Fuel pressure regulator test
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Fleet Mechanic
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Fuel pressure regulator test
Truck is a 90 with a 5.0. Vacuum line attached, I’m getting about 23 psi. Pull vacuum line and it jumps to around 38 psi. Bad fpr right? Making sure my thought is right or not..
There is no fuel in vacuum line.
There is no fuel in vacuum line.
Last edited by 90project5.0; Dec 9, 2025 at 02:23 PM.
Cargo Master
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From: W (BY GOD) V
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From: Central Mississippi
Yes. Removing the vac line from the FPR should cause a rise in your fuel pressure as measured at the schrader valve.
That's how it increases fuel when you put your foot in it.
38 might be a few pounds low.
That's how it increases fuel when you put your foot in it.
38 might be a few pounds low.
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Fleet Mechanic
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what caused the search is fully cold, it spins to start like a new battery. If you turn it off and try to crank within the next 15 minutes, it spins stupid slow like battery is dead and won’t start. I was waiting for someone to come jump me off when I realized time waiting would allow it to start quick again. I had the battery and all checked which tested fine at two different places. My next guess when would be vapor lock on the motor.
When I turn the truck off or stop priming the pump pressure drops to below 10 psi within 45 seconds. I pulled 3 random plugs and all were dry. All 8 injectors ohm’s between 14.9-15.1. I don’t have a noid test.
Last edited by 90project5.0; Dec 9, 2025 at 09:15 PM.
Lead Driver
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From: N.W. Alabama
"what caused the search is fully cold, it spins to start like a new battery. If you turn it off and try to crank within the next 15 minutes, it spins stupid slow like battery is dead and won’t start"
This sounds like timing too high, have you checked?
This sounds like timing too high, have you checked?
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Fleet Mechanic
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I had it hooked up to tunerstudio yesterday and timing was showing right at 18* which is where it’s set (12 on crank). Pressure is back up this morning as the video shows, but after running to grocery store and back, it won’t start back up immediately. The pressure takes a massive nose dive as soon as the truck is turned off also.
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These are the regulator tests out of the PCED (pinpoint test FDS6 in particular)
All of you interested should read every page, including the flex fuel stuff
It's just a matter of time before we all need to bone up on flex fuel
Been there and done some of that already with thousand dollar Taurus flex fuel pumps
The injector color and pounds per hour chart is good if hitting a junkyard for injectors
All of you interested should read every page, including the flex fuel stuff
It's just a matter of time before we all need to bone up on flex fuel
Been there and done some of that already with thousand dollar Taurus flex fuel pumps
The injector color and pounds per hour chart is good if hitting a junkyard for injectors
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From: Central Mississippi
Something I've experienced with 90s Ford is the tanks produce very fine rust in the tanks.
It'll settle out in the filter allowing vehicle to run right for a bit before choking down again..
You probably changed it recently, but you might want to pull it off ( I know a pain) & see what pours out of the supply side.
It'll settle out in the filter allowing vehicle to run right for a bit before choking down again..
You probably changed it recently, but you might want to pull it off ( I know a pain) & see what pours out of the supply side.
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Fleet Mechanic
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Something I've experienced with 90s Ford is the tanks produce very fine rust in the tanks.
It'll settle out in the filter allowing vehicle to run right for a bit before choking down again..
You probably changed it recently, but you might want to pull it off ( I know a pain) & see what pours out of the supply side.
It'll settle out in the filter allowing vehicle to run right for a bit before choking down again..
You probably changed it recently, but you might want to pull it off ( I know a pain) & see what pours out of the supply side.
Last edited by 90project5.0; Dec 10, 2025 at 09:02 AM.
Fleet Mechanic
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From: New York
What did you use for a replacement pump? Reason I ask is that when I first replaced my pump, I "cheaped out" and went with some no-name pump. Bad idea. Pressure went low first before the pump failed entirely. It never made it to 1000 miles on the new pump. Motorcraft pump has been fine ever since installing that.
Unrelated, but also semi-recently, I had a bad FPR which allowed the fuel to run through and not build the required pressure. New FPR solved that. Make sure you get the right one, as the 4.9 requires higher pressure than the V8.
Unrelated, but also semi-recently, I had a bad FPR which allowed the fuel to run through and not build the required pressure. New FPR solved that. Make sure you get the right one, as the 4.9 requires higher pressure than the V8.
Thread Starter
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Fleet Mechanic
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What did you use for a replacement pump? Reason I ask is that when I first replaced my pump, I "cheaped out" and went with some no-name pump. Bad idea. Pressure went low first before the pump failed entirely. It never made it to 1000 miles on the new pump. Motorcraft pump has been fine ever since installing that.
Unrelated, but also semi-recently, I had a bad FPR which allowed the fuel to run through and not build the required pressure. New FPR solved that. Make sure you get the right one, as the 4.9 requires higher pressure than the V8.
Unrelated, but also semi-recently, I had a bad FPR which allowed the fuel to run through and not build the required pressure. New FPR solved that. Make sure you get the right one, as the 4.9 requires higher pressure than the V8.