Hey yall, still having a problem with my ford. it’s 1992 4.9L 300 I6 2wd extended cab. I’ve had this issue for a few weeks and it’s gradually getting worse. I was testing fuel pressure and it was at 45 when idling but once is warmed up, it’ll stall and pressure will shoot up to 60. I thought that was very strange. any ideas why it’s doing that? It will do with when i’m driving too. itll start bucking and jerking then shut off when the rpm’s go lower. At this point i’m pretty confident it’s the fuel pump. i am currently trying to take the bed off, i got 2 bolts left to get out, but they are so locked in there that i think im gonna have to cut em out. anyone know the best way to cut the bolts out with an angle grinder? But anyway i just wanted to let yall know the status of it, if yall think if its something else or if it is the fuel pump, any way to get those dang nuts loose? i got 3 of em and ive been spraying them with blaster and wd40, but its been a huge pain.

 

When the truck is idling, vacuum is highest, and the fuel pressure regulator reduces fuel pressure.
When the vacuum decreases, the fuel pressure regulator increases pressure, because when you step on the accelerator pedal, vacuum decreases.
So either you're seeing the results of vacuum loss just before the truck stalls, or your fuel pump is running constantly, as long as the key is in the run position.
If you turn the key to the on position, does the fuel pump come on for about two seconds, then shut off?
Since you're well on the way to removing the bed, grind the heads off the remaining two bolts, if it comes to that. I had to cut my two front ones with a sawzall between the top of the frame rail and the bottom of the bed.
Check to see if the fuel pump shuts off after two seconds like it should.

 

Thanks for the reply man, yes the fuel pump turns on and shuts off like it should.

 

Then you might as well keep going with bed removal.
When you get the bed off, jumper "A" to "E" at the diagnostic plug and check for voltage at the fuel pump electrical connector, with the key in the run position.
Then, plug the pump back in and warm the truck up, to see if you can duplicate the stalling issue.
​​​​​Sometimes stalling after warm up is the result of a failing Ignition Control Module.
Do you have a tachometer?
If you can duplicate the stall, try restarting the truck and see if the tachometer moves while you're cranking the engine.
Also, after the stall, repeat the voltage test at the fuel pump electrical connector, but without the jumper in place at the diagnostic plug. See if voltage shows up for two seconds, when you cycle the key to the run position, and see if voltage shows up while you're cranking the truck.

 

unfortunately i don’t have a tachometer but yes i am planning on checking voltage once i get the bed off.
thanks for the help

 

With the jumper in place at the diagnostic plug, you're bypassing the computer's normal ground circuit to the fuel pump relay.
I forgot to post the picture, about jumping "A" to "E"


But, if the truck still stalls after warm up, with the jumper in place, you might be losing spark.
Do you have a spark plug tester?

 

no i don’t have one

 

If the truck stalls after warm up, with the diagnostic plug jumpered, judging from your fuel pressure readings of 45 and 60, I'd say you need to test for spark. You could do it the old school way of removing a spark plug, reconnecting it to the boot and laying it on the exhaust manifold, but I'd recommend using a tester.

 

alright thanks again

 

45-60 psi is the spec for your engine and I doubt the increase is causing a stall situation.I would look for a loss of spark since your condition happens when warm. Does the engine immediately restart or do you have to let it sit a while. You can either use a spark tester or an old spark plug to check for spark. I have used an aerosol circuit cooler to spray the ignition control module to see if the engine then fires up. The pickup coil and the ICM very often are temperature sensitive when they fail.

Checking for codes on these very often doesn't shed much information and give a pass code when there is indeed a problem somewhere.