fuel pressure issue - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 12 Old 05-20-2019, 08:43 PM Thread Starter
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fuel pressure issue

92 GT, 427w swapped. stock fuel lines from tank to fender, then a 8AN from fenderwell to Aeromotive 13101 regulator, pair of 6AN lines to the rails, then pair of 6AN's back to a "Y" at the stock return line.

Fuel pressure drops off IMMEDIATELY after turning key off. If the car sits a week or so, it needs to crank quite a bit to start.

Sounds like the pump's valve is dieing, BUT both of the walbro's I've had (255 and 190) in the other car did it from day one. They won't hold either but it gets driven daily.

Reckon a check valve added to the 8an line would help or?

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post #2 of 12 Old 05-20-2019, 09:49 PM
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unless an injector is stuck open, holding pressure is not really detrimental

can the prime hit the max fuel pressure?

can you you prime it a few times to achieve pressure?

if so, you may need to increase the amount of time for the prime, in the ecm


89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #3 of 12 Old 05-20-2019, 09:54 PM
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Yeah man, the pressure is held by the pump. In megasquirt you can adjust how long the pump runs before the injectors fire the priming pulses in the cylinders for startup. They call it lazy fuel pumps that take time to build pressure.. I don't think it's lazy, I think it's the increased volume of fuel from larger fuel lines overcoming the pump at rest..

I have mine setup to run 1.9 seconds because after it sits overnight the pressure goes and the fuel drains back a bit. You can hear the rush of fuel hit the regulator when you turn the key.

You might just need to key on a couple times..
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post #4 of 12 Old 05-21-2019, 12:22 AM
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I personally would try to fix this issue. If the pressure is bleeding off with multiple pumps I wouldnt suspect the pump. I helped my brother fix a van that would lose pressure as soon as you turned it off. We ran a flow test and found the pump wasnt meeting minimim flow requirements. After taking the tank out and inspecting the lines inside the tank we found the pressure line from the pump to the hat inside the tank had a small hole in it causing the issue. You could have the same issue. We replaced the line and the van has never ran better. Ive never seen a fuel injected car do that unless there is an issue. If you turn the key to the run position and prime it a few times how quickly does the gauge go back to 0? My car holds about 25lbs with the key on not running for quite some time.

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post #5 of 12 Old 05-21-2019, 08:19 AM Thread Starter
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Originally Posted by Dwain View Post
I personally would try to fix this issue. If the pressure is bleeding off with multiple pumps I wouldnt suspect the pump. I helped my brother fix a van that would lose pressure as soon as you turned it off. We ran a flow test and found the pump wasnt meeting minimim flow requirements. After taking the tank out and inspecting the lines inside the tank we found the pressure line from the pump to the hat inside the tank had a small hole in it causing the issue. You could have the same issue. We replaced the line and the van has never ran better. Ive never seen a fuel injected car do that unless there is an issue. If you turn the key to the run position and prime it a few times how quickly does the gauge go back to 0? My car holds about 25lbs with the key on not running for quite some time.

Had similar issue with the '93 LX (2.3). Fixed that. The thing is, if that kinda problem exhibits itself, the engine will be either dead or VERY weak/lean which was the case with the 2.3. The 427? Runs absolutely fine. Just hard to start after sitting a week or so.

INDY2000, never gave second thought to adjusting fuel pump prime from 3 sec (default), maybe 5 sec would do it. That's easy enough even for an electronically challenged person such as myself. I'm using binary editor and QH.
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post #6 of 12 Old 05-21-2019, 08:50 AM
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the pump might be sticking internally if sitting for a long time

you can current clamp the feed, or look at fuel pressure and see what is going on.

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #7 of 12 Old 05-21-2019, 10:06 AM
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You state the regulator is before the rails and the "Y" is after the rails. Swap the "Y" and regulator. The regulator should be in the return after the rails. The regulator restricts the return to control pressure. Fuel pump to "Y" then rails, then regulator and then return to tank. Look at the instructions for the regulator, there is diagram.

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post #8 of 12 Old 05-21-2019, 02:05 PM
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THAT would be embarrassing if that is the case

I read the same, but assumed it was incorrectly described

89 GT gr-40, KB2200(10psi), tweecer R/T,LC-1, 22gal cell, w/tailpipes.
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post #9 of 12 Old 05-21-2019, 06:04 PM
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Ive only seen this once and the car wouldnt run... What are the odds the return is just restrictive enough to provide the correct amount of fuel pressure

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post #10 of 12 Old 05-21-2019, 06:18 PM Thread Starter
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I was indeed incorrect in describing the line routing/setup.

it is a "typical" setup, done that way for good reason. Just described it incorrectly.

MLD54, that is the way it's set up. Y in front, reg in the return circuit.

Embarrassing.

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post #11 of 12 Old 05-22-2019, 10:52 AM
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Maybe need a checkvalve?

https://www.highflowfuel.com/i-23908...-8mm-5-16.html

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I spec'd my whole build to fit a cold air intake I had
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post #12 of 12 Old 05-24-2019, 08:53 AM
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Might be interesting to pull the pumps out and pressurize the system from a remote reservoir. Then watch and see if the fuel returns thru the pump which won’t hold pressure or thru the regulator which didn’t hold pressure.

One way or the other the fuel leaks back to the tank as you well know.

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