Quick summary: Idle is good, runs good at steady throttle (most of the time), runs good at high RPM (no load). I haven't been able to drive it yet so this is all driveway tech. When it's idling and you gas it (10-90% throttle) it cuts out, dead. You can feather the throttle and get it to high RPM's and the engine runs good, you can get it to off idle RPM's (>2000) and hold it steady and punch it and it cuts out. Mechanically the engine sounds and runs good its like the ignition or fuel is just cut. No stumble, no warnings, no nothing. It just cuts out.

Just bought 89 Cherokee, 79k miles. Started running bad, previous owner replaced fuel pump and filter and sold it. I found broken hard line to fuel pressure regulator (fixed), checked cap/rotor/plugs all in good condition, replaced heavily rusted pick up in distributor cap. Scoped TPS and CKP, TPS is good and replaced CKP. Runs better with new CKP but still cuts out. Fuel pressure is good, Vacuum is good and no leaks. Minor cooling system leaks.

Im thinking its a sensor or electrical problem because of how it cuts out but not sure where to go next. Anyone had similar problems or advice on where to go?

 

i got an 89 with the same problem and still dont know what is causeing it ive almost replaced everthing and am kinda leaning twords the tps, it is starting to get very annoying and pissing me off. let me know if you find the cause to this problem befor i go crazylol

 

After going over everything again (and again, and again) i was able to borrow a lab scope and found that the fuel pump was being supplied varying voltage. Then, BLAM! the fuel pump wire that comes off the starter relay fried. After not being able to decode the stupid wiring diagram on alldata I ran a power wire all the way to the fuel pump and it was running great! Stared right up, reved good, everything. So, there must be a short somewhere. But where? I gotta try to get a better diagram.

 

This may sound dumb.........

however, where your fuel pump relay plugs in, are there more relays there as well? If so, this might lead you in a good start to isolate the shorting you described.

on mine, I was driving from an errand to the store and the jeep just quit.

no warning, no check engine, nothing.

fortunately i was in an area where being on the side of the road did not impede traffic or cause any concern for safety...

Well sir, this is what I found....the block where the realys plug in, fuel pump, A/C, fan, shutdown, etc. etc. I wiggled the wiring harness feeding that and she started right up, so I get home and decide I gotta figure this out......

I take all the fuses and relays out of the block (disconnected battery just in case)...... remove the block assembly from its mounting bolts, took the thing as far part as possible to inspect visually whats what, and discover MANY MANY MANY corroded connections feeding into the fuse/relay block.
I was kinda amazed as the block is pretty much weather proof (not waterproof, but weatherproof)......

needless to say using a pin extractor tool I was able to get each wire/connector out fo the block, and sand and polish and filed and cleaned each one, thoroughly cleaned the block recepticle and re-installed all the wires/connectors, used a dab of di-electric grease on each relay tab and fuse tab, reassembled everything and have not had problem like that since.

problem was the auto-shutdown relay connections were really badly corroded and it finally opened up causing the jeep to shut off.

anyway, just some food for thought, maybe your fuse/relay block assy has a short somehow in it causing the wire to fry like you said.

my 2 cents sir.

good luck!

cheers

cpnwrench

 

I feel stupid. Can't remember if Renix had a MAP sensor.

 

so your saying that the power wire going to the fuel pump has a short some where in it?

 

Something in the fuel pump circuit has a short, not sure what yet. The fuel pump wire coming off the starter solenoid is what fried. The wiring diagrams on alldata are horrible and I can't tell if it's an isolated circuit or if it actually splices into many different things. It looks like it is splice into many circuits so a bypass may be in order.

 

I had the same problem is was the tps sensor washed the motor off and fried it lol

 

Fixed! Decided to pull the carpet and chase the wires. Found all three shorted/crossed/grounded where they come through the body and go over the hump under the rear seat. Had gotten real hot and melted the carpet and everything. Once that was fixed had a low voltage to the pump, bypassed the ballast and she runs great!