Misc. 1981 CJ5 2.5 Liter Electronic Control Module California Version

[guille]

I need help on how to get the codes from this unusual computer. I have the Feedback Carburetor Emissions System. Everything is there but I have the service light on, and my two manuals don't have this type of system in any of the pages. Anyone out there with info regarding this system? I appreciate you time. Thanks

 

[CJ]

1981 was before OBD (1988), OBD1 (1991) or OBD2 (1996). If it's the GM computer I think you have it uses a RS232 connection or you can count the check engine light flashes by triggering the maint. switch.

 

[gert]

Wow i can’t believe your system is still working, I thought everybody ripped that stuff out


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[guille]

1981 was before OBD (1988), OBD1 (1991) or OBD2 (1996). If it's the GM computer I think you have it uses a RS232 connection or you can count the check engine light flashes by triggering the maint. switch.

Hello. How can I trigger the maintenance switch? it has a 9 pin port as showed in the diagram. which one is the test lead? Thank you

 

[guille]

Wow i can’t believe your system is still working, I thought everybody ripped that stuff out


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hello, I which I could, but unfortunately California regulations are strict.

 

[gert]

Are you wanting it to give you a trouble code?


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[CJ]

Hello. How can I trigger the maintenance switch? it has a 9 pin port as showed in the diagram. which one is the test lead? Thank you

The 9 pin port is a RS232 jack. That gets hooked to a computer using pins 2 & 3 (transmit / receive (crossed)) or a specific reader. If you use a PC it must have a serial port and a terminal program. Then you have to set the baud rate, data bits, stop bits and parity. It's really old school. I have used RS232 to communicate with old machine tools.

I'll see what I can find on this setup so you can figure this out...

 

[CJ]

Best description I have found so far. Trouble codes are NOT saved.

Servicing Jeeps
The on-board diagnostic system built into the Jeep feedback carb system will not store trouble codes and does little more than provide data indicating various switch positions and basic sensor values. Notable failure points on the old Ford MCU-based system used in these Jeeps were corrosion at the ECM connector, which is located behind the glove box on some models, and corrosion on the ignition coil terminals.

A quick way to evaluate fuel control on the Jeep feedback carb is to look down the auxiliary air inlet with the engine hot and running to observe the position of the stepper motor pintle valve. If the idle A/F ratio is adjusted correctly, the pintle valve should be about midway in its travel. Assuming the engine has engaged closed-loop operation, the oxygen sensor voltage should also be about 0.5 to 0.7 volts. A scope or DVOM can be tapped directly into the oxygen sensor lead to perform this test.

The distributor used with the Jeep feedback carburetors is a Motorcraft unit that incorporates the standard mechanical and vacuum advance mechanisms. In some cases, the mechanical advance on some Jeeps failed to operate because the secondary spring in the advance mechanism has too much tension. A spring with slightly less tension can be installed to allow full mechanical advance at about 3,500-4,000 rpm.


In most cases, Jeeps of this era use the “blue grommet” Motorcraft ignition module to operate the Motorcraft ignition coil. The ignition module is generally located in a highly vulnerable position under the washer reservoir mounted on the inner driver’s side fender panel. Keep in mind that the blue-grommet ignition module is a high failure rate part. If the module is receiving key-on power and the distributor pickup meets resistance specifications, test the B- terminal of the ignition coil for dwell angle or duty cycle. If the module isn’t producing dwell or if the engine is stalling due to intermittent ignition failure, replacing the relatively inexpensive module is a good first step.

-->> https://www.underhoodservice.com/tech-feature-servicing-jeep-and-ford-feedback-carburetors/

 

[guille]

Are you wanting it to give you a trouble code?


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Yes, is that possible?