Don't know where you got that info but 28 psi is not near enough on a fuel injected 5.0l vehicle and if you knew anything about "single tank system " there is a 12 psi pump in tank that fills the single function reservoir which supplies the hi pressure frame rail pump and if the pressure builds between the two pumps it will bypass to return and is a very common issue on single tank f series and broncos. So that's the two pumps I'm talking about. And incase you were wondering the reason they have two pumps instead of one its because there is no bafle in tank so reservoir keeps a steady reserve of fuel incase fuel sloshes around and supply pump runs dry for a second or two there will be steady pressure at fuel injectors. If you don't know the system then your posts will be of no help to me.

 

I don't know where you are getting all the wrong information but a 5.0L engine will run at 28 psi and dies at about 26-27. We have posters all the time that report 28psi at idle but there gauges may be a little off.
When I run a 5.0L engine on just injector cleaner and I am watching the gauge I see the engine finally dies at about 27psi as it runs out of cleaner in the 3M can.
Your pressure is too high at idle for a 5.0L unless you have very low vacuum as in a vacuum leak.
I like to see the idle pressure at 30-33psi


There is no path to return fuel to the tank from the tank pump and there is also no way for the pressure to build between the two pumps as the high pressure pump would be pumping to the engine and and the fuel pressure regulator then re leaves any extra pressure back to the tank.
Also why would you want to bypass fuel back to the tank? You are using the same 12psi pump in the tank that they used on the carb fuel system and the float in the carb would block the flow most of the time.
Did you not look at the diagram I posted above.


As far as myself knowing about the fuel system I have a lot of Ford dealers and auto repair places calling me at home when they are stumped on this system. They say that they can not find anyone who knows more about the 1985-1997 fuel system than I do.



The type 2 fuel system:



Single Tank Reservoir:

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Didn't mean to offend but the paper that came with the brand new single function reservoir from ford says it bypasses at a certain psi and the valves can get stuck open.
I've checked all lines and they are all good except the looped one that I replaced. Have you ever seen an injector cause this type of issue? From tank to rail is all new and lines are good.

 

I don't see how an injector could cause a substantial drop in fuel pressure without fouling a plug or, more likely, hydro locking the engine.

 

So what would be most likely cause? If it was a blockage would I still get 40 psi as soon as the key is on?

 

Have you checked the volume output?

 

Why not ask the little piece of paper? Since YOU seem to want to tell everyone how EXPERT you are!!!

You need to slow down there junior, Listen to the guys here they KNOW what they are talking about!!

 

Listen to the guys on here tell me to check what's already been replaced? By the way the paper comes from ford motor who engineered the part so I think ill listen to the little paper before the people telling me check the obvious n sound like advanced auto parts counter guys.

 

Well, Have fun!!!!

 

Contrary to what the shop manual says just turning the key on will not tell you much. You have to ground pin #6 as in the above post.

I do not know why you have so much pressure at idle but my guess is that your in-tank boost fuel pump is not even running or is bad. I think that is why you are getting low fuel pressure at WOT. Could also be a bad frame HP pump but I dough it.

Unless they have changed the working from the one I have taken apart out of a 1986 Bronco II I do not see how that is possible. If the return check valve was stuck open it may cause your problem but I fail to see what could ever open it.



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First off , don't kick in my teeth here , But ( there's that word ) . I see a lot of guys stating 28 psi is ok ?! I use Mitchell and Snap On for my info . ( I know Sn On owns Mitchell ) They list higher specs . 32-35 min . In use I see anything under 31 -2 cause issues . I do not see 28 as acceptable . IMHO . Fetch.

 

My truck at idle:


Engine not running, 2-6 jumped key on:


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^ looks like 40 psi KOEO , 31 KOER . Looks OK . I see issues at 28 . IMHO

 

Thanks guys. That's what I thought too. Ok I fixed fuel pressure issue. It WAS #5 injector as I originally thought after all the testing of fuel supply. Now it doesn't lose fuel pressure at wot but I am now still in same boat. Wot it's breaking up and bogging down with no power at wot. Pulled spout n adjusted timing to 10,14 degrees with no difference except a little spark knock. Computer is taking over with spout in as it should. Any ideas anyone. Ive studied n learned fuel system but don't know much on Ford's ignition on 80's models. Our shop is more 2000 to current models. Any ideas on possible cause? I've checked obvious. Cap rotor wires plugs and wiring. All checks out good. Was wondering about fusable link at coil because it has a diode marking on it.

 

I still can't see how a bad injector is causing a loss of fuel pressure and the plugs are dry. Your last post sounds like it may be ignition... how did you check the cap, rotor, wires? It sounds like either a weak coil or bad wires to me.