Question about 1991 GMC S-15 Jimmy

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91 jimmy 4.3 will not idle cold or hot

I have replaced or tested the following: fuel pump,fuel filter,ignition module,pick-up coil,plugs,wires,cap,rotor,iac,tps,coolant temp sensor,and it has gotten better. It will starts after cranking a bit and will run if I keep slight throttle pressure and seems to have all of its power, but as soon as the throttle is released for an idle it will stall and sometimes is very hard to start again. I have been a mechanic for over 15 years and this has me stumped. Is there something I am overlooking or missing or could it possibly be the ECM. Ihave retrieved codes from the ECM (tps and O2) cleared and repaired so i figure that the ECM is operating properly.

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  • Barry Dec 16, 2008

    fuel pump is running,no fuel spray from throttle body injectors

  • Barry Dec 16, 2008

    yes there is pulse to the injectors, i noticed that the fuel pump is running erractic(high then low) it is new but maybe i have a bad one

  • Barry Dec 17, 2008

    i was ruling out the fuel pump because it is new, must be bad, fuel pressure is hit and miss ( sometimes there sometimes not) thats why i had no fuel spray Pulling tank maybe kinked vent line


  • Barry Dec 28, 2008

    I can drive this Jimmy down the road normal,it runs normal and has plenty of power, the only time it stalls or stumbles is when i let it idle. After it stalls in is next to impossible to get running again, when it does start it will run and drive like there is nothing wrong until i stop and let it come to an idle,then it stalls again. As long as I keep the rpm,s up it will stay running. Drilled out the idling screw and bumped the idling, still stalls at idle,could it possibly be the computer or the prom, there is notrhing left. thanks

  • miken277 Feb 01, 2009

    1989 Honda accord.  Idles low and rough, stalls out when applying gas.  When the coolant was low, it would cycle between high and low rpms wierdly, but that fixed it just idles low now.  Will not restart.  Exhaust smells like fuel.  

  • Barry Mar 12, 2009

    I have no pulse to the injectors, what make the injectors pulse

  • how can you have pulse and no injector spray if you have the right fuel pressure did you jump the injectors to see if they are opening sound like you have no fuel pressure

  • do you have pulse to the injectors

  • is the egr stuck open just alittle did you take it off and check? or is the pcv broke like an open vac



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The distributor module and pick up coil

Posted on Mar 14, 2009

  • Call me it would be easier @ Rocky's Performance Motors, ask for Joe. (772) 334-0789


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Posted on Dec 28, 2008


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My 92 f150 starts missing and losing power when ambient temperature reaches 85 degrees.Can a weak fuel pump cause this, truck runs great on cool days and at night

Check the fuel pressure when it's messing up ! Also check for strong spark ,pull a plug wire off a spark plug an hold to ground ! Ignition problem maybe - ignition module ? A weak fuel pump would be weak hot or cold ! Now electronics are a different story ! I have had ford pick-ups from the age run great cold but when they got hot quit working altogether ,then when they cold down , they started right up again ! The important thing is to test not guess , be sure what's wrong before you replace parts ! There is a good video on you tube from scanner Danner on a ford pick up you should check out ! Good luck ,hope this helps !

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Are you getting fuel and check for spark and if all is well, then move to your fuel pump and if checks out okay , ignition module and pick up module and coil have checked out .

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Did they do a fuel pressure pressure test to determine that its fuel pump? And if so what was the p.s.i.?It should be around 55 to 60 p.s.i. a few pounds under 55 p.s.i. Pump needs replaced, Your shop should have chk. this when it was there the first time. Did they by chance chg. the fuel filter, that can hinder it from starting too.

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Try replacing the ignition control module it is located under the distributor cap Cost is around $30.

Jan 10, 2009 | 1991 GMC S-15 Jimmy

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1995 gmc Jimmy

maybe bad ignition module or coil.. when they get hot sometimes they wanna die...

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make sure to check for and aftermarket ignition module installation in other words make sure the ignition module is factory and not aftermarket,
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