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Thread: Hard start cold or hot but runs good

  1. #11
    Member
    Join Date:  Sep 2019

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    fuel issue

    Quote Originally Posted by northeast dmc View Post
    Thanks for the feedback, I am guilty of adjusting it, slightly without using the dwell. And now that I have the timing dialed in and will get the dwell and fine tune the CO adjustment should put me in good shape. And hopefully work through the fuel issue. Then on to getting some of the finer details worked out.
    Well the saga continues. I finally emtied the fuel tank, cleaned it out, put fresh gas in ans still crud in the tank. Not sure what I missed. The bigger issue is after I clean the screens on the fuel pump, put it back together it wont acelerate. Starts fine idles fine but cant accelerate, if I get out and manipulate the pressure plate while moving the throttle it will run fine. I am thinking vacuum leak, but why wouldnt it show up initially? This morning I went out started it right up like it always does, drove 7 miles or so shut it off got my coffee, went back out it started right up and yup like every time cant accelerate beyond say 1300 rpm, tach gauge is alittle erratic. Drive home clean the screens, and it wont go beyond the certain rpm. If I let it sit and cool down in the past it will run fine. Is there something heat related that might cause a vacuum leak after it gets hot?
    Any help greatly appreciated, would like to get beyond this so I can work on the other items that need attention.

  2. #12
    Under Ron's watchful eye. Glory be to Ron! Michael's Avatar
    Join Date:  May 2011

    Posts:    4,054

    My VIN:    None of your business you creepy psycho vin counter...get a life

    Don't discount the fuel pump being bad or getting low voltage. Next time it exhibits this issue, check your voltage at the pump (possibly a corroded plug or wire splice) and the pressure to the distributer. One of the hallmarks of a pump going out is it fails at temp but runs perfect when cold.

  3. #13
    Member
    Join Date:  Sep 2019

    Posts:    76

    fuel

    Quote Originally Posted by Michael View Post
    Don't discount the fuel pump being bad or getting low voltage. Next time it exhibits this issue, check your voltage at the pump (possibly a corroded plug or wire splice) and the pressure to the distributer. One of the hallmarks of a pump going out is it fails at temp but runs perfect when cold.
    Update, I just drove the car for 15 to 20 minutes non stop, ran fine an occasional hickup, but other than the slight stumble at the low end ran until I got home. I pulled the pump and cleaned the screens, tried to drive again and still the issue with any acceleration. Idle all day, just dont try top go anywhere in a hurry. Relatively new pump and wires, and being I am constantly plugging and unplugging the connections are good. But the point of acting up when hot makes me wonder as if I let it sit and cool down it will run good. hmmm, guess it is time for fuel pressure gauge. What should the pressure be? I can look it up once I get the gauge.

  4. #14
    Senior Member Rich's Avatar
    Join Date:  May 2011

    Location:  San Francisco Bay Area, Calif.

    Posts:    1,686

    My VIN:    0934

    Club(s):   (NCDMC) (DCUK)

    Primary fuel pressure is ~75 psi regardless of temperature or flow rate.

    Quote Originally Posted by northeast dmc View Post
    What should the pressure be? I can look it up once I get the gauge.
    March '81, 5-speed, black interior

  5. #15
    Member
    Join Date:  Sep 2019

    Posts:    76

    fuel issue

    Quote Originally Posted by Rich View Post
    Primary fuel pressure is ~75 psi regardless of temperature or flow rate.
    Thank you.

  6. #16
    Member
    Join Date:  Sep 2019

    Posts:    76

    fuel issue

    Quote Originally Posted by northeast dmc View Post
    Update, I just drove the car for 15 to 20 minutes non stop, ran fine an occasional hickup, but other than the slight stumble at the low end ran until I got home. I pulled the pump and cleaned the screens, tried to drive again and still the issue with any acceleration. Idle all day, just dont try top go anywhere in a hurry. Relatively new pump and wires, and being I am constantly plugging and unplugging the connections are good. But the point of acting up when hot makes me wonder as if I let it sit and cool down it will run good. hmmm, guess it is time for fuel pressure gauge. What should the pressure be? I can look it up once I get the gauge.

    Well round 2 of updates, last for today. Well did deep cleaning of tank, AGAIN, left pump out, put fuel in and checked tank was crystal clear. Drove to mgas station running as usual, shut it off put about 8 gallons of 91 ethanol free in started it and same result, limped home. Checked the voltage at the fuel pump connection and read 11.5. Went to the back and checked the jumper post and read around 14 volts. Is the voltage reading of 11.5 low enough to cause an issue? I did check the voltage earlier today to verify the positive wire just to be sure and with the car off it read 13 volts. So is pressure gauge my next move, and where do you get the adaptor for the banjo bolts to go to the gauge? If it cools off enough I will try to get a reading at the pump with it cool tonight just for curiosity. Wont get to it until end of the week with work and all. Let me know if I should order the tester, probably cant hurt I assume.

    Thanks for the help.

  7. #17
    Senior Member
    Join Date:  Nov 2013

    Location:  NYS

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    My VIN:    Formerly 10372, currently 4728 & 4519

    I wonder if a failing RPM relay would cause that voltage symptom (?)

    If we get an affirmative on that, I'll bring you a replacement relay to try.

    I'm also planning to get a fuel pressure test kit, but not sure how soon it'll arrive.
    Last edited by Rich_NYS; 05-17-2020 at 08:03 PM.
    Livin' the dream....

  8. #18
    Senior Member Rich's Avatar
    Join Date:  May 2011

    Location:  San Francisco Bay Area, Calif.

    Posts:    1,686

    My VIN:    0934

    Club(s):   (NCDMC) (DCUK)

    I've never used a K-Jet pressure test kit. Here is one that pops up from a web search on those terms:

    https://www.amazon.com/Tool-Aid-33865-K-Jetronic-Injection/dp/B0002SR5NU


    I'm sure there are others. Somebody can comment on whether that's a quality tool or not.

    Quote Originally Posted by northeast dmc View Post
    So is pressure gauge my next move, and where do you get the adaptor for the banjo bolts to go to the gauge? If it cools off enough I will try to get a reading at the pump with it cool tonight just for curiosity. Wont get to it until end of the week with work and all. Let me know if I should order the tester, probably cant hurt I assume.
    March '81, 5-speed, black interior

  9. #19
    Senior Member
    Join Date:  Jul 2017

    Location:  Indianapolis, Indiana

    Posts:    144

    My VIN:    04629

    Any reason for a New Tool, Hell Yes....

    Quote Originally Posted by Rich View Post
    I've never used a K-Jet pressure test kit. Here is one that pops up from a web search on those terms:

    https://www.amazon.com/Tool-Aid-33865-K-Jetronic-Injection/dp/B0002SR5NU


    I'm sure there are others. Somebody can comment on whether that's a quality tool or not.
    I'm not a tool reviewer, but this looks very similar to a Bosch unit I have with the "T" fitting & valve, indispensable tool when trouble shooting K-Jet.

    Yes, you should buy it....!

  10. #20
    Delorean Guru
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    Club(s):   (DMA)

    From your comments it sounds like the problem is intermittent. It would be more likely to be an electrical problem than a fuel problem. A bad (contaminated) O2 sensor is usually less sensitive and acts more slowly. Running too rich for a while can contaminate it. A bad connection or a connector not making good contact in a plug are the most likely suspects.
    David Teitelbaum

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