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454 Will Not Stay Running

This is a discussion on 454 Will Not Stay Running within the Technical / Maintenance forums, part of the General Discussion category; 1994 GMC K2500 7.4L WILL NOT STAY RUNNING UNLESS I DISCONNECT THE VACCUM FROM THE MAP SENSOR BUT IT STILL ...

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    M4-SCOUTHUNTER
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    Exclamation 454 Will Not Stay Running


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    1994 GMC K2500 7.4L WILL NOT STAY RUNNING UNLESS I DISCONNECT THE VACCUM FROM THE MAP SENSOR BUT IT STILL RUNS RICH. WHEN I HOOK IT BACK UP IT DIES. I HAVE REPLACED THE FUEL PUMP AND SENDING UNIT, FUEL FILTER, MAP SENSOR, IGNITION CONTROL MODULE, TPS SENSOR, EGR VALVE, PCV VALVE, VACCUM LINES, TIMING CHAIN, CHECKED & CLEANED THROTTLE BODY, DIST.CAP & ROTOR, PLUGS AND WIRES, ANY IDEAS? :fsc: .
    Last edited by K2500BURBAN94; 04-19-2008 at 04:30 PM.

  2. #2
    GMC RULZZ NEUMANNZZ's Avatar
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    Re: 454 Will Not Stay Running

    check engine light on?
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
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    Re: 454 Will Not Stay Running

    when you disconnect the vacuum line going to the map sensor whats vacuum reading at the hose? how many miles on it? have you checked compression?
    Last edited by NEUMANNZZ; 04-19-2008 at 04:35 PM.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
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    Re: 454 Will Not Stay Running

    No Light On.

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    M4-SCOUTHUNTER
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    Re: 454 Will Not Stay Running

    149k, Compression Is Good As Far As The Reading I Dont Know

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    GMC RULZZ NEUMANNZZ's Avatar
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    Re: 454 Will Not Stay Running

    when you remove the vacuum hose whats the idle speed?

    when it wont stay running is it after you start it and then idle settles down or starts then shuts off immediately?
    when you removed the throttle body did you remove the iac valve and clean it also.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
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    Re: 454 Will Not Stay Running

    I had a similar problem with my Buick. Ran like crap and no check engine light. I plugged my GM OBD1 in and it pulled a stored coil pack fault code, even though the light was not on the computer will store old codes, so go to a Auto Part Store and they will check it for free. Hope that helps?
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    M4-SCOUTHUNTER
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    Re: 454 Will Not Stay Running

    it starts then shuts off immediately

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    Re: 454 Will Not Stay Running

    try to disconnect the est wire(set timing wire) if it starts and runs ok replace pick up coil.

    if it still immediately dies turn ignition on engine off jumper pin A and B of diagnostic port listen for iac moving.(not 100 percent sure this test will work)
    Last edited by NEUMANNZZ; 04-19-2008 at 06:03 PM.
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    Re: 454 Will Not Stay Running

    I can't try till Monday because its locked in a garage for the weekend but I will try that out.

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    Re: 454 Will Not Stay Running

    when you disconnected the vacuum hose did you leave it open or plug it? if open im thinking iac valve stuck shut. engine needs air to run at idle with throttle closed.(ecm controls idle speed with iac valve cold(high idle) to warm
    Last edited by NEUMANNZZ; 04-19-2008 at 06:51 PM.
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
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    Re: 454 Will Not Stay Running

    Open I think. I'm not 100% sure i'm not the only one working on it.

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    Re: 454 Will Not Stay Running

    IAC valve good, vac. line was plugged when off of map sensor. Now checking pick up coil and injectors more to follow. Any other ideas? This thing has been kicking my butt!

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    GMC RULZZ NEUMANNZZ's Avatar
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    Re: 454 Will Not Stay Running

    also there is another test for the pick up coil.(oh
    check with multimeter.
    go here:

    http://www.autozone.com/az/cds/en_us...rInfoPages.htm
    O2 GMC RCSB 4.8L V8 AUTO 3.73's
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    Re: 454 Will Not Stay Running

    my toyota did the same thing come to find out the vaccum hose came disconnected from the valve cover.. check too see if its tight.. worth a try worked for me
    To LA'GIT to QUIT!!!

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    Re: 454 Will Not Stay Running

    Pick up coil good. IAC valve good r&r'd it anyway. Injectors good. Brand new plugs fouled because it's running so rich when off the map but when I hook up map it dies? Do you think it might be the ECM playing games or is it a ghost in the machine?

  17. #17
    M4-SCOUTHUNTER
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    Re: 454 Will Not Stay Running

    Hey thanks for the tip but all vaccum lines are slap new and have been checked and rechecked. I'm starting to think this is something supernatural!

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    Re: 454 Will Not Stay Running

    This sounds very similar to what i was going thought last summer with my 88, basiccaly replaced everything you have gone thought trying to figure it out, it would start and run really really rough or would just shut off right away and it wouldnt give me any engine codes and it ended up being a bad ground on the thermostat housing so i would deffinatly check your grounds. Mine did not even look damaged but that was the problem the whole time.
    Good luck man

    -1988 c1500

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    Re: 454 Will Not Stay Running

    my buddies plow truck (older 454)was having some problems at idle and wouldn't stay running. We gave up and took it to dealer and it was a fuel pressure regulator?? I don't know about your situation, but it sounds like you've checked most everything. Also I was reading a thread the other day and a guy had a bad O2 sensor that was causing the truck to run rich and it had actually plugged a cat and the truck was slowly losing power and not wanting to run. Sorry I'm not much help just trying to throw some more ideas at you. GOOD LUCK!!

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    Re: 454 Will Not Stay Running

    When it dies, do you lose spark? Does it die like someone shut off the key?

    Get one wire off and put on a spark plug and ground it to the engine. Have someone start it up and watch when it dies, does the spark go away or does the spark keep sparking?

    Is the fuel pump priming? When you turn key of, does fuel pump come on for up to 2 seconds? Then when you start, does it stay on? (you'll need to be back under the tank to hear it). Best to use a fuel pressure gauge. Make sure you are getting full pressure and it must stay on.

    These 2 will give you direction....Fuel or spark.... It sounds to me like one injector might be locked on and dumping fuel and not spark related. Or FPR leaking fuel in the engine.

    Try this. Unplug the injectors (this is a safety issue!!!) and crank it and spray carb cleaner in the throttle body, can you make it run on it? If you leave injectors plugged in you have a high risk of fire, so PLEASE DO NOT DO!
    Last edited by N0DIH; 04-22-2008 at 07:25 AM.

 

 
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