Fuel Presure Low??

[duke16]

I just checked my fuel pressure to diagnose a misfire and popping under load and got these numbers.

Key in, engine off - 21 psi
Engine on, idle - 30 psi
FPR Vacuum hose off - 33 to 39 psi

According to the Haynes manual, fuel pressure with vacuum hose attached should be 30 - 45, without the hose it should be 40 - 50. So I'm just in spec, but do those numbers still look low enough to cause the misfiring and popping under load (which I believe means I'm running to lean). I have no trouble starting the Explorer.

 

[Premier]

i didnt get misfires, but mine was running at 29-30 psi not that long ago. i determined it was the fuel pump, and just paid to have it replaced because i didnt want to hassle with it.

oh and mine would start fine, but over 3k rpm's and i had a huge loss of power

 

[04mach1]

My guess would be fuel pump.

 

[Cobraguy]

What are your pressures when you get your misfire under load???

 

[duke16]

What are your pressures when you get your misfire under load???

The fuel pressure gauge isn't long enough to mount it outside of the hood, otherwise I would have checked that. Though I guess that would tell me for sure if it's the fuel pressure that's causing the problems I'm having. I'll see if I can find some sort of extension for it.

 

[Cobraguy]

When you extend it, just get enough so you can tape the gauge to the windshield. DO NOT run the gauge inside the cab. You do not want a pressurized gasoline line inside the car for any reason. Not even for a couple of minutes.

 

[duke16]

Managed to just get the gauge outside of the hood. Got the truck to start running rough by going up a hill, and the gauge stayed at 39 psi... didn't move at all. In fact, it never rose above 40psi no matter how hard I stepped on the gas. I'm not convinced that the fuel pump is my problem though. I would have thought that when the truck began surging going up the hill, I would see the psi drop.. but it didn't.