Please read before saying "search the topic DA". I have searched for a week now in multiple areas. My issue is similar to others with the stalling issue. It started when I was coming home from the Keys towing a boat on the freeway. It would stall for a milliasecond (all power dead even the gauges would flat line) and jerk and then run fine for 20 or 30 miles. Sometimes the stall/start combo would come and go in batches. Well this took place all the way home, 200 miles or so, until we got into some traffic close to home and then all hell broke loose and she was backfiring like a ghetto drug deal gone bad. But kept running with some neutral revs maneuvers and power braking keeping a load and RPMs up.

Fast forward to today, she'll start but sometimes takes some cranking but usually fires straight up, it will idle all day and rev to the moon with no issues. As soon as I put it in drive she'll go about 50 feet and die but crank right back up. I can keep it running by using the throttle and brake (power braking deal) and keeping the RPMs around 1300. Now get this, this is where it gets strange, I can drive the damn thing in reverse all day long without a hiccup. I drove to the freaking gas station, a couple miles up the road, in reverse and no issues at all. Made the wife go as a witness incase I got pulled by the man.

What I've done so far - I've replaced the fuel pump (the ol' girl has 339K figured it was time anyway) - no change, replaced the throatle body and all the sensors attached - no change, replaced the CPS - no change. This is starting to get expensive and there are no codes and the check engine light doesn't stay on. I'll ask for any solid advice because I know there is a cure out there. She's been a friend for many years and miles and I owe it to her to fix this problem.

 

Come on, I know someone has some additional experience in this area.

 

How much vacuum is it pulling at idle?

What are your upstream o2's reading?

 

The check engine light does NOT need to stay on for you to retrieve a "stored code". If the CEL has ever been on recently, there should be a stored code. Pulling that code or codes is definitely the next step. It is absolutely, positively what any good technician would do if you took it into a shop.

For a 98, you'll need either a code reader, a scan tool or take it to a parts store like Autozone where they will read the codes for free.

Good luck and keep us updated.

 

I'll check the vacuum. What is it supposed to be measuring at idle? It idles great though.

I have not idea how to get my upstream o2 readings. I did swap out the upper o2 sensor. No effect.

 

Still no codes as I had Advanced Auto hook up the scanner tool.

So far this is what I've changed out and tested.
- Fuel Pump (changed) and tested - it's got right at 49 psi. drops to 40 psi or so when I hit the gas but jumps right back up to upper 40's.
- Upper o2 sensor - changed
- Ignition Coil - changed
- All the sensors on the throttle body - changed
- Cam position sensor - changed
- Crank position sensor - changed
- Unbolted PCM and checked the connections

Next stop the land of the new PCM? Any recommendation on where to get one from a reliable source or is the dealer the way to go on this part?

 

What are your upstream o2's reading?[/QUOTE]

[QUOTE=skife;2818891]How much vacuum is it pulling at idle? Just tested, pulling 15 psi at idle and about 23 at 2000 RPM. Vacuum is steady.

 

Possibly "throttle positioning sensor" about $40 at autozone. Seems familiar to what I had in my 99 and in my s10

 

I'm still dead in the water with the issues. Going to get a new ECU. Any suggestions on the best place to buy one, used? or should I go new from the dealer? Need to get it flashed too.

Thank to anyone replying.

 

Did you check your injectors? Are you getting spark on all cylinders? It almost sounds like your timing is off (although I have no idea why that would change if you were in reverse). Check your distributor and wires? Is your throttle cable pushed all the way forward? That can throw off your TPS and other sensors. I would look at those before replacing a PCM.

That said, you should be able to pull one from a yard pretty easily if you decide to do that.

 

Clean all your grounds, one by dipstick tube, two by coil mount, and the one from the battery to the body. Check your engine harness from your
fire wall to engine. Look on the bottom, mine cut through and killed #3 injector and IAC valve. Maybe when you put it in reverse your harness moves enough to let it run.

 

my '93 had a similar stalling at first.. then it would run for 25 minutes and then stop.. turns out it was the MAP sensor .. Manifold Absolute Pressure.. I had to keep reving in order to not stall.. limped into a parts place. got the best one AC Delco.. 100,000 mile part.. been no problemo since... that sensor is above the rear of the head connected to the fire wall. has a vac line going to it... and elect. hookup..

 

Thanks to all that replied to assist with the fix for my Cherokee. Went back and double checked the wiring harness and sure as s#%* I found a rub right were the fuel injector rail ends at the back of the motor. The protective case was worn through and a small wire wire was exposed. Taped that SOB up and zip tied it off the injector rail and wham bam thank you mam she is good to go. Also replaced the Mass Air Temp sensor that crews into the intake manifold at the rear. Was the last sensor that hadn't been switched out. Fingers crossed she will be good for another 330k.

 

Cool, glad you found it.