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

[jawn101]

So, just as an update - Dave and Houston couldn't figure out what was causing the issue, and apparently the unit is going back to the manufacturer. I have a new one inbound, complete with external check valve. Looking forward to installing it and getting rolling again!

[NightFlyer]

So, just as an update - Dave and Houston couldn't figure out what was causing the issue, and apparently the unit is going back to the manufacturer. I have a new one inbound, complete with external check valve. Looking forward to installing it and getting rolling again!

Good deal - glad to see them standing behind the product! Thanks for keeping us updated

[Ryan S.]

Nice. Post some photos of the new pump. I am curious about the location and type of check valve.

[jawn101]

Nice. Post some photos of the new pump. I am curious about the location and type of check valve.

It's an inline one, as I understand it - the box should arrive Thursday and I doubt I'll be able to stop myself from installing it immediately. Pictures will definitely follow.

[DeLorean]

On a somewhat related note, has anyone done an amp-draw test on the new pumps Vs the old type? My guess would be there is probably a savings of an amp or 2 being that it is a more modern pump rather than an old Bosch roller type pump - true? Might be a bit of help to the fuel pump relay lifespan.

[Bitsyncmaster]

On a somewhat related note, has anyone done an amp-draw test on the new pumps Vs the old type? My guess would be there is probably a savings of an amp or 2 being that it is a more modern pump rather than an old Bosch roller type pump - true? Might be a bit of help to the fuel pump relay lifespan.

Something I would like to know also. If you test the current, do it with the engine running so you have a normal voltage.

[David T]

Something I would like to know also. If you test the current, do it with the engine running so you have a normal voltage.

The best test would be on a car with a nice, clean, well working electrical system. Getting a # off of a car with dirty connections, an old pump, and bad grounds won't mean anything.

[jawn101]

Ladies and Gentlemen (who am I kidding) - I am pleased to report that my spewing pump/power loss issue is 100% resolved!!

Before I continue any further it is very important for my own conscience that I start this post by saying that DMCH's new pump was **100% NOT AT FAULT** for the issue, and in fact was working as intended. It may even have saved me from a much bigger headache by doing what it was. I remain confident in the design of this part and very pleased overall with its performance.

That said, let's get on with the diagnosis.

After dozens of emails and a few hours of video chat with the incomparable Dave Swingle over the last few days, the culprit turned out to be none other than...





The high-pressure accumulator hose! As you can see in those photos (crap quality, but we all know that compartment is no easy place to see or photograph) the OEM hose had thermoformed a very hard kink in it. The pressure from the fuel pump must have been inflating it just enough for some gas to flow, enough to run the engine - but it was certainly a major restriction in the system. The weird thing was that the fuel pressure (tested with a K-Jet kit on loan) was 100% dead on at the fuel distributor. But that was at idle, with no way to test it under load.



Here you can see the hose cut out of the car and the extent of the kink. Everyone who is reading this post should please take this warning quite seriously - the OEM fuel lines on your car are *NOT* suitable for active use anymore! If you haven't replaced them all you are just asking for trouble. I have upgraded every one *except* these two at the accumulator, due to the difficulty of it. Look what that got me. The hilarious thing was that I had purchased new lines for this job and just had them waiting on my shelf. Very convenient that the fix ended up being a net $0 in parts!

Anyway, here's the beautiful result of all that work...



As you can see the pump runs smoothly and quietly, with no spewing. The baffle quietly fills up and overflows, just like it's supposed to. The sputtering under load with low fuel is gone.

Huge thanks to David Proehl, Clint W, Ryan S and especially Dave at DMCMW. Have you ordered anything from them lately?

[DMCMW Dave]

You have inadvertently settled another argument from long ago. The baffle will be full to the top all the time until the tank is dry.

This was interesting. . . .

A bit more detail - with the fuel link kinked, the "excess" fuel blew out through a relieve valve at the top of the pump. The fuel that got through the kink was enough to run the engine, usually quite well. The relieve valve excess came out with such force that it didn't land back in the baffle. There wasn't the usual return flow from the engine to refill the baffle due to the kink as well. The relieve valve is there to protect the pump in the event of, well, a kinked line or plugged filter.

Therefore the baffle ran low when the tank was low, effectively creating a hole in the pool of gasoline.

I contend that he would have noticed that the car ran out of power (gasoline) at wide open throttle very hard acceleration near redline, but he doesn't drive the car that way.

BTW - for future reference - a close to plugged fuel filter will cause exactly the same problem.

PS we also has some fun comparing the view out the front door.

[jawn101]

You have inadvertently settled another argument from long ago. The baffle will be full to the top all the time until the tank is dry.

This was interesting. . . .

A bit more detail - with the fuel link kinked, the "excess" fuel blew out through a relieve valve at the top of the pump. The fuel that got through the kink was enough to run the engine, usually quite well. The relieve valve excess came out with such force that it didn't land back in the baffle. There wasn't the usual return flow from the engine to refill the baffle due to the kink as well. The relieve valve is there to protect the pump in the event of, well, a kinked line or plugged filter.

Therefore the baffle ran low when the tank was low, effectively creating a hole in the pool of gasoline.

I contend that he would have noticed that the car ran out of power (gasoline) at wide open throttle very hard acceleration near redline, but he doesn't drive the car that way.

BTW - for future reference - a close to plugged fuel filter will cause exactly the same problem.

PS we also has some fun comparing the view out the front door.

Great additions, I should have included more of that. My mind is sort of soft from all the fumes today. Tomorrow I am going to verify that my mixture is still correct (this repair may have enriched it a bit) and then hit the highway with some gusto. See how she does. I have since filled the tank back up (took 13.2 gallons, so that should show just how empty I ran it) and it is driving great!!

Yes... we have very different views from our garages right now. You can have some of our perpetual spring if we can have some of your water....