1981 4-Cyl, California version - Emission Computer Help

1981 4-Cyl, California version - Emission Computer Help


I have 2 1981 CJ5's. One is 4-Cyl, 151 (California Model). The other used to be the same, but I converted it to an all-electric 4WD CJ-5.

I bought my first CJ5 in 1983. it's an 81 CJ5 (4-cyl, California version with C4 emissions control computer). It has run beautifully for all these years. My daughter and I tore it down and rebuilt everything when she turned 16 a few years ago. The vehicle is completely stock. Recently, though, it stalled on her. It starts up great but after a few minutes, it becomes totally gutless and stalls. I think I've gotten it down to a fuel issue which, in this vehicle, translates to first diagnosing the emissions control system and the rich/lean control from the mixture control solenoid.

The first step is to observe error codes that might be coming out of the computer (this was a very early version of the computer before ODB). The manual shows that the computer supports a "TEST LEAD" and a "TEST BULB". It says that you are supposed to install the TEST BULB, turn on the ignition (don't start the motor) and then ground the TEST LEAD and you should always get a blinking code diagnostic code for "NO TACHOMETER SIGNAL FOUND". I want to be able to read these codes to see if there is anything it can tell me.

Unfortunately, when I follow these instructions, I don't get any code. I replaced the computer, but still no code.

One of the diagnostic flowcharts also makes a comment that you will hear the mixture control solenoid make a ticking sound when the TEST LEAD signal is connected to ground and I DO hear this ticking.

The confusing thing that I'm struggling with is that the Jeep diagram shows that the wire that connects to the "TEST BULB" pin on the computer is actually "Tee-d" at the diagnostic test connector and the other end of the "Tee" goes to a push-in connector which is plugged into the fuse block and then connects to the switched +12V. I don't see how ANY TEST BULB could ever blink with the wire connected to the battery. I tried disconnecting the Tee'd signal to the fuse block, and then the voltage on TEST BULB (measured with a volt meter) is always 0.

I assume that connecting the TEST BULB, means connecting a test lamp between the TEST BULB pin of the diagnostic connector and GROUND, but I suppose this might be wrong. I'm using a cheap-o test lamp here (nothing fancy).

Does anyone have any experience with getting test codes out of this C4 emissions control computer?


Any advice will be appreciated......Tom
If you are sure that the carburetor is in good condition?
On my '81 with the 258 there were numerous Vacuum relays and sensors. After the engine ran for a short time I developed a Vacuum Leak and it was in the Vacuum Circuit.
Not sure how much help I've been but I would start with the Vacuum Circuit. I disconnected the Vacuum Lines (marked them first) and the problem went away.
My fix was to go with Fuel Injection because I wanted it to pass SMOG easily and you know how California is.
Thanks for the thoughts. I'm not sure of anything right now!

The vacume lines are old, so it probably would be good hygene just to change them all out--great idea.

I have another carburetor (non-california, though) from the electric jeep conversion. I thought about popping it on there just to see if that clears things up.

I stopped by my local mechanic this morning and he told me that the test lamp needed to be connected to be connected to +12V instead of GND...interesting. I'm going to check that next.

Thanks again for your advice. Tom.

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