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Thread: Engine bogs on acceleration under 2000rpm

  1. #1
    Senior Member
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    Question Engine bogs on acceleration under 2000rpm

    So, now that the car is running and the weather is nicer I can finally drive my DeLorean. However, there's a hesitation when I accelerate from a stop and occasionally when I change gears if I let the RPMs drop.

    The trigger seems to be about 2,000rpm. Above that mark and the engine sounds great, below that mark and the engine sputters and lacks power and RPMs slowly climb. It doesn't seem to matter if the engine is warmed up or completely cold. It also doesn't seem to matter how much gas I give it with the pedal.

    Looking to solve this problem but I'm not sure where to look. Anyone have any good experiments​ to try to figure out more details? Or maybe someone knows exactly what the culprit is...

  2. #2
    Senior Member Bitsyncmaster's Avatar
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    Probably a fuel problem if it started doing this after storage. How old is your gas? Have you ever adjusted the mixture?
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #3
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    Quote Originally Posted by Bitsyncmaster View Post
    Probably a fuel problem if it started doing this after storage. How old is your gas? Have you ever adjusted the mixture?
    I don't think it's the fuel itself. I filled up the tank about four months ago but I specifically got non-ethanol 91 octane because I knew it was going into "storage", I started it and drove it a couple of times through the winter. The times I drove it, it had the same problem.

    Also, I adjusted the fuel mixture last which was about four months ago too: https://youtu.be/BMU5bRmaSCA I think that was the last thing I fixed before winter really set in.

  4. #4
    Senior Member Jonathan's Avatar
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    Dave may be right that it is related to old fuel, however, I was initially thinking it was more an idle system issue since it goes away at 2,000+ RPM.

    Perhaps a simple thing to check for first, and at least rule out something none of us other than you can see, is that all your vacuum hoses and electrical connections are good and snug and not in disarray. Check the fuse and relay area behind the passenger seat as well as the ECU box area behind the driver's seat for any signs of mice or other nonsense.

    You might also want to go through all the other odds and ends on the car like lights, horns, stereo, windows, instrument cluster, etc. and just confirm everything is working as expected. If something got screwy over the winter within the electrical system, spotting something else not quite right might help you figure out what the common thing is and find the problem that way. Easy things to check and you don't have to take anything apart nor adjust anything you might not have needed to, and it's free to boot.
    One damn minute Admiral...


  5. #5
    Delorean Guru
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    Something quick to check, the base timing, mechanical and vacuum advance. Also vacuum leaks, they have a much greater effect at lower RPM's.
    David Teitelbaum

  6. #6
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    Quote Originally Posted by David T View Post
    Something quick to check, the base timing, mechanical and vacuum advance. Also vacuum leaks, they have a much greater effect at lower RPM's.
    How does one test the mechanical and vacuum advance?

    And what's the best way to check for a vacuum leak?

  7. #7
    Senior Member Jonathan's Avatar
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    Quote Originally Posted by spikeygg View Post
    And what's the best way to check for a vacuum leak?
    The best way? Probably some sort of smoke machine that when you put the "smoke" close to different parts of the engine, you would see it get sucked in to where the leak is.

    Next best, or practical in lieu of the smoke machine? Listen for hissing or look at your hoses carefully and see if any are cracked, especially at the ends, or not on very well all together.

    I hadn't realized earlier that you had this issue since before you put the car away into storage. What changed back then that you think might have contributed? What happened that you were inclined to adjust the mixture?
    One damn minute Admiral...


  8. #8
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    Cool

    The way I've always found vacuum leaks is to start with a cold engine, start up then spray carburetor cleaner at all like areas of leak, particularly at fuel injection rubber seals but generally anywhere vacuum could exist. As the engine warms up be very careful not to spray on hot surfaces like exhaust manifolds as they will ignite the cleaner long enough to melt wiring and engine paint. Another method is to use a thick grocery plastic bag over the top of the throttle body, if the engine dies then you have little to no vacuum leaks if it keeps running you got a leak that you will probably hear. Also vacuum at the power brake booster and behind the a/c module in the dash.

  9. #9
    Delorean Guru
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    To look for vacuum leaks you start by doing a visual inspection looking for any hoses that could be knocked loose, cut, split, or broken. For the sneaky ones you really do need a smoke machine. To check the timing you need a timing light.
    David Teitelbaum

  10. #10
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    Quote Originally Posted by Jonathan View Post
    I hadn't realized earlier that you had this issue since before you put the car away into storage. What changed back then that you think might have contributed? What happened that you were inclined to adjust the mixture?
    I had inherited this vehicle last year and it wasn't in the best of shape when I got it. There were several things wrong with it including a rebuilt engine that someone tried to tune without noticing that the WOT switch was stuck closed. The mixture screw was so lean that I had difficulty starting the car. Anyway, it might be a vacuum leak. I've got some things to try now.

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