2.3L ('83-'97) Fuel Pressure issues

[DandysRanger]

Trying to diagnose the running issues with the Ranger. Fuel pressure goes right to 37 PSI when priming and runs at about the same. It starts and idles OK until it starts to stumble, the exhaust gets smoky and the FP goes to 40 PSI. When it smooths out it goes back to 37 PSI. Also, when it shuts down the FP bleeds down slowly (10 minutes to from 37 to 20 PSI). What am I looking at here? Is 37 too low? Leaky injector? Both fuel pumps were replaced about 20K miles ago. The fuel filter was changed about 11K miles ago. I'll be installing a new one today.

 

[RonD]

Up thru 1997 30-40psi is correct running fuel pressure for EFI Rangers, 1998 and up used 55-65psi

So not a fuel pressure issue
Fuel pressure regulator(FPR) on the engine uses vacuum to maintain a stable pressure range, when engine start to stumble(misfire) that lowers the vacuum so fuel pressure will go up slightly, that's what you are seeing
Check the FPR's vacuum hose for signs of gasoline, FPR can leak a bit and raw fuel would be sucked into the engine, via that vacuum hose, causing Rich running, smokey exhaust

Dropping pressure with key off is not unusual, FPR and fuel pumps can leak fuel back to the gas tank, if it drops to 0 psi over a few hours it can cause hard Cold Starts, but no running issues

 

[DandysRanger]

Thanks RonD, It looks like I'm barking up the wrong tree.

 

[RonD]

If running issue only shows up at High Demand/high engine load it can be lower pressure, i.e. dirty fuel filter or weak fuel pump
Hard to diagnose that with static testing

 

[DandysRanger]

Well, I figured it out. Nothing to do with the fuel pressure. When I changed the cam seal, I had the timing off a couple of teeth. I had to put the plastic timing cover back on (glad I kept it) to make sure it was at TDC and then used a rope between the cam bolt and aux sprocket to time the cam sprocket. Runs like it used to now.
When all else fails, go back to the last thing you did. I keep having to relearn that lesson