Really weird RENIX problem

[Nevada City Sparky]

OK, pulling my hair out here. Here's what's new:
Coil, Coil Controller Module, Coolant Temp Sensor, New CPS (I tried 2) Cleaned Grounds.

Here's what happens:
Car will start fine and drive fine, but then just stall out. Not a fuel problem, and I can get it to restart by grounding the coil wire and jumping at the starter solenoid.

89' XJ 4.0, auto.

WTF could cause that?

Other symptom is the car is now starting to experience climbing RPMs at Idle. It'll idle at 650, then as it warms up, it will limb up to 1000. Also started overheating, just before I parked it 6 months ago in frustration.

 

[Johnnie Walker]

Fuel pump ballast resistor, driver side inner fender next to the air box. CHeck the connections, clean if necessary, reinstall try again. If that does not work, jumper the connection to bypass the resistor. If it solves the issue, Either make a jumper wire or splice the wires together.

 

[djgrayxj]

Note from DJ
Quote: I can get it to restart by grounding the coil wire and jumping at the starter solenoid.
Question which coil wire are you grounding?
Also looking for clarification on this; Starter Solenoid is attached to the top of the starter: Then there is the Starter Relay behind the battery, either one can be used to run the starter which one are you referring to?

 

[Nevada City Sparky]

The relay up top is where I jumped the post to the green wire. I'm grounding the center wire of the distributor to the AC compressor case.

I don't see how the ballast resistor would affect this.

 

[8Mud]

I thin you have multiple issues and may be looking for a single solution. Spark air/compression and fuel are what you need to keep it running.

Tr to figure out what is messing up.

 

[Johnnie Walker]

The relay up top is where I jumped the post to the green wire. I'm grounding the center wire of the distributor to the AC compressor case.

I don't see how the ballast resistor would affect this.

The FP ballast resistor is what allows the pump to run during normal operation. During initial start up it is bypassed. A couple weeks ago my Renix heep would start and die, unless I held the key in the start position, thus keeping the starter engaged. I then jumpered the ballast resistor wires and it fired up and stayed running.
Just saying, do not rule this out. In earlier models the ballast resistor was a TSB added item from customers complaining about the fuel pump being "too loud". Many, including myself, have by passed it with no ill effects.

 

[Nevada City Sparky]

I thin you have multiple issues and may be looking for a single solution. Spark air/compression and fuel are what you need to keep it running.

Tr to figure out what is messing up.

Spark!

I may have a manifold leak from loose bolts, but that shouldn't kill the motor when I'm driving.

Its as if the key was just shut off.

 

[8Mud]

I kill my ignition (spark) fairly often from running my Renix through the mud on my hunting lease. First thing I always check is the larger yellow wire at the ignition module for voltage. It will typically be a volt lower than battery voltage maybe a little more. This lets you know the front half of the system, voltage supply side, is likely OK or not.

Then the second most likely cause is the high voltage shorting out someplace between the module and the spark plug. The high voltage spark taking the wrong path to ground.

Then I move on to the sensors, most times it is the CPS. A new CPS won't help you much if the wring has a high resistance. The CPS typically puts out a half volt signal (pulse) and it really doesn't take much resistance in the wiring or a connector to seriously reduce this tiny voltage to a point where the ECU can't use it. It can be an intermittent type thing, sometimes it works and sometimes it doesn't.

Just a WAG (wild arsed guess) check the ground strap between the rear of the head and the firewall. Then the grounds at the engine oil dipstick tube. Make sure your batter is in good shape and the poles are shiny clean and oil free. Second best guess would be your ignition switch, the brown wire going to the switch has a tendency to overheat and to start melting down. Once the ignition switch gets toasted it can get unreliable.

Kind of sounds like you may have some sort of multiple sub system failure or degradation. This usually due to low voltage or grounds. Multiple systems share the same supply voltage and grounds.

Cruiser has a dandy check list for the Renix basics (search). Kind of a long list, but in all likelihood all it needs to be done before you start buying parts hoping to get lucky.

If the obvious and common stuff doesn't cure your problem, then we can move on to the complex and exotic stuff. I've found some really odd things, that were wrong, in both my Renix (87, 88) and my MJ. Many were one off events and drove me nuts trying to find the cause. Most times it turned out to be a harness problem of some sort.

 

[djgrayxj]

Note from DJ
First of all nobody hear is standing beside you to watch what you are experiencing so little details are important for us to coach you in solving your problem. So please don’t take offence in my look for clarification on different items.

Question#1: Did you ever find your Field Service Manual? Yes or NO
Question #2: When you turn the key to the Start Position will the Starter engage and the engine crank? Yes or NO

OK now I’m going to look over your shoulder from my keyboard.
I will pass on your climbing idle problem and your overheating for now and focus on getting your Jeep to start.

You have a Jeep that as of now that will crank but not start which is dependent on your answer to question #2 trying to read between the lines I will assume that it will crank with the key in the start position.

So you have made an attempt to check for spark with a jumper wire that you inserted between the main battery terminal and the solenoid terminal of the starter relay; which is the terminal with the larger Green wire located just below the main battery terminal which will allow you to crank the engine so that you look for good spark am I correct so far? If this is true did you have the key in the ON or Run position when doing this?

Also reading between the lines you removed the main large wire between the coil and the center terminal of the distributor cap from the distributor cap; you probably inserted a screwdriver in the cap end of the coil wire and held it with in a 1/2in of the A/C compressor case and look for spark while the engine was cranking with the aide of your jumper wire am I correct so far?

The key points hear are is the Jeep crank with the key in the START position and did you have the key in the RUN or ON position when checking for Spark?

8Mud made some good points

Note don’t give up keep us posted we will figure out your problems and get you back to happy Jeeping.

 

[blondejoncherokee]

TPS

 

[Nevada City Sparky]

Note from DJ
First of all nobody hear is standing beside you to watch what you are experiencing so little details are important for us to coach you in solving your problem. So please don’t take offence in my look for clarification on different items.

Fair enough, and I've been away all week without my Intardnet, so here goes:

Question#1: Did you ever find your Field Service Manual? Yes or NO

<<<YES!>>>

Question #2: When you turn the key to the Start Position will the Starter engage and the engine crank? Yes or NO

<<<YES!>>>

OK now I’m going to look over your shoulder from my keyboard.
I will pass on your climbing idle problem and your overheating for now and focus on getting your Jeep to start.

You have a Jeep that as of now that will crank but not start which is dependent on your answer to question #2 trying to read between the lines I will assume that it will crank with the key in the start position.
<<CORRECT>>

So you have made an attempt to check for spark with a jumper wire that you inserted between the main battery terminal and the solenoid terminal of the starter relay; which is the terminal with the larger Green wire located just below the main battery terminal which will allow you to crank the engine so that you look for good spark am I correct so far? If this is true did you have the key in the ON or Run position when doing this?

<<YES, key in ON position, but I'm doing this to "purge" the problem with the following next step:

Also reading between the lines you removed the main large wire between the coil and the center terminal of the distributor cap from the distributor cap; you probably inserted a screwdriver in the cap end of the coil wire and held it with in a 1/2in of the A/C compressor case and look for spark while the engine was cranking with the aide of your jumper wire am I correct so far?

<<YES, although I'm not using a screwdriver, its jumping from the wire to one of the A/C line's nuts. After I do this, I plug it back onto the distributor and it will start right up and run fine for anywhere from 1 day to a week, although the time between events is getting shorter. When it dies, its as if I switched off the key.>>


The key points hear are is the Jeep crank with the key in the START position and did you have the key in the RUN or ON position when checking for Spark?
<<Yes and Yes>>

8Mud made some good points

Note don’t give up keep us posted we will figure out your problems and get you back to happy Jeeping.

 

[Nevada City Sparky]

I kill my ignition (spark) fairly often from running my Renix through the mud on my hunting lease.

<<Well THIS TIME it ain't the mud . This is a problem that started over a year ago and has gotten progressively worse.

First thing I always check is the larger yellow wire at the ignition module for voltage. It will typically be a volt lower than battery voltage maybe a little more. This lets you know the front half of the system, voltage supply side, is likely OK or not.

Haven't done that yet. I'll give that a try.

Then the second most likely cause is the high voltage shorting out someplace between the module and the spark plug. The high voltage spark taking the wrong path to ground.

I'll root around, but the wiring is pretty clean.

Then I move on to the sensors, most times it is the CPS. A new CPS won't help you much if the wring has a high resistance. The CPS typically puts out a half volt signal (pulse) and it really doesn't take much resistance in the wiring or a connector to seriously reduce this tiny voltage to a point where the ECU can't use it. It can be an intermittent type thing, sometimes it works and sometimes it doesn't.

Just a WAG (wild arsed guess) check the ground strap between the rear of the head and the firewall. Then the grounds at the engine oil dipstick tube. Make sure your batter is in good shape and the poles are shiny clean and oil free. Second best guess would be your ignition switch, the brown wire going to the switch has a tendency to overheat and to start melting down. Once the ignition switch gets toasted it can get unreliable.

Only thing not verified here is the ignition switch. I'd replaced it about 8 years ago when I was doing the gound-up build. I suppose it could be funky now, the key is getting kinda loose.

Kind of sounds like you may have some sort of multiple sub system failure or degradation. This usually due to low voltage or grounds. Multiple systems share the same supply voltage and grounds.

Cruiser has a dandy check list for the Renix basics (search). Kind of a long list, but in all likelihood all it needs to be done before you start buying parts hoping to get lucky.

If the obvious and common stuff doesn't cure your problem, then we can move on to the complex and exotic stuff. I've found some really odd things, that were wrong, in both my Renix (87, 88) and my MJ. Many were one off events and drove me nuts trying to find the cause. Most times it turned out to be a harness problem of some sort.

I've been through Cruiser's List and MochaMike's two or three times on this beast.

So far, the most promising suggestion is your's regarding the yellow wire to the coil. I think (not near it now) it has been spliced and covered with tape. Either that, or its one nearby.

The plug for the O2 sensor broke the clip off and I currently have it tiewrapped together with its mate. I don't think funkiness there would kill the motor.

 

[Digger87xj]

Your list of repairs with no change in symptoms leads me to think it's the ECU.

Not common but not rare for the RENIX either. I've seen renix ecu's do some funny things when they are going out.

 

[8Mud]

Something I just remembered. I was getting random high RPM starts and occasionally the motor acted like it wanted to crap out. Turned out to be a bad splice in the harness. I eventually found it by ohm testing my TPS ground and shaking the harness by the injector harness by the firewall. My be your issue or it may not, just something to look at.

Best guess is you have a flacky CPS and/or the wiring between the CPS and the ECU has high resistance. If the resistance in your CPS goes up as it heats up it will eventually cause hard starts and stalling out. The CPS can be temperature sensitive, either ohm test it or test it for voltage pulse or both, cold and hot. The CPS connector also has to be oil free.

Check the torque on your intake/exhaust manifold bolts, don't try to tighten the end studs.

When I'm chasing down a vacuum leak I unhook and plug every vacuum outlet on the intake manifold with a short piece of tubing with a screw or bolt in the end. You can unplug and block off everything but the fuel pressure regulator and the MAP vacuum line. Plug the vacuum lines back in one at a time and listen for an RPM change, this will narrow down the possibilities.

Check your MAP vacuum line for chaffing or cracks.

If it stalls out when you release your foot from the gas pedal it is most likely your IAC. If it stalls while you are giving it some pedal, the first thing I'd check is the CPS and wiring. IAC problems are most commonly dirt and gummy oil on the piston and/or the seat and/or low voltage issues, battery or charging system.

A long time ago I pulled the connectors off of the ECU (on my 88) and tested the resistance between the CPS connector and the ECM connector. The lower the ohms the better pulse signal you are going to get to the ECU and the better it is going to start and run. While you have the connector off of the ECU gently tug on each wire at the rear of the connector. If any pins pop out push them back in deep enough to latch (the locking tab to catch). I've seen a bunch halfway in the connector, just making contact (maybe), on numerous Renix at the ECU and the TCU.

Your issues may be as simple as finding and fixing the vacuum leak and cleaning your IAC. Then you can troubleshoot your cooling system. If it still has the original radiator in it, it is likely partially plugged. If you still have the original fan clutch it is likely slipping.

 

[Sabalon Glitz]

Had a similar problem before my jeep would start sometimes and run fine. Sometimes it would cut off and not start then start the next day or so. Ended up being ignition control module.

 

[88trailcrawler]

Our 88 has a front manifold bolt that likes to loosen up on occasion and cause random idle fluctuations. It can be found by spraying a bit of starter fluid around while idling.

Check that vac line from TB to MAP also.

"I Think" our random renix sputter/limp mode is narrowed down to that factory "duct tape" harness splice, I haven't been motivated enough yet to find it. We just wiggle the crap out of the harness and be on our way.

 

[8Mud]

Our 88 has a front manifold bolt that likes to loosen up on occasion and cause random idle fluctuations. It can be found by spraying a bit of starter fluid around while idling.

Check that vac line from TB to MAP also.

"I Think" our random renix sputter/limp mode is narrowed down to that factory "duct tape" harness splice, I haven't been motivated enough yet to find it. We just wiggle the crap out of the harness and be on our way.

I found mine about 6-8 inches past the bend from the injector harness on the drivers side firewall, a black ground wire. The wires were just sitting in the splice, the splice was never crimped. There is a whole row of splices in the injector harness, any of witch may be flacky.

I found another bad splice in the harness on the passengers side wheel well, it was the yellow wire where it branches off and goes to the alternator. It was corroded and had green stuff growing on it, the wires were rotting.

 

[Nevada City Sparky]

Your list of repairs with no change in symptoms leads me to think it's the ECU.

Not common but not rare for the RENIX either. I've seen renix ecu's do some funny things when they are going out.

This is kinda where I'm headed now. I do have a few suspect wiring issues I can look at, particularly a slice on the wire to the coil controller. The bitch is, you think you have it fixed, only to find yourself on the side of the road, screwdriver in hand.

I found mine about 6-8 inches past the bend from the injector harness on the drivers side firewall, a black ground wire. The wires were just sitting in the splice, the splice was never crimped. There is a whole row of splices in the injector harness, any of witch may be flacky.

I found another bad splice in the harness on the passengers side wheel well, it was the yellow wire where it branches off and goes to the alternator. It was corroded and had green stuff growing on it, the wires were rotting.

I went through all the looms about 8 years ago when I went through the entire rig.

Thanks all, so far, if nothing else but confirming this is an odd one.

 

[djgrayxj]

Note from DJ
If you want to play the question and answer game again here we go.
In your original post you stated Quote: “New CPS (I tried 2)”
Questions:
Where are you purchasing new CPS at and why did you try two of them?
Did you replace now three CPS because of bad test results or just out of hope of repair?
When engine shutdown occurs is there any approximate time frame after start up this happens?
Example every time I drive my Jeep for one half hour while cruising along at 50MPH the engine shuts off.
What I’m looking for hear is there any type of pattern evolved to shut down that might indicate a thermal problem.
Last question for now what is the time frame between you’re engine shut down and your purging it which allows you to restart the engine?

My ‘88’s pattern was for about eight years was no start up hot or cold. I learned that if I looked at my tachometer and it was not bouncing while cranking it was time to raise the hood and unplug the and replug the CPS connector several times problem would be solved, I would also have engine shut down once in a while when costing to a stop same solution applied; but the only patter I had was it was going to happen sometime. In the meantime cruiser54 post information on how to increase the CPS output AC voltage. So after two engine shut downs on one short trip I declared the problem a safety hazard and the next day jacked up the Jeep and removed the CPS that I had ben professional replaced prior to my retirement and performed cruiser54 modification to the CPS and have had only one no start up since.

 

[old_man]

The big relay right by the battery can cause a ton of problems like you describe.

The TPS will not normally kill the engine.

Why do you jump the starter solenoid? Does the starter not spin when you turn the key? If that is the case, you have either a problem with the relay, wiring back to the ignition switch, or a bad switch.