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Thread: Car cranks but wont fire up after refuelling

  1. #1
    Junior Member
    Join Date:  Apr 2024

    Posts:    4

    My VIN:    7033

    Car cranks but wont fire up after refuelling

    Helo all,

    I have driven my Delorean without any starting issue for a year and yesterday I have experienced very strange problem. I arrived at the gas station, engine shutdown without any issue. Then refuelled the tank to maximum and all of sudden after rotating the key car cranks, but wont fire up.
    I started analyzing the issue right away and it seemed that fuel pump is silent, so I tried inertia switch, bypass of the fuel pump relay and measuring the voltage at the pump (Got 12V wile cranking), but she was still silent.

    Next day I tried ruling out one possibility after another, but I am starting to be desperate so I would like to ask others, with much more experince than I have, for help.

    What have I tried/know so far:
    - Fuel pump certainly makes some noise while cranking
    - not while connecting the battery (via cut-off switch), which I clearly remember it did for like 4 seconds (At least I hope it was a pump)
    - I do not remeber exactly but the noise seems to be more "bass" now? Not sure if this is healthy pump
    - I think it was more higher pitch noise when I flipped the cut-off switch on.

    - Analyzed bulkhead connectors
    - Unplugged and re-plugged all of them
    - Noticed one wire missing (Loose in the compartment) blue color, seems to be 47 pin (Cold start valve?)
    - Repaired this one
    - All others seems to be OK

    - Analyzed Coil and Rezistors
    - Continuty meter confirms good conenction
    - Rezistors and coil are a bit warm after cranking

    - Removed one spark plug, makes a great spark
    - Ruling out coil and spark plugs
    - Spark plug seemed to be dry? After so many crank attempts? Weird??

    - Fuel smell behind the car is present, but I would expect it to be much more than that after so many start attempts
    - Also the plugs were dry?

    Right now, I am again suspecting the fuel pump, might be faulty? But I need to verify that, somehow ...

    This is my first post here so I hope I will not violate any rules I might have missed.

    Thank you in advance for the help!
    Last edited by Silent159; 06-17-2024 at 05:44 PM.

  2. #2
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

    Location:  Leonardtown, MD

    Posts:    9,039

    My VIN:    03572

    You can try starting the car with the RPM connector jumpered.

    If you took a while filling up the the car after a long drive you may have a bad fuel accumulator.

    If your RPM gauge shows about 500 RPM when cranking you probably have spark so it's most likely a fuel issue.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #3
    Junior Member
    Join Date:  Apr 2024

    Posts:    4

    My VIN:    7033

    First of all, thank you for the suggestions!

    I have tried removing RPM relay (Also called Fuel Pump Relay). Jumpered brown and white/purple cables with 2 male spade connectors.
    Now I hear constant noise from the pump, the same noise I hear when i turn the key with relay in the socket.
    With the jumper I still was not able to start the car.

    I was filling like 3/4 of the tank and the distance to the pump was like 20km at maximum. Can I somehow verify that the fuel accumulator is bad?

    RPM gauge shows aroung 500-1000 RPM while cranking (Its slowly rising after few seconds)
    I also suspect fuel issue, but I am not sure where to start investigating and how to properly analyze the issue.
    Maybe disconnecting the fuel hose from the pump, use a bucket and see if it pumps properly? The disconnect the fuel distributor feeding hose and see if it pumps there?

    Are there any possibilities to "easily" measure the pressure in the fuel system around the distributor/injections??

    Thank you very much for the help!

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

    Location:  Leonardtown, MD

    Posts:    9,039

    My VIN:    03572

    Remove the air cleaner. Run the fuel pump for about 5 seconds. Lightly press that air plate you see where the air cleaner was. It should require a good amount of pressure to move it. Most cars will hold that rest pressure for an hour or more. When there is no rest pressure that plate will move with just a light touch (it will almost bounce).
    Dave M vin 03572
    http://dm-eng.weebly.com/

  5. #5
    Senior Member Rich's Avatar
    Join Date:  May 2011

    Location:  San Francisco Bay Area, Calif.

    Posts:    2,115

    My VIN:    0934

    Club(s):   (NCDMC) (DCUK)

    Welcome to the forum.

    Yes, good plan to get some idea about the fuel pressure with Dave?s air meter plate test.

    I might have missed a detail in your reports. Can you tell us whether the engine restarted at any time since that refueling? (Did you have it towed from the gas station?)

    From your work so far the fuel pressure is probably the issue to address. One other initial non-start test to try is to use spray-type starting fluid during cranking with air cleaner removed. If the engine fires at all with starting fluid then you know it has a fuel delivery problem.
    March '81, 5-speed, black interior

  6. #6
    Senior Member
    Join Date:  Jan 2019

    Posts:    268

    Quote Originally Posted by Silent159 View Post
    First of all, thank you for the suggestions!

    I have tried removing RPM relay (Also called Fuel Pump Relay). Jumpered brown and white/purple cables with 2 male spade connectors.
    Now I hear constant noise from the pump, the same noise I hear when i turn the key with relay in the socket.
    With the jumper I still was not able to start the car.

    I was filling like 3/4 of the tank and the distance to the pump was like 20km at maximum. Can I somehow verify that the fuel accumulator is bad?

    RPM gauge shows aroung 500-1000 RPM while cranking (Its slowly rising after few seconds)
    I also suspect fuel issue, but I am not sure where to start investigating and how to properly analyze the issue.
    Maybe disconnecting the fuel hose from the pump, use a bucket and see if it pumps properly? The disconnect the fuel distributor feeding hose and see if it pumps there?

    Are there any possibilities to "easily" measure the pressure in the fuel system around the distributor/injections??

    Thank you very much for the help!
    To properly diagnose fuel issues, you really need a fuel pressure gauge specifically for Kjet to verify that you are getting the correct pressures, just seeing if fuel is being pumped through is not enough. If the pressures are not correct, it will not be enough to open the injectors that rely on fuel pressure (not just fuel flow) in order to operate.

    You can also pull all your injectors out and place them in each individual jars, and jump the RPM relay as you did to get the fuel pump working. With the pump running, press the air meter flap under the air cleaner, if the injectors all open and begin to spray, monitor the spray patterns from each. Are they dribbling or do they have a nice mist pattern? Allow them to spray for a good minute and then compare the fuel levels of each jar that the injectors were in, are they really close in volume or are some more/less than others? With the pump still running and not touching the air meter, are any of the injectors dripping/leaking? Thsi can cause a flooded engine and would also cause the engine not to start.

  7. #7
    Junior Member
    Join Date:  Apr 2024

    Posts:    4

    My VIN:    7033

    Just to complete my story, I had to towe the car home. Have not been able to fire-up since the issue started.

    I bought ether spray and it started for like 1-2 seconds and stopped (Coil/Spark plugs healthy I assume).

    I tried Daves awesome plate trick and the amount of pressure required to move the plate was very low. Activating the pump has not changed anything.
    The one thing I wanted to aviod was messing with the fuel lines, but I had to, so I removed feeding fuel line from the fuel distributor and while the pump was running not even a drop of fuel went out.
    I tried messing with the pump, swapped output fuel hose from pump with my spare one and put other end to the bucket -> Not even a drop of fuel ...
    Then I have moved the pump a bit out, disconnected intake hose and dropped the pump back into the tank to be partially "submerged" -> Not even a drop of gas in the bucket after starting the pump.

    I am now certain that the pump, even if it is making some noise while powered, is faulty. I did this after all other steps because I heard "some noise" from the tank and assumed that the pump is running, wrong assumption.

    Now the only question is if replacing the pump will be the only problem to fix. I hope nothing else in the fuel system is not faulty, resulting in killing the pump. Is this even possible?

    Anyway, new pump is on the way and I would like to thank all of you here for the support and tips & trick you have provided. That helped me a lot!
    Last edited by Silent159; 06-18-2024 at 03:58 PM.

  8. #8
    Senior Member 82DMC12's Avatar
    Join Date:  May 2011

    Location:  Olathe, KS

    Posts:    1,723

    My VIN:    11596

    Quote Originally Posted by Silent159 View Post
    Just to complete my story, I had to towe the car home. Have not been able to fire-up since the issue started.

    I bought ether spray and it started for like 1-2 seconds and stopped (Coil/Spark plugs healthy I assume).

    I tried Daves awesome plate trick and the amount of pressure required to move the plate was very low. Activating the pump has not changed anything.
    The one thing I wanted to aviod was messing with the fuel lines, but I had to, so I removed feeding fuel line from the fuel distributor and while the pump was running not even a drop of fuel went out.
    I tried messing with the pump, swapped output fuel hose from pump with my spare one and put other end to the bucket -> Not even a drop of fuel ...
    Then I have moved the pump a bit out, disconnected intake hose and dropped the pump back into the tank to be partially "submerged" -> Not even a drop of gas in the bucket after starting the pump.

    I am now certain that the pump, even if it is making some noise while powered, is faulty. I did this after all other steps because I heard "some noise" from the tank and assumed that the pump is running, wrong assumption.

    Now the only question is if replacing the pump will be the only problem to fix. I hope nothing else in the fuel system is not faulty, resulting in killing the pump. Is this even possible?

    Anyway, new pump is on the way and I would like to thank all of you here for the support and tips & trick you have provided. That helped me a lot!
    Hopefully you bought a DPI fuel pump or similar "new style" because the "new" OEM Bosch style are garbage and will fail early.
    Andy Lien

    VIN 11596 Jan 1982 build - owned since Nov. 2000!
    Total frame-off restoration completed 2021-2023

    Photography and Backpacking is life.

    Was Fargo, ND
    Now Kansas City

  9. #9
    Senior Member glockworks21's Avatar
    Join Date:  May 2022

    Location:  lincoln ca

    Posts:    230

    My VIN:    nov 81 6900-

    two cents.

    I had issues with the connector on the fuel pump. Im no expert, and dont know what it would do if one or more of the 4 wires going into it wasnt making a connection, but it may be worth looking at.. i had mine locked in place with the factory connector and it seemed very secure. every once in awhile mine would do exactly as yours. there are many threads talkng about that connector coming loose.. mine was tight and still did it.. i since removed it and directly connected the wires to the fuel pump.. its never done it since...

    if the car didnt start i would just tap on the top of the connector and it fired right up..

  10. #10
    Senior Member glockworks21's Avatar
    Join Date:  May 2022

    Location:  lincoln ca

    Posts:    230

    My VIN:    nov 81 6900-

    to clarify my point, I dont know if that pump would make noise and not pump if just one of the four wires wasnt making a good connection...

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