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Thread: Starts and dies immediately; runs briefly if MAP hose disconnected

  1. #1
    Fuel Injected!
    Join Date
    Jul 2016
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    Weatherford, TX
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    37
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    Starts and dies immediately; runs briefly if MAP hose disconnected

    I am in troubleshooting hell, but I think I see the light. Maybe.

    Randomly died one morning 30 seconds after starting. For troubleshooting background, the Only thing that changed was it had idled the day before for an hour to charge the battery. My wife went and turned it off, reported that it seemed hot. No signs of mechanical problems.

    Now it will start, run for a second and die. I can see the fuel stop spraying from the injectors.

    Went back to a known good bin. Tried different PROM and PCM. Troubleshot fuel pressure, 14 psi steady. Tried spare injectors. Tried new ICM and ignition coil. Verified EGR valve is closed. Oil pressure is good. Tach reads seemingly accurate. O2 sensor output seems inline with what the wide band says. TPS voltage accurate.

    MAP pressure seems weird, but I don't know what normal is. Tried new MAP sensor, same problems. But, if I start it with the MAP hose disconnected, it runs for several seconds, then revs for half a second then dies. Watching the datastream, I can see that with the MAP disconnected, it runs rich for a few seconds, then tries to lean it out, and dies. If at any point I open the throttle at all it dies.

    I can make it idle if I tease the MAP hose on and off of the fitting. I will attach a log file where I was making it idle like that for a few seconds before I let it die.

    What in the ever loving hell is going on?

    The other wild card is that I found some mouse turds on the intake manifold. No chewed wires found, but I haven't taken off the dash or probed any wires yet.

    I'll buy a six pack for whoever can solve this damn thing.
    Attached Files Attached Files
    1994 Chevy G30 Van "Big Blue"
    5.7 TBI, Vortec Heads, Summit Intake, Thorley Short Headers with dual 2.5" exhaust, 4L80E transmission

  2. #2
    Fuel Injected!
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    As someone pointed out in a private message, I should clarify that it is the vehicle in my signature. 16197427 pcm.
    1994 Chevy G30 Van "Big Blue"
    5.7 TBI, Vortec Heads, Summit Intake, Thorley Short Headers with dual 2.5" exhaust, 4L80E transmission

  3. #3
    Fuel Injected!
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    No ideas?

    I've now replaced the distributor pickup coil. Same thing. Will idle for 5-10 seconds with the MAP sensor vacuum hose is disconnected. Starts and dies in uner a second if the MAP sensor is connected.
    1994 Chevy G30 Van "Big Blue"
    5.7 TBI, Vortec Heads, Summit Intake, Thorley Short Headers with dual 2.5" exhaust, 4L80E transmission

  4. #4
    Fuel Injected!
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    I guess I should have said that it uses the OE xdf.

    Here is a log I took today. I alternated between starting it with the MAP hose connected and disconnected. You can see which is which because with it disconnected the MAP stays at 100 the whole time.

    If you can look at the log and give ANY feedback at all it would be appreciated.
    Attached Files Attached Files
    1994 Chevy G30 Van "Big Blue"
    5.7 TBI, Vortec Heads, Summit Intake, Thorley Short Headers with dual 2.5" exhaust, 4L80E transmission

  5. #5
    Fuel Injected!
    Join Date
    Nov 2016
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    I had a similar issue when I built my setup but it sounds like your car was already running fine as is. My car had the map wires reversed. It was also doing strange things before I made the switch in the KPA rows. I also had a map sensor before that looked good but tested bad. Replaced it and that fixed the issue. How long have you ran it in closed loop? correct injector offsets? Is your battery dead again or low voltage?

  6. #6
    Fuel Injected!
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    Jul 2013
    Location
    Newzealand
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    are you running vehicle anti theft in the tune sounds a bit like its active.all the cars i deal with will start and die when vats is active

  7. #7
    Fuel Injected!
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    I think maybe it's the memcal. I'm looking for a known good one to try.
    1994 Chevy G30 Van "Big Blue"
    5.7 TBI, Vortec Heads, Summit Intake, Thorley Short Headers with dual 2.5" exhaust, 4L80E transmission

  8. #8
    Super Moderator dave w's Avatar
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    I have an unconventional and potentially dangerous way to help figure why the engine starts and dies.

    I'd pour about 4 oz of fuel down the throttle body and start the engine and see how long the engine will run with the map sensor connected. If the engine keeps running for more than a second, I'd pour another 4 oz of fuel down the throttle body to keep the engine running. If the engine keeps running by being bottle feed fuel, I'd be thinking there is a fuel problem to figure out.

    If the engine still starts and dies after being bottle feed fuel, I'd be thinking there is a spark or ignition problem.

    Fuel is very flammable and potentially explosive, proceed at your own risk!

    dave w

  9. #9
    Fuel Injected!
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    Quote Originally Posted by dave w View Post
    I have an unconventional and potentially dangerous way to help figure why the engine starts and dies.

    I'd pour about 4 oz of fuel down the throttle body and start the engine and see how long the engine will run with the map sensor connected. If the engine keeps running for more than a second, I'd pour another 4 oz of fuel down the throttle body to keep the engine running. If the engine keeps running by being bottle feed fuel, I'd be thinking there is a fuel problem to figure out.

    If the engine still starts and dies after being bottle feed fuel, I'd be thinking there is a spark or ignition problem.

    Fuel is very flammable and potentially explosive, proceed at your own risk!

    dave w
    I can keep it running on starting fluid ;)

    First thing I did was get a fuel pressure gauge. Fuel pressure and supply is good.
    1994 Chevy G30 Van "Big Blue"
    5.7 TBI, Vortec Heads, Summit Intake, Thorley Short Headers with dual 2.5" exhaust, 4L80E transmission

  10. #10
    Fuel Injected!
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    Weatherford, TX
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    I'm buying another running van tomorrow. I'm going to rob the memcal. I'll fix this damn thing if I have to swap every damn part one at a time.
    1994 Chevy G30 Van "Big Blue"
    5.7 TBI, Vortec Heads, Summit Intake, Thorley Short Headers with dual 2.5" exhaust, 4L80E transmission

  11. #11
    Super Moderator dave w's Avatar
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    Quote Originally Posted by wanderingturtle View Post
    I can keep it running on starting fluid ;)

    First thing I did was get a fuel pressure gauge. Fuel pressure and supply is good.
    What happens when a noid light is connected to the injector connectors?

    dave w

  12. #12
    Fuel Injected!
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    Does the engine still have an EGR valve ? If so is it operational and closed fully at idle ?

    TOM
    1994 3500 Dually , 502 (509) , 264HR , Edelbrock MPFI , PFI '7427
    2006 Forest river-Sierra 37' 5th wheel
    1999 Astro Van, L31 Vortec , 4x4 conversion
    1994 Pontiac Sunbird "Work ride"
    1993 K-3500 "Ex-diesel" 454/4L80E - '7427
    1992 454SS "Eh Stock" , Blower & '7427 swap .
    1992 S-10 434 SBC/Tremec - '7427
    1984 S-10 , SAS, 496/700R4/205 , D44/14BFF -'7427
    1980 Z-28 454/700R4
    1977 Olds 98 Regency 403/700R4

  13. #13
    Fuel Injected!
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    Jul 2016
    Location
    Weatherford, TX
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    I appreciate the replies. This situation is saddening and stressful. My boys and I have put a lot of hours into this van with the interior and upgrades, and now it seems like maybe we made the wrong choice. I really hope I can get this fixed.

    I got the other van today. The computer from that van put into this van yields the exact same results. The computer from this van into the new van runs just fine. So computer issues are not the problem.

    It does have EGR and it is closed.

    W
    1994 Chevy G30 Van "Big Blue"
    5.7 TBI, Vortec Heads, Summit Intake, Thorley Short Headers with dual 2.5" exhaust, 4L80E transmission

  14. #14
    Fuel Injected!
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    Weatherford, TX
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    Here is what it looks like with a noid light on the injector connector. The part where i fiddled with the tube was because I've had a few beers and I thought I needed to be clear that the tube was disconnected, lol.

    https://www.youtube.com/watch?v=86qn...ature=youtu.be

    It is dieing because of a lean condition.
    1994 Chevy G30 Van "Big Blue"
    5.7 TBI, Vortec Heads, Summit Intake, Thorley Short Headers with dual 2.5" exhaust, 4L80E transmission

  15. #15
    Fuel Injected!
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    Jul 2016
    Location
    Weatherford, TX
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    So here's where I'm at. Fuel supply is fine, judging by the fuel pressure gauge and the fact that by teasing the MAp tube off and on it can run indefinitely.

    It runs with the MAP tube being disconnected because apparently that triggers AE. I don't know why.

    So what remains is why is fuel being cut? All ignition parts are verified good. All fuel parts are verified good.

    I have not touched knock sensor or oil pressure sensor yet.

    I did try running with the O2 sensor disconnected. No difference.

    What is telling the PCM to cut fuel?
    1994 Chevy G30 Van "Big Blue"
    5.7 TBI, Vortec Heads, Summit Intake, Thorley Short Headers with dual 2.5" exhaust, 4L80E transmission

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