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Chevy S10/GMC S15-Sonoma: Problems & Solutions



  • jameywjameyw Posts: 1
    1998 S-10 2.2L 4 cyl. I replaced the fuel pump after I thought it was bad. When I turn the key on, the pump does not run. I checked for 12V at the pump connector when I turned the key on and the was no voltage. After reading more in my service manual, they menttion an oil pressure switch that cuts power to the fuel pump when the oil pressure gets too low. The oil is fine so I suspect the switch has gone bad. The only problem is, I can't find this switch. Is it the same unit that controls the gauge on the dash? I don't think it is because there is only one wire but the wiring diagram shows it to be a 3 or 4 wire device. Any ideas?
  • canufixitcanufixit Posts: 165

    I'm not sure on my answer - so take what I say with this with caution, but I "Think" the following may be helpful ...

    In my years with tinkering with engines ( pre 90's) I found the following to be true ...

    The oil would go "Through" the crank shaft at the back - then exit out the front end of the shaft ... At this point the pressure gauge is sometimes placed - so it can indicate that the oil is making that far. IF you have bad Connecting rod to Crank bearings - or bad main bearings - the oil would leak out there and flow back into the oil pan. Lack of oil flow / volume equals lower proessure - so the sending unit, when placed at the engine front, would help to give an indication that the oil pump is working "AND" sufficent oil flow (i.e., bearings are not too bad) is making it through to the front of the crank. From the front of the engine - the oils then goes to the push rods, etc ....

    So, ... I'd look for the sending units up and round the front od the engine ... Of couse I could be wasiting your time if you already looked there ... But I thought I'd try to help ...
  • alcanalcan Posts: 2,550
    Check ECM B 20A fuse in underhood fuse block. If OK, check fuel pump relay in same block.

    Document ID# 188830
    1998 Chevrolet/Geo S10 Pickup - 2WD

    Fuel Pump Electrical Circuit Diagnosis

    Circuit Description
    When the ignition is turned ON, the powertrain control module (PCM) turns ON the in-tank fuel pump. The pump will remain ON as long as the PCM is receiving ignition reference pulses from the electronic ignition control module (ICM). If there are no reference pulses, the PCM will shut OFF the fuel pump about 2-3 seconds after the ignition is turned ON, about 10 seconds after the reference pulses stop.

    The fuel pump delivers fuel to the fuel rail and fuel injectors, then to the fuel pressure regulator, where the system pressure is controlled to 283-324 kPa (41-47 psi) with no manifold vacuum or 214-303 kPa (31-44 psi) at idle. Excess fuel is then returned to the fuel tank.

    Improper Fuel System pressure will result in one or all of the following symptoms:

    Cranks But Will Not Run
    DTC P0171
    DTC P0172
    DTC P1171
    DTC P0300
    Cuts out, may feel like an ignition problem
    Poor fuel economy, loss of power

    Diagnostic Aids
    An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for a poor connection or damaged harness. Inspect the PCM harness and connectors for the following items:

    Improper mating
    Broken locks
    Improperly formed or damaged terminals
    Poor terminal to wire connections
    Damaged harnesses
  • joe3891joe3891 Posts: 759
    No oil pressure switch in system, power goes from pump relay to a connection where the power also goes to power the injectors. Between the pump relay and the pump is only one connection that goes to the injectors, if power out of pump relay I would check that next.
  • bone4bone4 Posts: 5
    Please help me. I have a 99 s-10 4.3 4x4. Ok i have a couple of things happening i had my fuel pump replaced not to long ago. Well my fuel lines makes a noise like a water hose thats kinked. Its the loudest right at the gas tank. you can grab them and feel it. Ok now even before i replaced the fuel pump it seems to sputter when im driving around 55 and go up a hill it wants to sputter but when i give it more gas it goes away. well when im at a red light it well idle funny sometimes its like the compressor kicks on and goes of but this is not the case. I have no check engine light on and no codes! one more thing when i go up a steep hill it makes a crazy noise like a piece of metal rattling. But it has no power but i just give it more gas it goes. It seems to make the noise also when i turn the truck left hard!! Please help me i cant pinpoint this problem thanks alot!!!
  • canufixitcanufixit Posts: 165
    Boy, That's a lot in one paragraph ....

    I'd first try to see if you have more than one problem .... Something like Fuel and/or timing (Knock) and or other Drive train Mechanical ...

    I'd start with the mechanical .. Having metalic noises when under load or in turning - may be the front wheel bearings or front u-joints or Main shaft u joints.
    Try driving on a flat surface/road in 2WD , keeping a constant speed and weave left right and see if you hear the noise - if so, I'd be concerned with the front wheel bearings / joints in front wheel drive shafts ... (My first guess would be a wheel bearing on an S10)

    Then going up constant incline hill (in 2WD) - driving straight - try various amounts of gas pedal. If you get the metallic noise there under light acceletation/load I'd check for Knock (Timing - but you should get a code for this) - Also, I'd check the Main drive shaft U joints.

    If the above is inconclusive - I'd have a shop check for fuel pressue and flow ...
    Good luck !!
  • bone4bone4 Posts: 5
    hey canufixit,

    I had a shop check it one day and i believe it was like 55 it was not 60 well when we turned off the truck it rose up to 60 or above!!!?? This fuel promblem has me the most puzzled. If i can fix it then i can see if it has something to do with my sputtering and going up a hill sputter!! But i can hear the gas going through the hoses at my gas tank from inside the cab!! thats not normal is it? i mean it just like a kinked water hose! you know when a water hose gets kinked how it will have a pulse! but its loud!! Thanks for the help.
  • draggn66draggn66 Posts: 2
    I have a 96 4WD 4 door S10 Blazer with a 4.3 engine and auto transmission. The trans has started making a whining sound when it's in gear. In neutral the is no noise. I've check the fluid level in the tranny and it was a little low so I added some. I went to check the fluid level in the transfer case and when I removed the top plug about 3 qts. drained out. That's way too much according to anything I've read. The tranny works fine with no slipping but the noise is very noticeable. Any ideas? TIA.....Randy
  • This is just a suggestion, I don't know if it warrants a serious consideration, but is there a chance it could be the fuel filter. How often do you run your tank down low? Do you drive on dirt roads alot so that you might acquire dirt in the tank. Just an idea. Another thing to check might be the fuel pump, but that is usually either works fine or not at all. Good luck.
  • mikeys10mikeys10 Posts: 7
    Have you check the EGR valve, it sounds it stuck
    open. Find the egr valve and apply vaccumn one or twice. It should close. Or replace it. just a suggestion.
  • canufixitcanufixit Posts: 165
    Wellll .... To my knowledge (and I use that term loosely);
    - The pump, when energized, will always pump to best Flow possible. If demand is met to the engine, then needed flow is then not needed/reduced and pressure goes up - and then a relief valve opens up and dumps the unneeded fuel back to the tank. There is bound to be "some" noise in this arrangement - and I have heard that some pumps are WAY more noisy than others ... What's the spec for min pressure for the Pump ?? Although it's noisy - if it meets the Flow / min pressures - and although it is way too noisy, - I'd start looking somewhere else. Some one else in this Forum mentioned changing the fuel filter - that's quick and cheap to do if you hav not already ... Also someone said the EGR Valve should be checked as well ...
    Anyone else here have better/more corrrect inputs - I just can't think of anything else at the moment ...
    Good Luck !!
  • canufixitcanufixit Posts: 165

    I take it you have already ruled out the Rear end ?? These can get noisy when the Pinion pre-load is not exactly correct .... ???
  • jae5jae5 Posts: 1,205
    As kycableguy mentioned, usually on a GM product the horn and the cig. lighter are hooked to the same fuse. If your horn doesn't work and the fuse is blown, more than likely the cig. lighter doesn't work either. This is usually caused by dirt build up in the cig lighter hole. Clean it out, then replace the lighter.

    If the door/cab lights are staying on, could be a short to ground. Assuming you have a wiring diagram, you can trace the path of the wires, see if any other wires are coming into contact or if the cab light wires are chaffed, touching a metal component. Also, with the door open, did you push in the little plunger, and if so, did the light go off?

    And as previously stated, I would check the switch. You may have bumped or turned it all the way on and forgot, causing the lights to stay on all the time.
  • i have the same problem with my 98zr2 and have had i checked but everyone thinks im crazy.
    its done it for about a year now but i keep rollin

    let me ask you, if u turn the ac on does it make it worse?
  • yevyyevy Posts: 2
    I seem to have the same problem with my 99 Blazer (same engine). It feels like the tranny slips out of gear and the engine revs up briefly, but the vehicle loses it ability to slow down. Let me know if you get a reply that explains this.
  • draggn66draggn66 Posts: 2
    Thanks for the reply. But without sounding like a dummy....if it was the rear end wouldn't it continue to make noise when I put the tranny in neutral while I'm rolling? there a seal that must have failed to allow tranny fluid to go from the tranny to the transfer case? TIA....Randy
  • bone4bone4 Posts: 5
    i have not had the truck really all that long but i dont believe it gets worse when the air is on. What is your doing just losing power when you go up a hill? Or when you give it gas it takes a sec for it to respond! When im at a stop and i floor mine it sputters and finally goes!!!!
  • When i accellerate from a dead stop about half way through the first gear it will loose rpm and then surge ahead almost as if something is binding.I had the tranny rebuilt 2 years ago and i have had it checked twice since and no one can find a problem. Also if i am running at highway speed let off the gas and then back into it it will do the same thing. At first i thought the overdrive might not be locking properly but i had that checked too. No dice. I really think it has something to do with the motor because when i run the ac it makes the problem much worse.
  • I have a 98 zr2 and I was told one of the motor mounts needs to be replaced. Is this expensive?
    Also, according to the Haynes book there are only two mounts. Is this correct?
  • bone4bone4 Posts: 5
    mine will idle funny at stop signs. but i dont recall my air makeing it worse. mine does the same thing mine will not spin a tire though which it may not anyway but it will just bog down!!!! then when im at like 55 and go up a hill it starts kinda shakeing!!! i honestly think something is in the injectors or something!! but im no mechanic. I think its something to do with my fuel some way!!
This discussion has been closed.