06-5.7 mpi mag starts,, stalls, starts stalls. ran fine last fall

[svb165]

i just this morning had time to get back to it. i reinstalled the fuel pressure tester at the rail shrader valve and started it. it starts okat abot 40 and then fuel pressure drops to 30psi and it quits. re start, same thing. no vacume to call for fuel?? as i mentioned the old AND new iac valve did not move when turning on the key.. but has power to it (key on) when i test with a test light ?

 

[svb165]

Does the fuel pressure stay close to 40 when motor is started and when it's stalling?

NOPE

 

[cwella]

i just this morning had time to get back to it. i reinstalled the fuel pressure tester at the rail shrader valve and started it. it starts okat abot 40 and then fuel pressure drops to 30psi and it quits. re start, same thing. no vacume to call for fuel?? as i mentioned the old AND new iac valve did not move when turning on the key.. but has power to it (key on) when i test with a test light ?

The fuel pressure drop is the main clue. Check if the pump is losing power or if pressure is falling due to a weak pump, clogged filter, bad regulator, or restricted supply.

The IAC may not visibly move with key-on on some vehicles. Since it has power, check for the ECU control signal and also inspect vacuum leaks, MAP sensor lines, and injector pulse.

 

[svb165]

its got a new fuel pump/cooler, press. regulator and the iac unit.
yep, i need to do a voltage test at the pump and see whats going on there. it seems t shut off, as it drops off right after starting. its got a recent pick up in the tank and a new water/fuel separator
not sure if it has an old style check ball in the top tank fitting or not? i will pull the hose at the seperator/ filter and see how the draw is there with a small pump.

 

[cwella]

its got a new fuel pump/cooler, press. regulator and the iac unit.
yep, i need to do a voltage test at the pump and see whats going on there. it seems t shut off, as it drops off right after starting. its got a recent pick up in the tank and a new water/fuel separator
not sure if it has an old style check ball in the top tank fitting or not? i will pull the hose at the seperator/ filter and see how the draw is there with a small pump.

Sounds like you’ve already covered a lot of the usual suspects. Checking the voltage at the pump while it’s running should give you a better idea of what’s happening. The separator/filter test sounds like a good next step too. Hopefully it turns out to be something simple and you’re getting close to having it sorted.

 

[alldodge]

i just this morning had time to get back to it. i reinstalled the fuel pressure tester at the rail shrader valve and started it. it starts okat abot 40 and then fuel pressure drops to 30psi and it quits. re start, same thing. no vacume to call for fuel?? as i mentioned the old AND new iac valve did not move when turning on the key.. but has power to it (key on) when i test with a test light ?

Since it's same time I think something is shutting the pump off (ground from ECM to FP relay, or fuel pump relay. Could hot wire the relay or fuel pump. A ground to the ECM side of the relay or go direct to FP by removing relay and connect direct to contact

 

[svb165]

whitling it down.. Its tough to do some of this stuff without a second set of eyes at times. and im still recovering from removing that frickin cool fuel pac !
another thing i was told to try is,, jumping the oil pressure switch and see if it isnt shutting the pump off after initial start up. that will have wait till the early AM when its cooler.

 

[cwella]

whitling it down.. Its tough to do some of this stuff without a second set of eyes at times. and im still recovering from removing that frickin cool fuel pac !
another thing i was told to try is,, jumping the oil pressure switch and see if it isnt shutting the pump off after initial start up. that will have wait till the early AM when its cooler.

Whittling it down, it’s tough to troubleshoot some of this stuff without a second set of eyes sometimes. I’m still recovering from removing that darn fuel pump module!

Another thing I was told to try is jumping the oil pressure switch to see if it’s shutting the pump off after the initial startup. That’ll have to wait until early morning when it’s cooler and easier to work on.

 

[svb165]

Since it's same time I think something is shutting the pump off (ground from ECM to FP relay, or fuel pump relay. Could hot wire the relay or fuel pump. A ground to the ECM side of the relay or go direct to FP by removing relay and connect direct to contact

You know, i DID replace the dash this spring, so i had much of the wiring apart. i took many pictures and put it back the same way and re checked it over and over. could i have screwed something up there i wonder? EVERYTHING looks to be working fine there. all lights ect..

 

[alldodge]

i just this morning had time to get back to it. i reinstalled the fuel pressure tester at the rail shrader valve and started it. it starts okat abot 40 and then fuel pressure drops to 30psi and it quits. re start, same thing. no vacume to call for fuel?? as i mentioned the old AND new iac valve did not move when turning on the key.. but has power to it (key on) when i test with a test light ?

Since it's same time I think something is shutting the pump off (ground from ECM to FP relay, or fuel pump relay. Could hot wire the relay or fuel pump. A ground to the ECM side of the relay or go direct to FP by removing relay and connect direct to contact

The oil pressure switch has nothing to do with your fuel pump, you have a MPI so the ECM controls the pump and everything else

 

[svb165]

Since it's same time I think something is shutting the pump off (ground from ECM to FP relay, or fuel pump relay. Could hot wire the relay or fuel pump. A ground to the ECM side of the relay or go direct to FP by removing relay and connect direct to contact

The oil pressure switch has nothing to do with your fuel pump, you have a MPI so the ECM controls the pump and everything else

i just checked all connectors and all looks good. fuel draws out of the tank easy enough with a hand pump attached to the line before the filter, so its not a check ball problem. i started it again several times after going over this stuff and its the same. primes to 40ish, starts normally but dies in a few seconds as the pressure drops off. i DID hear the pump start to run as it stalled one time, no other times though. if i grab the throttle and work it to try to keep it running the fuel pressure on the rail follows RPM up and down then it quits after a few moments working it. pressure always ends at 30 when it stalls. tyring to get a shop to scan this is turning into a royal pita either they dont have the propper plug, or no scanner at all.

 

[alldodge]

You need to get the motor scanned

The FP can be hot wired and it not effect the ECM, just remove the FP relay and place a jumper between pins 30 and 87. The FP will run as soon as the jumper is installed



Wiring

 

[durban]

You need to get the motor scanned

The FP can be hot wired and it not effect the ECM, just remove the FP relay and place a jumper between pins 30 and 87. The FP will run as soon as the jumper is installed

View attachment 417957

Wiring

View attachment 417958

A vacuum gauge reading will point you in the right direction , don't overlook exhaust restriction a vacuum gage reading will point this out too.