Renix stumble troubleshooting

Tracking down an intermittent electrical problem in my 1988 Renix Cherokee.

Trouble started a couple of years ago in Harlan when I lost one cylinder. I had five perfectly good running cylinders and one that simply did not fire.  After some experimentation, I found that swapping the injector wiring around would move the dead cylinder.  Tracing the wiring back under the dash led me to replace the ECU.

Replacing the ECU in my Cherokee is made even more difficult by the SCCA approved roll cage that I had installed back in my Rally Racing days.  The knee bar is right in the way for pulling some of the panels that would make access to the ECU a bit easier.  I had to remove the driver’s seat and mounts. Then laying the floor, work under the dash to get to the bolts and connectors on the ECU.

I was not able to find an exact match, so I used one from a 90 model with automatic transmission control.  This meant loosing the cute little shift light on the dash that I never looked at anyway.

The old ECU had a failed injector driver.  I am not good enough at soldering to try to make the repair so I will just go with the used unit form Ebay.

While it was nice to have all six cylinders working again, on my next trip to Harlan, I had a new problem.  Occasionally the Jeep would lose power and put out black smoke from the exhaust. I had to hold the throttle open to keep it running.  After a few moments of shaking it would go right back to running perfectly again.  This type of failure led me to think electrical connection somewhere.

This spring as I was leading the group up trail 15, my engine just died and would hardly run at all.  Of coarse it had been running fine back home before the trip but filed just as I needed it most.  I eventually got it to start and took it back to camp and hitched a ride the rest of the day.

C10 Connector

That night I remembered reading about the C10 connector that all the engine control wires go through. It is mounted up on the firewall on the driver’s side.  Chrysler wisely did away with such a connector when they took over in 91 but all the Renix Jeeps have this connection.

I used a 7 mm socket to remove the mounting bolt and sprayed a bunch of contact cleaner on both sides.  I then plugged it back together and tightened it down.  I also took loose the CPS connector and MAP sensor connected and gave then the same treatment.

The next day the Jeep ran without a hiccup. Just its normal running rich due to the injectors being too big.

As I was preparing for the 2018 Fall Crawl, I took the Jeep for a test run around the farm trails.  Everything seemed fine and I was getting ready to load it on the trailer.  Then suddenly the stumble was back and I barely was able to get it back to it parking spot beside the barn.

Since I had a ChampCar race coming up all my free time was dedicated to the Porsche, I made arrangements to ride along for the Fall Crawl and left the Jeep parked.

Once I had some free time, I pulled the Jeep in the shop to do some checking. Of course, it ran fine. I could not find any problems. I decided to wait until my Renix Engine monitor arrived to do any more trouble shooting.

As I was backing it out of the shop and pulling back into a parking spot it died suddenly and refused to restart.  I hiked back to the shop and got some tools.  I checked for spark and had a good strong spark.  I then checked the fuel rail and got only air out instead of a stream of fuel. 

This condition puzzled me for a moment when I decided to try the obvious first.   I added five gallons of fuel left over from the race. The fuel pump then made a different sound and the engine started.  I put all the electrical tools away and took it for a test drive on trails.

So, at least for now, my off road Jeep is running again. I did get to test with the Renix engine monitor and confirmed that it does run too rich most of the time.  So I will be ordering some injectors like I put in Dad’s Wagoneer.