Ωhm

More air, more fuel. O2S will always attempt to maintain a 14.7:1 air/fuel ratio, within its range of authority, otherwise ECU goes into open loop. High idle is vacuum leak or TPS adjustment.

Did you check O2S heater circuit? Disconnect O2S. On the component side measure ohms between pins C229_A and C229_B. Should read ≈6Ω's.

Check vacuum hose from intake manifold to MAP sensor for cracked, leaky conditions. O2, MAP and TPS are primary sensors used for fuel delivery.

You talking about LH and RH Courtesy Lamps? Should have both.

Are you grounding the Fan motor through the Coolant Switch? Shouldn't the Coolant Switch control the coil side of the Fan motor relay.

My mistake, I stand corrected.

4.0L only.

Check out Cruisers tip #13: http://cruiser54.com/

Is #1 cylinder on the compression stroke?

Its sole purpose is to direct heated air (heated by the exhaust manifold) to the airbox during a cold weather startup condition. Once underhood temperature rises enough, the airbox will switch from heated air (stovepipe) to the fresh air inlet.

No need to cap it off. You can just leave it as is.

Driver's side Seatbelt Switch. Goes to the Chime Module (CM). CM will turn Safety Belt Lamp ON (Instrument Cluster), when belt is not connected.

Does your boy have a auto or manual transmission?

Are you saying your missing the 4 pin Transmission Throttle Position connector, harness side?

Auto ECU (428) or Manual ECU (429) shouldn't matter when it comes to plug and play. Wiring harness should sort out the need for Upshift Lamp (Manual) or not to Upshift Lamp (Auto). Now I have heard that the manual ECU has a more aggressive timing curve used for ignition advance, while others say its the auto ECU that does. Without the proper documentation, no way to prove this one out. My guess is manual. Anyone else care to chime in on this one (Auto vs Manual).

As mentioned in previous postings, did you swap the Turn flasher with Hazard flasher and try the Turn Signals again? You say new fuse was installed. Was old fuse blown? Is new fuse blown?

Welcome to the Comanche Club. Great place for your questions.

Took myself a journey deep down into the dungeon. Found 1989 Medallion (RENIX/MS1700) diagnostic manual used for Engine Controls, Passive Restraints and MB/MJ Transmissions. Sure enough, all Engine Controlled DTC's are listed as a four digit number generated by the MS1700 tester. No listing for 1220 on the Medallion. Maybe someone has a diagnostic manual for Jeep Engine Controls (RENIX/MS1700)? Medallion manual was printed for Jeep/Eagle dealerships.

Gotta love the internet. Not sure, but is this similar or exactly to yours? Might help.

Could be what I'm saying is US market only. International stuff is a whole new world to me. On that blown transistor???, is it possible to trace the circuits and determine if one of the legs (transistor) goes to the ECU connectors? Knowing which ECU harness PIN_NUMBER could help in knowing which vehicle circuit is effected.

Kjell, I doubt very much that this ECU could set a DTC.

Fault Codes or Diagnostic Trouble Codes (DTC) never made it onboard with RENIX. The intent was there, as shown in the 4.0L Multi-Point Fuel Injection (MPI) manual (printed a year or two earlier), but the ability to read and store DTC's never made it to production. DTC's made their appearance with the Single Board Engine Controller (SBEC) on the 4.0L HO.

What year is your ECU?

No better place then here, to throw this question on the chopping block. Does RENIX Engine Control Units (ECU) use Volatile Memory? Myself, I think YES. Following are three (3) reasons why: 1) RENIX ECU has "Hot at all times" (C201_B7) circuit. WHY? 2) If ECU doesn't know Closed Throttle (CT) percentage, what happens during the next START, when someone has their fat foot pushing down on the gas pedal. Will that become the new CT percentage? 3) Does Long Term Fuel Trim (LTFT) really just stand for Next Term Fuel Trim (NTFT)? I don't think so. If that was the case, you'd only need Short Term Fuel Trim (STFT). Now are all ECU's created equal (early ECU's vs later ECU's)? As new strategies and improvements came along during the RENIX years, they were incorporated into the ECU's. Could this be the reason why some say YES to "volatile memory", while others say NO? So this is a good time to sharpen up your butcher knife and start swinging away.

Yeah, that what we were working toward. Looks like Engine Control Harness Splice_E. If it all red wires you found it.