Please help confirm bad fuel pump behavior

sizemoremk

Registered User
Hey guys, after sitting several years in need of multiple things, my Anni is back on the road.

Has mpiii, double IC, 15% OD, 50lb injectors, big TB, big MAF with appropriate sample tube, 255 walbro, snow alky kit with smallish nozzle and WW fluid, etc...

Car was tuned in the past with my eec tuner to have 11.75ish AFR at WOT verified by datalogs.

After some random work and HG replacement, emptying tank and new fuel filter, the car wants to go lean at WOT, like 13-14 AFR !!! Drives fine otherwise in closed loop.

I checked fuel pressure at rail with guage with vaccum line removed and when cold it goes right to ~40 psi. Then after warm, it drops to about 30 psi.

Pressure also seems to drop to 10 psi after shutting down for half hour or so.

I tried this two days in a row with same behavior.

I can suck and blow into a hose connected to FPR and the pressure drops and raises a bit. I cannot seem to find any fuel leaking from regulator.

When I connect vacuum source back to FPR, pressure drops to about 25ish psi.

Seems like it's time for a fuel pump, anyone got any other ideas before I drop the tank for a pump?
 
I have no idea, but you said it sat for several years, when was it tuned, is it a quarter horse, is it possible that the battery is dead on it and it's running a base tune?
 
Dropping pressure when sitting would make me think an injector is stuck open or something.
 
It is an eec tuner, it is eeprom I assume, I don't believe it has any battery? The fuel pressure at idle wouldn't be impacted by the tune anyway would it?

I can hear all of the injectors clicking via stethoscope, I also submerged them in cleaner when I did HGs recently. Surely it would run rough if an injector wasn't firing wouldn't it? I know a 302 will run like garbage with a stuck injectior.

The weird thing is how it has good fuel pressure when starting cold, then drips when warm.

I ordered an electric fuel pressure guage I can put in the cabin, so maybe that will confirm.

Thanks!
 
My 4.6 bird had a bad ECM last year that left the #2 injector open constantly. It ran really rough at idle and low RPM and ran fairly well at high RPM. I've never heard of listening for clicks - fascinating.
 
I've never heard of listening for clicks - fascinating.

When checking codes with a stock ECU, there is a test that will kill each injector in turn, causing the engine to stumble on cue, making it easy to spot a dead cylinder and/or failed injector.
 
In this case, my fuel pressure was OK when I checked with an electric gauge ran into the cabin. The old mechhanical guage I had on the rail must have been screwed up.

I checked it over a couple of days and fuel pressure seemed to get close to 58psi or so at full boost.

The AFR also seemed to get more inline (11s) after driving it a bit, it will be on the dyno tomorrow and will get to see what the "lab grade" WB will read.
 
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