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1994 TBI runs rough on last 1/2 mile home, now won't start.

Discussion in 'GM Powertrain' started by mktylor, Sep 23, 2010.

  1. mktylor

    mktylor New Member

    My wife was driving it so I don't know how it was really behaving, but when I got home, it won't even start. I have the kid try to crank it while I watch the TB, I've got spray from both injectors. Looks like enough to start on. I was basically checking that my fuel pump was functioning.

    Plugs, wires, cap, rotor, ign module and pickup coil are all about 1 year old. The only thing leading up to this that might point to cause would be that it's been experiencing a little flat spot in take off lately, causing a bit of a jerk when taking off. I can't seem to get as smooth a take-off from a stop.

    I checked spark coming out of distributor with an in line spark tester. I didn't check all, just about 4 of them to make sure fire should be getting to the plugs.

    Not sure what to check next. I did see something about the 5.7 TBI being a bit picky about the timing. I may loosen the distributor and see if I can get it to crank with a little timing adjustment.

    Any suggestions?
  2. murdog94

    murdog94 Epic Member 5+ Years 5000 Posts

    I would for sure get a fuel pressure guage and check the actual pressure since 1PSI on a TBI can mean the difference between running and not. Also do a sweep test on your Throttle position sensor (there are severl threads about this here).. There is a chance that it let go. But for sure start with the fuel pressure test. You should be no lower than 12PSI.
  3. mktylor

    mktylor New Member

    here's a long everdue update on a vehicle that I no longer own.

    I had good fuel pressure per the test.

    I did move the distrubutor around and that was the only way to get it to start. Then, it was still a bit difficult.

    I tested the ignition coil 3 times:
    1) tested OK
    2) tested faulty (I hate to replace parts as a means of troubleshooting so I tested it again)
    3) tested good.

    I made the assumption the my 2nd test was faulty and not the coil itself. I had checked the price and they were only $20 or so bucks, but decided not to replace since it tested good afterall.

    After I could no longer figure out what was wrong, and blowing up my muffler from starting with the altered timing, I sent it to the shop for repair.

    It WAS a bad coil. It was so weak that it would only start by advancing (i think) the timing to a point where even the weak fire would crank it.

    Shop charges were $475 for mostly labor. They did change the O2 sensor, and had went into the timing chain to see if it was in bad shape (it did sound like it had a timing issue, even with timing set correctly, due to the poor firing).
    Muffler shop was $150 for new exhaust from the muffler back.

    So $650 later I was good again, all for a $20 part I could have swapped if I had figured it out properly.

    Hope that helps someone in the future

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