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CSS Output Voltage Question (Renix 4.0)

tempest411

NAXJA Forum User
Hello,


I've owned my '88 XJ for over 20 years now, and except for some CSS issues when I got it, it's run very reliably. Those CSS issues were solved with the Chrysler issued kit that included a new sensor and harness that patches directly into the ECU connector. Last spring I was driving down a road and it just died on me. I was able to restart it right away and drove the rest of the way home without incident. At first I tried to dismiss it as a freak anomoly, but then it did it again a week later to my wife...and then again to myself. I immediately suspected that the CSS sensor was just old and was now failing. It'd been in there since 2000. I did some research and found Cruiser54s write-up about the required output voltage needing to be about .5V. I measured mine, multimeter set to AC, at about .25V (250mV). I changed the sensor with another new one I 'had around' from so long ago, and it also had a measured output of .25V. The Jeep drove ok for a day or so, but then resumed it's stalling behavior. At this point I started thinking about the ECU, the C101 connector, and other possibilities. Over the summer I've cleaned the grounds at the dipstick tube and at the DS fender, replaced the C101 connector with a pair of sealed Deutsch-tech connectors, swapped the CSS sensor AGAIN with a known new factory Chrysler part, replaced the fuel pump, and swapped ECUs (Cardone unit). The symptom has only gotten worse! The last few times I drove it, besides the stalling, I had a great deal of trouble starting it. I could hear it fire a little bit at first, then it would just spin with the starter. Wait a little bit (five minutes), and it will start up and drive as if nothing was ever wrong. And, btw, the CSS voltage output is still about .25V, which leaves me wondering if my meter(Fluke) is measuring it differently than Cruiser54's (peak-to-peak, or not...). What ever's going on is very intermittent, and has an on/off behavior to it. I have replaced the ignition module...got one from O'Relly's, but made in USA...but have not attempted to drive it anywhere. I'm not real confident that the ICM would be it as I've read they almost never go bad, though the description fits. Could something have happened to my flywheel over time that has effected the way it interacts with the CSS? I have read about drilling out the mounting holes to get it closer to the flywheel, but I'm hesitant to do that without be able to take accurate measurements. That would not be easy. There's just barely enough room to install the damn thing! They could've put it at the front of the motor...Hmm..The only bright side to this is that it's now failing often enough that I can bring some stuff with me and reliably test different things on the spot.



Any thoughts on this? I appreciate your suggestions!


Rick
 
WTF is a CSS sensor?
 
CSS=Crankshaft Speed Sensor. AKA Crankshaft Position Sensor, Speed Sensor, Reference Sensor, Crankshaft Angle Sensor. The factory text uses CSS, so that's how I've referred to it here.
 
Have you closely inspected the CPS plug itself? Ever wiggled it while cranking or just unplugged it and plugged it back in when this happens?

You might bypass the fuel pump ballast resistor and see what happens. It could be intermittently shutting the fuel off.
Have you tested fuel pressure?
 
I have seen a number things cause that none. None were the CPS/CSS.

I had factor mopar CPS that worked for ages with only .24 volts output.

Other XJ rigs wanted 0.50 volts to always start. Once the engine is running the CPS output voltage jumps to 4-5 volts and is no longer an issue. IMHO.

Cap and rotor, spark plug fouling on any or some or all is number #1 possible cause.

I had an ICM go bad slowly, drove me nuts isolating it till it actually died.

I had an Intake Air temp sensor cause no starts, and random hot engine high idles. That was a fun one to figure out.

A failing TPS can cause random dying, random rpm changes and high idles.

So can a poor sensor ground.

A sticking EGR valve, stuck open can cause dying and hard restarts.

A loose, cracked Vacuum line from the throttle body side to the MAP sensor can cause sudden dying, backfiring, and hard starting as the Vacuum line wiggles around.....

All be tested with a volt-ohm meter or eyeball inspected.

Other obvious to most of issues are loose battery connections, ran out of gasoline....
 
I have seen a number things cause that none. None were the CPS/CSS.

I had factor mopar CPS that worked for ages with only .24 volts output.

Other XJ rigs wanted 0.50 volts to always start. Once the engine is running the CPS output voltage jumps to 4-5 volts and is no longer an issue. IMHO.

Cap and rotor, spark plug fouling on any or some or all is number #1 possible cause.

I had an ICM go bad slowly, drove me nuts isolating it till it actually died.

I had an Intake Air temp sensor cause no starts, and random hot engine high idles. That was a fun one to figure out.

A failing TPS can cause random dying, random rpm changes and high idles.

So can a poor sensor ground.

A sticking EGR valve, stuck open can cause dying and hard restarts.

A loose, cracked Vacuum line from the throttle body side to the MAP sensor can cause sudden dying, backfiring, and hard starting as the Vacuum line wiggles around.....

All be tested with a volt-ohm meter or eyeball inspected.

Other obvious to most of issues are loose battery connections, ran out of gasoline....


What symptoms did you experience with the IAT sensor going out? What ever's going on is electrical, I'm sure. I'd like to think that if a coolant or intake air temperature sensor signal was lost that the ECU would just default to some middle of the road spark/fuel table to keep the vehicle running, but I have heard of other pre-OBDII systems that did that, just give up the ghost and refuse to start/run.



Thank you very much for your suggestions!
 
I'll do that. I did try disconnecting and reconnecting the CSS and it worked once, a few weeks back when I got stuck after it stalled out on the road. But the next time it happened I had installed a new OEM CSS, tried it again, and it did nothing. I even tried disconnecting and reconnecting a few other random body harness connectors under the hood, and nothing happened. But on the 11th try, it started and ran as good as ever like nothing had happened. I just ordered a coolant and IAT sensors. I'll see what they do. I'm going to have a look at what's in there...The coolant sensor was changed with the engine back in '07. I've read it can have a serious effect on fuel injector pulse duration. The IAT sensor has never been changed, so it's a 31 year old part. The official Jeep part is unavailable, but it looks like the commonly available GM sensor has resistance values that are right on the money.
 
IAT won't cause what you're experiencing anyway.

I have never even seen a failed one. The IAT and cTS can be easily tested.

I have the charts with the values, but can't post photos on NAXJA to help people out without paying $45 per year. That ain't happening.
 
I have and it caused the same problems, no start when cold or hot. wanted to be about 80-100 F to start and run right. Too hat or too cold, no start. Hot to oper temp and idle would run way up 1200+ rpm. New IAT fixed it 12 years ago. Others have reported bad ones in recent years. Mostly on Facebook renix thread



IAT won't cause what you're experiencing anyway.

I have never even seen a failed one. The IAT and cTS can be easily tested.

I have the charts with the values, but can't post photos on NAXJA to help people out without paying $45 per year. That ain't happening.
 
If you have replaced the CPS multiple times, I would rule that out. Have you visually inspected the wire. They can get up against the exhaust manifold and burn through.

250mv is a workable level for the sensor and should be fine.

My first bet would be a bad coil. I have gone through two coils in the last 20 years on mine. They get real finicky with temperature variations. Are you getting any spark. If so, the CPS is pretty much going to be good. If the injectors are firing, the CPS is good.
 
It would cause a non start if the engine was too cold, early morning, or a non start after a long hot drive and a short stop/engine off for a few minutes. Once running it never died, but once hot the idle would keep creeping up till it was unsafe in drive at a stop light. My theory is the ECU was over fueling (fuel trim mods by the ECU) when it was hot and under fueling when it was a cold morning, first start. Depending on what the IAT temp is reporting in error, higher or lower than actual, if mine was stuck at high resistance, fixed resistance and someone else's was stuck at a low resistance, theirs might idle low and die when hot and be hard to start (reverse of mine). It would depend on the actual amount and direction of the IAT resistance error. It is not a common problem!!!!

But mine, more often than no,t are not common, LOL. I always pick up stuff others tried the common stuff on and gave up on :D.

What symptoms did you experience with the IAT sensor going out? What ever's going on is electrical, I'm sure. I'd like to think that if a coolant or intake air temperature sensor signal was lost that the ECU would just default to some middle of the road spark/fuel table to keep the vehicle running, but I have heard of other pre-OBDII systems that did that, just give up the ghost and refuse to start/run.



Thank you very much for your suggestions!
 
If the photo is on your web site already, just post the html URL link here or post it with the html code (? I think that works here?)

"
" less the quotation marks, code so it displays the image already on your web site

IAT won't cause what you're experiencing anyway.

I have never even seen a failed one. The IAT and cTS can be easily tested.

I have the charts with the values, but can't post photos on NAXJA to help people out without paying $45 per year. That ain't happening.
 
I have an anecdote about the coil and module. About nine or ten years ago I decided that I wanted to change out the ignition coil and ICM as a matter of preventative maintenance. I bought a Standard Ignition (SMP) coil and module, and within a few weeks the coil burned out (literally). I put the old one back in and it worked fine for about a month. Then the ICM started going out on me. It would die as I'm going down the road, though it would always restart. I even became pretty good at shifting into neutral, restarting it, and back into drive without skipping a beat. Because I was determined to get a new coil and ICM on it, I went to the dealer and ordered new parts from them, so the coil and module are not that old I would say, and I've only put about 50K on it in that time. I really doubt a factory part could go bad in that time, especially since they're not known for going bad very often at all, regardless of age or mileage.



Thank you all for the help. I've had to work a lot recently, so I haven't been driving it. I have to wait until I can afford to be stuck somewhere for an unknown amount of time...waiting for a tow if necessary.
 
When I first got my 88 (used) I had multiple issues. The vast majority were wiring connector corrosion issues. The corrosion at the connectors (or splices, or ground rings) would change the ohm values for the sensors. Some were ground issues, some just corrosion on the connector pins and/or connector pins that had backed out of the connector body.

My solution was to dismount the ECU and measure the ohms at the sensor and again through all the connectors at the ECU connector. I even found some pins that had backed out of the ECU connector making iffy contact. I got so most any time I disconnected or reconnected a connector I'd gently tug all the wires behind the connector with needle-nose pliers. If I found any unwanted resistance (ohms) at the ECU connector, I worked backwards up the harness, splices and connectors to eliminate it.

One of the better helps I found was a good quality contact spray to make sure all the oil, coolant or corrosion was off of the connector pins. You can get an almost invisible coating of oil on the connector pins which can mess with the resistance (ohms). A little unwanted resistance here and a little there adds
up.

It has been my experience that swapping out sensors and components hoping to get lucky is one of the poorer ways to troubleshoot and correct issues. It has also been my experience that the vast majority of my issues were the wiring, connectors and splices. I've had two Renix and the number of sensors or components I've swapped out on both could be counted on half a dozen fingers over nearly 30 years. The issue was invariably mechanical or a wiring issue.

Random shutdowns, first guess would be the ballast resistor shutting off sufficient fuel. Very few sensors will completely shut down the motor, CPS, the MAP can two ways, no Map signal at all and the injectors shut down, or MAP default is full rich which can flood the motor. Some ignition issues can also shut the motor down. Either high voltage ignition issues or ignition system power in. The Yellow wire coming from the ignition switch can be a trouble spot at various points in the harness/connectors. Check your ignition switch for indications of overheating, scorch marks etc. Test that yellow wire at the ignition module for battery voltage. Check the ignition module ground.
 
The wiring for the fuel pump goes through half a dozen connectors,the ballast resistor and the ground near the fuel pump. All have caused me issues at one time or another. I found one connector inside near the left rear fender well that had been gently cooking off for a long time, contact got iffy, came and went as the connector slowly melted down. Ballast resistors get hot, hot metal flexes, so function can be intemittant.
 
I did some research and found Cruiser54s write-up about the required output voltage needing to be about .5V. I measured mine, multimeter set to AC, at about .25V (250mV). .....And, btw, the CSS voltage output is still about .25V, which leaves me wondering if my meter(Fluke) is measuring it differently than Cruiser54's (peak-to-peak, or not...).


It's not a sine wave or at 60 Hz so non-rms meters are going to show different things. It's a series spikes when cranking, that starts to look more like a sawtooth pattern once it's running. Somewhere way back in the naxja archive, I posted a few o-scope pics when we were arguing about whether adding a capacitor in parallel would boost the voltage (it did, but adding too much also caused problems at higher rpm). You could try the other tricks like washers under the mounting bolts to move it a little aft, or slightly closer to the flywheel too. But as mentioned, if the injectors are going, it's working.
 
I agree.

I discovered that the cheap/low cost HF meters, $5-$10 ones can read half of what the good meters read. Fluke would be in the good meter class.

You can boost the signal like lawsoncl said, I have done both lowering it closer the teeth, and moving it the rear. I got the most increase moving mine to the rear, after moving it lower. Mine reads .60 volts cranking now on 295,000 87 Wagoneer.


It's not a sine wave or at 60 Hz so non-rms meters are going to show different things. It's a series spikes when cranking, that starts to look more like a sawtooth pattern once it's running. Somewhere way back in the naxja archive, I posted a few o-scope pics when we were arguing about whether adding a capacitor in parallel would boost the voltage (it did, but adding too much also caused problems at higher rpm). You could try the other tricks like washers under the mounting bolts to move it a little aft, or slightly closer to the flywheel too. But as mentioned, if the injectors are going, it's working.
 
When I first got my 88 (used) I had multiple issues. The vast majority were wiring connector corrosion issues. The corrosion at the connectors (or splices, or ground rings) would change the ohm values for the sensors. Some were ground issues, some just corrosion on the connector pins and/or connector pins that had backed out of the connector body.

My solution was to dismount the ECU and measure the ohms at the sensor and again through all the connectors at the ECU connector. I even found some pins that had backed out of the ECU connector making iffy contact. I got so most any time I disconnected or reconnected a connector I'd gently tug all the wires behind the connector with needle-nose pliers. If I found any unwanted resistance (ohms) at the ECU connector, I worked backwards up the harness, splices and connectors to eliminate it.

One of the better helps I found was a good quality contact spray to make sure all the oil, coolant or corrosion was off of the connector pins. You can get an almost invisible coating of oil on the connector pins which can mess with the resistance (ohms). A little unwanted resistance here and a little there adds
up.

It has been my experience that swapping out sensors and components hoping to get lucky is one of the poorer ways to troubleshoot and correct issues. It has also been my experience that the vast majority of my issues were the wiring, connectors and splices. I've had two Renix and the number of sensors or components I've swapped out on both could be counted on half a dozen fingers over nearly 30 years. The issue was invariably mechanical or a wiring issue.

Random shutdowns, first guess would be the ballast resistor shutting off sufficient fuel. Very few sensors will completely shut down the motor, CPS, the MAP can two ways, no Map signal at all and the injectors shut down, or MAP default is full rich which can flood the motor. Some ignition issues can also shut the motor down. Either high voltage ignition issues or ignition system power in. The Yellow wire coming from the ignition switch can be a trouble spot at various points in the harness/connectors. Check your ignition switch for indications of overheating, scorch marks etc. Test that yellow wire at the ignition module for battery voltage. Check the ignition module ground.

This^^^^^^
 
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