Low fuel pressure on 92 4.0

Another problem just reared it's ugly head on my son's newly purchased '92 XJ 4.0 Auto.

He drove it ~ 2 miles up to the grocery store and it ran fine. Then got in and started up just fine and as soon as he tried to drive it it stalled/died. Fired up and idles ok but if you get it gas it wants to die.

So a couple hrs later I take him back up to look it over. Put my fuel pressure gauge on the schrader valve to see ~ 32 psi at key on and ~ 32 psi steady at idle and revving the motor. It will drive, but sputters a bit unless you give it a lot of gas and it wants to die. I was thinking it could be the pressure regulator, fuel pump going out, or a clogged fuel filter (none of which we've had a chance to chance yet since purchase)

My understanding is there should be 49 psi +/- a couple pounds. Is this true for the 92 4.0 HO? If so, what could cause the low pressure and what would you check?

Any suggestions are appreciated.

The difference between 32 and 49 psi isn't going to make it run bad. New Jeep? Start by checking spark plugs, easy stuff. I've had vehicles ten fine with way less fuel pressure.

49 psi is the fuel pressure spec for later model XJs.

For a 92, the spec is 31 psi at idle so you're good there, although there is an additional step of testing you need to perform to verify the regulator. Remove the vacuum line leading to the fuel pressure regulator and the pressure should jump to approximately 39 psi. Be sure that the vacuum line to the regulator is not wet with fuel which would indicate a ruptured fuel pressure regulator.

Is the check engine light on or have you seen it? If so, must retrieve codes for guidance.

If no codes, I'd start with a full tuneup which is a good idea for any "new-to-you" vehicle. That means Champion copper plugs gapped to .035, quality plug wires, distributor cap, rotor and fuel filter.

Then see where you are at. Simple stuff first. Always.

winterbeater said:

The difference between 32 and 49 psi isn't going to make it run bad. New Jeep? Start by checking spark plugs, easy stuff. I've had vehicles ten fine with way less fuel pressure.

Click to expand...

birchlakeXJ said:

49 psi is the fuel pressure spec for later model XJs.

For a 92, the spec is 31 psi at idle so you're good there, although there is an additional step of testing you need to perform to verify the regulator. Remove the vacuum line leading to the fuel pressure regulator and the pressure should jump to approximately 39 psi. Be sure that the vacuum line to the regulator is not wet with fuel which would indicate a ruptured fuel pressure regulator.

Is the check engine light on or have you seen it? If so, must retrieve codes for guidance.

If no codes, I'd start with a full tuneup which is a good idea for any "new-to-you" vehicle. That means Champion copper plugs gapped to .035, quality plug wires, distributor cap, rotor and fuel filter.

Then see where you are at. Simple stuff first. Always.

Click to expand...

Thanks a bunch. I'll run the extra check on the fuel pressure and verify the pressure jumps when the regulator vacuum line is disconnected ...

I'm sure this one needs a tune up. It just seems that when there is vehicle trouble, it happens in BUNCHES around my house... My son's 'new' 92, then my '01 XJ and my wives '03 KJ all having issues at the same time.

My '01 needed a new Coil Rail, KJ needed a new PCV valve... and now to get my son's '92 lined out. He needs more money to pay for all the parts...