Hot start problem resolved due to failed check valve in the DMCH fuel pump

[jawn101]

I agree that this setup seems to be a big improvement over the original. I haven't had any issues with my fuel sender not reading correctly on the new unit. And DMCH is now selling the new setup with a brass external check valve (with a price tag now of $419 instead of the original $399). Of all the units that have been sold thus far, this is the only one that I've heard of having this type of a leak.

Just my awesome luck...

[Ryan S.]

I also cleaned my tank twice between repairs. Mine was very clean. Didn't really have to clean.

[Bitsyncmaster]

So far it seems it fixed the old problem of the pump buzzing when the fuel gets hot. I think that buzzing was causing most pump failures.

[Grover]

Just my awesome luck...

I've been using the unit since it first came out. I am on my 4th pump and it seems to be working now (I also installed an in-line check valve). The problem that I have now is that the sender will always read 1/4 tank too high. So when I fill up my gauge is 1/4 past full. This creates an issue since now when the check engine light comes on I have .5 gallons left (ask me how I know, got lucky deciding to fill up).

This has been the case with two pumps so far and can't find the issue. Working on replacing the float arm but can't figure out an easy way to remove it to put the replacement one on. If that doesn't solve the problem I am thinking maybe it is an electrical box issue (the box that came with the unit). I have one of the first ones and it is not sealed, I am thinking maybe it is not reading the resistance correctly from possible moisture entering the box? It shouldn't matter if the float arm is bent or not as the contact point on the swing arm for the gauge should read full no matter what, not push the gauge 1/4 past full.

Has another else run into this problem?

[jawn101]

I also cleaned my tank twice between repairs. Mine was very clean. Didn't really have to clean.

I cleaned my tank again today too, since the whole thing was open and the car is immobile anyway. It was very clean, but I did see one chunk of the old boot that I could grab with my fingers - about 0.5mm around maybe? Unfortunately the second I touched it it turned to dust. So I wiped down the whole freaking thing again - no sense cutting corners!

[DeLorean]

I have the DMCH fuel pump, and I just ordered the usplastic check valve. Now... I can't diss the product, It is nice to have someone selling improved products for these cars, but....... It seems like pretty frequently there is not a whole lot of real world testing of products done by DMCH before they put such things on sale. True to the original manufacturer I guess? I have bought their ball joints, their headlight switch, and now their fuel pump assembly, all of which have proven defective in a time test of actual use.

Now. the headlight switch (so far) has required an uprated fuse to function properly, and the fuel pump (hopefully) will just require this check valve to be reliable, and the ball joints, well... those were just made wrong.

I would love if a new product they intend to sell they would install on a car of theirs for 3 months, drive it 12,000 miles in that time, to verify that they actually FUNCTION properly before they sell them to hundreds of customers, as their test mules.

People who actually drive their D's this stuff just has to work right.

[David T]

I have the DMCH fuel pump, and I just ordered the usplastic check valve. Now... I can't diss the product, It is nice to have someone selling improved products for these cars, but....... It seems like pretty frequently there is not a whole lot of real world testing of products done by DMCH before they put such things on sale. True to the original manufacturer I guess? I have bought their ball joints, their headlight switch, and now their fuel pump assembly, all of which have proven defective in a time test of actual use.

Now. the headlight switch (so far) has required an uprated fuse to function properly, and the fuel pump (hopefully) will just require this check valve to be reliable, and the ball joints, well... those were just made wrong.

I would love if a new product they intend to sell they would install on a car of theirs for 3 months, drive it 12,000 miles in that time, to verify that they actually FUNCTION properly before they sell them to hundreds of customers, as their test mules.

People who actually drive their D's this stuff just has to work right.

DMCH does test their new products but you have to understand that they cannot spend the time and money to run a thorough testing program for all of the possible conditions. That said you still expect better than what history has shown. My guess as to what is happening with the fuel unit is that most of the time you are replacing the old stuff because it got old and cruddy. If you do not COMPLETELY clean the tank spotless, any dirt will just mess up the new parts. Now you start blaming the new parts you put in, not realizing the dirt ruined them. That doesn't explain leaks. Or the inaccurate fuel level indicator.

[Bill6298]

DMCH does test their new products but you have to understand that they cannot spend the time and money to run a thorough testing program for all of the possible conditions. That said you still expect better than what history has shown. My guess as to what is happening with the fuel unit is that most of the time you are replacing the old stuff because it got old and cruddy. If you do not COMPLETELY clean the tank spotless, any dirt will just mess up the new parts. Now you start blaming the new parts you put in, not realizing the dirt ruined them. That doesn't explain leaks. Or the inaccurate fuel level indicator.

David,

Do you think other dirty fuel-related parts could be part of the overall problem? e.g. spotless tank but the return fuel is coming back in contaminated from other K-Jet components.

Bill

[jawn101]

David,

Do you think other dirty fuel-related parts could be part of the overall problem? e.g. spotless tank but the return fuel is coming back in contaminated from other K-Jet components.

Bill

Most people who install the new fuel pump kit have already overhauled the rest of the system, so there should be no contamination to return. New fuel lines are a must in this car at this point. So if your flex lines and filter are new, injectors/WUR/FD are clean, hard lines are flushed, tank is clean and free of 30 year old rubber parts - there should be nothing to come back and gum anything up.

Sounds like your fuel system definitely has a way to go, but don't despair - you'll get there! K-Jet is just incredibly sensitive.

Edit: Not to mention that there shouldn't be anything to decay downstream of the fuel filter in the first place. I'm turning the system over in my head and if anything, the fuel that's returned to the tank should be cleaner than the fuel that left it, barring significant pre-existing contamination.

[David T]

Most people who install the new fuel pump kit have already overhauled the rest of the system, so there should be no contamination to return. New fuel lines are a must in this car at this point. So if your flex lines and filter are new, injectors/WUR/FD are clean, hard lines are flushed, tank is clean and free of 30 year old rubber parts - there should be nothing to come back and gum anything up.

Sounds like your fuel system definitely has a way to go, but don't despair - you'll get there! K-Jet is just incredibly sensitive.

Edit: Not to mention that there shouldn't be anything to decay downstream of the fuel filter in the first place. I'm turning the system over in my head and if anything, the fuel that's returned to the tank should be cleaner than the fuel that left it, barring significant pre-existing contamination.

In my mind I believe most fuel system problems begin in the tank. That is where dirt, stale fuel and water get into the system. In that same light, when you start working on the fuel system the tank is where you begin. Theoretically the filter is supposed to trap any dirt but if you have stale fuel it is already downstream of the filter. There is a filter in the CPR and each injector has a screen but by then it is usually too late. If you find, after cleaning the tank, you are getting dirt and junk back into it, it means the system is contaminated and you are flowing the stuff back to the tank from the fuel lines and PPR. Keep cleaning the tank and eventually it should clean up. If you see a tank full of junk the injectors need to be cleaned.