Fuel Pressure

[seth959ci]

Hello all, once again calling on the knowledge of other forum members to try to get the kinks worked out of my '89. i just checked the fuel pressure and With the key on it was about 40 psi and then it dropped to 30 psi over the course of 90 seconds. Pressure was about 30 psi when running.

From my understanding 40 psi is correct but should the pressure drop like that?

 

[Mikel89us]

The static pressure is ~40 psi, and it will bleed off because the pump doesnt continually run while the engine is not running. And while the engine is running the fuel pressure regulator tunes back pressure, its supposed to be 32 i think, but 30 will still run fine. Are you having a running issue? Or is this just something you decided to check? With the pressures you are running it should still run ok.

 

[shane96ranger]

Was the vacuum still hooked up? When checking static fuel pressure, the vacuum should be disconnected and the line (source) blocked off. The number I've lived off is actually 39 psi, however 40 should be within range.

 

[seth959ci]

ive been having a miss/studder under a load in 4th or 5th gear that is intermittent but that sometimes builds up to a rapid fire violent shaking. This is primarily under 2500rpms. above that the engine runs fine.

I've replaced about all the sensors so now im looking at fuel or maybe the alternator. Could a weak alternator cause these issues?

 

[shane96ranger]

When was your last tune up? Plugs, wires, PCV, fuel filter, etc......

Sent from a Commodore 64 using a 300 baud modem

 

[seth959ci]

plugs, wires, coils, tps, iac, fuel filter are new. PCV checked out ok( it rattle when i shook it). speaking of the PCV, a guy at the local ford dealership says the PCV system is incorrect on my truck.

So for clarity, the system consists of an oil separator on the block, a large line that runs from the oil separator to the pcv valve that sits on the firewall side of the intake manifold. And from the other side of the pcv valve a line runs to the bottom side of the intake near the throttle body. does that sound right?


but any way... yes the truck is tuned up properly, But has a frustrating glitch somewhere in the system. thanks for any Help

 

[adsm08]

To be perfectly honest, your issue sounds like a misfire. The Triton V8's do something similar as the ignition coils begin to fail. If you have the dual-plug EDIS ignition system, i would suspect a failing coil pack.

 

[seth959ci]

i guess i'll have to try a new coil.. I've been having issues with the stereo cutting out intermittently and the voltage gauge drops off when the heater or the headlights get turned on.. would a weak alternator show the same symptoms as a coil? Thanks for the timely input too, makes a big difference in overall diagnosis time

 

[adsm08]

That is pertinent information. I'm going to go out on a limb and guess that flipping on the turn signals, head lights, high beams, and tapping the brakes are all precursors to the cutting out.

Hold off on the coil and check your battery cables and charging voltage. A weak alternator could cause this, but IME it is more likely that the alternator is actually working fine and that you have a loose or weak connection at the battery, either on the posts or at the fender solenoid.

 

[seth959ci]

They are not pre cursors to the cutting out, its very random but ill be sure to go over all my connections

 

[shane96ranger]

its very random

I've had plenty of random issues with battery connections over the years.

 

[adsm08]

They are not pre cursors to the cutting out, its very random but ill be sure to go over all my connections

Let it go and they will be. The big clue that you have a battery connection issue is that changes in the electrical load seem to be made right before your symptom occurs. The means the alternator is working, it just can't keep up with the sudden changes in demand, which is one of the battery's jobs.

 

[seth959ci]

Well unfortunately i cleaned up the battery connections and the main ground wire and the issue is still there.. ill get some multimeter readings later to see if anything is out of the ordinary

can the ground wire appear to be ok but have internal issues? it is 23 years old after all lol