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Chevy S10/GMC S15-Sonoma: Problems & Solutions



  • canufixitcanufixit Posts: 165

    Maybe this can help ???

    Fuel System - MIL ON/Rough Idle on Start-Up

    File In Section: 06 - Engine/Propulsion System

    Bulletin No.: 00-06-04-003B

    Date: February, 2003


    Rough Idle After Start, And/Or A Service Engine Soon (SES) Light
    (Unstick And Clean Central Sequential Fuel Injection (CSFI) Poppet
    Valves or Convert to MFI)

    1995-2002 Chevrolet and GMC S/T Models
    1996-2002 Chevrolet and GMC C/K, M/L, G, P Models
    1996-2001 Oldsmobile Bravada
    1999-2000 Cadillac Escalade
    with 4.3L, 5.0L or 5.7L Engine (VINS W, X, M, R - RPOs L35, LF6, L30, L31)
    Except 2002 VIN X - RPO LU3 Models

    This bulletin is being revised to update the Warranty Information. Please discard previous copies of Corporate Bulletin Number 00-06-04-003B with warranty chart (Section 06 - Engine). This copy is for Dealers in the state of CALIFORNIA ONLY.


    Some customers may comment on rough idle after start-up, especially if the vehicle has sat overnight. These symptoms may be intermittent. The Service Engine Soon (SES) light may also be illuminated. Current misfire or history misfire codes may be detected with the Tech 2 scan tool.


    A deposit build-up on the CSFI poppet valve ball and/or seat may cause the poppet ball to stick open or closed. In either case, the specific cylinder will be mis-fueled, resulting in a cylinder mis-fire condition.


    A new injector unsticking and cleaning process has proven to be effective in restoring poppet valves to an "as new" condition. CSFI injector replacement should NOT be considered as a correction for this customer concern.

    Check the vehicle history to determine if the vehicle is returning for a second fuel system repair for this condition. If the fuel system has been repaired for this condition previously, then inform the customer that an alternate fix is available. A new MFI fuel system has been developed that will back service the CSFI fuel system. The MFI fuel system eliminates the CSFI poppet valve ball and seat. The CSFI fuel system will need to be replaced as a unit. Refer to Central SFI to MFI Conversion instructions in this bulletin.

    Notice : Individual CSFI injectors can not be replaced with MFI injectors. The entire CSFI fuel meter body will need to be replaced. The bracket used to retain the injectors in the fuel meter body is different between the CSFI and MFI unit. The unit may not seal if you mix injectors. Severe engine damage could result.

    Cleaning the CSFI injectors is the preferred repair. The CSFI unit should not be replaced until cleaning has been attempted. If the vehicle should return for the same repair, then the CSFI unit can be replaced with an MFI unit. If the vehicle is out of warranty, the customer should be given the option of which fix to pursue.

    Important : "GM of Canada" dealers require District Service Manager approval prior to replacing the CSFI unit with a MFI unit under warranty.

    The first step of this process is to use the J 41413 Evap Pressure/Purge Station, in conjunction with the J 44466-10 pressure regulator/hose assembly, to provide the required high pressure (150 psi) source to perform the unsticking procedure. The J 39021 fuel injector tester and accessories provide the means to "energize" the injector. Some later model-year vehicles may utilize the Tech 2(R) to "energize" the injectors.

    The second step of this process is to run the engine on a solution of 10% Top Engine Cleaner and 90% gasoline. This will effectively clean any deposits from the ball and seats of the poppets. It is very important that the engine fuel system is separated from the vehicle fuel system. Top Engine Cleaner may have detrimental effects on the fuel pump.
  • 87vette87vette Posts: 1
    Canufixit, I'm new to the site and have a question re. 95 S10 2.2 2x2 I bought recently as a project. Plan to replace engine w/ mouse motor out of 2001 camero which received a 383 stroker but for now just playing with the 2.2. Pulled and replaced cyl head, cleaned injectors, new tps, new iac, new plugs,wires, fuel pressure regulator, etc. Now engine idles fast and has no power. Strong fuel smell at tail pipe. I'm thinking stuck exhaust valve on new head. Any ideas? Thanks. Bill Mc
  • canufixitcanufixit Posts: 165
    Ok, One more suggestion ...

    I have "heard" of the intake manifold to head gasket leaking in the front or rear ends of the manifold. This will allow coolant into front or rear cylinders ... If it is just leaking a little - you get a rough engine - if it's leaking a lot - it can fill up the pistons affected and cause a hydrostatic lock - and the engine will not turn .... Try a compression test on the cylinders ..... and look at the plugs when you pull them to see if they look wet (and smell them for the antifreeze ...).

    All I can think of right now ....

    Good Luck!
  • canufixitcanufixit Posts: 165
    In My case (on my truck) - the sweet spot is at 40 MPH. Just under /around/ just over 40 MPH on a light load on the drive train - the rear end whines. Take your foot off the gas - and it goes away. give it a little more gas and it gets louder - give it a lot of gas and it almost goes away. This is listed as "Normal" at 40 MPH in the shop manual for my Sonoma. It's not bad - so I just ignore it - but the root cause is incorrect pinion gear loading (shims) when the rear end finally broke in and the mechanicals finally seated ...
  • I recently purchased an 02 S-10 from a local Dealer (not chevy) and have discovered the carpet on the driver's side is soaked during rains. I can't find any source for the leak. Suspect cowling under wipers but don't know. Any thoughts suggestions? I can't find any information on the drainage sytem for the cowling fresh air intakes.
  • canufixitcanufixit Posts: 165
    See an Earlier Post I made on this - not sure if this is your problem though - Mine was the seam between the roof and the corner post not being sealed in the inside ...

    Good Luck!
  • canufixitcanufixit Posts: 165
    HI Bill,

    If memory serves me - a vacuum gauge will quickly show a stuck valve. Instead of a steady state at Idle the needle will "dip" drastically on every revolution of the engine ...

    I'd do a Cylinder pressure test (wet and dry) on each cylinder as well. With the pressure test and vacuum checks you'll have a better idea of the mechanicals and also a record for future reference ...

    A stong fuel smell at the exhaust may be Ok when the engine is still cold as more gas is poured into the engine until it get up to Temp. But as you said a "Strong" smell may not be right ...

    Good Luck!
  • canufixitcanufixit Posts: 165
    Can you jumper the fuel pump ?? - if you can get the pump running and the engines runs OK for a good while - at least you'd know that the pump is OK and its' the supply voltage/circuit to the pump that's the problem. This may help you in removing some of the variables in the equation. If it does not run - re-check the pump - it it runs - troubleshoot the wiring....
  • canufixitcanufixit Posts: 165

    I had an uner chassis rear rattle on intial engine start up - turned out to be a loose baffle plate inside the muffler.

    I'd get under the truck and really shake the exhaust - check both the muffler and the Converter (expecially the heat shield!!!)

    Good Luck!
  • dgh50dgh50 Posts: 3
    I was having the same problem with my 2002 S-10. I had a coolant leak at the thermostat housing and needed to drain the radiator but could not find an easy way to "turn" the plastic petcock. After maneuvering an inspection mirror into position, I could see an allen head fitting in the center of the petcock. I inserted a 3/8" allen wrench into the center of the petcock, and turned it counterclockwise approximately one quarter of a turn. It "popped" out slightly allowing coolant to flow from the radiator.
  • pbernardpbernard Posts: 1
    Hi, I have a 1991 GMC Sonoma, 4x4 with the 4.3L engine. When I bought the truck new, it did not have air-conditioning. The dealer had a after-market air-conditioner installed. I now need to replace the heater core, and do not know if I need the one that is for air-conditioned models or non air, as it was when I bought it. My question is: If a after-market air-conditioner was installed, was the original heater core replaced with one for air-conditioning? Thankyou in advance.
  • Got as real strange problem. Driving down the road and the tack reads 2.5 to 3.0 then all the sudden the truck stars bucking and stalling and the tach is jumping all over the place. then it suddenly drops to zero and the truck runs fine. occasionally it will jump back up to about 1.5 sputter then back to zero.I replaced the camshaft positioning censor and it ran fine for about 3 days. Now its back to its old tricks again and getting worse. Talked to alot of people and they have no clue PLEASE HELP!!! ITS A 99 V6 4X4 engine class W with OFF ROAD PACKAGE. And if this helps i do regularly scheduled maintenance, i replaced all the fuel injectors about a year ago and im on my 3rd transmition
  • coopmancoopman Posts: 1
    I'm seeing a lot of scarring on the rear plastic (?) fender flares on my 2003 ZR2. It is obvious that the ZR2 tires extend out beyond the fenders, and they do throw a lot a road debris from the front tires to the rear fender flares. Is this just a poor engineering job by Chevy ? Is it possible that Chevy will replace the rear flares since it is still under warranty ? I added mud flaps early on to help cut down on the damage. The mud flaps help a little, but they don't eliminate the problem. Has anyone else seen this ? Also, any suggestions on what tires to buy once the originals are worn out ?
  • bbarlowbbarlow Posts: 1
    I am having the same problem w/95 s10.No water thru windshield,but lots of water thru doors when it rains or even when I run the wipers. Air bag light just started coming on intermittently. I am afraid the airbag may deploy just for the heck of it, or NOT deploy if I'm in a wreck. My mechanic said that the little seal that runs around the door had a hole in it,and to fill the hole in w/ silicone, and that should stop the leak. I'm pretty sure the sensor fix is expensive.
  • jae5jae5 Posts: 1,205
    Thanks for the additional info on the drain. I knew there was a recess in there but wasn't for sure if it was hex or square. And the service manual wasn't helpful at all, just the standard "remove the petcock" statement. Will be picking up new hoses as well. Is there a gasket that goes between the housing and the intake or does the gasket around the thermostat do the sealing?

    Will have to check to see if I have a 3/8" allen, if not, a good excuse to get some more tools.
  • dgh50dgh50 Posts: 3
    Glad to help. There is not a gasket between the housing and the intake. The gasket or "seal" that goes around the thermostat is all there is. Just take note of the position of the old seal before you remove it, because one side is slightly different than the other.
  • dtl379dtl379 Posts: 3
    Have you checked to see that your fuel to air mix is right? You may be running lean, or it may not hurt to check your ignition system. Good luck!!
  • dtl379dtl379 Posts: 3
    I have a 97 GMC Sonoma with the 4.3 X throttle body injection. About 1 - 1.5 years ago it started misfiring.Ihave replaced the plugs wires, cap and rotor about 5 times. We also replaced the ignition ciol, fuel filter, air filter, PCV valve, and cam position sensor. On top of that, we have run injector cleaner, repositioned the distributer, timed the motor, and have run throttle body cleaner. You can smell carbon sometimes, but I've been told it most likely not the injectors. we are still recieving random misfire codes on all cilinders. In October of last year, the service engine code came on for "hard misfire" and "cam position sensor circut malfunction". But here is where it gets fun. Before we fixed the engine, it stopped missing. It ran rich, but never missed a beat. Anyone have any idea at all? My mechanic is stumped, and the truck has been the talk of the shop. Please help!! It only misses at steady driving speeds above 35 MPH.
  • I have just spent a year on rebuilding this 2.5 in my S10. We have everything hooked up, and ready to start it. The problem is, it won't start. I'm getting spark and fuel, but the truck isn't even trying to fire up. Please Help.
  • I have a '94 S10. Whenever I start my truck it starts okay. Once i rev the engine it begins to sputter and backfires some and then finally dies. It also has a smell of gas after reving. Im not sure what the problem is. I've already changed the fuel filter but that didn't help. Please help.
    Thank you
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