Renix Gremlins (seeking advice on next phase)

88, 4.0, Auto, probably somewhere around 170K miles (havent checked in a while)

Need to eliminate this Renix gremlin (sputter, hesitation, backfire, crank-no start)

It is intermittent sometimes a few times a day, sometimes nothing for months at at time. Issue has never left us stranded, as it usually fixes itself by sitting or unplug/replug the MAP and we are on our way. There in NO pattern (cold/hot - idle/accelerating)

Fuel pump sounds good when key is turned. Fuel squirts out of the fuel rail valve when pushed in.

Jeep is driven only 5-10 miles a day, it is my kids high school car. It runs good and strong other than this intermittent problem.

Plugs/wires/rotor cap changed 5 years ago
All sensors changed out about 2 years ago
Don't hear any VAC line leaks, line from MAP to TB looks good
Problem dates back to original owner who said dealer never could fix it

Here is what I am thinking next (figure all or most are a good idea anyway)
- New battery and ground wires
- New ICU and coil
- Wires/Plugs/Cap (it's been 5 years)
- Maybe new distributor assembly (doesn't seem to expensive)

I would appreciate comments on my plan of attack:
- Is it a good idea?
- Might it help eliminate the Renix issue
- Best parts/parts sources
- Any potential upgrades
- Any additional suggestions

The goal is to have confidence in the reliability of the rig so that I can proceed with trail worthy upgrades.

Any input/links, etc would be greatly appreciated.

Testing the fuel pressure by depressing the valve is *NOT* a valid test. You need to use a fuel pressure gauge.

Have you tested the sensors recently?

Check all your grounds.

upgraded mains and grounds will help your situation. 5-90 on the board here makes a great set and he is a super great guy to work with. Tempermental is a great way to describe the renix rigs, The upside I found with it was the minimal electronics in the engine bay.

Try this first. Don't skip any steps and add the grounds if you can afford it.

Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, and wasted money replacing unnecessary components.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
　
　
If you want to upgrade your grounds and battery cables in general, contact Jon at www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
　
Revised 11-28-2011

I pulled my CPS and cleaned all the oil and crap off of it and it help a boat load for my hard starting an no starting problem. I also sanded down the bracket where the bolts go thru too

scottmcneal said:

I pulled my CPS and cleaned all the oil and crap off of it and it help a boat load for my hard starting an no starting problem. I also sanded down the bracket where the bolts go thru too

Click to expand...

Very common, especially on manual trans models. The debris that comes off the clutch, which has some metal in it, sticks to the CPS because it is basically a magnet. Easy way to be sure of the condition/output of your CPS is to check it for AC output voltage while cranking:



Renix CPS Testing and Adjusting
　
　
Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.
Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.
The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.
Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected.
You should get a reading of .5 AC volts.
If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer.
Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.
A little trick for increasing the output of your CPS is to drill out it’s mounting holes with the first drill bit that just won’t fit through the original holes. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.
　
Revised 11-29-2011