98 Jeep grand Cherokee, problems. Help maybe?

[B.M.800]

New codes...

12, 21, 43, 43, 21, 11, 21, 55.

43 being a cylinder misfire. Now, would a person be able to hear a difference because of that? When I first start it up it has a low idle then after a minute or so it (to me) runs great.

Also might have figured out part of why the 21 O2 sensor code shows up... On the downstream o2 sensor one of the wires is pulled out of the plug. Not on the sensor plug, but the one thats going up in the Jeep wiring harness.
How is that to put back in anyone know?

 

[Doc Sprocket]

Have a story, and a moral...

Back a whack of years ago, I had a cool little '85 Fiero. LOVED that car. It came to be after awhile, that now and then with no warning, it would start running extremely rough, with the Check Engine light on. I'd continue driving, and after some time, the light would go out, and it would run smoothly. There was no rhyme or reason to it, it would do it totally randomly. I ran the codes many times- it was throwing several, and not always the same codes.

One evening it did it. I opened the hood, and the manifold was literally glowing in the dark, cherry red...

I tried nearly everything I could come up with, short of replacing every sensor on the engine. Frustrated, I made a date with my local GM stealership for them to have a look.

A couple days before my appointment, I noticed it hadn't acted up lately. I did some extended driving with no issues, and called the dealer to cancel the diagnostic (which would have cost me $100 just to hook up the computer).

The day me appointment WOULD HAVE been if I hadn't cancelled, it acted up again. Severely pi$$ed off, I punched the center console and swore (would I do that?). Magically, the light went off and the engine smoothed out. Could it be? Nah. I couldn't help it- I punched it again. Wouldn't you know it? The light came on, and it ran like spit. Punched it a third time. Wanna guess what happened? Yup. Did it about 10 times in a row, and each time, it changed states. So- what happened?

The computer is buried under the console. I dug into it- loose connector. Figures. Plugged it in tight, and never had another issue. Moral? Several.

1) Sometimes it pays to hit stuff. LOL
2) Computers ain't half as smart as we think. In fact, they're dumb as a bag of hammers.
3) All the "codes" in the world don't mean spit sometimes.

 

[devino246]

On the same line as TS's story, have you checked to make sure that the PCM ground isn't corroded? A bad ground can cause all sorts of havoc.

 

[B.M.800]

^^Im pretty sure it is good. I will examine it tomorrow if its not raining. Im going to reset the comp too, see if that might make a difference.

Couldnt find the sensor I was looking for, of the Jeeps they had there very few of them had it... and the ones tat did werent the right year. Doah.

 

[devino246]

^^Im pretty sure it is good. I will examine it tomorrow if its not raining.

Don't just examine it, test it. Multimeter- set it to read ohms. One lead on the battery negative, the other on the PCM ground. I don't have an exact spec for you, but it shouldn't be crazy high.

 

[B.M.800]

Alright Ive got a list of things Im going to check out want to check here pretty soon I hope.
Hopefully Ill have some progress.