- Location
- MilkyWay Galaxy
I just cycled the ignition switch, did not crank or start the engine, fuel pressure is 40 psi, set a 30 minute timer.
Will post data in 25 minutes.
Will post data in 25 minutes.
-
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.
Engine miss above 2000 RPM
- Thread starter Ecomike
- Start date
- Location
- MilkyWay Galaxy
Went from 40 psi to 25 psi in 30 minutes.
- Location
- MilkyWay Galaxy
Still had 21 psi 60 minutes later and 20 psi 24 hours later. So leakers (fuel injectors) in the off position is not the problem according to cruiser54.
I pulled both possible O2 sensor heater relays (will the real O2 sensor relay please stand up, LOL, literature, manuals and Google images show 2 places it could be LOL) so I pulled them both before a cold start, and yet my jeep went closed loop in seconds at idle.
WTF???? If the low voltage O2 data at idle is indeed lean, that might explain how it got and stayed hot enough to go closed loop with no power from the O2 sensor heater relay????
Then I ran the speed up and down, accel, decel, disconnected the vac for the EGR (no differences), and at idle it was closed loop most of the time.
My MT-2500 scanner consistently claimed it was Rich on decel (as it should be), and lean on accel. I forget what the voltage was reading.
Note that the MT-2500 scanner displays both the voltage and the rich or lean status at the same time!!!!
BUTTT!!! In closed loop it claimed low voltage was rich at idle, and high voltage was lean,
BUTTT!!! In open loop it claimed low voltage was lean at idle when I got it to mess up and stumble at higher rpms and then I let it idle.
So half the time my scanner is lying to me????
WTF???
So I considered that on decel it should be trying to run rich, and open loop, and decided that at that voltage it must the proper rich reading voltage, but I forget what that reading was, and not sure the injectors could follow the ECU instructions anyway, if those instructions were right in either direction.
I am so confused now.
So lets focus on why the engine goes closed loop with no heater voltage from pulled relays that power the O2 sensor at idle. It was a cold (90 F outside) start up and hit closed loop before I got to the scanner, 4-5 seconds to get to it after starting the jeep.
Could that be it running lean and thus getting the O2 sensor hot enough to go closed loop?
I was always told (read) that the heater in the O2 sensor was to keep it working at idle when there is not a high enough temp to keep it operating???? Is that true or just in cold weather first start ups?
But the T-stat is 180 F and the CTS never got over 80 *C , and the IAT never got over 65*C IIRC (after a 30 minute run yesterday), in fact the first 10 minutes were lower than that!!!
I am still leaning to a fuel injector issue right now so:
I will pull the other 4 spark plugs to see if they have changed the last 1-2 weeks since this started. Maybe one will show a suspect injector.
I may also need to try a full set of FR5 spark plugs to see if the difference between plugs 1&2 versus plugs 3-6 is causing a problem it did not cause for 18 months. I have the mildly hotter plug, the FR5 in cyls 1 & 2, because they have the leaky oil, worn valve steam guides.
What am I missing here gurus?
Last edited:
- Location
- MilkyWay Galaxy
Since my 87 Renix Jeep is showing STFT to be about 30-50, way under 128, I looked this up in the Jeep-Snap-On MT-2500 guide book.
STFT: ST fuel trim numbers lower than 128 indicates that the ECU is commanding a short term lean mixture.
But the Renix Jeep manual says that low O2 sensor voltage is a rich mix, and that is what I am seeing in open loop at idle when I get it to hang up in open loop at idle after holding it in the higher rpm miss fire state for a while according to the book (the scanner says it is lean, LOL)
So if I assume the low O2 sensor voltage I am seeing of about .6-.9 volts out of 0-5 volt range, is a rich signal, as open loop should be, then it makes sense that the ECU STFT would trying to move it back to 2.45 Volts by commanding a leaner condition in order the get it back to closed loop status, as it does on mine (it is slow sometimes 2 minutes to get back to closed loop, but it does get there), then I can make sense of the data I am getting and then suspect that one or more injectors is sticking open and leaking excess fuel making it rich, while the STFT and ECU are trying to correct it?
At this point this is just an unproven theory as there is nearly equally conflicting data out there on what low O2 sensor data is saying.
The part that bothered me was that I was always under the impression that ECUs switched to a rich mode in open loop (failure of closed loop mode), but that may not be true ( I know this is heresy LOL) as if the ECU is in rich mode it may be commanding a lean direction switch to try and get the rig into closed loop!!!!! Perhaps there is a time domain delay where if the ECU can reach closed loop mode it stops trying after a few minutes and then switches to a data table rich mode and ignores the O2 sensor????
But how does one know when or if that is happening???
EDIT: Then the manual says that in open loop the ST Fuel trim goes to a fixed value, usually 128. WTF, now they tell me,
But mine is switching from 30-50 in open loop, not parking at 128 after a rev up and operation with the miss going on for 10-30 seconds.
So is Open Loop, truly open loop, or is their a permanent open loop, and part time open loop?
The manual suggests comparing Injector on time to the STFT value. May need to do that later.
It is dawning on me that the O2 sensor data is live sensor data, while the STFT is a what the ECU is telling the injectors to do, a command!!!! One is sensor output data the other computer control instructions. I was confusing the STFT with data with sensor data, it is not.
STFT: ST fuel trim numbers lower than 128 indicates that the ECU is commanding a short term lean mixture.
But the Renix Jeep manual says that low O2 sensor voltage is a rich mix, and that is what I am seeing in open loop at idle when I get it to hang up in open loop at idle after holding it in the higher rpm miss fire state for a while according to the book (the scanner says it is lean, LOL)
So if I assume the low O2 sensor voltage I am seeing of about .6-.9 volts out of 0-5 volt range, is a rich signal, as open loop should be, then it makes sense that the ECU STFT would trying to move it back to 2.45 Volts by commanding a leaner condition in order the get it back to closed loop status, as it does on mine (it is slow sometimes 2 minutes to get back to closed loop, but it does get there), then I can make sense of the data I am getting and then suspect that one or more injectors is sticking open and leaking excess fuel making it rich, while the STFT and ECU are trying to correct it?
At this point this is just an unproven theory as there is nearly equally conflicting data out there on what low O2 sensor data is saying.
The part that bothered me was that I was always under the impression that ECUs switched to a rich mode in open loop (failure of closed loop mode), but that may not be true ( I know this is heresy LOL) as if the ECU is in rich mode it may be commanding a lean direction switch to try and get the rig into closed loop!!!!! Perhaps there is a time domain delay where if the ECU can reach closed loop mode it stops trying after a few minutes and then switches to a data table rich mode and ignores the O2 sensor????
But how does one know when or if that is happening???
EDIT: Then the manual says that in open loop the ST Fuel trim goes to a fixed value, usually 128. WTF, now they tell me,
But mine is switching from 30-50 in open loop, not parking at 128 after a rev up and operation with the miss going on for 10-30 seconds.
So is Open Loop, truly open loop, or is their a permanent open loop, and part time open loop?
The manual suggests comparing Injector on time to the STFT value. May need to do that later.
It is dawning on me that the O2 sensor data is live sensor data, while the STFT is a what the ECU is telling the injectors to do, a command!!!! One is sensor output data the other computer control instructions. I was confusing the STFT with data with sensor data, it is not.
Last edited:
cruiser54
NAXJA Forum User
- Location
- Prescott, Az
what brand O2 sensor are you using?
Fuel trims are ECU commands as you learned. The O2 live data should always be live data.
Although in some cases the computer may have an "expected" or "target" value based on its commands. I find it hard to believe something RENIX area would be intelligent.
O2 sensors generate (high) voltage when they register rich and generate (low) when they register lean. This is a universal function of all O2 sensors ever created. Also, O2 sensors typically fail (low) lean, or get lazy and stuck.
If the ECU thinks the mixture is too lean, it will command the mixture rich, and add fuel (make fuel trim +).
Engine controls default to rich under WOT and things like that.
If the computer things the mixture is too rich, your fuel trims will go negative (in modern vehicles, whatever that corresponds to in RENIX era stuff).
It's easy to remember, unburnt fuel is a coolant of sorts, and keeps the engine from self destructing. Lean is for warmed up and easy going conditions in simplified terms.
ECU's try to make the mixture as lean as possible, without causing problems.
Pre-cat O2's should be switching rapidly rich-lean rich-lean as that's what desired for optimal catalytic converter performance.
If a Post-cat O2 switched at the same rate as the Pre-cat, it would mean the CAT isn't present or isn't working properly.
The cat should be hotter at the outlet than the inlet otherwise its not doing something right.
IMHO, you don't need fancy scan tools to diagnose older fuel injected engines because frankly they weren't that smart. Being able to read sensor output on a scope like a Vantage is very helpful though.
Although in some cases the computer may have an "expected" or "target" value based on its commands. I find it hard to believe something RENIX area would be intelligent.
O2 sensors generate (high) voltage when they register rich and generate (low) when they register lean. This is a universal function of all O2 sensors ever created. Also, O2 sensors typically fail (low) lean, or get lazy and stuck.
If the ECU thinks the mixture is too lean, it will command the mixture rich, and add fuel (make fuel trim +).
Engine controls default to rich under WOT and things like that.
If the computer things the mixture is too rich, your fuel trims will go negative (in modern vehicles, whatever that corresponds to in RENIX era stuff).
It's easy to remember, unburnt fuel is a coolant of sorts, and keeps the engine from self destructing. Lean is for warmed up and easy going conditions in simplified terms.
ECU's try to make the mixture as lean as possible, without causing problems.
Pre-cat O2's should be switching rapidly rich-lean rich-lean as that's what desired for optimal catalytic converter performance.
If a Post-cat O2 switched at the same rate as the Pre-cat, it would mean the CAT isn't present or isn't working properly.
The cat should be hotter at the outlet than the inlet otherwise its not doing something right.
IMHO, you don't need fancy scan tools to diagnose older fuel injected engines because frankly they weren't that smart. Being able to read sensor output on a scope like a Vantage is very helpful though.
Last edited:
- Location
- MilkyWay Galaxy
Same brand Renix jeep O2 sensor I used, and that I have used for 12 years on 2 rigs with no issues. The current O2 sensor has worked perfectly since Feb, with no issues. I use only Bosch O2 sensors on Renix as they designed and patented the oddball Renix O2 sensors and they were the OEM supplier.
cruiser54
NAXJA Forum User
- Location
- Prescott, Az
Have you tested the heater resistance on that sensor?
- Location
- MilkyWay Galaxy
MD, the Renix O2 sensor is an odd ball that was designed by Bosch, one of the first O2 sensors on vehicles, and it DOES NOT GENERATE a VOLTAGE. It is a variable resistor, that changes resistance as a function of O2 concentration difference between the O2 concentration out side and inside of the sensor. The Renix ECU supplies a 5 Volt input to the sensor and then reads the voltage drop across the resistor.
cruiser54
NAXJA Forum User
- Location
- Prescott, Az
So, heat increases resistance and you get a low voltage reading when lean?
- Location
- MilkyWay Galaxy
No need to retest it since it is going into closed loop within seconds of start up with no power to the heater, at this time. It has less than 1000 miles on it, it has worked perfectly since feb, when I installed it new.
The question is why does it go into closed loop with out power (I pulled the heater power relay to try and force it into open loop for tests, and it went close loop anyway, must be running lean on start up to get hot enough(?) or everything I read about the heater in the O2 sensor at idle is a lie in summer weather?????
cruiser54
NAXJA Forum User
- Location
- Prescott, Az
Did you pull the correct relay?
- Location
- MilkyWay Galaxy
1) the O2 sensor needs to be at least something 600 F to work. When hot its resistance is not a function of temperature. It is a function of the O2 concentration between out door air and exhaust air it is sensing.
2) yes getting low voltage in open loop, and normal switching voltage in closed loop.
3) Only way I can get it into open loop is force multiple misfires for say ten seconds than take it back to idle. Then for 10-120 seconds it will go low volts at idle in open loop, idles smooth, then switches back to closed loop after a 10-120 second period.
It always, 100% of the time idles smooth in idle in park or drive at idle, hot or cold. I have to rev it hard and fast or take it to 2000-3000 rpm (peak rpm needed varies) to make it stumble and and eventually misfire/backfire out the exhaust.
4) At this point there is so much conflicting info everywhere in manuals and online on the Renix lean-rich voltage I am not sure if low volts is lean or rich anymore. And I was the last expert here on that for about 8 years now LOL. But I damn well plan to figure it out with tests. I have a working rig I plan to test today and see what happens if I pull a spark plug wire and if I pull and injector while I kill the power to the O2 sensor heater at idle.
- Location
- MilkyWay Galaxy
I pulled the far right and far left relay to make sure I did, LOL, as that too has two locations listed on line LOL. The the four relays on the passenger side near the battery and the ICM-HV coil. I pulled #1 and #4, the far right and far left. Those are the only two internet photos claim to the the right relay????
- Location
- MilkyWay Galaxy
That is why I posted this earlier here:
"Since my 87 Renix Jeep is showing STFT to be about 30-50, way under 128, I looked this up in the Jeep-Snap-On MT-2500 guide book.
STFT: ST fuel trim numbers lower than 128 indicates that the ECU is commanding a short term lean mixture. "
Which means the ECU thinks it is running too rich. That agrees with the what you said below for OBD-II STFT .....Which is what it should be in open loop, but I think my scanner was also saying in words it was lean in open loop at low voltage and calling for it to go leaner, which can't be right? I need to check my notes.
Edit: yes the manual says that low volts is running rich, and in open loop mine had low volts in open loop, but on the same screen it showed LEAN(?) in the Mode menu, and the MT-2500 mentions nothing about that display and what it means, I thought it meant it was running LEAN, when everything else indicated it was and should be running rich, open loop at low voltage and with a low STFT number.
"Since my 87 Renix Jeep is showing STFT to be about 30-50, way under 128, I looked this up in the Jeep-Snap-On MT-2500 guide book.
STFT: ST fuel trim numbers lower than 128 indicates that the ECU is commanding a short term lean mixture. "
Which means the ECU thinks it is running too rich. That agrees with the what you said below for OBD-II STFT .....Which is what it should be in open loop, but I think my scanner was also saying in words it was lean in open loop at low voltage and calling for it to go leaner, which can't be right? I need to check my notes.
Edit: yes the manual says that low volts is running rich, and in open loop mine had low volts in open loop, but on the same screen it showed LEAN(?) in the Mode menu, and the MT-2500 mentions nothing about that display and what it means, I thought it meant it was running LEAN, when everything else indicated it was and should be running rich, open loop at low voltage and with a low STFT number.
Last edited:
- Location
- MilkyWay Galaxy
I am starting think I may have a sticking injector that is making it run rich, and misfiring (back fire out the exhaust, and stumbling-shaking engine) and throwing it into open loop till the injector unsticks in idle an excess fuel is used up????
Next steps today, check the other 4 spark plugs, retest the TPS (it is only about 10 weeks old, worked fine...) for any noise on reving, run the MT-2500 scanner on the working jeep and see what data I get for all conditions, and then clear the ECU memory of any KAM memory of history and restart the LTFT....
Also I had to fix a fuel rail QC leak weeks ago near the firewall (That is the fuel supply side I think, flowing to the injectors(?)), maybe some dirt go in there?????
Next steps today, check the other 4 spark plugs, retest the TPS (it is only about 10 weeks old, worked fine...) for any noise on reving, run the MT-2500 scanner on the working jeep and see what data I get for all conditions, and then clear the ECU memory of any KAM memory of history and restart the LTFT....
Also I had to fix a fuel rail QC leak weeks ago near the firewall (That is the fuel supply side I think, flowing to the injectors(?)), maybe some dirt go in there?????
- Location
- MilkyWay Galaxy
I tested the good, I thought, LOL, working jeep with the Snap-on MT-2500 and it started and ran in open loop (I pulled the O2 sensor heater power relay), with the LTFT and STFT both rock solid at 128. In closed loop the STFT moved up over 128 at times when I reved the rig. LTFT was solid at 128.
It took about 10 minutes to reach closed loop with the O2 sensor heater power relay removed, while mine went closed loop at idle in 2-3 seconds with the relays removed, so my exhaust on the problem rig is hot, so some cylinders must be real rich (open loop rich mode) and some lean (HOT) on mine heating that O2 sensor up so fast???
In closed loop the good rig read RICH for low voltage, but I discovered that the scanner RICH/LEAN message is locked in an old data state when the rig is in open loop. That is what threw me, in part. Its a red herring.
In open loop the good rig voltage was low, so low voltage is a rich state. In closed loop it read rich at low voltage and lean at high voltage and switched very quickly which confirmed that low voltage is rich.
I disconnected the battery on my problem rig, and still got the same test results as before. No changes, very low STFT, like 30 +/- 20 at idle in open-closed????, arg my notes don't say loop, and read 128 on both fuel trims in open loop at 1500 RPM, but it seemed to run smoother, but still has a problem, stumble miss, just not as bad and happens at higher rpms today. Still goes to about 1.0 Volts open loop after a miss from reving or higher rpms, and takes a while at idle to get back to closed loop.
At 1500 RPM it was down to 1.3 Volts, rich, open loop and the STFT went to 128??? WTF??? I guess the Fuel trims are now both going to 128 in open loop after clearing the memory from disconnecting the battery.
So Renix does store sensor and performance optimization data as I have been saying for 8 years!!! Just no know way to retrieve it yet.
TPS passed all the tests. All the sensors on both rigs tested the same, all working good in spec.
It took about 10 minutes to reach closed loop with the O2 sensor heater power relay removed, while mine went closed loop at idle in 2-3 seconds with the relays removed, so my exhaust on the problem rig is hot, so some cylinders must be real rich (open loop rich mode) and some lean (HOT) on mine heating that O2 sensor up so fast???
In closed loop the good rig read RICH for low voltage, but I discovered that the scanner RICH/LEAN message is locked in an old data state when the rig is in open loop. That is what threw me, in part. Its a red herring.
In open loop the good rig voltage was low, so low voltage is a rich state. In closed loop it read rich at low voltage and lean at high voltage and switched very quickly which confirmed that low voltage is rich.
I disconnected the battery on my problem rig, and still got the same test results as before. No changes, very low STFT, like 30 +/- 20 at idle in open-closed????, arg my notes don't say loop, and read 128 on both fuel trims in open loop at 1500 RPM, but it seemed to run smoother, but still has a problem, stumble miss, just not as bad and happens at higher rpms today. Still goes to about 1.0 Volts open loop after a miss from reving or higher rpms, and takes a while at idle to get back to closed loop.
At 1500 RPM it was down to 1.3 Volts, rich, open loop and the STFT went to 128??? WTF??? I guess the Fuel trims are now both going to 128 in open loop after clearing the memory from disconnecting the battery.
So Renix does store sensor and performance optimization data as I have been saying for 8 years!!! Just no know way to retrieve it yet.
TPS passed all the tests. All the sensors on both rigs tested the same, all working good in spec.
- Location
- MilkyWay Galaxy
Update, plugs 3 and 4 did not look good.
I had switched them from the working plugs I had used for ages to another brand style plug, before I got Ill in 2014 and forgot.....Will replace all plugs with 6 new FR5 NGK plugs today and retest.
Is it just the plugs (I doubt it) or something else that is wrong (but what?), but what ever is wrong had plug 3 looking as bad as plug 1 did when I replaced it last week. Plug 4 was not as bad, buy not looking new like the Bosch platinum plugs I had used for 10 years did on cyls 3-6.
Could be the Renix controls do not like different plugs in different cylinders? But I was trying to run slightly hotter plugs (according to my deep research) the NGK FR5 is slightly hotter than all other Jeep 4.0 plugs, on the two lowest compression oil fouling cylinders till I had time to work on the engine/head job....
I doubt the new plugs will fix the problem, but they are now part of the problem, even if they are just a small part.
I had switched them from the working plugs I had used for ages to another brand style plug, before I got Ill in 2014 and forgot.....Will replace all plugs with 6 new FR5 NGK plugs today and retest.Is it just the plugs (I doubt it) or something else that is wrong (but what?), but what ever is wrong had plug 3 looking as bad as plug 1 did when I replaced it last week. Plug 4 was not as bad, buy not looking new like the Bosch platinum plugs I had used for 10 years did on cyls 3-6.
Could be the Renix controls do not like different plugs in different cylinders? But I was trying to run slightly hotter plugs (according to my deep research) the NGK FR5 is slightly hotter than all other Jeep 4.0 plugs, on the two lowest compression oil fouling cylinders till I had time to work on the engine/head job....
I doubt the new plugs will fix the problem, but they are now part of the problem, even if they are just a small part.
Last edited:
Green XJ Jeep
NAXJA Forum User
- Location
- Spanaway Wa
You never know. I have seen some really strage spark plug failures. From cheap ones and expensive ones.
old_man
NAXJA Forum User
- Location
- Loveland, Colorado
I recommend you hit a junk yard and pull a set of sensors, including the CPS, MAP, Air Charge Sensor, throttle position. If nothing else, put them in a baggie under the back seat for emergencies. I would also grab a coil and ignition module.
I kind of went through what your are trying on the same issue, and I finally pulled a used CPS out of the bag and tried it and presto. Being an Electrical Engineer and working with sensors all day, I would have given it less than one in a thousand odds that it was the cps, because it ran flawless until it hit the higher rpms.
I have also seen cracked coils and bad ignition modules cause similar issues.
I kind of went through what your are trying on the same issue, and I finally pulled a used CPS out of the bag and tried it and presto. Being an Electrical Engineer and working with sensors all day, I would have given it less than one in a thousand odds that it was the cps, because it ran flawless until it hit the higher rpms.
I have also seen cracked coils and bad ignition modules cause similar issues.
