1988 F150 302 4x4 single cab short bed.

I've read a bunch of posts on here about fuel pressure causing rough or no start conditions when the engine is warm started. I have a similar issue where it starts fine cold, but warm is a little harder and the idle especially is bouncing around, almost like a vacuum leak.

I read fuel pressure at ~30 psi by letting the pump build pressure and while the engine is running. Same setup with the FPR unplugged reads 40 psi. Is this good to eliminate fuel pressure as a potential cause of slow start and rough idle?

I can't 100% rule out vacuum leak because I have yet to do the starter fluid spray test. I did just replace the vacuum lines according to this post on the bronco forum http://www.fullsizebronco.com/forum/...es-rubber.html

 

Another symptom I think may be related is that when i'm accelerating and the RPMs are climbing it seems like its running out of breath or its just getting restricted.

 

30 is definitely on the low end for what the truck wants - it should be 35-45. A healthy pump/regulator will produce 40 or more.

Check the vacuum line to the fuel pressure regulator - if there is fuel in the line, or you can smell fuel, it probably needs replacing.

Bouncing idle could also be a dirty idle air control valve, but based on the rough start/no start condition you have I would say make sure the fuel is being delivered first

 

I checked the IAC valve yesterday. I moves freely but there are the typical carbon deposits. I'm assuming if the rod slides easily, the IAC valve is fine?

I also checked if pressure changed when I switch between front and back fuel tanks and it remained at 30 PSI.

 

Yeah 30psi is just barely enough to keep the truck running. When was the last time you changed the fuel filter?

 

I just changed the fuel filter a few weeks ago. It only has the canister style filter on the inside frame rail right?

 

Correct. It would be highly unlikely that both fuel pumps would be producing low pressure, but not impossible. That's why I suggested fuel filter and FPR. If the fuel filter is new then double check the FPR.

What year/motor is your truck by the way?

 

Sorry I forgot to mention that! I guess I should have a sig.

1988 F150 302 4x4 single cab short bed.

Would a bad FPR affect fuel pressure with and without vacuum attached? Would there be an "across the board" drop of say 5 psi if its bad or what?

 

You should definitely see an increase in fuel pressure when you pull the vacuum line to the FPR - it basically should be operating at max pump pressure with no restrictions.

If there is a fuel smell in the vacuum line to the FPR it needs to be replaced - the diaphragm inside is shot.

There are other things to check too - does it hold pressure? If you pinch off the return line do you see an increase in pressure?

 

UPDATE:

I replaced the FPR and it definitely seems to run better. I'll run down to Autozone sometime this week and get some actual numbers because, well, I'm just curious.

Here's the zinger though...

I had advanced the timing to 12* about 2 weeks ago. It ran noticeably better but still seemed to have the original issue this thread addresses where it seems to struggle at higher RPMS when accelerating, like its running out of breath.

As part of tuning up the truck I replaced wires, rotor, cap, and coil with nice Ford racing 9mm and MSD. I installed these after I bumped the timing. Afterwards, I noticed a pinging sound, almost like something rattling. So I thought I put in too much timing so I backed it off and the sound persisted.

Finally, I remembered someone saying to make sure wires 7 and 8 are separated as much as possible or you'll get crossfire. Lo and behold, my wires were right next to each other. I rerouted the wires when I was installing the FPR and it drives like a champ now!

I wonder if both or just one thing fixed it!?

What are some symptoms of crossfiring wires?