for white fateige areas if it is old.
  • tomf8tomf8 Member Posts: 6
    i did buy this truck new in 99 it has never had radiator changed . this is a new problem the heater problem came first. i changed thermostate hopping to fix heater problem but it didn't. i'm guessing actual temp . it runs about 1to 2 small lines above 100 according to guage. if you turn off for 5 min. then restart guage will read halfway between 100&210 then will go back to where it was before shutting off. i had same problem as flashman3000 code 303 misfire #3 end up being spark plug wire. i'm going to back flush heater core to try to solve heater problem. hopeing not to have to change heater the heater core. that will be a pain in the butt.
  • mickeymouse2mickeymouse2 Member Posts: 161
    Very doubtful its your heater core. Most likely it is a problem with the heater control valve. You can't trust the position read out of your temp gauge. There are a number of things that can effect that; bad sending unit, wrong coolant mixture, incorrect voltage ect. If the upper radiator hose get a little hot after driving, the engine is getting warm enough to opperate your heater. Good luck
  • toneygtoneyg Member Posts: 19
    You need to locate you heater control valve on the inlet side of your heater core. It should be attached to the engine block on the passenger side, it also has a vacume line on it. This valve is stuck either half way open or closed position. Check the vacume first, if it has a strong vacume, the line is OK. Suggest you replace the valve unit, and put a hotter thermostat in it also.
  • flashman3000flashman3000 Member Posts: 24
    It all sounds logical and makes a lot more sense looking at it that way. Actually, it's all good news considering the other alternative. I'll get after it this weekend and get back to you. I'm a gear head at heart and love to turn a wrench with the best of them. However, I don't enjoy turning wrenches just for the sake of chasing my tail on a gig like this. Thanks for the insight and guidance...it's truly appricieated more than I can say.
  • xtmfanatic4xtmfanatic4 Member Posts: 7
    well tom, i have a 97 s-10 with the 4.3. ive never changed the radiator, but i know it has been flushed once. uhh im not sure if its actual temp or what but my gauge will read almost the exact same. But im not sure if it will read much different after 5 minutes or so. I'll have to look into that one. other that that im almost sure that its pretty close to the actual temp that my motor will run. But im not completly sure. ya good luck on the heater core man, they are a pain. Try to find someone who has flushed their core and see if you can find out what their results were.
  • flashman3000flashman3000 Member Posts: 24
    I swapped out the coil last night and it obviously is running a bit better. Took it for a small test drive on the freeway and it still seemed to be missing at 60-75mph though I couldn't be sure. Will drive it the rest of the week and see if it comes back. Seems to be the way of this gremlin as I swap components out it seems to get better then gradually comes back leading to a SES light P0300 code.

    Checked on the fuel guage at Autozone last night. Didn't have one for my model truck's shrader valve. Will have to look around. I'll post back with an update this weekend after I confirmed the fuel preasure. It should be around 55psi-60psi right?
  • mickeymouse2mickeymouse2 Member Posts: 161
    Yes the fuel pressure spec is 55-60 psi depending whom you ask. There are slightly different specs listed but it is always over 55psi. You may hear some specs like 55-61 ect. As long as fuel pressure is around that and doesn't drop below 55psi at any time, there isn't a problem with the regulator, pump or fuel delivery.

    I remember you posted that you did a major tune up, thats good that is out of the equation. I hope you remembered to lube the spark plug boots with tune up grease or the proper name dielectric grease? The wires you bought come prelubed but there is never enough in them.

    I think your the one that posted you have a scan tool. Thats good. I'm not familure with your model, only snap on and fluke. Does you scan tool have a data read out so you can monitor incoming data to the PCM?
  • flashman3000flashman3000 Member Posts: 24
    Nope, I don't think so. I probably should have bellied up for the better model. This one ran about $150.00 bucks from AutoXray.com. It comes with it's own code library, emmissions system check, code reset, and can download to your pc for GM, Chevy, Ford and Chrysler 98 and above models but that's about it. Never really thought I would have to to onboard/running diaogostics.
  • flashman3000flashman3000 Member Posts: 24
    No luck finding a fuel preasure tester for the 99 Sonoma at the local autozones and such. They have plenty in stock up to 98 GM. I'm guessing there is a difference in the connections at the rail or something? Where does it connect to by the way? Any thoughts on finding one? If not I may just through it in the shop and have them take care of the fuel and cylinder compression tests to get them out of the way.
  • mickeymouse2mickeymouse2 Member Posts: 161
    I can't believe these idiots at autozone don't have a guage. There should be a shradder valve on the fuel rail that you screw the tester too. There is usually a black or blue dust cap that you unscrew first. If you cant get the right tool, use a tire valve core removal tool to temporarely remove the shradder valve. It comes out unscrews just like the little valve in bike tires, but those little valves are not the same at all, but the tool will work fine on both. Then slip a hose over that threaded part and clamp it. Then attach a guage to the hose. Don't loose that little shradder valve. If you do, your only option is junk yard or buying a new fuel rail. GM, FORD, Chrysler all of the dealers don't sell that little valve sepperately, so be very careful with it. If you have a Harbor Freight Tools near you they sell a kit that will work for about $10.00 for testing fuel pressure. That tool for removing the little valve is in the tire section of Autozon with the tire plugs and stuff.
  • flashman3000flashman3000 Member Posts: 24
    Sounds like a plan....I'm sure I can get'er done today. I'll post back when I'm through...have to change the brakes on the grocery getter first
  • flashman3000flashman3000 Member Posts: 24
    Okay so here is the rub.

    Book Says: Key On Engine off 55psi-61psi at normal Operating Temp
    It Reads: 52-54psi at first then slowly climbs to about 58psi in about 30 seconds and holds.

    Book Says: Engine On at idle it should drop 3psi-10psi
    It Reads: Quivers really bad...doesnt' hold between 52psi-54psi but does drop the 3-10psi as the books states.

    Running at 65mph-75mph it reads about 54psi-58psi but quivers so widliy during the run it's hard to tell. Only holds constant under a modertat/solid load of acceleration then readsbetween 56psi -58psi. It will spike occassionaly just above 60psi one time only and then settle back down to around 56-58psi until I let my foot off.

    When I let my foot off the gas it drops to 50psi-52psi and quivers between the two so that I can't really read the gauge for exact preasure. Various readings between 52-56psi when traveling around the back streets under 50mph ( the gauge will be fluttering back and forth between that range unless I put my foot into it a bit and give it a smooth acceleration load.

    Should the needle be realtively solid and move smoothly with the increase or decrease in preasure? It appears that the preasures are within the book specs just not sure if the readings should be steady throughout the diagnoses and not fluttering back and forth. Any thoughts?
  • blackdayzblackdayz Member Posts: 16
    I am working on a friends 1997 s10 2.2L auto.
    It was running rough so i changed plugs and was getting ready to change wires and oil.I let the truck run a little after changing plugs to see if it ran better. a stong smell of gas was very noticeable and when i checked the oil it was overfull and smelled badley of gas.Anyone have any ideas on what could be wrong?
  • mickeymouse2mickeymouse2 Member Posts: 161
    The 2 most likely causes are;

    Fuel injecter stuck open flooding a cylinder where as the fuel slips by the rings and enters oil pan.

    Rings are bad in a cylinder and normal fuel delivery is slipping past the rings.

    First test to see if fuel pressure drops after initial prim, key on engine off. If pressure is slowly or quickly dropping, suspect fuel injecter, use a fuel pressure guage!! Next close off return fuel line to verify regulator isn't allowing pressure to bleed off excessively. Repeat first test. If pressure is dropping still, remove all spark plugs and see what cylinder is receiving constant fuel. You will have to look at each cylinder with the intake valve open, so some cranking will be needed to turn the engine. If one fuel injecter is bad, play it safe and replace all of them.

    I do not suspect a compression problem, and a compression test would not be accurate if the rings are reseated due to constant fuel entering the cylinder. If this testing reveals no excess fuel, run a compression test to find a suspected cylinder problem. Reinstall spark plugs and disconect the injecter plug for that cylinder that is suspect, and run the engine to see if fuel gets into the oil again. The running problem and fuel in the oil are most likely due to a fuel injecter stuck open. The raw fuel has probably effected compression on that cylinder. After the fix, and the engine is run for a while, the compression should come back. Good luck
  • flashman3000flashman3000 Member Posts: 24
    I changed out the coil with no change in conditions. Checked the fuel preasure with ignition on/engine off at normal temp it starts at about 52-54psi then slowly climbs to 58psi and holds in about 30 seconds.

    At 70mph during steady acceleration it reads 58-60psi until I let off then drops to 52-54psi until I put my foot into it a bit and speed up then returns to 58-60psi. I lubed the boots extra when I put them on so I think that's out of the way.

    Could and EGR and PCV valve or combo failure cause this missfire? Could an intake leak on the prone vortec series cause the same conditions? The code has not come back on since I swapped out the coil but it's still seems to be missing a bit on the highway and I'm still getting 275 miles per tank. Any thoughts? ....running out of options on this pig.
  • mickeymouse2mickeymouse2 Member Posts: 161
    Sounds like fuel pressure from the pump is not an issue. Did I understand you correctly, that after 30 seconds the pressure is bleeding off and dropping down below spec with the key still on? If so, you may have a leaking injecter and that is your problem. If it is bleeding off; How fast does it bleed off? A leaky injecter can cause random misfires due to too much fuel constantly dripping fuel into the manifold. If you need to know how to check for that, repost.

    Let me explain about the EGR. Even if it were sticking open at high speed, this is when they open anyway. EGR malfunctions cause idle and low speed running problems by causing a lean condition.
  • flashman3000flashman3000 Member Posts: 24
    Thanks for the EGR info...fundamentaly understand the recovery system at work just not all the things that could be associated so that makes more sense now.

    The fuel preasure with the key on/engine off and at normal operating temp...guages at 52-54psi first and then slowly climbs to 56psi-58-psi and holds. This takes about 30 seconds.

    Starting the engine the preasure drops to around 52-54psi at idle. The needle will be twithcing back and forth between the two and not holding on one or the other during this process. The book says this model should drop 3psi-10psi during this process as well so it seems to be in spec?

    During operation under acceleration it's between 58psi-60psi. When i let my foot off and decelerate the gauge reads 52psi-54psi.

    Correct me if I'm wrong but if these specs are right then my options are

    1. Compression test to rule out a valve train issue
    2. Vaccum leak test: intake manifold, lines...
    3. PCV Valve...maybe don't really know but it's one of the only things I haven't swapped yet.
    4. Distributor change out????
    5. Take it out to the field and bash it in with the faulty shredder from my office. Just don't know man.

    Thanks for all your past guidance and any ideas you can offer.
  • mickeymouse2mickeymouse2 Member Posts: 161
    Its not going to be a compression problem, your PCM would find a miss on a certain cylinder, not random. Your fuel pressure spec is barely there at idle. It should be no less than 55psi at any time. But your problem is not at idle, but high speed. Hmmm, I think you have ruled out fuel pressure. You can replace your PCV there only about $3.00, thats not the issue though.

    The shaft in your distributer might be worn causing a wobble at higher speeds and random misfires. Take the cap off and check to see if there is any side to side motion on the shaft at various positions. This problem would have showed up during a scope analysis when you had it at the dealer, if they did one. I have to tell ya, that without a scope, you sometimes have to remove the distributer and turn it with your hand to rule it out. It should turn freely out of the vehicle with no binding spots, or areas during the turn that are more difficult to keep turning it.
  • flashman3000flashman3000 Member Posts: 24
    I've been avoiding that diagnoses for sometime now though addressing everything else still was the right thing to do. I've thought about just pulling it and replacing it with a hi performance distributor just in case the pick up coil in there was going/failed all together. I guess I'll try inspecting it and if needed see where the white rabbit leads. Thanks for your advice I'll post back after round 8. Yikes!
  • flashman3000flashman3000 Member Posts: 24
    Well I guess maybe that technical bulletin was rightl. It was the injector harness. Opened the the intake and there was a lot of fuel down in the wells. Changed out the harness and will road test it today. I'll post back later this evening to let everyone know how it went.
  • flashman3000flashman3000 Member Posts: 24
    Well I took off the intake and fuel was everywhere. I swapped out my injector harness and that seems to have done the trick. Gas mileage is up to 18.5mpg in the city from 15mpg. I have a bit more tweaking to do to get the mileage back up in the low 20's where I think it should be but so far so good. Thanks for all of your help and advice.

  • blackdayzblackdayz Member Posts: 16
    I have been working on this truck and cant seem to find out whats wrong.the truck has less than 70k on it.
    codes came up... idle air controle valve and random missfire.
    It idles very rough with a strong smell of gas also very sluggish at low rpm.cuts out at higher rpm when just reving.I replaced coils,plugs,fuel fliter,fuel injector on #2 cyl.IACV,wires,air fliter, checked fuel reg,checked all hoses,replaced battery term. checked timming still same problem.When I changed the oil it had some gas in it.Im thinking either cat or comp...........please any suggestions.
  • pre_elitepre_elite Member Posts: 7
    "The Elusive Misfire" This truck is killin me. First had a cylinder 2 misfire constantly. In all have replaced plugs, wires, coils, crank sensor, #1,and 2 injectors, checked for vacume leaks, checked compression static and running, all within specs. Has cold air intake and exhaust. Have no cat on it. 150,000 miles. Only thing I have not done yet is check fuel pressure and regulator. Which I am going to do soon. Basicly had a misfire on cylinder #2 and changed plugs and wires and coils and crank sensor. Lost even more miles/tank of gas. Down to about 230 or so. Used to be around 360 or so. Seems like every time I work on this truck it gets worse. Changed injectors 1 and 2, problem swiched to random misfire instead of steady #2 and intermitten cylinder 1 misfire. Have checked egr and even blocked it off to see if that would eliminate the problem which it did not. Also when the truck is cold the misfire is not present untill about 2 to 3 min's of run time then has a steady mis at idle and all through driving speeds. Holding steady at about 1500 to 2000 rpm mis is obvious. So far everything I have checked comes up nominal. But like I said every time I work on this truck it sure seems to get worse. Obviously the exhaust smells rich! No codes either. If when I check fuel pressure and it happens to come up nominal, really going to be stumped. Any advice would be appreicated. Thanx
  • pre_elitepre_elite Member Posts: 7
    Also forgot to mention, have changed fuel filter and it was definatly restricted. Havent checked timing. Does have a bit of a chatter once the oil warms up, read in here somewhere about the timing chain tensioner going bad on these trucks. Possibly out of time. The truck used to give a lean sneeze once in a while when you would stomp on the throttle but that has long passed. Doesnt have near the power it used to. Eventho it misses it doesnt seem to show under a load like an arcing plug wire would. The mis also seems to change once in a while. Rare but every once in a great while it will run pretty good.
  • acheys10acheys10 Member Posts: 1
    1.I have a 97 S10 V6 manual and when i shift into a higher gear i hear a churp or squeak sound. I have no idea what it is and have had problems with my tranny b4 (so is it just another one?)
    2. I am also loosing coolant without any spots showing up one the driveway. what could it be?
  • electechelectech Member Posts: 2

    I have a hose on my 91 chevy s10 with the 4.3L TBI enging that broke.

    It is connected to the rear of the intake manifold, it has a funny looking device that goes from hose to tubing. But the piece that broke is a threaded piece that threads into the manifold. I can get the piece out but what the heck do I order so that I get the piece that threads into the intake manifold. It is broken so no way to use it like it is. It corroded and just snapped.

    The hose has to be a heater hose and I see a hose called a Dorman / Heater Hose Assembly. Will this have the threaded piece, it is a special order so I can't go and look at one. Is this what I need?

    I do not see it listed anywhere in my Chiltons manual. Sure hope someone can help me!!!


  • flashman3000flashman3000 Member Posts: 24
    I agree...rule out fuel preasure but after normal checks also test it on the road as well to see what it's doing at driving speeds. I stretched mine through the back of the hood and strapped it to the drivers wiper.Mine was within specs but at the low end showing signs of needing replacement soon but it still wasn't my problem. If it's within specs you may want to consider swapping out the injector harness. Check the 8th digit on your VIN to see what kind of injection system you have. X should be a CSEFI, W should be a MFI or similar acronym.

    Problem I found with my 99 4.3..same code...same symptoms...same replacements....was the CSEFI harness and regulator are one component located under the intake. Had no way to really test the regulator so decided to swap it all out. My mpg went from 15-20. Also, I first had a vacum leak test with a "smoke machine" done just to re-verify my garage tactics where not off. No leaks so I went with the harness swap.

    I posted a technical bulletin from GMC only released in Cali on another site stating that it was determined that the CSEFI units where faulty from the get go.You may have to go back to early Jan 08 postings to see it on this site but it should still be there for more info. Not saying this is your problem...just what worked for me.

    I still have a small exhaust leak, haven't gotten to the cold air and cat back duel exhaust yet but I'm sure I can get it up 2-4 mpg afterwards. Also, if the above doesn't work, timing belt and distributor pick up may be faulty or reaching end of service life. I doubt it but it's just somthing to think about. Hope this helps.
  • flashman3000flashman3000 Member Posts: 24
    You may want to go to www.LMCtruck.com. Not an immediate fix but can call their technical support line, order a parts manual for your make and model...free. They make all of the OEM parts you can/can't get at the dealership.

    I've used them and their manuals since the early 80's to diagnose/order unkown parts. Their manuals have "exploded" views of most any component for your vehicle giving you a shot at finding out what the OEM called it.
Sign In or Register to comment.