Possible CPS fix!

My grandson now has my '89 Cherokee with Renix control system. He called me and said it would crank but not start. I told him to unplug the CPS and replug it. It started and ran fine. Since this had happened to me before, I got to thinking how to prevent this problem. My idea: connect one CPS wire through a relay that is only on when the ignition is on. I used CPS plugs from a parts Jeep and connected them to a relay like the stock ones Jeep and Volvo use. The wire that isn't controlled by the relay is just spliced together to always stay connected. The relay's magnet coil is connected to ground on one side and to the fuel pump resistor on the other. I connected it to my '90 Cherokee and it worked as expected. I took it back out and my grandson installed it in the '89. He had been driving it with no problem since the one time it wouldn't start, so the fact it is still running OK doesn't prove anything. If it NEVER gives trouble again I'll claim victory over an exasperating problem. The cost is very low, so it's worth a try if you think it might help you...

Chrysler service bulletin 18-51-88

Fix for the problem.

Thanks! I hadn't seen that before. Any further trouble and I'll try Chrysler's fix. But I think I'll leave the relay in to see if it works long-term.

The reason it fixed it was likely dirt or corrosion in the connectors, not the act of unplugging the connector and plugging it back in changing anything about how the ECU and CPS interact. Sorry to burst your bubble, because it is a pretty neat idea.

It will actually make a quite effective antitheft system, just put the coil of the relay on a hidden toggle switch instead of the fuel pump feed wire. If the toggle is off, the engine isn't going to start no matter how much someone messes with it.

I had thought of dirty plug connections. I always use contact cleaner spray and then fill the plugs with tune-up grease to prevent entry of dirt or water. As for anti-theft, that's a good idea, but our Jeeps are so ugly people usually give them a wide berth...

heavyequipment said:

I had thought of dirty plug connections. I always use contact cleaner spray and then fill the plugs with tune-up grease to prevent entry of dirt or water. As for anti-theft, that's a good idea, but our Jeeps are so ugly people usually give them a wide berth...

Click to expand...

Actually, XJs are stolen frequently.