chaser

i have a 90 cherokee and just recently its starting to act weird. when im driving or sitting still it acts like its not getting gas it cuts out really bad. the fuel pump sounds like its working and we thought it might be water in the gas so i treated it and put fresh gas in and its just getting worse. someone suggested the mass air flow sensor but i want to know what else it could be when it starts to cut out i pin the gas pedal and it stops cutting out but doesnt get alot of power

TwoXJS

First thing to check is fuel pressure at the rail. Should be able to get a pressure gauge from any auto parts store. I think it should be somewhere around 35 to 40 psi, correct me if I'm wrong? If it's not in spec, could be a bad fuel pump.

chaser

well without using a gauge i pushed the pin or whatever you wanna call it on the rail and usually gas come out and when i did it today no gas came out so bad fuel pump?

TwoXJS

Sounds like it. Either that or you've got a broken fuel line somewhere, or no gas in the tank. I doubt the last one very much....

EDIT: Or even a fuel pressure regulator, but someone else would need to confirm that for me

tjwalker

You really should verify fuel pressure with a gauge; it's the only way to get accurate data you can count on.

Your 90 XJ needs approximately 31 psi to start and should stay at that pressure at idle. Then disconnect the vacuum line leading to the fuel pressure regulator and the fuel pressure should jump to approximately 39 psi. Be sure that the vacuum line to the FPR is not wet with gasoline, which would indicate a ruptured fuel pressure regulator.

Also whenever symptomatic, it's a good time to review tuneup parts status. When were they replaced last? That would include fresh Champion copper plugs gapped to .035, quality plug wires, distributor cap, rotor and fuel filter. The importance of fresh tuneup parts cannot be overstated!

Start there; use a testing based strategy to figure it out.

Good luck and keep us updated!

freegdr

Might wanna check wiring to Cps for brittle/bare spots contacting to ground causing intermittent issue.

chaser

i do regular tune ups however i will be checking the fuel filter today to make sure. i am noticing the pump making a little bit different noise than it usually makes. i will also be checking the pressure at the rail today and clean up any bad connections i see

highmileage

We do not have a mass air flow(MAF), but we do have a Manifold Air/Absolute? Pressure(MAP) sensor. For what you have going on that is a good place to look. If you have access to a GM vehicle(88-94) or another JEEP(87-90) borrow the MAP sensor and see if it cleans up.

DFlintstone

And besides all that...there is a ceramic ballast resistor in the inner fender by the air cleaner. It's just there to quiet the pump a bit. Check those connections as well, power out the rear goes straight to the pump. It can be by-passed altogether.

The pump should run a couple of seconds when you turn on the ignition. That deal there on the rail is called a schrader valve, (same as on the wheels). Yea, fuel should spurt from there into the rag you are holding there right after you have turned on the ign.

chaser

When i unplug the MAP sensor it completely dies so i dont think its that

cruiser54

Check the fuel pressure!! Is there an echo in here?

chaser

Im trying to get ahold of one

chaser

If the fuel pressure is low then its prolly the pump right? And if the pressure is fine whats the next thing

cruiser54

Nevermind the NEXT thing. Check the frickin fuel pressure.

chaser

Shut the **** up im trying if your not going to help why bother commenting