So I was on my way to what would have been the greatest Thanksgiving party in history when my '89 decided to be weird. First it was hesitating a little, then a lot, then it just died. It started again and reluctantly got me back to within a mile of home before dying, again. It eventually started again but as soon as I put it in gear it died.

I had it pulled to my driveway where, instead of being at an epic party, I was covered in gasoline and underbody grime. I could hear the fuel pump priming so I decided to replace the fuel filter since it looked old. No luck. So I pulled a plug and checked for spark. No spark. Tested the coil and got the proper resistance.

I pulled the CPS and, in the process, broke the silly plastic thing that covers the HUGE hole in the tranny bell. I'll replace the CPS tomorrow and when that doesn't work I imagine I'll be replacing relays and fuel pumps and regulator solenoids and ECUs and whatever that other thing is until next spring. Sorry, I was just really hoping it wouldn't be like this.

Oh well, the fuel filter's super shiny. I may wax it tomorrow when I get frustrated trying to get that top bolt in the CPS mount.

Happy Thanksgiving everybody!

 

Hope these help. Don't just throw parts at it.

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 3.5 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.
RENIX TPS ADJUSTMENT
Before attempting to adjust your TPS be sure the throttle body has been recently cleaned.
It's especially important that the edges of the throttle butterfly are free of any carbon build-up.
IMPORTANT NOTE: Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connector
of the TPS . The letters are embossed on the connector itself.
Touch the black lead of your meter to the negative battery post.
If you see more than 1 ohm of resistance some modifications to the sensor ground harness will be
necessary. The harness repair must be performed before proceeding.
I can provide an instruction sheet for that if needed.
MANUAL TRANSMISSION:
RENIX manual transmission equipped XJs have a three-wire TPS mounted on the throttle body.
This manual transmission vehicle TPS provides data input to the ECU. The manual transmission
TPS has three wires in the connector and they're clearly embossed with the letters A,B, and C.
Wire "A" is positive.
Wire "B" is ground.
Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors..
Note the voltage reading--this is your REFERENCE voltage.
Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your
OUTPUT voltage.
Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For
example: 4.82 volts X .17=.82 volts. Adjust the TPS until you have achieved this percentage. If
you can't achieve the correct output voltage replace the TPS and start over.
AUTOMATIC TRANSMISSION:
RENIX automatic transmission equipped XJs have a TPS with two connectors. There is a flat three-
wire connector, same as the manual transmission vehicles have, and it is tested the same as the
manual transmission equipped vehicles--FOR ENGINE MANAGEMENT RELATED ISSUES.
However, the automatic TPS also has a square four-wire connector clearly embossed with the letters
A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module.
Key ON, measure voltage between "A" positive and "D" ground. Note the voltage. This is your
REFERENCE voltage.
Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT
voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage.
For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage.
If you can't, replace the TPS and start over.
So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and
the other side feeds the TCU. If you have TRANSMISSION issues check the four-wire
connector side of the TPS. If you have ENGINE issues check the three-wire connector side of
the TPS.
For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is
stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced.


 

I don't know if this applies to your model year, but also check your O2 sensors and all the way up their wire harnesses. In mine, the wire insulation got brittle and started flaking off under the loom, causing problems similar to yours.

 

Thank you Cruiser! I'll be out in my driveway with the laptop and my multi-meter in a bit. I'm going to pick up a new CPS, just in case but before I install it I'll reinstall the original and follow your testing, if nothing else, just so I have the experience. Prior to this I drove an '86 Audi 4000 which was notoriously unreliable model yet I managed to get 300K miles out of it before it would no longer pass CA emissions. I had every vacuum line and wiring diagram committed to memory, now I'm starting over. A little frustrating but I'm looking forward to the adventure.

Thanks again for the awesome write-up.

 

I'll be checking in periodically so post up what you find.

 

Sorry if this is a silly question but what is a "TPS"? Still learning abbreviations and acronyms.

 

Throttle Position Sensor

 

Thanks Cruiser.

Danian, I'll check the O2 sensor and wiring while I'm down there.

 

It LIVES! As I said, I pulled the CPS (which I'm getting really good at, btw) and noticed right away that the probe looked like a Chia Pet covered in iron fuzz. I spent a good hour scrubbing it up, getting all the grease and grime off as well as the stuff sticking to the magnet. I also repaired the plastic bell housing cover that I broke taking the CPS out the first time. Woke up early this morning and got everything put back in it's place, had my multi-meter all ready to go but decided to plug it in and give it a try, just for the heck of it. It fired immediately. I used to take 2-3 seconds of cranking before it fired... not anymore.

In the process I also discovered that one of the plug wires (#6) had not been connected inside the rubber boot for who-knows-how-long! Fixed that, too.

It's not all rainbows and unicorns, though. In my haste to test my sparkly clean CPS I failed to slip the lead into the retainer on the bell housing and thus, melted it to my exhaust manifold. I'm going to pull it again and see how bad the damage is. That's what I get for attempting complicated tasks when not fully awake with a turkey hangover. DOH!

If I have melted through the insulation, what are the thoughts on splicing? I'm concerned that it'll muck with the impedance but I really would like to save the $30-$40 for a new CPS if possible.

Thanks again, Cruiser. I had my laptop sitting on the passenger seat reading through your write-up as I worked.

 

Oh, and pictures to follow...

 

Solder and shrink tubing and you'll be fine. Check the output just for fun, too.

 

Awesome, that's what I'm gonna do. I'll admit, I was a little disappointed that I didn't get to run all the diagnostics so I'm going to do it anyway (after splice, if necessary) just so I have the experience.

 

Alright, here are the pictures from this morning...


Freshly cleaned CPS and repaired plastic bell housing cover.


De-fuzzed magnet. I also replaced the foam on the inside of the plastic cover with something a bit sturdier... the old stuff had mostly disintegrated.


I know from my previous searches that several people have had a tough time locating the CPS on the bell housing and I thought this photo might help future searchers. For anyone attempting, it's probably not going to be easy the first time but there are things you can do to be prepared. I happened to have a 24" 3/8 extension for my ratchet which worked perfectly when fed in the direction of the CPS (from underneath) beginning at the transfer case. I had a wobble end on it with a 7/16" socket. One thing I discovered is that it's easier to slide under the car head first from the passenger side. The first time I tried this I did it from the driver's side and, while I was successful, I had to contort myself into horribly uncomfortable positions to do it. Going in from the passenger side meant that my arms bent the way they were supposed to and I could comfortably thread my hands all the way up to the CPS with enough room to use my fingers to remove the bolts after they were loosened.


Poop! Don't be like me and get ahead of yourself. This is what happens when you don't replace the CPS lead into the clip on the bell housing, it gets melted by the exhaust manifold. Fortunately, it only burned through the outer insulation and not the red and white (there was no copper visible) so rather than splice, I wrapped it in friction tape then zip-tied the tape to keep it from coming undone when it gets warm.


While I was in there I cleaned the throttle body. It wasn't too bad but I figured as long as I had the rubber snorkel off to look, I might as well clean.

It runs so much better now that it has all six cylinders and a sparkly CPS... plus the new fuel filter.

 

I spoke (wrote) too soon. I pulled out of the driveway and it immediately died. This time the starter wouldn't engage [turn key, nothing happens]. I let it sit for a second and it started and ran long enough to back it into the driveway, then died. I managed to start it again and it idled happily for a minute or two and then started sputtering and died.

I think I'll replace the CPS but I'm going to run the diagnostics on this one first. I'll let you know. I'm guessing the next step will be to check fuel rail pressure... I have no idea how to do that and probably don't have the equipment necessary.

One thing I did notice the second time I removed the CPS (to patch the melted part) was that the magnet was again picking up metal filings. Is there really that much ferrous crap in the bell housing and will that affect the performance of the CPS?

Also, the starter looks new so I suspect that it's been replaced recently.

 

Well, I tested the CPS and it's showing zero [OL] resistance and 0.00 - 0.02 AC volts when cranking so I think it might be toast.