trucker

My "check engine" light do not come on. Could it be just bulb or PCM mess-up?

Bustedback

Replace the bulb first.

Gee oh Dee

Does the truck run?

I'd look into the bulb inless you've got a spare working ECU you can borrow from someone and test with.

trucker

The truck runs, but have some issue. Coming to red lights, when I hit the brakes, the rpm start surge, drop down and the pick up again and run smooth. When I turn the keys on, I do not see the check engine lights.

Bustedback

Sounds like you have a lazy IAC motor, you can clean it and then end up replacing it in a few weeks anyway, or just replace it now and clean the throttle body while you're there. Replace the bulb for the check engine light.

trucker

I did change the light and is working. Is stay on all the time. I try to check the engine code by turning key ON-OFF-ON-OFF-ON and I have no codes coming- stay on, but no blinking. While idling- I unplug the IAC motor and had no change at all. The IAC could be shut. 1996 Grand Cherokee with 4.0L engine. Am I turning the key on,of in right procedure?.

Bustedback

I think that only works on the 95 and older Chrysler products, 96 and newer are OBDII and have more codes than a blinking light can muster.

Gee oh Dee

If its OBD-II just take it up to a parts store and they'll be able to read the codes for free.

trucker

After reading someone advice, I back down the 2 screws on PCM plate and the check engine lights work as supposed to. After plating with key(on-off) I got code 12 and 55. I know 55 is end but the 12 I got somewhere stated "A Camshaft Position - Timing Over-Retarded". How do I adjust the timing on this truck or it is computer controlled?

country_boy454

The key on-off works on OBDII chrysler vehicels. I use it all the time on both my 96s and my 97. It is key on,off,on,off,on and leave on to get codes. 12 and 55 are normal codes. 12 is Direct battery input to PCM was disconnected within the last 50 Key-on cycles.

trucker

Thanks. Going down the road, I do not have "check engine" lights on, but still dropping the rpm when goes to stop. I guess, the next step will be to clean/replace the IAC motor. What it is the story with those 2 screw being too long on PCM under 1st and 3rd connector? I put 2 small washers under and works fine. The strange "thing" is, that was working fine until about 2 weeks ago.

trucker

Just spend $50 on IAC. Clean the throttle body. It was dirty as hell.
I still have rpm too low. Could it be that my timing is "too low". There is bolt on distributor to adjust timing. The "old days" i run it high until I heard the valve pinging and then back a little. I have no idea if that would work with computer controlled car.

country_boy454

Just throwing this out there, my 97 4.0 would do the same thing when the battery is getting to the end of its life. I would get the erratic idling at stop lights like you described. Have you tried cleaning the battery terminals? This may not be the case for you but it was for me!

trucker

The battery is 4 month old and I did clean the terminals,cables. It trowing me now code 21. Where I can find all codes for my truck? (beside dealer). I hate to go to jeep dealer. Does the second O2 sensor( back of cat) will have something to do with?

Gee oh Dee

Codes, search.

Rear o2 sensor, it could, but the CEL code will tell you exactly. If it is indeed the rear o2 sensor, its not gonna effect how your truck runs.