crazy fuel pressure

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kirkland2887
Posts: 86
Joined: Sun Jan 29, 2012 6:00 pm
Location: Albion, Idaho

crazy fuel pressure

Post by kirkland2887 »

My 88 2.9 has been randomly dying on me. i know it is a fuel problem. what i dont know is how to tell which pump it is for sure. i hooked up a snap on digital gauge and my fuel pressure bounces all over the place. between 12 psi and 36 psi. i think it is the high pressure pump on the frame rail. but if the transfer pump isn't supplying enough fuel then the high pressure pump can't do it's job. does anyone know how much pressure the transfer pump puts out? it never dies on me going down the road. only when i come to a stop light or yeild. Key on engine off i only get up to 15 psi and always have to crank multiple times to get it to start. i have alldata at work but it only tells you what the high pressure pump should put out and how to service transfer pump in tank. doesnt say anything about high pressure pump or the plastic reservoir between tank and high pressure pump.
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tekatlarge
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Location: Coastal, Worshington

Re: crazy fuel pressure

Post by tekatlarge »

Don't Panic... :eek: What it sounds like to me is a bad fuel pressure regulator! :mad:

Try this first: Pull the vacuum line off where it goes to the fuel pressure regulator. Look to see if it is wet with gas. If it is wet replace the regulator. If it is not wet and you have a hand held vacuum pump attach the vacuum pump to the vacuum port on the regulator. Pump up about say 10 PSI and verify the vacuum gauge stays steady. If it bleeds down it is Bad. OK, if it holds pressure Then try to fire the engine. If the engine starts and you can get the correct fuel pressure by adjusting the vacuum pump. the fuel pressure regulator is working.

If your regulator is OK replace the fuel filter. I hate to just shotgun parts so that is the way I would look at the problem. Just thinking I would probably pull the tank Sending Unit / Fuel pump and look for crud in the tank or clogged pick-up screen. My experience has been when a pump goes it goes rather suddenly. It almost sounds like the high pressure pump is starving for fuel. You mentioned the canister between the hi speed pump and the low speed pump. That's the fuel accumulator, it is just before the high pressure pump. That accumulator holds a volume of fuel so the hi pressure pump will always have plenty of fuel available in case of maybe UN porting of the fuel tank pickup when the fuel level is low and your in a hard turn or sudden stop or acceleration. I am more suspicious of the in tank pump.

There you go, go forth and repair..
The Tek @ Large
Coastal,Worshington
Livin life on the dole on the Coast
kirkland2887
Posts: 86
Joined: Sun Jan 29, 2012 6:00 pm
Location: Albion, Idaho

Re: crazy fuel pressure

Post by kirkland2887 »

I pulled the filter and it is not plugged. pulled the pump out of the tank. it hasnt been very long since it and the strainer were replaced but it never hurts to look. The pump and strainer still look new. i will test the regulator tomorrow at work. but here is another weird thing. i relieved the pressure at the schraeder valve on the fuel rail, and it seemed like there was air coming out. almost like a supersoaker that is running low. i have a full tank of gas and i dont see any leaks in the fuel system.i wonder if the plastic acumalator between the high and low pump is putting air into the system. that would also cause the pressure fluctuations.
kirkland2887
Posts: 86
Joined: Sun Jan 29, 2012 6:00 pm
Location: Albion, Idaho

Re: crazy fuel pressure

Post by kirkland2887 »

I forgot. i pulled the line off the regulator and it is dry. did you mean apply 10 in/hg or apply vacuum until i have 10psi. im gonna guess 10 in/hg
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tekatlarge
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Re: crazy fuel pressure

Post by tekatlarge »

You were correct. I got my in. and psi switched.

OK, one more thing to think about. The fuel line as it exits the tank could have an internal collapse or the line could be kinked somewhere.

If the accumulator were leaking air into the system you would probably have a tell tale fuel dampness on is from when the system was shut off.
The Tek @ Large
Coastal,Worshington
Livin life on the dole on the Coast
kirkland2887
Posts: 86
Joined: Sun Jan 29, 2012 6:00 pm
Location: Albion, Idaho

Re: crazy fuel pressure

Post by kirkland2887 »

sorry it took a few days. i have been busy as hell. so since i have pulled the filter and in tank pump, my idle has gone from 7-800 to 1000 and in the morning when i start it before work it smells like it is running rich. i just put a vacuum gauge on the regulator. i am getting 15in/hg from manifold. when i unhook the vacuum line from the regulator and plug it, my fuel pressure doesn't change. even if i am revving the engine. hooked vacuum pump to regulator and started at 5in/hg and gradually worked my way up to 17in/hg with no effect on fuel pressure. even when revving. even though it smells richer in the morning, my mileage hasn't changed, and my fuel pressure is doing the same thing. it could be running more rich because of ambient temp i guess. it has been getting pretty chilly at night around here. all data says the regulator is spring and vacuum controlled so i'm not sure if it is working properly or not. of course it doesn't give any specs on regulator or how to test it. only how to change it. i don't see any obvious leaks in the fuel system. i think on payday i am gonna go ahead and get a high pressure pump for it. i wish i could find a motorcraft pump for the dang thing but ford says they are discontinued.
williamsb2
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Re: crazy fuel pressure

Post by williamsb2 »

ignition on, engine off all fuel injected models should have 40 psi at schrader valve, sounds like you are sucking air somewhere.
williamsb2
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Re: crazy fuel pressure

Post by williamsb2 »

I had a fuel pump failure about a year ago, not sure which failed first. when we tested each off the truck with 12 volt power both were non functional. figured when one failed the other followed, replaced both as well as in tank screen and filter and havnt had any problems since. when the pump failed truck ran sputtering for a few hundred feet then quit and didnt start again, fuel filter was fine but replaced anyway.
williamsb2
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Re: crazy fuel pressure

Post by williamsb2 »

One more thing, theres a fuel pump relay on the pass side fenderwell just behind the factory airbox. its cliped to the fender along with the eec relay and ac relay. faulty relays sometimes work and then short out intermittently, my eec relay did this and would shut the truck off going down the road, I would turn the key off then on again and the engine would restart. after a week of checking every electrical connection i shook each relay while engine was running and when i reached the eec relay it shut off, after i replaced it i shook it next 2 my ear and could hear something rattling around inside. again no further problems after it was replaced.
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tekatlarge
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Re: crazy fuel pressure

Post by tekatlarge »

:D kirkland2887 You Got Mail :idea:
The Tek @ Large
Coastal,Worshington
Livin life on the dole on the Coast
kirkland2887
Posts: 86
Joined: Sun Jan 29, 2012 6:00 pm
Location: Albion, Idaho

Re: crazy fuel pressure

Post by kirkland2887 »

So i took off the accumulator. there was no filter and i could not find a filter anywhere there would fit in there. but therw was a lot of dirt in the bottom of it. i can see why people have a hard time getting them to seal. i ended up buying a filter that didnt fit just for the o ring. i replaced the high pressure pump and the inline filter after the high pressure pump and my truck is running perfect. i have 35 psi at an idle, and when i rev it i have 42 psi. guess the high pressure pump eas just getting tired. i am a little bumbed that motorcraft doesnt make a pump anymore. had to go to airtex.
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tekatlarge
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Re: crazy fuel pressure

Post by tekatlarge »

Glad to see you got it back together and your running good. Lets hope no more problems..

:cool:
The Tek @ Large
Coastal,Worshington
Livin life on the dole on the Coast
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