OE 1.7 Fuel Pump fails only when hot?, NOT Vapor Lock Options

[jrmdir]

Hi: After months of battling all the d-jet and fuel delivery woes there could be in a car that sat for 3 years +, I finally had a breakthrough week and it's running/driving like a real car. Still needs fine tuning but I was able to actually test drive it for 15 min. Then let it idle in my driveway while doing more fiddling.

Ready to put it back in the garage and it wouldn't start. All crank / no fuel (pressure gauge still installed.) So I pulled the FP relay and ran 12v directly to the pump relay output socket - nothing. After a while I decided to put it on the lift to see if I could see 12v at the pump and lo and behold it started right up. FP running normally.

This is an original 1.7 three barb fuel pump. Are there any anecdotal stories of this sort of failure mode? I'm eventually going to redo everything fuel-related with new pump and SS lines but those projects are down the line right now and I'm not sure if I should trust it as is while I keep sorting out other issues.

TIA

Ron

[StarBear]

The classic hot no-start issue? If so, not so much a fuel pump issue. See Mark Henry’s thread on this. Replaced the starter solenoid with Ford unit from the early 80s IIRC. About $25 and 25 minutes. (IMG:style_emoticons/default/biggrin.gif)

[76-914]

The "Hot start" issue is when it will not crank. Sounds like the pump or a faulty connection. Do you have the fuel pump flow chart for diagnosing? (IMG:style_emoticons/default/beerchug.gif)

[jrmdir]

Thanks StarBear but I don't think its a solenoid issue since the starter kicked in and turned the engine over just fine. It was just the zero pressure on the fuel pressure gauge that led me to hot wire 12v directly to the pump via the relay socket. Still no pressure.

Rethinking this I suppose it could be vapor lock, if the symptom of that is that the pump is pushing air and can't build pressure to the engine, but one thing that conflicts with that diagnosis is that I could not hear the pump running, plus no tiny spark when touching the jumper. Plus there was no 1.5 second pump noise when turning on the key.

Going to do more experimenting later this weekend.

Ron

[jrmdir]

Thanks 76-914 - yes I have the full diagram and am going to start by inspecting the wiring between relay pump. Might attach a test wire at the pump + connection so I can check for voltage w/o getting back under the car. IF I can get the issue to repeat.

Regards,

Ron

[wonkipop]

i just rebuilt two of these original fuel pumps.

it could be its just at the end of its life and its an internal failure.
when they go its sudden and over with.
usually a piece of one of the brushes breaks off and jams the commutator in the internal electric motor. but yours went again so it isn't that. its unlikely that its anything internal to the pump that is heat related.

on the other hand it ran before you switched it off.
so i would check all the electrical connections to the pump.
and relays. a 1.7 is differently wired up than a 1.8 which is what i have, so i'm not sure exactly how they go.
but i watched very recently a video by dr914 (AA) on youtube where he goes over the relay board and he talks about this very thing, the fuel pump suddenly dying.
he goes through the checklist of how to test it and get it running again, its very easy to follow on the video. i think its his relay board video. look it up on youtube.
under automobile atlanta channel.

relays can be affected by heat. i have had the experience of that. even current running through them internally can heat them up and then when they cool down internally they will operate again. 30 years ago i had a similar sort of problem, but it was a 1.8 so the way the fuel pump operates in the circuit is a little different. but it turned out to be a remnant of the seat belt interlock system that was still in the circuit. the relay in question was under the passenger seat. i would get the same problem sort of, but i would not get a crank at all. however leave the car for half an hour and it would restart and run. it was that relay that was intermittently failing from internal heat buildup.

[wonkipop]

here is the vid.

he goes through the fuel pump scenario at about the half way point.

https://www.youtube.com/watch?v=YLgQxpNHzIU

[JamesM]

So I pulled the FP relay and ran 12v directly to the pump relay output socket - nothing. After a while I decided to put it on the lift to see if I could see 12v at the pump and lo and behold it started right up. FP running normally.

This is an original 1.7 three barb fuel pump. Are there any anecdotal stories of this sort of failure mode? I'm eventually going to redo everything fuel-related with new pump and SS lines but those projects are down the line right now and I'm not sure if I should trust it as is while I keep sorting out other issues.

Most recent d-jet car I brought back to life I struggled chasing an intermittent fuel pump issue. Wound up swapping multiple relays, boards, etc.


If you are still running a stock 3 port pump in the stock engine bay location I would say your risk of heat related vapor lock is high (ethanol fuels have made this far more common) however from what you have described it does sound like it could potentially just be an electrical issue.

BUT you need more data on the issue.

If 12V direct to the pump runs it every time the problem occurs then its probably not the pump itself or vapor lock. Working backwards from there, you mentioned you jumpered the pump relay, did you test for 12V output at the fuel pump connector when you did this? Just bypassing the relay doesent mean there is not a connection issue at the relay board itself.

Test for 12v at every point in the circuit all the way out to the pump connector. guessing you may have a weak connection at the relay board, possibly where one of the pins is riveted to the traces.

If you can isolate it to being an intermittent 12v issue, I have had good luck with this stuff restoring connectivity though the board.

https://www.amazon.com/Hosa-D5S-6-DeoxIT-Co...r/dp/B00006LVEU

[ultra3000]

I had the same problem. It was the connection at the pump. Crimped on new ends to fix.