DMCH new style fuel pump thoughts.

[hippieman9]

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 DaveÂ’s RpM relay. So youÂ’re saying a 6mm check valve? Like this? https://www.amazon.com/Return-Check-...ck+valve&psc=1

[FABombjoy]

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 Dave’s hot start relay? Thats what I’m referring to. I tested a lot of stuff with kjet but never the hot start relay function.

[Bitsyncmaster]

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.

[hippieman9]

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 Dave’s hot start relay? Thats what I’m 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.

[FABombjoy]

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.

[Ron]

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.

[FABombjoy]

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.

[hippieman9]

For anyone interested I just finished installing the new DMCH fuel pump. I noticed that it has a plastic cap now for the OE style level sender and comes with a check valve in the feed line. I took this a step further and installed nylon fuel line instead for using the rubber (it seems as though that was the major issue with this style pump.) install was easy. Cleaned the fuel tank, but it wasn’t very dirty because my car is driven. Here are a couple pics of the final install.061165DE-B61C-489C-B392-CD63D1A6A863.jpgC751679A-A45A-4434-A42F-CC23E5B9A316.jpg

[FABombjoy]

Did you get 5/16" nylon line to fit on the provided check valve? If so, tip of the hat, I never would have expected it to fit!

[hippieman9]

Did you get 5/16" nylon line to fit on the provided check valve? If so, tip of the hat, I never would have expected it to fit!

YES!! after many, many tries and fails. LOL I found that I held the nylon fuel line in my Brake tubing flare tool, clamped it in the vise, used a hair drier to warm up the tube, then used needle nose pliers to open up the tube a little, then taped the check valve in with a hammer, slowly. I found that you have to have less tubing than you need on the heat side for the clamp, then move it out a little at a time or the tubing will, bend and kink. Wasn't easy thats for sure, and I was bummed I couldn't get any clamps on the check valve, but it is not leaking so, Fingers crossed!