New here and have a question. I have a 97 GrandCherokee with 200,000 miles. I replaced the exhaust manifold because it was cracked and when I went to turn the car over, it wouldn't start. Couldn't figure it out so I took it to a mechanic. It would run with the exhaust manifold completely off the car but not with the manifold on the car. He finally was able to get the car to run with the manifold on the car and he brought it back to me. the car ran fine for a day and then started sputtering and died. Sent it back to mechanic.

He has replaced the main engine computer and has checked the wiring and he's not able to figure out the problem. Before I took it to him I replaced the CPS and the TPS. The car has new plugs, wires rotor and cap. The car also has spark and adequate fuel pressure at the rail.

I am good with old cars (50s) but the computerized stuff stumps me. I am thinking timing because I have compression, fuel and spark but the car won't run properly. That seems like timing to me. Also there is loads of unburned fuel being dumped into the exhaust system.

At this point I'm thinking the distributor, the pick up coil, and the O2 sensors might cause the car to run poorly. I'm suspecting these because the CPS and TPS have already been replaced. I need help with this as I'm pretty sure I know what the problem is (timing) but don't know what steps I should

 

Time to get a new mechanic, one with an up to date scan tool and knows how to read live stream data. The fact that your mechanic replaced the PCM without really confirming there was a problem with it kind of worries me.

 

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Great advice. Get your own scanner and pull the codes yourself if you haven't done so. You're engine light had to of come on?

 

No lights came on. I'm definitely getting a new mechanic. He was recommended as a jeep "expert". There is no check engine light. Before I replaced the exhaust manifold there was a light and I had autozone check the code and it said that the fuel/air mixture was off. I think it said it was too lean, which I attributed to the crack in the manifold allowing more air to pass through to the O2 sensor.

The code recommended replacement of the 02 sensor which has not been done at this point. Could that be the culprit? I think this mechanic's heart is in the right place but he is in over his head. He has basically given up on it and has asked me to come pick it up.

I'm trying not to through a load of money into this $1,600 car. Is there a cheap way of getting the live stream data read. I basically need a diagnosis and then I can repair the thing myself. I'm just no good at diagnosing cars with sensors and computers in them.

 

Also, given the fact that the CPS, TPS and ECM (i think that's the right acronym) have been replaced, I can't image what else it could be besides the Cam sensor in the distributor (timing) or the O2 sensors which could smooth out the amount of fuel being dumped into the cylinder and causing the rough idle and eventual stalling.

 

Look on ebay for an old Snap-On red brick scanner, you can find them for about a hundred bucks, but the info and things you can do with it is priceless. Code readers that you can buy at any parts store are only for reading and clearing codes. A scan tool will show you the live data stream, read codes, clear codes, do actuator tests, help diagnose ABS and transmission problems.

 

Ima mechanic, get a new one. Sounds like a clogged cat. To test pull the o2 sensor out b4 the cat, and see if it runs fine. Sounds like to much back pressure, that is y it runs with manifold off. If u pull the 02 sensor OUT and it runs better, then it is a clogged cat.

 

Just because you replaced a sensor doesn't mean the new one is good. I've heard crank sensors are notorious for being junk from get go. I've also heard if its no mopar it might not even work right.

 

The cat was definitely clogged. The mechanic said that there was lots of gas in it and that he replaced it and that it became clogged again. I think that the cat being clogged is a symptom of the timing being incorrect, but I might be wrong.

Regarding the sensor being new but defective, are you talking about the CPS, the TPS or all of them? I appreciate the advice.

I had heard that a bad CPS would cause the car to not start but because it's starting an running poorly after it runs for a while I'm thinking the 02 sensor as they only activate at a certain temperature (or so I've been told). That would seem to explain why the car runs fine at first and then runs poorly after a while of driving. Am I way off base with this assumption? Thanks again.

 

bump

probably getting the car back this weekend and I'm trying to develop a plan of attack. Anybody? Thanks.

 

if the cat was already replaced, because it was full of fule, I would lean towards a front o2 sensor

 

Thanks Tiwvr1. That's kind of what I was leaning towards as well. From there I was thinking about replacing the pickup coil in the distributor. We'll see how it goes. Thanks again.