i have an 87 f250 with the 302ci 5.0l v8 single tank. since purchased it has had an issue where at wot it sputters and boggs down with less power than at half throttle. i have replaced in tank pump, one slightly kinked fuel line, single function reservoir, rail pump, fuel pressure regulator, checked and set timing by light and by ear. fuel pressure gauge stays at 35-40 psi at idle and holds pressure when turned off but as i raise rpm it drops and at wot to about 25-28 psi. no fouled plugs and no wet plugs. i am an ase engine and transmission tech and my boss is an ase master tech and we are both stumped. has anyone had an issue like this? any input is appreciated

 

Did you replace the fuel filter?

 

Does it have a second fuel filter ? I remember some having a canister type also .

 

Oh yeah. I forgot to put that also. I did change single function reservoir filter and rail filter and in tank sock filter.

 

Do you have proper voltage and ground to the pumps when it happens ? If both pumps are new , and all other parts you listed , and it is still happening ? I would ck voltage and grounds at both pumps .

 

13.1 volts and .1 drop on ground.

 

I'd say one of your pumps is faulty, some of the aftermarket replacements are weak or DOA right out of the box.

 

Good voltage ,and ground . Flow test the supply pump . It may not be supplying enough to the pressure pump . No restrictons ? sounds like a bad pump .

 

Its crazy because we already did warranty on both pumps twice, and original pumps bench tested ok.

 

That's 3 rail pumps and 3 tank pumps. And single function reservoir is brand new updated design straight from Ford

 

When I call my local dealer for a pump for a Crown Vic , and they have 30 in stock, there are issues ! On yours , I would try a different supplier or brand . I see a lot of bad pumps , even from the dealer .

 

The single function reservoir has no moving parts and it is just that a reservoir with maybe a filter in it. So there is no reason to replace it ever if you do not brake it.

I do not understand why your fuel pressure is that high at idle. Sounds like you have return fuel lines pinched and may be also the supply lines. Or a very strange fuel pressure regulator.

What fuel pressure do you get with the engine off and with the self-test plugs pin #6 grounded and the key on?



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Actually the single function reservoir does have moving parts. It has valves that release when pressure between the two pumps gets too high and bypasses it back to the return line. I've done extensive study on the fuel delivery system and that's why I'm stumped because all the common things you'd think would be an issue are checking out fine. From fuel tank to fuel rail is all replaced plus if it where a pinched return line I sure wouldn't be dropping to 28 at wot. And ford systems usually operate around 35-42 psi at idle. I'm to the point of checking fuel injectors if one is dumping fuel near wot

 

I've worked on 96 n up Ford's from gas to diesel and just about every make car from chevy to $130,000 Mercedes Benz abc system (and yes i said abc system not abs) and have never been stumped like this before. I need an 80s era ford engine performance tech to help figure this one out.

 

No it does not for all practical purposes. There are two check valve but the one on the return side will never open unless the fuel line is blocked between the single function reservoir and the tank. The other one is opened by the tank pump and just stops fuel draining back into the tank so the fuel lines have fuel in them when the pumps run for one second when the key is first turned on.
You only one tank and one tank pump. So what two pumps are you talking about?
Are you saying it has a safety valve that sends fuel back to its own pump?
They are not pressure valves, they are check valves.
But a pinched supply line would.
Wrong, Ford 's fuel systems usually operate around 28-32 psi at idle.That is why I said you may also have a pinched return line. Or you could also have a vacuum leak to cause the higher fuel pressure at idle.
WOT with the engine under load the fuel pressure is around 42psi.
That sounds like a waste of time.


Single Function Reservoir:



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