SOOOO, working on a 1995 F150 2WD 4.9/automatic

It came to me missing horribly under throttle/load, I installed an EGR restrictor plate with two small 1/8" holes. Check engine light cured and engine runs much better.

BUT
On cold startup it will fire and die immediately then restarts without issue... this in itself isn't my concern, just mentioning it for the sake of transparency.

The issue: the truck will go down the road Ok (not great) when cold but once it warms up it misses if I give it 1/4 throttle or more, if I keep my foot to the floor it will start to miss more. It will gain speed but sputters its way up in RPM and sounds like it's losing fuel or spark.

*ALL new tune up parts were on it when I got it, cap, rotor, plugs, wires etc.
*No codes No CEL
*fuel pressure gauge shows a rock steady 35 PSI idling, WOT etc.
*Have not detected any vaccum leaks
*unplugged the Fuel pressure regulator vacuum line and it didn't really change anything.
*Plugs are nice and clean, look like they are burning at the right temp.

Any ideas from you gents?

 

Fuel psi 35 isn't what the 300 needs.

45-50 psi, 45, is the lowest it will run correctly with. Will increase to 50-60 psi with vacuum removed from FPR.

V8's are maintained at 30 psi, with 5-10 psi increase with vacuum removed FPR.

 

Hmmmm, strange. Are the injectors finicky on the 4.9's or something?

 

No........

 

The difference in the injectors are the flow rates.
The 300 has 14lb/hr and the 302, 351 are 19lb/hr, with the 460 24lb/hr.

 

Seems logical, I've had 302's run great with 30-40psi. Seems odd to me that these would require more (I know the book says so) if there's a Simple nozzle difference it could make it spray lazy with lower pressure I suppose. I just figure I'd have seen a wet plug in at least one cylinder if that was the case. This morning I'm going to pull the filter and see if she's plugged up.. Then on to the pump

 

Removed the filter which appears new and it is not plugged at all. I can blow right through it easily. On to pump... Certainly hope this fixes it. Otherwise it's getting a Molotov cocktail.

 

Your fuel pressure is 35 PSI no matter what? Even if you bump the throttle WOT, it stays rock steady at 35 PSI?

 

Correct, In my experience you would experience a drop at WOT if the pump was bad but I'm not finding a lot of info on the 4.9 and its apparent need to really high fuel pressure. So I'm sort of taking educated guesses at this point.

 

Then either your fuel pump is really weak, the regulator has no vacuum line attached, or the regulator is faulty.

 

I'm suspecting the pump now that I've studied the fuel pressure more extensively. Once completely warmed up It does actually dip a few psi when you blip the throttle (under hood turning the throttle body). And if I hold the RPMs at 1500-1800 the psi will dip about 5 psi and then it will level out again.. But it's NOT increasing from 35 psi under any circumstances or rpm.

 

Fuel pressure should be 45-60 psi for the 300. If it's lower it won't run properly. You say if it's hot it's even worse? Sounds like a fuel pump to me. I just went through the same issues, replaced both tanks pumps and now my 95 300 runs great. I posted on the topic myself.
https://www.ford-trucks.com/forums/1...imination.html

 

Just read your write-up. I plan on doing the pump today. Wish me luck!

 

So I installed the new pump, made sure my butt connections were nice and tight. Plugged it all in and the new pump is showing zero psi on the fuel rail... Tried cranking and cranking to no avail. Swapped the relay with a known good one and no change. Shows I'm getting 5 Volts key on engine off at the fuel pump pigtail. I would think it should show more than that?? But either way the old pump made 35 psi with the same wiring... Inertia switch is fine as well. Any ideas or am I missing something?

 

I should also note that the gauge reads 1/3 tank with the key OFF and empty with the key ON. It worked fine before and the truck actually has a bit less that 1/4 tank. There were ZERO wiring changes to the sender so I have no idea what heck that's about. Input on that welcome as well.