johnmoon

New here and have a question. I have a 97 Grand Cherokee 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 take to fix it. Thanks

jcwclm

Wrong section. Try the Grand Cherokee section.

Zj heep

I had the same problem with my 93 zj v8 replaced cps css main computer fuel reg. All of thet and it ended up being the fuel pump. Hope that helps

johnmoon

Sorry about posting in the wrong spot. How would I move the post?

Would it be the pump even if I have good pressure? I don't know if there's a sensor in there that would affect the car or not. Thanks for the help.

jcwclm

You can't, a mod will.

notop46

It should not matter where this is posted since this is not a unique "grand" problem :-)

If your O2 sensor was OK before the exhaust manifold change then it was likely good after. If during the manifold change the battery was disconnected for a long time, the ECU may be in re-learn mode (It certainly is now if replaced). This mode allows the ECU to take the feedback from the O2 sensor, and your driving style and calibrate how much fuel it should provide in the different areas of the "fuel map table" (engine RPM vs manifold pressure). There are fueling corrections for O2 feedback, air and water temp, TPS etc, but RPM and MAP are the big ones. After a reset, it starts out rich (to protect the engine from lean conditions that can melt pistons), and eventually (I've read up to 50 cold start cyles (search injector swap)) tunes the FI system to where it runs good.

You may need to give it some time and let it re-learn. I ran a while with a bad O2 sensor and lost about 3 MPG from 16 to 13 city. No other issues other than the rich smelling exhaust, and when I replaced it, it recovered imediately.

Good luck, hope this helps.

413maxwedge

Make sure that the exhaust and intake manifold aren't loose or miss aligned. But you should post it in the grand section in case someone there also has a suggustion.gl ( the computor will be in limp mode till it relearns your driving habits to correct the above comment).