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Fuel Pump Rest Pressure Testing

posted Jun 19, 2016 04:25:42 by CharlesAcosta
For awhile I've been having three seconds crank time. Priming it once will start quicker. Not until I've completed section 16 is when I wanted to look into it. It gave me the direction i needed to find what the problem was.
But first at WOT my fuel trims were high, though not high enough to set a MIL. I noticed my O2 were lean at WOT and my Baro Hz PID was way off. Cleaning the MAF didn't help so I decided to replace it and test drive the truck. Now the the trim numbers were balancing out at WOT and O2 going rich. Section 12 is what guided me for the MAF.
I thought the fuel pump was the culprit for those fuel trims but it wasn't. Now the long crank time issue. I guess for being anal I've waited till i finished Section 16 without skipping previous ones to investigate Lol. My truck has Mechanical Returnless system and 40 - 65 psi at idle.
It took two primes to get it up to 64 psi.
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8 replies
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CharlesAcosta said Jun 19, 2016 04:27:44
Before I can turn the car on I noticed the psi was starting to drop.
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CharlesAcosta said Jun 19, 2016 04:39:29
Once the car was on it shot up to 64 psi. Snapping the throttle would not make it go higher but it didn't drop the needle either, only on deceleration. I did two more test to check for power and grounds. I have 6 amps and a 7700 rpm. The second test shows how the amperage is doubled during cranking. I just can't determine if it's the regulator or the check valve. The pressure line is braided. But regardless the regulator is part of the pump so it needs to be changed.

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Tyler said Jun 19, 2016 16:26:51
Man, sounds like rest pressure is dropping like a stone after the pump stops running!

Yeah, it's pump time, unfortunately :-( Which sucks, since your pump motor waveform looks textbook. I've often had "new" aftermarket pump assemblies that will fix a problem, but the after current waveform will look like trash compared to the OE pump...
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Noah said Jun 19, 2016 22:00:54
The second test shows how the amperage is doubled during cranking.

I wonder if that is to be expected on this system.
If the duty cycle to the pump is increased for cranking enrichment, would not the amperage also increase?
Just thinking out loud.
I agree it's pump time. When I was driving my Explorer I put several pumps in it, through a sweet trap door i put in the floor. Those tanks can be a real can of worms if you happen to live in the Rust Belt.
Massachusetts, USA
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Noah said Jun 19, 2016 22:19:56
I wonder if that is to be expected on this system.
If the duty cycle to the pump is increased for cranking enrichment, would not the amperage also increase?

Just looked it up, guess not with the mechanical returnless system.
Massachusetts, USA
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juergen scholl said Jun 20, 2016 02:09:35
Tyler,

more often than not the brushes on a new pump need some kind of run-in until they match perfectly to the commuter. This goes for OE pumps as well....
If you have the chance take another current waveform of a new pump after a couple of days and compare it to the first waveform after installing the pump....
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AndyMacFadyen said Jun 20, 2016 12:47:04
It depends on the type of fuel line but it might be possible to fit an inline no return valve or an inline solenoid opperated valve beteen the pump and the tank.
"Rust never sleeps"
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CharlesAcosta said Jun 20, 2016 18:22:17
I'll update you Tyler with the new waveform.correct me if I'm wrong. The check valve is the problem not the regulator? The valve only matters when the pump is off
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