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GMC Jimmy Misfiring, Backfiring, Spark Plugs

daytripper540daytripper540 Member Posts: 2
Our 1993 GMC Jimmy started building up carbon in the EGR Valve. We Seafoamed it, but that didn't seem to help. We later put a new gasket on the EGR that has a screen on it. That has seemed to fix the carbon problem.

As of right now, it keeps fouling spark plugs. It sounds like it has a huge cam in it, which I'm taking as it not running on all its cylinders. When I take the plugs out, they seem to have gas on them. Any idea on what's causing it and how to fix it?
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    lynderaelynderae Member Posts: 4
    First off let me say thank you for youre help with camshaft position sensor in distributor. I have also replaced the coil, the truck ran like a champ yesterday. Today however, I didnt get out of the driveway and it started misfiring. It is rainy today, but it was wet out yesterday. I cant figure this out, any help would be appreciated.
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    repairdogrepairdog Member Posts: 948
    Did you change the cap/rotor to rule them out?
    Crank sensor is under the front of the motor and they can act up without a code or the connector can get wet/dirty. Any SES light and codes?
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    frschevyfrschevy Member Posts: 2
    I have a 04 chevy blazer 6 cyl 4 wheel drive.
    I purchased in Jan 07. (39,000 miles)
    Its been back to the dealer 4 times for stalling.
    I'm just driving down the road and its shuts off.
    I still have power but the engine quits.
    so for all that has been done is (replaced)
    the distributer cap and roater,the coil and something attached to it. They can't figure it out. I don't get any
    check engine lites. Im pritty sure the problem is electrical,but who knows. Can anyone help this is driving me crazy.
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    repairdogrepairdog Member Posts: 948
    Running too rich so look at the CPI and nut kit (injection and hoses) under the upper intake. Posts on that and how to look at can be found by a search in the forum. Do you smell gas also? Hows the oil consumption - if high look at clogged PCV or worn valve seals - never stated the mileage. Then air filter should be clean also and vent to other valve cover attached and good.
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    daytripper540daytripper540 Member Posts: 2
    It has 175,000 miles on it. And yes, I do smell gas when I run it. I replaced all the spark plugs and it still seems like it is misfiring. Thanks for the information. I will look into it.
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    quickfoxquickfox Member Posts: 2
    How to change middle sparkplug on driver"s side of 1996 Jimmy with 4.3 V6- problem is steering shaft blocking acess
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    repairdogrepairdog Member Posts: 948
    2 ways used and 1 is short plug socket and open end wrench thru the wheel well or 2 is unbolt the steereing shaft at the flex and move the shaft - change plug and reinstall shaft.
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    jlflemmonsjlflemmons Member Posts: 2,242
    You can also use a 3/8 socket, an adapter from 3/8 down to 1/4, use a 1/4 extension, and come in through the wheel well. Using the adapters and thinner extention gives enough play to get around the shaft. Just barely, but enough.
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    quickfoxquickfox Member Posts: 2
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    unicorn747unicorn747 Member Posts: 15
    after replacing the thermostat because of it overheating now there's a noisy lifter- could this be caused from the engine getting too hot? it also due for an oil change. :confuse:
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    repairdogrepairdog Member Posts: 948
    Oil and filter and hope the lower intake gasket isn't leaking into the valley. Keep a close watch on the reservior - fill it to the hot line when cold and look at each day and make sure its not dropping. No leaks either so look around. Replace the radiator cap with a new one now also. Hope you flushed the system out with that new thermostat and refilled with 50/50 Dex cool mix.
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    unicorn747unicorn747 Member Posts: 15
    WELL WE CHANGED THE OIL AND THE FILTER- BUT THE LIFTER NOISE IS STILL THERE! WHAT DO I CHECK FOR NEXT? :mad: :confuse:
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    repairdogrepairdog Member Posts: 948
    Look for water dropping - #1 cause on 4.3 is the lower intake sprays a fine mist into the valley and the lifters make noise. You will normally NOT see any water in the oil when this occurs only the res dropping and morning lifter noise. Then if thats stable you got the engine so hot that you cooked some oil on or in a lifer or two so go buy some lifter cleaner that gets added to the oil and follow the instructions. Often takes 100 plus miles to quiet down, assuming no water getting in.
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    unicorn747unicorn747 Member Posts: 15
    GOOD NEWS IS THERE ISN'T ANY WATER GETTING IN!YOU WERE RIGHT ABOUT IT BEING BETTER ONCE THE ENGINE GET WARMED UP! I'LL PUT SOME OF THAT LIFTER CLEANER IN IT TODAY & I'LL LET YOU KNOW IN A COUPLE OF DAYS OR SO THE RESULTS! I'M PRETTY CONFIDENT THAT THE RESULT'S WILL BE "GREAT"! WHEN SHOULD THE OIL BE CHANGED AGAIN (3,000 MILES)? THANKS FOR ALL OF YOUR HELPFUL INFORMATION!! :shades: :):)
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    unicorn747unicorn747 Member Posts: 15
    ONE MORE QUICK QUESTION- COULD THE SERVICE ENGINE LIGHT STAYING ON NOW BE CAUSED FROM THE STICKY LIFTER??? LAST TIME IT HAD COME ON WAS BECAUSE THE GAS CAP WASN'T ON CORRECTLY & I ALREADY TRIED THAT AGAIN. :confuse:
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    repairdogrepairdog Member Posts: 948
    Get the code read out at any Advance or AutoZone for free to know. Read the instructuions on the lifter bottle as some require a change sooner, some don't. I do all mine every 3000 and only use the Valoline MaxLife 10w-40 now as my 4 are all over 100k miles. Do not use the $2 oil filters either - I have used the mid grade Fram Toughguard ones for years or best is WIX or NAPA Gold - forget the ones with Teflon in them. Hope all works out noise free!
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    unicorn747unicorn747 Member Posts: 15
    YOU SAID THAT 4 ALL WITH OVER 100K MILES- WHAT KIND OF VEHICLES ARE THEY?? ALSO THE BOOK THAT CAME WITH MY JIMMY SAY'S TO USE 5W-30 OIL IN IT. MY JIMMY ALSO HAS A LITTLE OVER 100K MILES NOW. AS FAR AS THE NOISE- WHEN I STARTED IT THIS A.M. (COLD) THERE WAS NO NOISE. I DIDN'T EVEN PUT THE LIFTER STUFF IN YET. I JUST DROVE IT YESTERDAY ABOUT 45 MILES AFTER THE ENGINE WARMED UP SO THE NOISE WAS GONE, BUT THE LIGHT WENT OUT FOR MOST OF THAT TIME & THEN IT CAME BACK ON. I'LL LET YOU KNOW WHAT HAPPENS THOUGH! THANKS AGAIN!!
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    repairdogrepairdog Member Posts: 948
    All Blazers and after 100k I switched to 10w-40 MaxLife as all the bearings and seals have worn and I'm in FL so always hot! Great if the lifters already are quiet - new oil must have flushed the sludge stuff off.
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    daylyndaylyn Member Posts: 12
    My Jimmy drives fine around town. I've just replaced cap and rotor, spark plugs, O2 sensors, and catalytic converter.
    The problem is every time I try to drive up a steep incline the truck will lose power, then chug and sputter like it's gonna die. If I turn around and go back down the hill, the sputtering and chugging stops and she runs fine again! What is going on? Any suggestions?
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    repairdogrepairdog Member Posts: 948
    Assuming no SES light on and codes present.
    Change the fuel filter and if then check the fuel pressure.
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    daylyndaylyn Member Posts: 12
    Previously had a 0300 code-multiple misfire, but didn't get another code during or after this incident. Fuel filter was replaced under a year ago, but will change it out, and hope that helps.
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    repairdogrepairdog Member Posts: 948
    Thats a hard code to clear sometimes as like 8 possible causes. Have you changed the plug wires? At night spray a fine mist on the boots and see if they arc. Then the coil could be failing so a load results in a weak spark. The crank sensor can be intermittant as it starts to go (under block and the pulses tell the PCM the crank position). Then the ign IC on the coil heat sink (not common). Or fuel pressure low so lean mixture results - again check pressure at fuel rail. Injection system problems also can cause.
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    daylyndaylyn Member Posts: 12
    Plugs and wires were replaced. We're wondering if maybe it's the MAF sensor.

    How would I find out if the coil was failing? Just replace it?

    It seems that the truck only behaves this way on one hill, which is at a high altitude. If the MAF sensor was malfunctioning, would it cause the truck to behave this way in high altitudes?

    Any way of knowing if the MAF or MAP sensors are malfunctioning before spending money to replace? I did lightly clean the MAF last nite, and made it up the hill a little further before truck crapped out......
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    repairdogrepairdog Member Posts: 948
    Dirty MAF does effect the mileage as runs richer so possible - clean with MAF, brake, or electronic cleaner but not carb (leaves residue).
    Have to test the primary and secondary windings and some auto stores can test for you free.
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    nevrbyajimmynevrbyajimmy Member Posts: 5
    This 4.3 liter starts up easily like nothing is wrong , start heading down the road and after about 10 minutes of driving the engine loses power, { the more you push the gas pedal the slower you'll go } untill it then stalls , while still coasting I can put it in neutral , and restart the engine like nothing happened and go down the road , { engine runs fine } Then after a few miles it starts acting up again . And when it is acting up if you floor it it will backfire under the hood { carberator ? }
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    nevrbyajimmynevrbyajimmy Member Posts: 5
    If General motors wonders why they are losing sales , it is because of vehicles like mine 1998 GMC Jimmy , It has been nothing but a money pit , from wheel bearings at over $150 a side tto the fuel pump at over $600 , to having to replace all four ball joints at 80,000 miles , and I haven't even mentioned the rear braking system , I go through brakes about every 5000 miles , I have replaced rotors calipers and pads up to 3 times a year . And now I can't figure out why it stalls ? It has been at the shop for over a week ! That is why I bought a Toyota ! whatever happened to buying american made automobiles that would last and be easy to fix ? If I could order a new truck and chose the year I would order a vehicle engineered in the mid 80's with no fuel injection ! no ABS , no electrical transfer case , etc ...
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    repairdogrepairdog Member Posts: 948
    Well lets start with the backfiring etc - what code do you get as the SES light must be ON? You have a timing problem for the backfire so has it got a new cap/rotor? Then cam sensor in distributor which effects that (starts OK then probems start) but get the code - also a crank postion sensor tells the PCM where to fire. Then if the fuel presure is bleeding down possible fuel regulator leak under the upper intake. A good GM garage can find these in an hour.
    As for the brakes the rear calipers must be replaved with rebuilts each brake job - cheap plastic piston and the slides are in the braket and must be pulled out (rubber boot pulls out) and greased or you will eat rotors. Assumes that the rotors are straight and the lines clean.

    The other repairs you did are known Blazer/Jimmy ones and soon the AC compressor will go, the alternator, water pump, and keep that cooling system changed every 3/36 or look out heater core and lower intake gasket.
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    nevrbyajimmynevrbyajimmy Member Posts: 5
    Well my mechanic called and said that the fuel pump was drawing so many amps that when you activate the brake lights or turn signals that the fuel pump changes tone with the flash of the signals or when the brake is applied thet pump changes tone , also he said you shouldn't be able to hear the pump running over the sound of the engine , I just changed the fuel pump not even 3 years ago !! $600 . whatever happened to the $30 fuel pump change ? I'm not impressed to say the least . and yes i've changed the water pump , alternator 3 times and yes the heater core plugged up on me 2 winters ago , DEXCOOL ! what a great coolant "NOT" ! SO I flushed it out and then I caused it to leak , I then put 4 bottles of BARS stop leak into the syatem to seal that up , I couldn't afford the $400 that the dealership was going to charge to replace the heater core , P.S anyone want to buy a jimmy for cheap ?
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    repairdogrepairdog Member Posts: 948
    Well, only the Delco pumps seem to last at all in these vehicles and Airtex has a replacement connector for the pump top that solves many of the corroded connector problems and voltage/amperage problems and a good ground is alos a must. All of the pumps can be heard when the vehicle is running if standing by the drivers side but not while in the cab windows up. Old mech pumps ran at like 10lbs and new injection requires 60 plus.
    I have 4 of these so I know when each part dies first hand. When all is fixed they run well and handle pretty well too but as you know they are not without alot of repair and if you have to use a shop gets very expensive fast.
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    nevrbyajimmynevrbyajimmy Member Posts: 5
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    daylyndaylyn Member Posts: 12
    Just wanted to update all on what we finally figured out with this problem.

    We replaced every "suspect" part on the damn truck, as follows:
    Transmission (needed to be done, was slipping badly)
    Cap & Rotor
    Spark plugs & wires
    Distributor
    Catalytic converter
    O2 Sensors, MAF sensor, MAP sensor, cam position sensor, ignition control module sensor.
    Intake manifold gasket
    Fuel filter, fuel pump
    Oil filter, air filter
    Ignition coils
    Radiator

    And the problem was that the exhaust valves were burned. One exhaust valve had gotten sooo hot, that it was misshapen, and actually was thinning out.

    Eventually, the thing got so warped, that the piston came in contact with it, and I lost all compression in that cylinder. This is the only way we would have ever guessed that this was the issue. The valves cost $35.00 each. Lots of labour - 8 hours, but the end result was a fix of $1300. Which is less than 1/4 the amount of money we spent trying to fix the damn thing.

    We researched this issue for months and months. We never had anyone even guess that it might be exhaust valves. The only issue we had was high emmissions, and a random cylinder misfire code, which was intermittent (P0300).

    Hope this information helps someone else out.

    For additional info or input, feel free to send me an e-mail: daylynbc@hotmail.com
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    steverstever Guest Posts: 52,454
    Hopefully you'll be good for another ten years now that you have all those new parts on it. Thanks for the report!
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    mtrotter70mtrotter70 Member Posts: 3
    If you would of had it hooked up to a shop's computer diagnostic machine it would have let you know that the cylinder wasn't firing, yes? Sounds like you wasted a ton of money on stuff that was not broke.
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    daylyndaylyn Member Posts: 12
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    daylyndaylyn Member Posts: 12
    That's the problem. I had two seperate compression tests done at two seperate shops that were both showing compression in all cylinders.

    Not until the valve actually warped and burned, did we find out that was the problem.

    The original problem was the valve getting too hot.
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    brammermjbrammermj Member Posts: 2
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    brammermjbrammermj Member Posts: 2
    Have a 2000 Jimmy, 114,000 miles. When taking off after starting vehicle, get tach around 2grand and while pushing accelerator the vehicle wont accelerate. Can push to the floor but nothing, tach will stay steady. Does not miss, bog down, nothing else unusual. After a couple of seconds it will take off. Is now at GM shop but they 2 hours in it and cant find anything. No codes, fuel pressure good, checked cap and rotor, nothing wrong can be found. He did say that in park and while pushing accelerator it doesnt seem like it picks up the RPMs like it should.
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    vicedetectivevicedetective Member Posts: 2
    So here is the lay out. I have 1996' GMC Jimmy that has a misfire problem, its the #6 cylinder. I stared with the simple things. I changed my plugs and plug wires, changed my o2 sensors, changed my fuel filter and now just at a loss. I dont really have to much loss of power at the gas petal, sometimes a small delay when hitting the gas at a red light and also when starting I have to give the truck alot of gas. I started to worry maybe I have a blown head gasket but I dont have any real symptoms of it. My truck is not over heating, I have no white smoke out my tail pipe nothing. Thanks for any help that can be givin in advanced.
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    lynderaelynderae Member Posts: 4
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    repairdogrepairdog Member Posts: 948
    New cap and rotor to rule out and do not use cheapos like Wells. Misfires can also be caused by a bad or clogged injector, burned valve, or leaking head gasket as you said.
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    98jimmy98jimmy Member Posts: 4
    I have a 98 jimmy 4.3 liter 106,000 miles. The problem started 3 years ago when moving from Alaska to nevada. In hot weather only, driving fast or slow or idling, the engine will intermittently die after getting warmed up. No problem with restart--I am use to popping it into nuetral and restarting on the fly. The engine is smooth as pie before/after this happens. my gas mileage is normal. No error codes, no other symptoms--headlights fine, music keeps playing during these events. This might happen 3-4 times in a row ,once in a while or not at all when the GM mech is driving it. This is only a maybe but it seems like just pulling over , turn the ignition off/on maybe helps a little. I tried new ignition switch and fuel filter. local GM folks got nothin' I don't mind shotgunning the problem is I had a likely list of culprits. Help!
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    repairdogrepairdog Member Posts: 948
    Idle air control (IAC) valve on the throttle body - replace it and that is controlled by the PCM and sets the idle and mixture. Have to pull the throttle body off to remove the side mounting screws and clean inside the air passage seat area so the new plunger fits cleanly. Part about $75 (aftermarket)-125(GM). If only at or approaching an idle that the intermittent part. They must of tested the fuel pressure already.
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    98jimmy98jimmy Member Posts: 4
    Thanks for the input. This IAC will effect the engine dying at 80 mph as well as at idle? This problem does occur at any speed as long as the weather is warm enough.
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    repairdogrepairdog Member Posts: 948
    No, at idle or as rpms drop to 600 so at 80 that wouldn't happen. I would put a new cap/rotor on and not a cheapo but use a Delco or Standard Motors Product one. Rules that out. Then on to wires, plugs, intermittent sensors (such as crank position sensor under front that tells PCM where to fire plugs), clean the MAF sensor, is the temp gauge reading correctly as it also feeds the PCM, then again check that fuel pressure hot at test port. These ones are a pain to find. Then theres always the coil and ign module, the cam position sensor in the dist, and loose grounds or othetr wires or connector plug ins - sorry.
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    98jimmy98jimmy Member Posts: 4
    Thanks for the list. I will start at the top and see if anything helps. Again thanks for taking the time
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    98jimmy98jimmy Member Posts: 4
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    rickwbrickwb Member Posts: 6
    NEW BOARD MEMBER HERE - My daughter's 2001 4.3 liter gmc jimmy sometimes revs to about 3000 rpms when the clutch is depressed. IF however you let the engine rpms drop below 1100 rpms before depressing the clutch the engine will idle normally. Also if the engine is shut off and restarted the engine will idle and return to idle normally if the accelerater is depressed and released, After some period at speed however the engine will rev to about 300 rpms again when the clutch is depressed. Seems to occur mostly when engine is warm and did go quite some time between the last couple of occurances. Sometimes will act up on a regular basis then go away for a while. I'd appreciate any guideance I can get. Thanks in advance.
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    tidestertidester Member Posts: 10,059
    Please don't take this the wrong way but have you experienced the high revving yourself? Because you said it was your daughter's Jimmy I'm just wondering whether it's inexperience at driving a manual. It takes a little time for beginners to properly synchronize easing off on the gas while pressing the clutch pedal.

    tidester, host
    SUVs and Smart Shopper
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    rickwbrickwb Member Posts: 6
    Thanks for the reply - Yes I have experienced this myself on several instances. The latest was just an hour or so before my original post. It is very strange. Mostly occurs after some amount of highway driving and acts just like I described. Push in the clutch and the engine rpms go to about 3000. BUT if I get the rpms low (below 1100 in gear) before depressing the clutch the rpms will stay at idle until accelerating and shifting up through the gears. At that time the engine rpms will rise to 3000 rpms again ( and stay there) when the clutch is depressed. This occurs when shifting anywhere above the 1100 or so rpms I described earlier. I have removed my foot completly from the accelerator pedal and it still occurs. I hooked my toe under the accelerator and lifted thinking it was possibly sticking with no luck. Operator inexperience is not an issue here. This started after owning this vehicle for a couple of years and this is her 3rd vehicle with standard transmission. Thanks again. Hopefully some fresh minds will get me pointed in the right direction.
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    grose67grose67 Member Posts: 5
    I had the same type of sporadic issue a couple of years ago on my 95 Blazer. The idle speed controller was going out.
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