New problem - Fuel pressure drops off - 75 280 L Jet, w/ composite injectors, ProtunerZ rail, 3 bar FPR

[HusseinHolland]

EDIT - Note that the cause was the EFI system relay failing

Tried to take the Z out for dinner last night, and only got a block from the house, no throttle response, engine stalled. Restarted readily, but would only idle. WBO2 indicates that the system goes waaay lean when any demand is placed on the delivery system. 

Today I looked it over. Again, the car would idle fine - but - sometimes (ugh) the pressure (mechanical gauge after filter, before rail) drops off until the engine stalls. Blipping the throttle would sometimes make the regulated pressure pop back up.

YT Vid

What is bugging me is what the heck in the system could cause the pressure to drop off & then pop back up? I'm not familiar with the workings of the air flap meter to understand if there is  an element of it that can shut off fuel delivery.

I replaced the fuel filter to eliminate a possible flow restriction. After that, I swapped out the fuel pump, no change. Removed the pulse damper, no change. I pulled the cover off the AFM, couldn't see anything out of order, checked the connector & pins.

When the pressure drops off, the pump doesn't get louder, so I don't think it's a flow restriction with the tank or feed side.

By the end of all my futzing the car was running normally again. Very frustrating, since I haven't found anything concrete.

Did remember to put the protector plate back in finally. Couldn't find the original screws though

 

 

Edited May 15 by HusseinHolland

[SteveJ]

If air is flowing through the AFM, the flap is open. If the engine dies, the flap closes, and the car kills the power to the fuel pump.

Are you sure the tank is clean. I have read about people having rust in the tank, and a flake blocks the outlet. The car dies and the flake falls down. The car starts, but when the tank is stirred up, the cycle repeats.

[HusseinHolland]

14 minutes ago, SteveJ said:

If air is flowing through the AFM, the flap is open. If the engine dies, the flap closes, and the car kills the power to the fuel pump.

Are you sure the tank is clean. I have read about people having rust in the tank, and a flake blocks the outlet. The car dies and the flake falls down. The car starts, but when the tank is stirred up, the cycle repeats.

The thing is, if that were the cause, I would expect the pump to start whining as the restriction takes effect  - I manually crimped the feed hose with the engine running and the pump noise increases significantly. when the symptom manifests, there is no change in the pump sound, and the fact that blipping the throttle & holding an steady elevated idle can 'pop' the pressure back up. Makes no sense to me .

[darom]

I'd also put the multimeter leads directly on the fuel pump and watch the voltage when someone operates the throttle. Voltage drop there won't do any good to a fuel pump operation.

[HusseinHolland]

1 minute ago, darom said:

I'd also put the multimeter leads directly on the fuel pump and watch the voltage when someone operates the throttle. Voltage drop there won't do any good to a fuel pump operation.

Great idea. I thought about checking the pump control circuit, and didn't get to it. I'll figure out a way to monitor the voltage at the pump connections & see what I get.

[Zed Head]

I had a similar problem with mine.  It was the fuel pump relay portion of the combined EFI/pump relay.  I posted about it long ago and posted a picture too.  The solenoid coil looked cooked, I took it apart.  It was actually a "spare" that had come with the car, that I had put back in to test.  I guess that's why it was out.

I was able to get home because I had already installed a relay bypass and power control switch under the dash.  Because I didn't trust the old electrical stuff.

[HusseinHolland]

8 minutes ago, Zed Head said:

I had a similar problem with mine.  It was the fuel pump relay portion of the combined EFI/pump relay.  I posted about it long ago and posted a picture too.  The solenoid coil looked cooked, I took it apart.  It was actually a "spare" that had come with the car, that I had put back in to test.  I guess that's why it was out.

I was able to get home because I had already installed a relay bypass and power control switch under the dash.  Because I didn't trust the old electrical stuff.

Awesome! That makes sense, and would explain why the pump didn't get louder.

[HusseinHolland]

Looking back through some earlier threads, I see that the Fiat L-Jet control relay I have on hand (...127) has the same pinout except for the 85 ground location. I'll try running that while I figure out whether it's worth making a more drastic change, given that all this will be coming out int he next year or so.

[HusseinHolland]

Swapped out the stock relay for the Fiat one, after moving the 85 pin to the other relay socket Thanks again, @Zed Head  for sharing your experience with the relay failing.

Took the old relay apart, to see how it looked inside:

Contacts are crusty, definitely didn't smell as cooked as I thought it might, given how it was cutting in and out. The contact plate definitely looks rough.

Since I was under the dash, I started figuring out the wiring for the pump primer circuit. It will tuck nicely up under the steering column, and I will make it insertible, so I can remove/delete it without harming the factory harness.

 

Started right up & hasn't faltered since. I do need to add a pulse damper back, as it doesn't sound as clean as it did at idle before I removed it. Instead of putting the stock one back, I ordered one that will screw into the ORB-8 fitting on the protunerZ fuel rail.

 

 

Edited March 20 by HusseinHolland

[Zed Head]

Hope that was it.  Here's what mine looked like.  I think that the theory is that the insulation breaks down on the coil wiring, causing a weaker magnetic field.  A short between wires but not a short directly to ground.  Fewer circuits around the core.  Can't remember exactly what I was testing or saw with those leads.  Should have measured resistance through the coils.  But it seemed to be heat-related so hard to reproduce.  Probably wouldn't have seen anything.  Maybe if I had hit it with a heat gun.

[HusseinHolland]

Added the three sec primer circuit after work today. I could actually make it anytime duration but 3 seconds seems more than long enough.

Harness tucks neatly up under the dash

YT Vid

Edited March 21 by HusseinHolland

[HusseinHolland]

5 minutes ago, Zed Head said:

.  But it seemed to be heat-related so hard to reproduce. LI.

I drove it yesterday evening , probably 30 miles, and to work and back again today. No hiccups.

Yeah the coils heating up and then opening the circuit makes sense in hindsight, because as soon as it cools down electrically speaking then the circuit would be engage hence the tying in with me blipping the throttle, which was obviously coincidental to the relay coil cooling off enough to reengage the pump. That's what I'm assuming anyway.

Edited March 20 by HusseinHolland