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Thread: DMCH new style fuel pump thoughts.

  1. #31
    Senior Member hippieman9's Avatar
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    My VIN:    06668 81' Grey interior, 5 speed, Grooved hood. Previous owner of 16301, in 2001.

    Quote Originally Posted by FABombjoy View Post
    Feed side only. Needs to be rated for gasoline fuel injection.

    Without the check valve the accumulator spring will decompress and drain fuel back into the tank through the fuel pump, causing a loss of rest pressure. Since deleting the check valve I can now hear this at every shutdown (a slow "bong.... bong.... bong... noise from the center of the frame). If you have EFI it doesn't matter since they don't vapor lock like K-jet.

    If you have a hot start relay it honestly might not matter either. The HSR will help purge the fuel lines via the CSV at every startup which helps eliminate the rest pressure portion of the accumulator's job.
    I have Dave’s RpM relay. So you’re saying a 6mm check valve? Like this? https://www.amazon.com/Return-Check-...ck+valve&psc=1

  2. #32
    '82 T3 Turbo FABombjoy's Avatar
    Join Date:  May 2011

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    No, that one is probably cheap garbage. Look toward Jegs or Summit and see if they have anything. You can adapt just about anything to work, so quality should precede fitting style.

    Do you have Daves hot start relay? Thats what Im referring to. I tested a lot of stuff with kjet but never the hot start relay function.
    Luke S :: 10270 :: 82 Grey 5-Speed :: Single Watercooled T3 .60/.48 :: Borla Exhaust :: MSD Ignition :: MS3X Fully SFI Odd-fire EFI :: DevilsOwn Methanol Injection

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  3. #33
    Senior Member Bitsyncmaster's Avatar
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    The problem with loss of rest pressure quickly is the injector hoses fill with bubbles. You can prime the fuel system but that will not do anything for the bubbles in the injector lines. The air plate has to move down to start purging those lines.

    The hot start relay will fire the CSV and most likely get your engine turning fast enough to move that air plate down a little. But it can take a minuet or two to really clear all the injector lines of bubbles.

    Hence the hot start relay is really not the correct fix for rest pressure falling to quickly. My RPM relay can be jumpered to extend rest pressure for 3 more hours but you need to hold rest pressure for at least one hour for that to work.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  4. #34
    Senior Member hippieman9's Avatar
    Join Date:  Jan 2018

    Location:  Haw River, NC

    Posts:    128

    My VIN:    06668 81' Grey interior, 5 speed, Grooved hood. Previous owner of 16301, in 2001.

    Quote Originally Posted by FABombjoy View Post
    No, that one is probably cheap garbage. Look toward Jegs or Summit and see if they have anything. You can adapt just about anything to work, so quality should precede fitting style.

    Do you have Daves hot start relay? Thats what Im referring to. I tested a lot of stuff with kjet but never the hot start relay function.
    No I don't have his Hot Start Relay, Just the Rpm Relay.

  5. #35
    '82 T3 Turbo FABombjoy's Avatar
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    Quote Originally Posted by Bitsyncmaster View Post
    The hot start relay will fire the CSV and most likely get your engine turning fast enough to move that air plate down a little. But it can take a minuet or two to really clear all the injector lines of bubbles
    Ah, gotcha. Never tried it and I definitely would keep the accumulator for K-Jet. Even if you could cure the hot-start without an accumulator, transient fuel response would suffer.

    Seems like a lot of OEMs came up with solutions for K-jet hot starts. Mercedes added a solenoid to force the plate to move if long cranking times were happening:
    http://www.peachparts.com/shopforum/...startlores.jpg

    Some Porsche 928 Euro had a hot-start valve that drops control pressure to 0 when cranking.
    Luke S :: 10270 :: 82 Grey 5-Speed :: Single Watercooled T3 .60/.48 :: Borla Exhaust :: MSD Ignition :: MS3X Fully SFI Odd-fire EFI :: DevilsOwn Methanol Injection

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  6. #36
    Administrator Ron's Avatar
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    Quote Originally Posted by FABombjoy View Post
    Ah, gotcha. Never tried it and I definitely would keep the accumulator for K-Jet. Even if you could cure the hot-start without an accumulator, transient fuel response would suffer.

    Seems like a lot of OEMs came up with solutions for K-jet hot starts. Mercedes added a solenoid to force the plate to move if long cranking times were happening:
    http://www.peachparts.com/shopforum/...startlores.jpg

    Some Porsche 928 Euro had a hot-start valve that drops control pressure to 0 when cranking.
    I'm thinking you deserve the Daily DMCTalk Research Award.

  7. #37
    '82 T3 Turbo FABombjoy's Avatar
    Join Date:  May 2011

    Location:  Lansing, MI

    Posts:    624

    My VIN:    10270

    Quote Originally Posted by Ron View Post
    I'm thinking you deserve the Daily DMCTalk Research Award.
    Trivial research anyway I really wanted Turbo K-jet to work well and read a lot of service literature from Volvo, Porsche, and other companies that ran K-jet for years after DMC ceased operation. It's interesting how OEMs had many different ways of improving the mousetrap.
    Luke S :: 10270 :: 82 Grey 5-Speed :: Single Watercooled T3 .60/.48 :: Borla Exhaust :: MSD Ignition :: MS3X Fully SFI Odd-fire EFI :: DevilsOwn Methanol Injection

    Console5.com - Game console parts, kits, games and more. [shop] [wiki] [RSS] [f] [t]

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