Fuel Pressure to high?

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Oct 11, 2015 | 02:49 PM

#41

TheWarlock

Senior Member

Joined: Sep 2014

Posts: 366

Likes: 78

From: Dallas, TX

have you tried directly supplying 12v to the fuel pump after disconnecting its original electric feed? There is some ECU function to cut off fuel supply on the later cars if it's not firing, then there the inertia/rollover switch etc. So doing this would allow you to diagnose if it's really a fueling issue or electrical.

Oct 11, 2015 | 03:20 PM

#42

bhamilton

Member

Joined: Dec 2013

Posts: 72

Likes: 19

From: vermont

No but I like that. I will try giving the fuel pump a direct supply and keep the relay unplugged and see what I get.

Thank you.

Oct 11, 2015 | 04:34 PM

#43

bhamilton

Member

Joined: Dec 2013

Posts: 72

Likes: 19

From: vermont

Update

Got to thinking about the CTS comments. Went over and measured mine and it is in Mohms. Jumpered the CTS and the car started and I was able to move it around and put it back in the garage.

CTS is root cause.

Thanks and hope this helps others at some point.

Nov 26, 2017 | 09:16 PM

#44

aerokurt

Junior Member

Joined: Nov 2017

Posts: 2

Likes: 0

From: SoCal, NoVa and SRQ

Been chasing the same ghost here for weeks - part time - yup it was the cts.
Thank you all, now on to fixing the aav to get the idle below 1600 rpm.

Cheers, Kurt

Jul 18, 2022 | 05:48 PM

#45

808PUNABOY

Junior Member

Joined: Dec 2021

Posts: 5

Likes: 0

Quote:

Originally Posted by Greg Edge

It appears those are the correct regulators. Your pressure does not make sense. If you remove the return line and let that flow freely the pressure is still 62 psi, correct?

Are we sure the gauge you are using is accurate? You have it connected in the right place. It has to be before the left regulator. The left regulator is the one with a hose barb rather than a threaded fitting for the outlet.

Lets try something else for a second. Disconnect your coolant temp sensor and jump the terminal together. See if the car starts now. A bad sensor or corroded terminals will give the ECM a false input and send the fueling to super rich and the engine won't start.

Fuel pressure at 62psi with the proper regulators and no restriction in the return defies logic. I would check your fuel pressure gauge. You can connect it to a compressed air line that you know the pressure and verify it is accurate. I have been burned a few times in my career by defective tools.

The failure mode of a fuel pump is lower output. If the output is too high the voltage may be high but since you are only cranking the voltage is normal. Also the regulators will drop the pressure.

The failure mode of a regulator is lowered pressure due to a ruptured diaphragm. This will push fuel out of the vacuum port. Even if there is no vacuum the pressure would not be 62psi. Besides there is little to no vacuum during cranking.

Lets approach your problem from another angle. You have determined the fueling is too rich. The other likely and easy to test culprit is that coolant temp sensor.

Feel free to contact me via email or if you want to discuss on the phone I am glad to talk.

I am also having the almost exact issue with a 94' XJ81 V12. Fuel pressure reading @ 70lbs. & 60lbs. with secondary pump disconnected. Extremely high pressure. Stumble starts w/ ether starting spray but won't stay lit.Also found former owner cut and crimped return line around fuel filter. I would appreciate all and any info on and about the coolant temp sensor. Please & Thank you. -- A.A.