I have a 1990 cherokee sport.
4.0 straight six 4wd

I took my jeep to a friend who is a mechanic and had him replace the flex plate. After paying him $300.00 I go to pick up my jeep and he says for some reason it is running like crap. So I start the jeep and it is idling rough and when I go down the road it spits and sputters and absolutely would not go over 10 mph. It's almost like it's out of time or something. He says when he did the flex plate there was nothing that he did that could cause this problem. I need help because now I am out of a car and can't figure it out.

 

Can you compare the old & new flexplate?

 

Thats probably it, the crank sensor looks at the flexplate and if there is a significant difference it can run like crap or not run at all

 

I compared them and they looked exactly the same. I didn't count the teeth or anything but the bolts lined right up and they looked the same.

 

should I have him take it back apart and compare just to be sure?

 

I would pull the CPS and make sure it doesnt have any dings on the reading side, if it gets nocked at all it will cause problems that you are experiencing, is the an engine light on?

 

If there is an inspection cover might be able to check/compare somewhat.
Who ordered plate and from where?

 

CPS can be tested. Also make sure the wires aren't melted on the exhaust manifold.


Renix CPS Testing and Adjusting



Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.

Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.

The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.

Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected.

You should get a reading of .5 AC volts.

If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer.

Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.

A little trick for increasing the output of your CPS is to drill out the upper mounting hole to 3/8” from the stock 5/16”, or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.




Revised 01-26-2013

Also make sure the tube from the throttle body to MAP didn't get damaged in the repair process.

 

thanks guys it was the cps