• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

Testing Jeep O2, Oxygen sensors

So I finally had a chance to do some more troubleshooting. I located the 5v wire coming out of the ECM and verified that I’m not getting the 5v out of the ECM. Sometimes it will read .2v but never anything more than that. Is this an ECM problem then and if so where do I get one?

You would need to disconnect the wire harness from the ECU and O2 sensor and test the 5V wire and verify if is less than 1 Ohm of resistance to confirm the wire is good, and or test to see if the 5V pin on the ECU has 5V at the ECU, to confirm if the wire itself, and connector at the ECU have good contact/continuity.

If the wire and connector are electrically good and there is no 5 volts at the ECU (power ign switch on, and ECU connected to the harness bulk connector), then one of the power supply parts or bridge resistor in the ECU circuit that is on that connection is bad. It might be repairable. Lots of used one are around. 89-90 are the best ones.
 
You would need to disconnect the wire harness from the ECU and O2 sensor and test the 5V wire and verify if is less than 1 Ohm of resistance to confirm the wire is good, and or test to see if the 5V pin on the ECU has 5V at the ECU, to confirm if the wire itself, and connector at the ECU have good contact/continuity.

If the wire and connector are electrically good and there is no 5 volts at the ECU (power ign switch on, and ECU connected to the harness bulk connector), then one of the power supply parts or bridge resistor in the ECU circuit that is on that connection is bad. It might be repairable. Lots of used one are around. 89-90 are the best ones.

The pin on the ECU does not have voltage. I did a search online but all I can find for my year model (89) is for the 6 cylinder and mine is a 4 banger. There are plenty for 91-95 but they look different. Where would I get it repaired?
 
Nickintime is one you might ask. He would love to have to one to try and fix I think? There are some links in the link below to sites that might have ready to use serviced ones and some you tube videos on repairing them. One is Nickintime videos, the guy that cracked the Renix ECU code and that is making live data mini-scanners for the renix ECUs the last 2 years. I'd give him a holler first.

https://www.google.com/search?q=1989+jeep+cherokee+2.5+L+ECU&ie=utf-8&oe=utf-8&client=firefox-b-1
 
The pin on the ECU does not have voltage.

Hello all! Joining late and haven't read much yet, but you mention checking for the o2 supply voltage?

I feel bad for the 2.5L Renix folks because info is REAL hard to find. As you have noticed, most of it is for the 4.0Ls and some areas are quite different.


From the 1990 FSM (hosted on my site in the downloads page btw):

The 4.0L uses a 12v supply from the o2 heater relay and the sensor spits out a 0-5v signal to the ecu.
___-____
(A)(B)(C)
-----------
A = 12v from o2 Heater Relay
B = Ground
C = Output to ECU (0-5V)

The 2.5L uses 12v Ignition as supply and the sensor will spit out a 0-1v signal to the ECU.
___-____
(A)(B)(C)
-----------
A = 12v Ignition
B = Ground
C = Output to ECU (0-1V)


The pin you probed was probably the input, and thus only random noise will be found there. Are you using an o2 sensor for the 2.5L and not the 4.0L?

And I hate to shill, but this is why I prefer scanners. You can easily get a readout directly from the ECUs brain and continue troubleshooting from there.
 
Do what? The Renix 2.5 L uses a different O2 sensor than the 4.0?

The 4.0 L Renix (87-90) O2 sensor is a variable resistor that changes resistance in response to the O2 concentration difference between what it sees inside and outside the exhaust manifold. The 4.0 Renix ECU supplies a 5 volt signal to the O2 sensor and uses a bridge circuit to measure the voltage drop across the O2 sensor, input versus output.

The 1991 and newer HO 4.0 systems use a voltage producing O2 sensor that produces its own voltage, 0-1 volt.

Are you saying the Renix Era 2.5 L, 4 bangers used the newer style 0-1 volt output sensors that generate their own voltage???

Also, C is not an O2 sensor output, it is the input on 87-90 Renix 4.0s to the O2 sensors. It is an output from the Renix ECU. And the 87-90 uses a common sensor ground. The ECU senses the drop in voltage to the O2 sensor using a Bridge circuit. Old_Man here is the expert on those, he as EE.

IIRC the 91 and up used two independent grounds on the O2 sensors.

What kind of O2 sensor did 2.5L Renix use? Was it a throttle body injector or multiport injection in 87-90?

Hello all! Joining late and haven't read much yet, but you mention checking for the o2 supply voltage?

I feel bad for the 2.5L Renix folks because info is REAL hard to find. As you have noticed, most of it is for the 4.0Ls and some areas are quite different.


From the 1990 FSM (hosted on my site in the downloads page btw):

The 4.0L uses a 12v supply from the o2 heater relay and the sensor spits out a 0-5v signal to the ecu.
___-____
(A)(B)(C)
-----------
A = 12v from o2 Heater Relay
B = Ground
C = Output to ECU (0-5V)

The 2.5L uses 12v Ignition as supply and the sensor will spit out a 0-1v signal to the ECU.
___-____
(A)(B)(C)
-----------
A = 12v Ignition
B = Ground
C = Output to ECU (0-1V)


The pin you probed was probably the input, and thus only random noise will be found there. Are you using an o2 sensor for the 2.5L and not the 4.0L?

And I hate to shill, but this is why I prefer scanners. You can easily get a readout directly from the ECUs brain and continue troubleshooting from there.
 
Good news!!!

The 86-90 XJ, 2.5L, 4 banger, seems to have been a throttle body injection system (it is not multi-port injection) using the other style O2 sensors, the ones that generate there own voltage, 0-1 volt. The ECU does not feed a voltage to the O2 sensor on the 2.5 Liter per Nick, and I seem to vaguely recall hearing this about the 86 four banger and he looked it up in the manual.

So your ECU may be OK!!!! Your O2 sensor may be bad, or may even be the wrong type????

So tell us the whole story on your rig, new sensor? Part number and source? Did they sell you 4.0 sensor by mistake?

The test method for your O2 sensor will be the same as for the 91-01 HO 4.0's.

The pin on the ECU does not have voltage. I did a search online but all I can find for my year model (89) is for the 6 cylinder and mine is a 4 banger. There are plenty for 91-95 but they look different. Where would I get it repaired?
 
Oxygen Sensor History « Walker Products


www.walkerproducts.com › O2 Sensor Training Guide
Oxygen sensors were developed by the Robert Bosch Company and first used on Volvo applications in the late 1970's. Originally, automotive oxygen sensors had only one or two wires and were made from zirconia in a thimble shape. ... The first versions were three wire sensors that employed a case ground for the sensor signal.

Oxygen sensor - Wikipedia


[url]https://en.wikipedia.org/wiki/Oxygen_sensor

[/URL]Volvo was the first automobile manufacturer to employ this technology in the late 1970s, along with the three-way catalyst used in the catalytic converter. ... Modern spark-ignited combustion engines use oxygen sensors and catalytic converters in order to reduce exhaust emissions.‎Automotive applications · ‎The probe · ‎Operation of the probe · ‎Sensor failures





A History of the Oxygen Sensor - On The Line - European Car Magazine


[url]www.superstreetonline.com
› Features
[/URL]



Jul 18, 2004 - Volvo was the first to use an oxygen sensor, in 1977, when it equipped California-bound Volvo 240 models with the device. It did not take long ...




Bosch Invented the Automotive Oxygen Sensor 40 Years Ago ...


[url]https://www.autoserviceprofessional.com/.../bosch-invented-the-automotive-oxygen-s
...
[/URL]



Jul 7, 2016 - The automotive oxygen sensor was developed by Bosch as emissions systems were beginning to be established in the 1970s. ... As an early adopter of the technology, Volvo was the first manufacturer to equip its vehicles with automotive oxygen sensors, starting with the 1976 Volvo Lambda Sonde.
 
Last edited:
I and a few other NAXJA/ECU tuning guys are working on reverse engineering the entire RENIX ECU (both hardware and software) but we haven't touched the 2.5 one yet. It is very different from the 4.0L one, TBI vs MPFI, only one MCU instead of two on the PCB, etc.

I do have a spare 1990 2.5 manual ECU but I need it for our project and it sounds like the ECU is probably not the problem here.
 
The 4.0 L Renix (87-90) O2 sensor is a variable resistor that changes resistance in response to the O2 concentration difference between what it sees inside and outside the exhaust manifold. The 4.0 Renix ECU supplies a 5 volt signal to the O2 sensor and uses a bridge circuit to measure the voltage drop across the O2 sensor, input versus output.

Well, it looks like we both got to learn something today. After double checking some documents and vehicle testing, this checks out.

The 4.0L ECU does provide a 5.02v pull-up voltage on Pin D9 "Oxygen Sensor Input" to provide the base for the voltage divider circuit. The o2 sensors resistance will change on Pin C which cuts down the voltage at the input pin junction. So it would be considered a "Richness Potentiometer" as the french manuals like to say.


As for sensors types, I love referencing rockauto for part years

81-86 2.5L:
NTK 22534 1 wire male plug

87-90 2.5L:
NTK 23502 3 wire male plug

87-90 4.0L:
NTK 23553 3 wire female plug


I and a few other NAXJA/ECU tuning guys are working on reverse engineering the entire RENIX ECU (both hardware and software) but we haven't touched the 2.5 one yet. It is very different from the 4.0L one, TBI vs MPFI, only one MCU instead of two on the PCB, etc.

That. sounds. awesome! I'd love to chat sometime about your work if you're interested. I've been doing tons of work decoding the data streams lately, but I'd love to know what else is hiding in those chips.
 
You do know that Nick (nickintimevideos youtube and facebook...) has already built something like 100 Renix ECU scanners ( REMs ) in multiple versions the last 18-24 months right? We have a group of over 1000 renix owners now on the facebook page. Very active. I have been referring many questions over there to over here where we have indexing, searchable FAQs and threads like this one.

He is using open source code .....

I and a few other NAXJA/ECU tuning guys are working on reverse engineering the entire RENIX ECU (both hardware and software) but we haven't touched the 2.5 one yet. It is very different from the 4.0L one, TBI vs MPFI, only one MCU instead of two on the PCB, etc.

I do have a spare 1990 2.5 manual ECU but I need it for our project and it sounds like the ECU is probably not the problem here.
 
Yeah, but we're looking to reverse engineer the firmware and hardware of the ECU. Basically attack the problem from the other end of what he's doing. What we know so far - combination of my work and others -
- the ECU contains two MC6801 chips on 4.0L, each with its own 4kB onboard mask ROM which cannot be modified after manufacture
- it also contains 2kB of SRAM and 8kB of EPROM storage that are used by the main MC6801 for engine and vehicle specific firmware and data storage
- one 6801 is dedicated to realtime operation of important engine subsystems, the other controls overall EFI strategy, peripherals, and comms
- I think I've already posted the info I have on the ECU connector part numbers.

I can't really give much more info as we are still working on it and I haven't had time to poke at it in a week or two now, but I'm approximately 1/4 of the way through disassembling the main MC6801's onboard mask ROM contents by hand. So far it looks like the reset handler and I/O configuration/setup and I'm 99% sure the part I'm working through at present is the serial comms handler.

My hope is to help answer any unanswered questions as to what sections of the serial comms output data means for the REM project and ideally improve RENIX tuning availability, though it will almost certainly require ECU modification as the 8kB EPROM is an OTP type (One Time Programmable) which means it will have to be desoldered and replaced with a socket or EEPROM device on any ECU that is to be tuned. There is a tiny chance that the 2kB SRAM can be used for small amounts of tuning patch code... but don't cross your fingers. I would like to crack this thing wide open and allow full tuning (HONDATA style - mod your ECU hardware, write whatever tune you want to it) and possibly add better diagnostics features to the ECU, for example broken sensor/wire detection, stored codes, etc etc. The ECU only has 32 bytes of nonvolatile RAM and I'm not sure how much of it is used by the existing codebase, so stored codes may be an impossible pipe dream, though I haven't found any use of the nonvolatile address range yet.

I won't speculate further until we have more solid information, and I'd like to thank Mark Nelson and Chris from Christuned for the opportunity to help work on this. Last time I got to reverse engineer something like this was far too long ago, it's fun.

That. sounds. awesome! I'd love to chat sometime about your work if you're interested. I've been doing tons of work decoding the data streams lately, but I'd love to know what else is hiding in those chips.

Would love to discuss it once we have better data. The last thing I want to do is mislead anyone with preliminary information that may be entirely wrong.
 
Good news!!!

The 86-90 XJ, 2.5L, 4 banger, seems to have been a throttle body injection system (it is not multi-port injection) using the other style O2 sensors, the ones that generate there own voltage, 0-1 volt. The ECU does not feed a voltage to the O2 sensor on the 2.5 Liter per Nick, and I seem to vaguely recall hearing this about the 86 four banger and he looked it up in the manual.

So your ECU may be OK!!!! Your O2 sensor may be bad, or may even be the wrong type????

So tell us the whole story on your rig, new sensor? Part number and source? Did they sell you 4.0 sensor by mistake?

The test method for your O2 sensor will be the same as for the 91-01 HO 4.0's.


I actually just purchased this jeep and the previous owner mentioned the hard starting in cold weather. I haven’t changed the O2 sensor so I have no idea what is actually in it. I’ll have to dig out my old analog meter and see what the voltage does.
 
Cold starting with renix is common with old batteries, corroded battery/ground contacts, and low battery cranking voltage. ECU must see 10 volts minimum from the battery at the ECU. Mine needed at least 11.5 or so cranking volts at the battery posts for the engine to turn fast enough for the CPS to produce enough voltage for the ECU to see the crank signal, otherwise the ECU does not wake up and fire spark and inject fuel.

Also today's CPS's are need to be moved closer to the crank shaft to boost the cranking voltage of the CPS. It generates its own voltage, from a permanent magnet at the tip and induction coil. As the teeth and teeth gaps fly by the magnet tip, it induces an EMF force that creates the crank signal. Needs to be at least .50 volts AC to always start. That voltage changes, with cranking rpms, that change with battery condition and engine temp...etc

I actually just purchased this jeep and the previous owner mentioned the hard starting in cold weather. I haven’t changed the O2 sensor so I have no idea what is actually in it. I’ll have to dig out my old analog meter and see what the voltage does.
 
Cold starting with renix is common with old batteries, corroded battery/ground contacts, and low battery cranking voltage. ECU must see 10 volts minimum from the battery at the ECU. Mine needed at least 11.5 or so cranking volts at the battery posts for the engine to turn fast enough for the CPS to produce enough voltage for the ECU to see the crank signal, otherwise the ECU does not wake up and fire spark and inject fuel.

Also today's CPS's are need to be moved closer to the crank shaft to boost the cranking voltage of the CPS. It generates its own voltage, from a permanent magnet at the tip and induction coil. As the teeth and teeth gaps fly by the magnet tip, it induces an EMF force that creates the crank signal. Needs to be at least .50 volts AC to always start. That voltage changes, with cranking rpms, that change with battery condition and engine temp...etc

The jeep has a new battery and I even hooked jumper cables to my truck but it didn’t change anything. I put my timing light on the number one plug wire so I could observe the spark. It took a few revolutions before the light would blink and then the engine would fire. I measured the voltage coming from the CPS and it was only showing .0-.1 volts while cranking. There is no adjustment on the CPS mount to move it closer to the flywheel. I figured the CPS was bad so I got a new one from NAPA. When I went to move the jeep into my shop it wouldn’t start at all so I changed it right where it sits. It still wouldn’t fire with the new CPS installed. I measured the voltage coming from the new CPS while cranking and it shows .0 volts. After cranking it numerous times it finally fired. The new CPS acts just like the old one did. Takes a few revolutions to See a spark in the timing light if it starts at all. I’m pulling my hair out over this starting issue.
 
Not all test meters are super accurate. I have seen 50% + variations in the meter readings for the CPS. First you must use AC not DC setting on the meter. Second the CPS must be disconnected from the harness.

The CPS can be moved closer by drilling the CPS mounting holes to a larger hole size. One drill size larger helps a lot. I found on my 87, that putting a super thin washer between the bell housing and the CPS mounting arm, think 1/32" thick shims doubled my CPS output from .24 (with the larger holes already) to .60 volts AC.

Also I was in a recent chat with someone who we think had dirt/rust stuck in the flywheel spaces (windows if you will) that trigger the CPS signal.

Not sure why you posted on the O2 sensor thread????

Also what year is your rig? Renix 87-90???? If it is newer HO 91-01 the CPS does produce any voltage. The ECU supplies it...

The jeep has a new battery and I even hooked jumper cables to my truck but it didn’t change anything. I put my timing light on the number one plug wire so I could observe the spark. It took a few revolutions before the light would blink and then the engine would fire. I measured the voltage coming from the CPS and it was only showing .0-.1 volts while cranking. There is no adjustment on the CPS mount to move it closer to the flywheel. I figured the CPS was bad so I got a new one from NAPA. When I went to move the jeep into my shop it wouldn’t start at all so I changed it right where it sits. It still wouldn’t fire with the new CPS installed. I measured the voltage coming from the new CPS while cranking and it shows .0 volts. After cranking it numerous times it finally fired. The new CPS acts just like the old one did. Takes a few revolutions to See a spark in the timing light if it starts at all. I’m pulling my hair out over this starting issue.
 
The discrepancy is probably because of true RMS vs non true RMS and/or sample rate. Cheap meters typically use lower sample rates and non true RMS (they assume the signal is a perfect sine, read the peak voltage and multiple by square root of 2 to get volts RMS) while a good meter will have a higher sample rate and true RMS which will give you a different answer from true RMS if the signal is not a perfect 50 or 60hz sine wave.

It may also be input impedance related, though even the cheapest meters are typically at least 1 megohm input impedance these days and shouldn't be loading the CPS signal down at all.
 
Not all test meters are super accurate. I have seen 50% + variations in the meter readings for the CPS. First you must use AC not DC setting on the meter. Second the CPS must be disconnected from the harness.

The CPS can be moved closer by drilling the CPS mounting holes to a larger hole size. One drill size larger helps a lot. I found on my 87, that putting a super thin washer between the bell housing and the CPS mounting arm, think 1/32" thick shims doubled my CPS output from .24 (with the larger holes already) to .60 volts AC.

Also I was in a recent chat with someone who we think had dirt/rust stuck in the flywheel spaces (windows if you will) that trigger the CPS signal.

Not sure why you posted on the O2 sensor thread????

Also what year is your rig? Renix 87-90???? If it is newer HO 91-01 the CPS does produce any voltage. The ECU supplies it...

I was trying to read it DC so I will go back and try it AC. I also have a better fluke meter that I will use. This jeep is an 89 so the CPS should put out voltage. I originally was thinking this cold starting issue was related to the O2 sensor but I’ve since eliminated that as a cause, but we just kept discussing it on this thread. Thanks for the input.
 
I was trying to read it DC so I will go back and try it AC. I also have a better fluke meter that I will use. This jeep is an 89 so the CPS should put out voltage. I originally was thinking this cold starting issue was related to the O2 sensor but I’ve since eliminated that as a cause, but we just kept discussing it on this thread. Thanks for the input.

I measured the voltage on the CPS AC and it was showing .4 volts. So I did as you mentioned and enlarged the holes in the mount and moved it closer to the flywheel. It started putting out .6 volts which now allows it to fire rather quickly instead of having to crank it for 10 minutes on a cold morning just to get the first fire. But it’s still very cold natured. Now it fires quickly but immediately dies. I have to keep doing that 15 or 20 times to get it to stay running. When it does finally get warmed up it seems to run much better so hopefully I’ve made progress. Any tips on how to cure the extremely cold natured starting now?
 
Well congratulations!!! Well done.

How about we move the remaining cold start question to a new thread? And as you mentioned the O2 sensor is not used in starting or running while cold. ECU ignores it till its warmed up.

I measured the voltage on the CPS AC and it was showing .4 volts. So I did as you mentioned and enlarged the holes in the mount and moved it closer to the flywheel. It started putting out .6 volts which now allows it to fire rather quickly instead of having to crank it for 10 minutes on a cold morning just to get the first fire. But it’s still very cold natured. Now it fires quickly but immediately dies. I have to keep doing that 15 or 20 times to get it to stay running. When it does finally get warmed up it seems to run much better so hopefully I’ve made progress. Any tips on how to cure the extremely cold natured starting now?
 
Back
Top