Intermittent hesitation

[joester1908]

So I am working on a friend's XJ (1990, 4.0l, AW4) and I am at the limit of my knowledge. Here's some background:

 

We bought this Cherokee from a guy who said he went down Cruiser's thread on it just because. When you would accelerate, it would build up to 2500 RPM then lag around there for 5-10 seconds before shifting. Other than that it was in great shape and rust free.

 

We got it back home and I adjusted his TPS. It was way off and it had been over tightened, causing the adjustment to not stick because it wanted to go back in that cracked spot.

 

Adjusting his TPS solved the shifting issue, but now there is a hesitation off idle. Say you back out of the driveway, put it in drive, and just lightly give it throttle it will stall. You can start it up again and drive it for a while problem free. Then all the sudden it will act up again, hesitating/stalling from a stop. Sometimes, if you just barely push the pedal, it will idle very very low and seem like it will want to stall out. Other times, not at all. You can power through the hesitation, however.

 

We decided to replace the TPS due to the crack in the housing. I readjusted it. Reset the battery. Still no luck. Swapped my Comanche's IAC on his Jeep. Still nothing. Replaced the MAP sensor. Reset battery. Still nothing. Checked for vacuum leaks. Nothing. PO replaced cap and rotor. Distributor itself looks really clean inside. Maybe that was replaced? Checked fuel pressure. 32 PSI at idle. Checked all the grounds. Like I said, the previous owner went down Cruiser's thread and did most all of the stuff he said to do. Dipstick ground was refreshed. Added aux battery ground. Replaced ribbon ground cable on the back of the block with a normal, thick cable. Went to check the computer. Someone has had it out because it has junk yard grease pen on it and it wasn't installed properly. Checked the connectors anyways.

 

I'm kind of at a loss at this point. I don't think it's a CPS issue because it doesn't have a no start issue. Should I look at 02 sensor next? Could EGR be giving us these issues?

 

Thanks in advance.

[SVPete]

I guess I'll venture out here....

While our truck was still under warranty (that's along time ago and it was my wife's when new, the truck, not the wife), it started dying when you first started to drive in the morning. Restart, and it would run fine the rest of the day. 

Wow - looked in the file and I still have the paperwork from the dealer for that issue. It says:

 

"hesitates, surges, won't go in first gear, dies in a.m." "tuned, replaced plugs, cleaned intake manifold, set base idle". (I don't remember surging or not going into first gear)

 

Parts reflect: plugs, and TPS and O2 sensor ordered.

 

I remember my wife told me they disconnected something so it would run while they were waiting for the parts to come in (O2 I think). The truck ran fine while whatever was disconnected and ran fine when the parts were installed.

 

Now, for EGR....I hypothesize that the EGR could cause some issues like this also. I had hesitation issues and random stalling for a long time until around October 2015. After working through many of Cruisers tips, I firmly believed the EGR was the root of my problem. Unfortunately, while waiting for my EGR to come in (and separately I had ordered new plugs, wires, and coil {original was still installed}) I broke a plug wire.....so when the EGR came in I had to wait and replaced everything mentioned at once. Truck ran like it was supposed to for the first time in 9+ years. I took the old transducer apart (which comes with a new EGR) and discovered the diaphragm spring had rusted to nothingness, the vacuum bleed port was clogged, and the exhaust pressure port was clogged. The old EGR appears to be partially open, but I haven't really investigated that although I still have it.

 

So, in my experiences, both the O2 sensor and EGR were connected to stalling / hesitation issues. Nobody wants to just "parts swap", but perhaps start with the cheaper of the two, probably the O2 which won't really hurt you to replace.

 

Hope it helps. 

[joester1908]

Wow thank you for the information. I will have to do some 02 swapping. We also decided to put a stock air box in it and replace all the vacuum lines and the EGR system. It seems like the best option. Thanks for the info

[Tex06]

Only issues off-idle?  The rest of the RPM range is ok?

[joester1908]

Only issues off-idle?  The rest of the RPM range is ok?

no sometimes it idles down when driving. 

 

O2s ok.

replaced all the vacuum lines. did find ANOTHER vacuum leak. it is much more powerful and responsive now. 

put the stock air box in.

 

I did notice an exhaust leak at the manifold. I am only working on it a few times after work so I don't have a lot of time to spend. but i am going to pull off the intake manifold. clean it. replace the exhaust manifold. replace the gasket. and go from there. ill keep you all posted.

[cruiser54]

Did you use my method to adjust the TPS on the Engine side?

 

Have you done tip 5? 

[joester1908]

Did you use my method to adjust the TPS on the Engine side?

 

Have you done tip 5? 

Yes! Like I said, the previous owner went down your list and claimed he did everything. which i thought was strange. and he didnt do it right obviously because it drove like crap. I used your method to adjust his TPS and it was way off. But he had over tightened the sensor so much that it cracked the slots it moved in. After adjusting it it ran awesome and finally shifted, but it would loosen up due to the cracks. However, it wasnt until I adjusted the TPS that this stall with light throttle started happening. I then inspected the throttle body to be sure it was clean and the butterfly valve was moving properly. Satisfied, we replaced the TPS due to it being damaged, adjusted it again following your procedure, and it still stalls. That is when we went down your list and cross checked the work he had done.

 

We did find some minor vacuum problems and I found some stuff i didn't exactly like. I threw my MAP sensor on his Cherokee and we drove it around for about 10 minutes without it stalling. I thought we had solved the issue. He purchased a new one and I installed it, only to have it stall immediately. My theory is that the engine cooling must have had something to do with it?? It happened every time its cold, but then very intermittently.

 

I pulled off the intake tube again. I swapped my IAC on his Jeep and cleaned in the TB as much as I could. With my IAC, it still stalled. I will most definitely check the resistance from the flat 3 connector to the battery terminal. 

 

Do you think a leak at the manifold would cause this type of issue? My theory is if exhaust is leaking at the head, what's to say intake isnt either? and if its past the IAC and TPS it would be unmonitored and could cause it to lean out? 

 

I also just wanted to say thanks for all the help you give the Jeep community. I have had my Comanche since 2012 and I have been down your list with that and the many other XJs ive had 

[cruiser54]

An exhaust manifold leak won't cause your issue. 

 

Try exercising the EGR with your fingertips. Is it sticky or rough feeling?

 

The line from the throttle body to MAP is very critical. try spraying carb cleaner along that and where the intake manifold meets the head while idling. 

[SVPete]

Any resolution?

[joester1908]

An exhaust manifold leak won't cause your issue. 

 

Try exercising the EGR with your fingertips. Is it sticky or rough feeling?

 

The line from the throttle body to MAP is very critical. try spraying carb cleaner along that and where the intake manifold meets the head while idling. 

i was thinking if the exhaust is leaking at the manifold, the intake could be leaking too?

 

havent had a chance to look at the EGR yet but i plan on replacing the vacuum line from the TB to the MAP

 

Any resolution?

not yet, i havent had a chance to do anything more on it