I have a 1992 single cab long box f150 with an E4OD & 302. 185 000 miles.

I’m having an issue where the truck will start to shake & act like it’s cutting out while driving, so far it only ever happens when the engine is up to operating temperature & especially happens randomly while cruising at 40-50 mph or sometimes when accelerating.
The weird part is when it’s doing this roughing rough/ cutting out/ shaking etc. if I floor the throttle the truck will snap out of it & get up & go like there’s nothing wrong anymore.

I have not unhooked the battery recently nor are there any codes.
I’ve been trying to track down this issue for a bit now but not having any luck.

I have checked for a vacuum leak & haven’t found anything as well as the EGR is new due to a previous code & it being stuck.
I have replaced the ignition coil 2 weeks ago due to it failing during testing with high resistance on the secondary, this helped things but the above issue is still there. I replaced it with a motorcraft part & tested the part before installation.

I then turned to considering it a fuel related issue. Only reason I didn’t check fuel pressure first is I didn’t have my own gauge but now I do. These are the results when I tested fuel pressure:

Front tank first prime: 20 psi
Front tank while engine running: 32 psi

Rear tank first prime: 24 psi
Rear tank while engine running: 33 psi

With fuel pressure vacuum hose still connected if I slowly press the gas pedal with the gauge hooked up & bring it up to 3000 rpm the fuel pressure doesn’t change & hovers around 32 psi. However if I sharply floor the gas pedal the fuel pressure it will jump up to 38-40 psi.

Then with the fuel pressure regulator vacuum hose disconnected the fuel pressure reads about 40 psi on both tanks. & that vacuum hose did have a bit of a raw fuel smell.
So I decided to replace the fuel pressure regulator but after that & taking the truck for a test drive it still has the same issue.

Someone suggested the fuel pumps could be getting weak but they still output within spec for a 302. Also the fuel filter is new.

Any ideas would be greatly appreciated as I would love to get this problem squared away & the truck running like it used to.

 

Any ideas?

 

If the throttle position appears to have some effect on the symptom, I'd test (don't replace or even disturb more than necessary) the TPS as this page explains:

(click this text)


If it passes, go to the NEXT page and test everything else. If all that passes, test the ignition system using the procedure in Haynes Ch.5 (usually Sec.5 or 7 depending which edition you use):

(click this text)

 

I have read through your links & will test as described.

One other thing I want to add is when looking at the spark plugs they are all a grey colour indicating the engine is running lean.
Would you think this means it’s a lack of fuel fuel issue?

In my first post when I first turn the key to prime before starting & get about 12 psi, Is this normal or should it prime to 30-40 psi?

Also with the fuel pressure gauge hooked up & vacuum line on the regulator when I press the gas pedal to bring the truck up to 2500-3000 RPM the gauge still reads a steady 32 psi. But if I snap the gas pedal to the floor quick the gauge will jump to 40 psi.
Should fuel pressure not gradually rise as I press the gas pedal?

& again this time with the vacuum line off the fuel pressure regulator the gauge will read 40 psi.
This leads me to believe the pumps are capable of outputting 40 psi & are fine,
am I right to assume that?

 

Compare them to the inside back cover of any Haynes. But since you didn't post pics of them, I'm not sure you're reading them right.The definition of "lean" in this context is "not enough gasoline for the amount of air passing through the engine". So yes: that's what it would mean.I've never found any use for a fuel pressure reading when the engine is NOT running. I don't care if it's 0 psi or -2000. I'm only interested in the pressure while the engine is running.Yes, it should NOT.Right.