I need some help shaking down a fuel delivery problem!
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5.0 and 5.7 Discussion, I need some help shaking down a fuel delivery problem! in Cadillac Engine Technical Discussion; Alright, so the other day my '87 307 totally just copped out on me on the way home from work. ...
  1. #1
    FrankieSixxxgun is offline Cadillac Owners Fanatic
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    I need some help shaking down a fuel delivery problem!

    Alright, so the other day my '87 307 totally just copped out on me on the way home from work. It now has a COMPLETE loss of power, and will barely do 35mph. I went in and replaced ALL the vacuum lines, and detatched the exhaust, so I'm pretty sure it's no related to vacuum leaks or a clogged cat. The exhaust is abnormally hot, like too hot to put your hand near, so I think it's either running lean or sparking on the exhaust stroke. You can hear the car huffing now and then out of the exhaust pipe, kinda like a minibackfire but just a pfft, and it accelerates the same regardless of the position of the throttle. Help! I need my baby back on the road.

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    90Brougham350's Avatar
    90Brougham350 is offline Cadillac Owners Connoisseur
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    Re: I need some help shaking down a fuel delivery problem!

    Any codes?

  4. #3
    FrankieSixxxgun is offline Cadillac Owners Fanatic
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    Re: I need some help shaking down a fuel delivery problem!

    No SES light, I haven't tried pulling codes. I'm thinking the problem is deeper than just fuel delivery. The exhaust was REALLY hot, so I might've jumped a tooth on the timing chain or something and now the exhaust valves are slightly hanging open during the end of the combustion stroke. I'm gonna snap my timing light up to it and see if the timing jumped back like 20-30 degrees all of a sudden.

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    FrankieSixxxgun is offline Cadillac Owners Fanatic
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    Re: I need some help shaking down a fuel delivery problem!

    Alright, so the timing is at 18*, which is acceptible to me since I set it at 20* last year. Compression is around 140 PSI, and the fuel pump is delivering fuel at lesat to the filter on the carburetor.

    Now, the engine has codes: 12, 13, 23, and 45 stored. 13 and 45 are O2 sensor related, and 23 has to do with the IAT sensor. How can I bypass these to see if they're causing the problem or if they're just detecting a problem? Is it time for a new carburetor after 207k miles?

  6. #5
    kdrolt is offline Cadillac Owners Member
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    Re: I need some help shaking down a fuel delivery problem!

    Lack of fuel would also cause it to run lean. Bad fuel pump, clogged fuel filter(s) or both. I'll assume you have a mech fuel pump given the Qjet... and the diaphragm in the FP may have failed. You should check the oil dipstick for any smell of fuel (if so -- change the oil and replace the pump).

    You already changed out all the hoses (ruling out a vacuum leak) but there's always a chances that one of the hoses popped off, or that a previously good hard vacuum line failed. So you miight have to check these again.

  7. #6
    FrankieSixxxgun is offline Cadillac Owners Fanatic
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    Re: I need some help shaking down a fuel delivery problem!

    The fuel pump is fairly new and I pulled the fuel line to verify it was spraying fuel when cranked. On man was it!

    Turns out the problem was the Q-Jet itself, I'm assuming the metering solenoid went bad finally. I pulled a carburetor off of a car with 87k on the odometer today at the junkyard, bolted it on my car, and bam, the car runs fine. In fact, it runs even better than it did when I bought it. The junkyard carburetor only cost me $40 too!

  8. #7
    N0DIH's Avatar
    N0DIH is offline Cadillac Owners Master
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    Re: I need some help shaking down a fuel delivery problem!

    If you can make the car stall (unplug HEI is best) the M/C solenoid should be ticking for a few seconds till it realizes the engine is no longer running. That is a good way to do a quick M/C functionality check.

    Glad it wasn't too bad. Now you have a great parts carb!

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