Natejones75

Continued from my other post

Working on a 95 f150 (2wd 5.0 aod) has a stumble and shake when running. When accelerating sometimes will backfire and pop so i was thinking running lean/ fuel problems. Isat a long time before work on it to get it on the road. In the last few months its had a new Delphi fuel pump, new rail fuel pressure regulator, and about 4000 miles ago a fuel filter. Using my guages , it is within spec though on the low end. Here's what I got:
fuel pressure : KOEO 39 psi
KOER 31 psi
.when you.pull the vacuum line off the fuel pressure regulator running, the pressure jumps to about 40 psi. Also check the vacuum line going to the FPR and it's supplying about 20 inHg

Any of this seem oit of whack to anyone? What should I be looking for?

raski

Fuel pressure is fine.Specs are 30-45 psi. Look at the plugs to determine a lean miss condition. The ignition, intake sealing and EGR systems should also be in good condition as well as the vacuum plumbing.

manicmechanic007

Looks good to me too
Vacuum looks good as does the fuel pressure (doing what it's supposed to do)
Take a close look at the cap and rotor for carbon tracking
Ohm out the plug wires, and inspect the boots for a pinhole or the wire inside loose, or replace the wireset
(7500 ohms a foot for the plug wires)
The ignition coil, check the secondary terminal (high tension) plug wire side for white powdered aluminum on the post (corrosion).
Do test the engine for a vacuum leak at the manifold
Use brakleen or propane or even just H2O.
Good luck
Report back findings

raski

To check the secondary ignition components for breakdown, squirt water on the cap, coil and wires at night and see if you get a "light show".

Natejones75

Checked everything at night, no light show. Also sprayed everything with water while running, no difference. Still think it fuel. Something I should have said is when I start it up KOER or just turn the key on , it takes 15-20 seconds for the fuel to build up and steady foe the fuel pressure reading. I was thinking other cars I worked on in the past it was almost instantaneous. Is this right or sign of a problem?
also when you pull that vacuum line off of the fuel pressure regulator and I got that 9 psi jump, ianthat the sign of a bad regualtor?

Natejones75

Hooked the fuel pressure guage to the engine and ran it up to the window so I could watch it while driving. Today, engine running and idling it was right at 30 barely in spec. Driving down the road you can punch on it and put it under a load and the highest it will teach is about 36 psi. When you let off and let it decelerate, it drops to 28-29 psi

Natejones75

Anyone?

manicmechanic007

That fuel pressure is okay
Injector flow tests
Cylinder balance test
You say it pops
Ignition secondary needs checked and or replaced
How old are the wires, cap and rotor?

Natejones75

New cap and rotor btw, not sure about the plug wires but the plugs are new. Stock coil

manicmechanic007

One way is with a squirt bottle of water at night
Look for lightning when soaking the plug wires, boots and cap. (running cold engine)
Visually check the rotor for carbon tracking
Other way is with a scope at a shop