Fuel presure too low??? What do you think. Help

[Stick4503]

1996 Explorer with 4.0 ohv. Have had hot start issues and now occasional cold start.

Fuel pressure is 29 at rail with key cycle engine off, 29 engine running, 38-40 with vacuum line to FPR removed. Engine is a little rough all the time but I have no power loss with acceleration.

Starting problem is when warm, car cranks over and fires but runner for just a few seconds, skips and sputters like it is only running on a few cylinders then dies. I have changed both temp sensors, cleaned MAF, changed fuel filter, swapped fuel relays, changed crank sensor, tested coil.

Haynes repair says psi 30-45. I have 29 psi key on and running. Can here pump running and can here fuel being delivered back to the tank.

Any ideas? ASAP please.

 

[crazymind]

See if you can get a vacuum tool ( can't think of the name off hand) and apply a vacuum to the fpr. To me it sounds like your not getting a good vacuum on it. When you have it disconnected you have good pressure which rules out the fuel pump. Also check the hose see if it has any small cracks on it too.

 

[Stick4503]

I thought your pressure should decrease with vacuum

 

[crazymind]

No it'll increase. When you step on the gas and you lose vacuum to accelerate you need more fuel therefore loss of vacuum will increase fuel pressure.

 

[imp]

Why not replace the damn pressure regulator rather than mess around? Pressue in the 20s is too low for reliable starting; vacuum is highly variable during cranking. imp

 

[Stick4503]

No it'll increase. When you step on the gas and you lose vacuum to accelerate you need more fuel therefore loss of vacuum will increase fuel pressure.

Ok, yeah I see, I miss quoated myself. My pressure as you can see above does increase with vacuum removed.

 

[Stick4503]

Why not replace the damn pressure regulator rather than mess around? Pressue in the 20s is too low for reliable starting; vacuum is highly variable during cranking. imp

You are one chipper SOB. The reason to not just replace the "Damn" thing is because my test don't show that the "Damn" thing is the Damn problem. Now thats not saying that it is not but then again thats why I posted here.

Pressure regulator----$76.00

Fuel Pump----$100.00

Money for one not both. Fix the right thing have hard earned money left over.

See how it works!!!!!!!!

 

[crazymind]

Another reason not just replace the damn thong as you say, if the hose has a crack in it and you put a new regulater on it'll do the same thing that's part of diagnostics to find were the problem is coming from and fix it and not waste money by just throwing parts at it.

 

[budwich]

Why not replace the damn pressure regulator rather than mess around? Pressue in the 20s is too low for reliable starting; vacuum is highly variable during cranking. imp

I don't think that the OP indicted that his measurements were taken (or he was trying to take) during cranking.... but rather with "key on" which I assume is for "static levels" not running, and during "running", which is self explanatory.

He might want to perhaps try monitor his engine vacuum in general to see if there is an issue associated therein along with the suggestion of getting a vacuum pump/tool and establishing a known vacuum level into the FPR.