I have a 1989 jeep cherokee with a 4.0. It runs good like for 15 min then it starts to spudder and loose power. If I turn it off for a minute or two it runs good then again spudders. I can here it backfire at the air intake. What can it be? Map sensor, fuel pump, crank sensor?

 

yes. Or even the camshaft position sensor...or poor grounds....or intermittent shorts.....but you have a Renix and sure people with experience will chime in. I`m often wrong with those typical .... Renices

 

I'm sure no expert, but the backfire from the intake sure sounds like a lean condition. Maybe the fuel filter is not allowing full flow (?) The fact that it runs OK for short periods, then starts the sputtering, kinda sounds like fuel starvation....

Just an idea.....

Of course it could be ignition I suppose....like the coil overheatng etc

 

Just changed the fuel filter and still does the same. Don't hear any vacuum leaks.

 

Only other thing I can think of is the filter on the pick up tube in the gas tank collapsing. Been there a few times, with the sock type filter.
What type fuel system ? TBI, carb ? port, etc??

I know zip about an '89...

 

Rent a fuel pressure tester from the parts store and test it.

Probably the fuel pump is failing or the internal hose from pump to module is bad.

 

I have one injector for every cylinder. I think it's called tune port injection.

 

It's multi-point injection and you have an injector for every cylinder. Still need to do a pressure test.

 

Checked the fuel pressure and it was 28psi at idle with hose on and 38 with vacuum disconnected. Is that a bad fuel pump?

 

Looks like your pressures are in the ball park. The manual says 31 with the vac line connected, and 39 with it dis-connected..

Since it ran OK for a bit and then acted up, maybe it will change after it's running for for a while (??)

 

Map sensor checked good. Going to switch out the crank position sensor. Has lifetime so it wont hurt to change it out.

 

I'd revisit it for sure.

CPS on a Renix is usually dead or alive or intermittent.

 

Seems there's always something going on with it?

 

How old are your ignition wires?
A failing coil wire can cause these symptoms.

 

Changed the crank position sensor and still same problem.