cherokee77

Hi everyone I am new here. I have a 1990 xj with a 4.0, I just bought tonight, on the way home it was missing and spuddering. If I barely press on the gas it is ok but when try to accelerate harder it starts backfiring through the intake and wont go.

I stopped to get gas and tryed to start it and it was running on a couple cylinders then dies. Then it took forever to get it to start again and all the way home it ran like total crap.
What could it be? PLEASE HELP.

PS I am new to jeeps.

Abovetimberline

Did the previous owner have it smogged? it could be a clogged cat,poor fuel pressure,cps is going out,those are a few things,it should of had a smog cert on it before it was sold.
Welcome to the site.

cherokee77

He had it smogged last year, but took 800 dollars off if I took care of it myself. Scared now

I was thinking fuel to but it runs better firewalled.

Abovetimberline

Yea i would be,I would honestly do a compression checked first,make sure it is ok.
There is a reason he took that much off,if it smogged legally last year then he should not be to worried this year.
Something else to look at is the egr,it maybe popping in to strong and causing a huge vacuum leak.
Check compression first,the lets go from there.
If it is running better floored then it is not the cat.
I had the same thing happen to me once in Wyoming and what it was is the rubber hose on the fuel pump in the tank came loose and would not give me enough fuel pressure unless it was floored,I drove threw 3 states floored,except towns of course,so it could be fuel,pump,filter,regulator,once i tightened the line it still runs fine.

cherokee77

I know motor is fine because when I got it home and let it sit I started it back up and all cylinders are firing.

When I rev it up it kinda stumbles and pops.

From my exspierence with motors which I am a gear head, it seems electrical or ignition.

Abovetimberline

That could be a fuel problem or egr,it is also possible it could be the cps is going out,just need to start checking things one at a time.
get yourself a fuel pressure guage,multi meter,and a good manual. They are all good tools to have.

cherokee77

What is cps, I know tps but not cps

Abovetimberline

crankshaft position sensor.

cherokee77

Wow ok these have a cps I didnt think so with having a dist. Learn something new everday I guess.

cherokee77

where is the cps at?

Abovetimberline

It is located on the top left side of the bellhousing,in 91 jeep started to use a camshaft position sensor along with the cps. But yours doe not have the camshaft position sensor,just the cps.

cherokee77

Thankyou I will work on it more tomorrow.

cherokee77

Anyone else have some advise, How do I check the cps sensor?

cherokee77

Cps sensor is brand new and still doing it.

Abovetimberline

This is a list of items it could be,but you need some tools to check them.
fuel pressure
ingnition control module
coil
egr
Those are a good start but I would check them first before replacing anything.