1987 XJ Renix 4.0 Laredo Manual transmission

Hey gang, I've been having some fuel problems with the ol' Renix. The jeep would crank and crank but not start. I replaced the fuel pump and that didn't help. After a week of maintenance, I swapped the 'new' fuel pump for the bosch pump I had taken out of the tank. The new fuel pump was broken it turns out, and replacing it with the old Bosch got the jeep running again. I drove about 200 miles across a few days, and then one rainy afternoon, it cranks and cranks and won't start.

Problem is that it will start, I can drive it for maybe 3-5 minutes, then it shuts off as if there were a thermal failure or something switching from direct power to a fuse or a relay. It will start back up 5 or 6 times, but eventually it will shut off and then just crank and crank and crank.
Could it be that the Fuel pump module is bad/intermittently? Could it be a blown fuse?

Followed the Cruiser's tips: 1-6,8,9,11,19, 20, 40.
During the week of repairs/maintenance: I replaced the CPS, cleaned the IAT, replaced the O2 Sensor, replaced the ICM, Distributor Cap and Rotor, replaced the fuel pump Relay, upgraded the ECU to a 1990 (still have the '87), upgrade and cleaned all grounds, cleaned the C101, and cleaned all electrical connections.

a few things: No fuel pump ballast resistor on this one; there is a fuel pump wire that goes down by the starter and then into a harness where it 'loops back on itself' (don't know what that is for); I hear the pump prime almost every time I turn the key, but not every time...

 

What kind of CPS voltage do you have?

Next time it does this, unplug the CPS and plug it back in. See what happens.

You MAY have an Ignition Control Issue although that is quite rare.

 

Thanks for the reply! When the problem initially occurred, I was unplugging the cps, waiting five to ten minutes and then plugging it back in, starting the car, then driving for 500' and then doing it again. Did it 5 times in a row.

When I thought about it, I reckoned it was just the Jeep needing to "cool off" for 5 or 10 minutes, and that unplugging the CPS and reconnecting it was unnecessary.

I tested the CPS back then, and when the jeep would run, I was surprised that I didn't see anything out of the ordinary when back probing and checking for alternating current.
I will check again tomorrow and report back with some real numbers (if I recall it was up and down near 0.5 AC).

I noticed this yesterday: Jeep started up and was idling. After about 7 minutes or so, it coughed as though it weren't getting enough gas or as if there was a bad electrical connection.
I waited just a bit, and started it again to idle. I kept the probe on the battery because I was suspicious if the alternator had something to do with the issue. The battery was reading 12.6, and when the jeep fired up it went up to mid 13's and then into the 14's when revving. I figured it wasn't an issue until the jeep started to 'rattle' again and then the voltage dropped from 14+ to 7 and then back up , and then down, etc. just all over the place, and then it shut off (like always).

So, figured I'd change the alternator just for good measure; it's old. I have a new one and a new belt ready to install tomorrow.

 

Good plan.

 

Replaced the alternator and serpentine belt while I was at it. Jeep fired up and then after about 3 minutes or so began to buck, rattle and shake then turn off.

It was getting dark, but I did check the CPS while the jeep was running. Set to AC, it's putting out 1.8v - 2.2v. Piece is a Standard CPS.
When the jeep starts to buck, the CPS reading is up and down. I will do a check to get the crank reading and see what's going on with it as the jeep goes from "starting right up" to "long crank no start".

When I first get to the jeep and turn it on it will run for 3-10 minutes at idle. It shuts off, I turn it back on and it will run for 3-5 minutes before shutting off. And then it will run for 1 minute, a couple times.
Then it will buck and shake but not get to idle. After awhile (about 10 times of turning it over with diminishing idle times) it just cranks and cranks and won't start.

So, left it last night at the long crank no start, and when I go back this afternoon it will perform exactly the same way. Ideas? What's the Ignition Control Issue?

 

I don't know of a tried and true way to test the ICU.

 

Finally the Jeep is back on the road! Ultimately, deleted the C101--electrical/ wiring problem gone.

Had a friend sit in the driver's seat and turn the Jeep on. Since I've tested all the electrical connections, I just shook the harness to see if there was something wrong with the wires themselves.
Well, as the jeep was about to stall, a good shake of the harness near the fuel injectors and C101 brought it back.
There was some exposed wire showing (very very little) on the engine side of the C101. I cut, spliced/soldered, shrink wrapped at these spots, but that wasn't it.

In the end, I cut out the C101. I had cleaned the connection weeks ago and scraped the 'tar' from the engine side but I hadn't scraped or considered the 'tar' on the firewall side! There was some crud in there!
I was committed to removing it and only thought to clean the firewall side when I knew I would need to see what went into what terminals. Scraping out an inch of the black crud coming out the firewall side, the CPS white w/ black stripe wire was missing some insulation at the connector. Between that and the factory crimps, I decided to remove the C101 and remove the crimps and solder the whole beast.

Back on the road, strong and quick starts, every time.

 

Follow Up:

Made it 100 miles into a cross country trip before the jeep died and wouldn't start... same problem as before.
Just now getting back to it, and decided to replace the ignition switch.

Dropped the column, took off the old switch, and it was burnt on the center terminal.

It made sense that the ignition switch was turning the car off and then not sending a signal to turn it back on.
The bad switch accounted for the erratic behavior of the problem.

Hope this update helps.

 

Thanks for the update!!

 

That,s exactly what the the 80,s chev truck do. Did it to me last year

 

Same part!! LOL