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Chevy Suburban/Tahoe Rough Idle and Stalling



  • pear69pear69 Posts: 20
    Your factory fuel injection system is called a Sequential Port Fuel Injection system (SPFI). That is what the dealer means by sequential. There has been a lot of problems with this system. You said you installed the updated fuel injection version, make sure you tell them this. The updated version is called Multi Port Fuel Injection (MPFI). At the dealer they may want to run an injector cleaner through your updated system, this could cause problems with the updated system you installed. If it were me I would check the distributer first and replace/or/fix it before taking it to the dealer, you have to take it there anyway to get it timed after messing with the distributer and to have a crankshaft sensor relearn proceedure done. Changing the plugs and wires to A/C Delco is a very worthwhile decision. Keep me posted
    P.S. sorry I couldn't reply last night, the site was down.
  • Thank you. I bought the spark plugs last night $6 a piece and will install it maybe tonight and the wires.

    Thanks again and have a great weekend.
  • Hello Pear69. Brought the Suburban to the Chevy dealer and they are replacing the whole entire Sequential unit even after I told them I bought a new one already. The truck runs great now. They fixed and replaced the injectors at no charge under California Special Warranty on Sequential unit up to 200,000 miles. They also replaced my distributor assembly, but have to pay for that job.

    Thanks for all the help and advises that you have given me.

  • woodyjwoodyj Posts: 6
    What causes Engine Reduce Power to show up on my instrument cluster. Everytime this happens, my engine dies down to an idle and loses power. I have to turn off my suburban and restart it after about a minute. I would appreciate some pointers.
  • pear69pear69 Posts: 20
    Elorenzo39, You are welcome. I am curious about the condition of your distributer gear. Was is worn out? That's great that you had the dealer change the injectors for free--A/C Delco plugs are expensive but they last for 100,000 miles--I'll help anytime--good luck. Let me know about the distributer gear if you can--thanks.
  • Hello Pear69,

    I wish I could tell more about the Distributor Assembly. I did not see it myself. Dealer just called me and asking me for approval to replace it and I approved the work over the phone. They are jam pack with a few Suburbans and Silverado's with the same issues. They actually had my Truck for a few days. Dropped it off Last Friday and did not get it back until Wednesday morning. Service advisor told me that they are working on alot of vehicle that has the same problem as mine.

    Thanks again for all your help.

  • gators27gators27 Posts: 1
    Its not pulling any codes and the Dealer isnt sure what it is either the fuel pump pressure is good they changed the filter, and it still stalls out after its bin running for a couple hours like it ran out of fuel they also told me it could be the cadeletic converter but they werent sure it is only a hunch well i wasnt spending over $1000 on a hunch when they werent sure. Can someone help?
  • mkotzurmkotzur Posts: 1
    I have a 2001 chevy suburban 1500 2wd and I've replaced the plugs and wire set. Now the vehicle is running rough and the check engine light is on or blinking. I've checked for a possible bad wire and plug and they are fine. When I hold a spark indicator against each of the wires and only one will show a stronger spark. Switching the wires around still give me the same strong indication. I've also switched the plug wire module around with no effect. Could it be the ignition control module and where is it located on the engine compartment?
  • woodyjwoodyj Posts: 6
    I would suggest checking on your throttle position sensor. Either it would be bad tps or bad wire connector. Secondly check on the spark plug module wiring harness, and could be due to bad wires.
  • woodyjwoodyj Posts: 6
    Double check your spark plug gaps and check your spark plug module harness connection on both sides of the engine. The check engine blinking indicates short/misfiring. If there is short in the harness, you can check it by moving around the wires close to connector one by one while the engine is running. Have your check engine light checked and post the codes. I would have better understanding of what the problem is.
  • pear69pear69 Posts: 20
    Did you install AC Delco plugs and wires? If not you are wasting your time. AC Delco ignition parts are the only parts that work on Chevy engines. I know they are more expensive but that's just the way it is with the high voltage Chevy ignition systems.
  • elorenzo39elorenzo39 Posts: 20
    I have this problem not too long ago on my 99 Suburban after the intake manifold gasket was replaced. I have a good all buddy helped me out on this forum. I bought a non ac delco parts and nothing has change, but when he suggested to replace it with ac delco, the truck ran better. I had a rough engine and showing a code of P0304 misfire on cylinder #4 and a blinking ses light when at a speed of 35 - 45 mph. California vehicle had a special warranty up to 200k mile on their fuel injection system and dealer checked and replaced. Car runs great now.

    I did not catch the whole story. Please provide me some symptoms that you are experiencing and what year and type. I will share with you some of my experiences.
  • elorenzo39elorenzo39 Posts: 20
    Did it give you any codes?
  • alanrsalanrs Posts: 25
    Having a problem with my Suburban, began at a little over 80k miles. SES light activated on interstate at 70mph while towing an empty trailer. Filled up with "better" gas, light out within 50 miles. Light back on within 100 miles, showing a 300 DTC. Cleared code a couple of times, returned as 305 or 300. I figured it was time for a tune-up, replaced plugs and wires. [Note: OEM plugs were DENSO platinum type]. New plugs Iridium, 0.60 gap as specified in manual and engine compartment sticker, new Delco wires. Rough idle still present, 305 code returns after clear.

    Have since changed/tried: New fuel filter, swapped coil units beween cylinders, sprayed brake cleaner around intake (as leak detector). No change. Removed and sent injectors for professional cleaning. Still no change. I broke down and took the Burban to the dealership. $184 later, and no diagnosis of the actual problem. They say electronics and fuel system are ok, performed leakdown test, with no issues. Wantd to "disassemble" top of engine suspected "grooved camsaft" or other valve train issue. I declined permission to take the engine apart.

    Would be happy for any advice I can get at this point.

  • elorenzo39elorenzo39 Posts: 20
    Please tell me what year, what code does it have. What state are you in. I had the same problem before and I was showing P0304 cylinder 4 misfire. Let me know. Check compression on each cylinder while the SES light is still on. My Burb did that for 1 year and the problem on mine was the Spyder injectors that was replace for free in the State of California and is waranteed up to 200k mile. A month later it showed up again P0304 and my compression was dead on that cylinder. I ended up getting the engine replaced then sold it due to high gas price in California.
  • alanrsalanrs Posts: 25
    I am in Michigan. The code is 305. The engine passed compression and leakdown tests. This is a 2001, injection has fuel rails with individual port injector units, and a plastic composite intake manifold.
  • pear69pear69 Posts: 20
    Try changing or swapping out number 5 cylinder injector with another known good injector. P0305 code is cylinder 5 mis- firing. Denso plugs are ok for these type of coil/over ignition systems but A/C Delco are the best. What is the fuel pressure? Did you check the TPS sensor?
  • alanrsalanrs Posts: 25
    The injectors were removed, tested, cleaned, retested, and yes I re-installed with 2/4 and 3/5 in different locations. Injectors are not the issue. The Denso plugs CAME in the engine FROM GM. I was surprised too...... I replaced with Autolite, only because they were only ones I could find with the specified 0.60 gap in an Iridium type. #3 and #5 coils were also swapped. Tech2 showed no issue with TPS, and I get consistent readings from it on my scan tool as well. Dealer says there is no electrical or fuel issue, and BTW, I measured fuel pressure between 46 and 50 PSI.

    The Tech2 showed a misire history stored in the computer that was heavily at cylinder 5 (over 50,000 the day we read it), with way too many (but about 1/10 of cyl 5) on cyl #4. Others showed single digits or zero. I wish I knew of someone with an engine smoker in my area, so I could check the intake gaskets.......

    This is perplexing. I love this truck, and am bummed that it is running poorly. Been driving for 40 years, his is the first time I have had any issue like this. I run most of my cars/trucks 150K miles or more with no engine problems. :(
  • pear69pear69 Posts: 20
    Your fuel pressure should be 55 to 66 psi. Make sure the fuel filter that's attached to the fuel lines is new and installed properly (this filter is directional). If this filter is good then the filter that attaches to the fuel pump (inside of the tank) is probably dirty. This filter ( I believe) is not serviceable. I suggest replacing the fuel pump. When replacing the fuel pump on these chevys it is VERY important to replace the fuel pump chassy harness connector ( this is the electrical connector that plugs into the fuel pump). This connector is a one shot deal -- meaning that it can only be plugged in and out once -- because of a design flaw. Failing to replace this connector will cause the pump to shut off and/or arc creating the potential for a fire. Also, the ground for your fuel pump is connected to the frame close to the fuel tank -- find this (black wire) ground and disconnect it and clean the area around it real good and then reconnect it. This ground corrodes and it is usually better to cut it off and re due the entire connection.    This may not be the mis-fire problem but it is important to have the proper fuel pressure before you change everything else (like is seems you have done already). A code 305 is specific to a mis-fire to cylinder 5. Make sure all the wire connections are connected properly.  Pull cylinder 5 spark plug and pull another plug that is firing. Is there any difference in the appearance? What do they look like?

    I believe you mentioned that you sprayed brake cleaner to look for an intake leak. Try spraying some CRC electrical contact cleaner all around the intake--it is safer. Do this with the engine running at idle -- if the idle changes then (of course) you have an intake leak.

    Also, is your coolant low? These engines are famous for the lower intake gaskets to fail. If the coolant is low and there is no outward signes of a coolant leak, then the intake gasket may have failed inside of the engine and coolant can leak into cylinder 5 causing a mis fire. Check your oil to be sure that there is no coolant in the oil. Looking at the plugs will confirm whether or not there is coolant leaking in no. 5 cylinder.
  • arriearrie Posts: 312
    One thing that I was told by the GM dealer is that in general misfire trouble code does not indicate fuel delivery problems. It only tells about the quality of the spark, i.e. it measures if correct resistance is present at spark plugs for correct spark. So it means misfire code indicates electrical problems.

    Here I explain what happened to my "04 Tahoe 5.3L Flex Fuel engine very soon after I got the car. I have posted about my problems several times in this forum before but this all is very difficult to find I assume. Here are a couple of easy checks.

    1. After only about 1200 miles my Tahoe started eating too much gas. This means 18 mpg went down to 13 mpg on highway driving. During the trouble shooting process, which I had to do myself while the dealer did nothing during warranty period, I first changed spark plugs. After that I get misfire trouble codes. As I had only changed the plugs this obviously had to be related to plug change. As a result it ended up being very simple problem. Some of the aluminum metal shields around spark plug booths that my Tahoe engine have were grounding spark to engine ground. For trouble shooting purposes I removed the metal grounding spring from the end of the shields, which allowed me to even see the problem, i.e. when it was dim lighting conditions I could see a spark between some of the shields and engine parts, mostly exhaust manifold.

    When spark plug wires get old they can crack and other vice loose isolation properties and start leaking spark to the shield. Because the shield is grounded to the engine with that spring in the end of it the spark has direct contact to ground. This will lead to misfire as the resistance for spark forming changes.

    This same problem easily happens when spark plugs are changed. When the plug wires are pulled from the plugs sometimes they are very tight. This can cause the plug connector inside the boot slide out. When this happens the boot does not go over the new spark plug deep enough leading to spark leak around the boot to shield and this was exactly what happened to me. Some of the wire boots did not go on plugs deep enough and spark leak was very bad. This can also happen with new wires as all of them do not have plug connector deep enough inside the boot.

    There is very easy way to trouble shoot for this, i.e. remove all aluminum boot shields. They are used only for heat shield purposes so you can take them out and drive a few miles and see if that fixes the problem. I actually took mine out and drove for a week without them. I could smell a little burning rubber but they did not catch fire or anything. Then I went and bought a set of high performance spark plug wires for $5 less than stock wire set from dealer cost, a set that does not require using boot shields and have been trouble free from this problem since. It was not the cause for low fuel mileage though.

    If your engine does not have the aluminum heat shields around plug wire boots then above does not apply to you.

    2. This happened to me just 2 weeks ago. I was working on the car again for fuel mileage, which has been back to around 17 mpg highway but not 18. I decided to change O2 sensors, the first one in each bank. Went to Auto Zone and they had a Bosch sensor for $65.00. This sensor was of the universal type, i.e. It did not come with wire harness and I had to use the one from old sensor. Further more, the instructions in the package did not explain which wire is the signal so I tried to guess. As we all know Mr. Murphy does not take days off so my guess was wrong, i.e. it is the BLUE wire that is the signal, not white.

    But very interesting thing happened while I tried to run the engine with wrong O2 sensor wire as signal wire. I got probably all of the misfire codes the computer can give. And the engine was running VERY ROUGH!

    So, your problem could be with oxygen sensor too. It just takes a new sensor to try. There are ways to test a sensor but if you already have 80 000 or so miles on it it might be a good time to change O2 sensors anyway.

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