Low Fuel Pressure?

[MorePower7701]

I have a 90 Ranger with a new 4.0 engine. I am trying to deside if my fuel regulator or fuel pump has gone bad. The problem I am having is the fuel pressure is only 28 psi with the key on and 28-30 psi with the engine running. When you kill the engine, and turn the key off, the pressure with sit at 28 psi and slowly move to 30 psi and hold there for serveral minutes. With the engine running you can pull the vacuum line of the regulator and it will go up about 5 psi, but still under 35 psi. I used a hand pump to pull a vacuum on the regulator, it held fine, the diaphragm must be alright. I pulled the spark plugs, as you would expect, they show signs of the engine running "very" lean. I have changed the fuel filter, and all six injectors, had a bad injector, had them all rebuilt, replaced all.

What do you think, Regulator or Pump?

 

[88BII]

pump

 

[MorePower7701]

Ah........ that sucks, well all there is left to do, is do it.

 

[MorePower7701]

I hope Someone Can Help

Well, I changed the Fuel pump and my pressure droped. My fuel pressure went from 28psi to 20psi, the new pump is quit, the old Ford OEM was very loud and worn.

Have any ideas?

 

[Ford_4.0]

I'm having similar problems, only worse.

It started with a bad regulator, and the pressure would bounce around 50-60 PSI. you could smell it was dumping gas in and the Engine would fluctuate in rpm to the changing pressure. I replaced the regulator, and that fixed that, but now it's running at 15 psi or less... almost makes me think my pressure gauge broke.

This might be the same problem as MorePower, but maybe not.

Dumb question: what does a spark plug look like when running lean? I think it turns white?

 

[MorePower7701]

I might have it figured out

I think the pressure regulator might be bad, I removed the return line and it was leaking gas with only 25psi of pressure.

My plugs are a good example of a engine running lean, they are white, very easy to tell.

I will replace the regulator, I hope this is what the problem is.

 

[MAKG]

That sure sounds like a bad regulator.

Too bad you already went through the trouble and expense of changing the pump.