96 jeep cherokee 4.0 problems

[alsjeep]

Ok so I've owned this jeep for over a year now and knew when i bought it it would be a personal fixer upper. But the jeep has run like a top and hums pretty when she started. My fuel pump went out on her and so i had that replaced by a shop partly because the nightmare for me having to drop the tank and replacing the fuel pump was not something i wanted to get into. They said that when they replaced the pump the wiress were burnt so they had to replace those as well. I took her home and right away noticed drivability issues. It had no power, would not accelerate, bogged down. Needless to say took her back to the shop.
While at the shop they could not find the answer to the problem and after a month of them trying to find it determined it was the ecu itself. Changed that out with put a new one in and also changed the heater sensor. Not sure if that's the correct term but that's what they replaced.
After picking up the jeep i started to notice even more problems, although the jeep seemed to run great when it reached operating temperature it would
idle rough. Hard crank to start and run like crap for apt half a block before driving normal again. It was especially noticeable if i stopped to run in the store for ten minutes and come back out. Hard to start spit sputter and it finally drove me crazy enough i took it to autozone to read the codes. Found out out was an 02 sensor. I decided to replace both the upstream and downstream sensors. Still no change. Although the 02 sensor fault codes had now disappeared. I was still stuck with the hard crank and rough idle issue.And the spit and running like crap after it got warmed up. So this is what I've replaced so far.

Fuel pump
Heater sensor
Fuel filter
02 sensor upstream and downstream
Cleaned manifold
Cleaned iac valve really gunked up
Decided to replace iac valve
Still no change and ran worse
Changed tps
No change
Changed map sensor
Ran better but still hard to crank to start except when cold
Replaced coolant temperature sensor
No change
Noticed to air ambient temperature sensor was broke replaced
Ran great for about a day then back to crap running when warm
Replaced thermostat
Changed the oil and filter
Replaced spark plugs
Spark plug wires
Cap and rotor
Replaced the distributor stator
Had the fuel linjectors cleaned.

I was getting the code of p0171 running lean. But after each part i replaced i also reset the codes. Cel come back on with a running lean code after about 50 miles but no drivability problems. My gas mileage is excellent almost 20.5 on the highway and 18 in road. I also changed the air filter. No other codes have come up. Now all these parts i mentioned were not changed out all at once. I would replace a part and test the results of changing that part.

I tested my 02 sensor upstream with a voltomer and at the engine harness key on engine off was only reading 4 volts traced the wires and no break. Ground side was good. Thought it might be a relay issue replaced the relay and still running lean. Any suggestions?

 

[TerryMason]

Welcome to Jeepz.com. It sounds like you've had a heck of a time, ever since the shop changed out the fuel pump, and associated wiring. Any chance you have an intermittent short there?

If they swapped out the fuel pump, and it's never been right since, I'd start my investigation there.

 

[greg92jeepxj]

Has the fuel pressure been read since the pump,was replaced ? To get a lean condition would mean insufficient pressure which would also mean to double check the fuel pressure regulator if stuck open and passing fuel back to tank consistently. I don't like the sound of the burned wires either , besides a relay , the pump,is pcm driven too . Hoping the wiring fix is good and the pcm ok even after replacement. Hate to see a good PCM get shorted if the wiring isn't done right. Hard to mess that up since it just involve running new wire and checking continuity and no shorts but if butt splices were used and bundled together , it's possible they can arc. Found that to be true on my '92 after an electrician supposedly fixed for my dad , the PO. I corrected it and hasn't been a problem since but I taught me not to trust mechanics. That's why I do my own. Praying for you that they did right and the problem is just in the fuel system and not further complicated by a bad wiring job . I'm with Terry on this , the wiring should be checked to be sure and fuel pressure as well. Sounds like your doing a good job on your own but I think the fuel pressure is contributing to a hard start , poor idle and loss of power. Don't quit , I'm sure it's a nice jeep .

 

[Jeeprancher]

In my experience , aftermarket in tank fuel pumps are a big problem . Even though the cataloging shows these pumps to be direct replacements for the OE part . They are indeed sub par . Usually not putting out the required pressure to effectively operate the system that the manufacturer notes them as applicable to .
If there is one replacement part on the entire vehicle that I would spend the extra money on from the Jeep dealer , it would be an in tank fuel pump . After spending a number of years in the auto parts industry , I can only say that we'd had nothing but problems with in tank pumps . Even if they worked correctly in the beginning , the life expectancy was pittiful . A lot of the outlets like Auto Zone and O'reilly offer a lifetime warranty on this stuff , but you're the one that's going through having to drop that tank repeatedly to swap out one pump after the next . So not worth it at all ! If this is the problem , and chances are it is , get a pump from the Jeep dealer and do the job once and be done .

 

[Dragon5126]

first have your fuel pressure tested, I don't agree with the mopar parts, high performance parts work fine cheap OEM parts DONT. Your O2 sensor voltage is a bit low. if those are parts store variety or Bosh dump them and put in NTK (NGK manufactured) This brand is cheaper and far superior to Mopar (jeep) brand sensors. NEXT, find out if they used a boneyard PCM. this is a never do! first off the PCM MUST be reprogrammed to match your Cherokee's setup, exact year options and everything else or you will experience all kinds of odd issues very similar to what you are. This is done either by a dealer (pay for it) or by purchasing from a company that programs them before shipping them out, they look up your VIN and use the info from Jeep/Chrysler to program it. This, once again, is why you must deal with a mechanic that knows jeeps, too many don't, and do stupid things that cost the jeep owner twice as much in the end.

 

[alsjeep]

Oh thank you guys for the reply. I'm going to have the fuel pressure tested thats what i was thinking too. It has to be the new pump. I also went back to the coolant temperature sensor wiring i noticed that the connection was a bit loose. I unplugged it and noticed that the two prongs on the oem one i bought at oreilly were smaller than my original. It was not making good contact with the wiring harness on the jeep. So i did try to make them smaller by using a knife to close them in a bit. Low and behold the jeep started even at operating temp and even seemed a bit cooler while running. Weird i know. So that gets me thinking. Are all the parts that i have replaced smaller at the connection? Makes an interesting dilemma

 

[alsjeep]

Oh and also the replacement pcm was my own pcm from the jeep that they suuposedly reprogrammed. Could this be another issue?

 

[Dragon5126]

Oh and also the replacement pcm was my own pcm from the jeep that they suuposedly reprogrammed. Could this be another issue?

First I don't trust ANY O'Reilly electrical parts, from repeated bad experiences, such as sub par connector sizes.

On the PCM, it could be a major issue, the big question is did they exercise and fully test it before reprogramming it? IF they didn't, reprogramming it doesn't mean a thing since there still can be issues in it. For example, I purchased one from one company and screwed up, and didn't send in the core to activate the warranty, 6months later the voltage regulator went out. (regulator on the 98 GC 4.0 is in the PCM) I was screwed. So I popped it open just to educate myself, the jelly on the regulator board was burned away traces were burned on the board and diodes were fried, Had they run the proper diagnostics the diodes would have shown up as weak ( I'm an Electronics Engineer, this is old hat to me) since the stator in the Alternator wasn't shorted, which is the only thing that would have fried all the diodes in the regulator. So I ended up ordering one from their competition, and it worked fine. Reprogramming is only half of what the PCM needs done. I'm not suggesting this is the same in your case, but when there are certain jobs that you need done, it is simply unwise to cut corners, some examples are replacing timing chains and not the gears, changing oil and not the filter,,, you get the idea.