Strange misfire>>>> please help!!

[Dcoy1283]

Are you sure the fuel rail is what you are reading? The IR temp tools read an area, that gets wider as you back away. It is not a point source temp, and is not a precise location temp. It is a great tool, but has its limits. That said, it sounds a little too hot to me, I think mine runs about 160-180 max at the worst.

Try an eye dropper and some soapy water (so it wets out better) on the rail to cool it, and see if anything changes?

The IR that my dad has a laser on it to see where your looking, i was pretty close to it and if I would go on either side of the rail the temp would change. I hava plans on wrapping the rail with header insulation just to see if it helps and opening my hood when I get home to let more heat out. If it does improve, could this be a sign that the cats are clogging and heating up more? I checked the temp after driving 30 minutes today and it got to 225* back near the fire wall

 

[Ecomike]

The laser is misleading. Try putting a hand held shield (cardboard maybe or sheet metal ) behind the rail, and see what the IR reads. It may be reading the head & intake manifold temp more than the rail. It is looking at an area around the dot, not the dot itself.

Insulating it may make it worse.

I doubt it would indicate anything about the cats.

The temps vary a lot over a short distance where the injectors and head meet the intake and exhaust manifolds. The 225 reading may be too close to the head and exhaust manifold to real indication of the fuel rail temp. Mine varies by 400 F over 1/2" distance at the front of the head near the T-stat, where the first exhaust port pipe is located.

 

[tbburg]

Removed due to stupidity.


Asked about the coil rail: missed the whole conversation on Pg-2.

 

[Dcoy1283]

The laser is misleading. Try putting a hand held shield (cardboard maybe or sheet metal ) behind the rail, and see what the IR reads. It may be reading the head & intake manifold temp more than the rail. It is looking at an area around the dot, not the dot itself.

Insulating it may make it worse.

I doubt it would indicate anything about the cats.

The temps vary a lot over a short distance where the injectors and head meet the intake and exhaust manifolds. The 225 reading may be too close to the head and exhaust manifold to real indication of the fuel rail temp. Mine varies by 400 F over 1/2" distance at the front of the head near the T-stat, where the first exhaust port pipe is located.

I see, I see, I'll try the sheild thing tomorrow. Thanks.

 

[Dcoy1283]

The laser is misleading. Try putting a hand held shield (cardboard maybe or sheet metal ) behind the rail, and see what the IR reads. It may be reading the head & intake manifold temp more than the rail. It is looking at an area around the dot, not the dot itself.

Insulating it may make it worse.

I doubt it would indicate anything about the cats.

The temps vary a lot over a short distance where the injectors and head meet the intake and exhaust manifolds. The 225 reading may be too close to the head and exhaust manifold to real indication of the fuel rail temp. Mine varies by 400 F over 1/2" distance at the front of the head near the T-stat, where the first exhaust port pipe is located.

Hey there, I have a question for you.... What is open loop, and closed loop? and could this have anything to do with why this problem only happens when the jeep is cold? Today at work A buddy wanted to hear my issue first hand so we went out to my jeep and I started it up, it ran a little rough as usual and we sat there for a few minutes discussing everything i have done to it and we both could hear it clear up basiclly and run smooth after a few minutes. I then drove it and it didnt act up ( no misfire code ). So he said it sounds like a problem when its in closed loop which means nothing to me..... do you have any insight?

 

[Ecomike]

Open loop means the computer is ignoring the O2 sensors, and using data tables in memory to control the fuel feed rate. The cold start up is open loop.

Closed loop means the computer is reading the O2 sensors and using the O2 sensor data to control (trim) the fuel feed rate, the open time of the fuel injectors.

The O2 sensors need to hot to work properly. If the 12 volts, or ground is missing to the electric heater in the O2 sensor, they will not work when cold, but will work when cruising, as cruising gets them hot enough. But idle usually does not get them hot enough. But newer cars with precats eliminated the electric heated O2 sensors. So if yours is just a cold warm up problem only, check the ground and 12 volts at the O2 sensor!!!

The 12 V goes through a fuse and relay!!!!

https://www.google.com/search?q=o2+...s=org.mozilla:en-US:official&client=firefox-a
​

 

[Dcoy1283]

Open loop means the computer is ignoring the O2 sensors, and using data tables in memory to control the fuel feed rate. The cold start up is open loop.​

Closed loop means the computer is reading the O2 sensors and using the O2 sensor data to control (trim) the fuel feed rate, the open time of the fuel injectors.​

The O2 sensors need to hot to work properly. If the 12 volts, or ground is missing to the electric heater in the O2 sensor, they will not work when cold, but will work when cruising, as cruising gets them hot enough. But idle usually does not get them hot enough. But newer cars with precats eliminated the electric heated O2 sensors. So if yours is just a cold warm up problem only, check the ground and 12 volts at the O2 sensor!!!​

The 12 V goes through a fuse and relay!!!!​

https://www.google.com/search?q=o2+...s=org.mozilla:en-US:official&client=firefox-a​

Thanks I will check them out.... and my bad he did say when they're in open loop is when I have an issue, and my problem only happens in a cold warm up, and once it warms up I have no issues.

 

[Dcoy1283]

Open loop means the computer is ignoring the O2 sensors, and using data tables in memory to control the fuel feed rate. The cold start up is open loop.​

Closed loop means the computer is reading the O2 sensors and using the O2 sensor data to control (trim) the fuel feed rate, the open time of the fuel injectors.​

The O2 sensors need to hot to work properly. If the 12 volts, or ground is missing to the electric heater in the O2 sensor, they will not work when cold, but will work when cruising, as cruising gets them hot enough. But idle usually does not get them hot enough. But newer cars with precats eliminated the electric heated O2 sensors. So if yours is just a cold warm up problem only, check the ground and 12 volts at the O2 sensor!!!​

The 12 V goes through a fuse and relay!!!!​

https://www.google.com/search?q=o2+...s=org.mozilla:en-US:official&client=firefox-a​

I checked the fuse and swapped some relays around and still have the problem. How and when should I check the O2's for 12v and ground? Should I do it when its cold and still in open loop or does it not matter? Any Idea on which wire should be 12v or ground? I have 4 wires per sensor

 

[90xj06]

my cousin has a 2000 xj with the same problem. i was constantly turning the check engine light off. one day when i was under the hood fixing the a/c i noticed a crack at the rubber hose on the side of the intake by the throttle body. it was an elbow. got a piece of vacuum hose i had lying around and replaced it. so far the light has not come on.

oddly enough it would come up with multiple cylinder miss fire but mostly just one cylinder.

 

[Ecomike]

my cousin has a 2000 xj with the same problem. i was constantly turning the check engine light off. one day when i was under the hood fixing the a/c i noticed a crack at the rubber hose on the side of the intake by the throttle body. it was an elbow. got a piece of vacuum hose i had lying around and replaced it. so far the light has not come on.

oddly enough it would come up with multiple cylinder miss fire but mostly just one cylinder.

That is the vacuum line to the MAP sensor, one of the most important sensors!!!!

 

[Ecomike]

I checked the fuse and swapped some relays around and still have the problem. How and when should I check the O2's for 12v and ground? Should I do it when its cold and still in open loop or does it not matter? Any Idea on which wire should be 12v or ground? I have 4 wires per sensor

Disconnect the O2 sensor, and test the harness side of the connector. Using ohms on your test meter, two wires should be less than 1 ohm (usually black wires on DC automotive), dead short to ground. With the engine running, one of the two other wires using DC volts on the test meter should read 12-14 volts. The 4th wire should not read any voltage. The 4th wire is the signal wire from the O2 sensor to PCM computer.

 

[Dcoy1283]

Disconnect the O2 sensor, and test the harness side of the connector. Using ohms on your test meter, two wires should be less than 1 ohm (usually black wires on DC automotive), dead short to ground. With the engine running, one of the two other wires using DC volts on the test meter should read 12-14 volts. The 4th wire should not read any voltage. The 4th wire is the signal wire from the O2 sensor to PCM computer.

strange, everything checked out ok, had ground on 2 of the wires, 13.89 volts on one, but the 4th signal wire ( harness side ) i was getting between 1.5 and 2 volts, jumping around? is there anything else that works on the open/close loop or are the O2's the only sensor for this operation?

 

[Ecomike]

strange, everything checked out ok, had ground on 2 of the wires, 13.89 volts on one, but the 4th signal wire ( harness side ) i was getting between 1.5 and 2 volts, jumping around? is there anything else that works on the open/close loop or are the O2's the only sensor for this operation?

I am pretty sure the fourth wire should have no voltage on it, but we should check some others here that are more familiar with your year set up than I am.

If I am right, it sounds like there is a shorted hot wire in your harness that is leaking voltage into that 4th wire!!!!

Did you check both front O2 sensors? Did they both have 1.5-2 volts on that wire? or just one? If it is just one of the two front O2 sensors with that voltage, you found your problem!!!!

 

[Ecomike]

The later year Jeep (91-2001) O2 sensors generate their own voltage, 0-1 volt, so their should not to my knowledge be any standing voltage on that 4th wire, disconnected, especially not 1.5-2.0 volts (?) but I seem to recall someone mentioning something about it before and a problem with reading it ........., I just don't recall the details. In other words, I might be wrong, that voltage might be OK?????? But the jumping around voltage also sounds odd, like a short....

Ask Cruiser54, he might know. Or one of the other late model gurus here.

 

[Dcoy1283]

I am pretty sure the fourth wire should have no voltage on it, but we should check some others here that are more familiar with your year set up than I am.

If I am right, it sounds like there is a shorted hot wire in your harness that is leaking voltage into that 4th wire!!!!

Did you check both front O2 sensors? Did they both have 1.5-2 volts on that wire? or just one? If it is just one of the two front O2 sensors with that voltage, you found your problem!!!!

both did the same thing

 

[Ecomike]

I found it. There is a small reference voltage on the 4th wire according to this post:

http://www.naxja.org/forum/showpost.php?p=244784413&postcount=31

Check out this thread too:

http://www.naxja.org/forum/showthread.php?t=1012701&highlight=sensor+test&page=6

But they are suggesting it should read .45 V on that loose signal wire?

I suggest reconnecting the O2 sensors, and use an analog volt meter (high impedance) if you can beg borrow or steal one, and back probe the O2 sensors live on the sensor wire and the ground, to see if it operates like described in the testing O2 sensors thread.

 

[fazio8118]

Check for vacuum leaks.

Also, I chased a misfire on a TJ 4.0 for weeks. It would only misfire at highway speeds and would always cut injectors and make the jeep not go past 50mph, but after a restart it would be fine. Changed injectors, plugs, coil, ect just like you. What I ended up finding was that someone had previously installed the crank position incorrectly. The air gap/adjustment was done incorrectly and the cardboard/paper spacer was still stuck on the tip of the sensor. This caused the PCM to incorrectly detect a misfire and would cut injectors making us think it really had a misfire.
Might be worth checking....

 

[Dcoy1283]

I found it. There is a small reference voltage on the 4th wire according to this post:

http://www.naxja.org/forum/showpost.php?p=244784413&postcount=31

Check out this thread too:

http://www.naxja.org/forum/showthread.php?t=1012701&highlight=sensor+test&page=6

But they are suggesting it should read .45 V on that loose signal wire?

I suggest reconnecting the O2 sensors, and use an analog volt meter (high impedance) if you can beg borrow or steal one, and back probe the O2 sensors live on the sensor wire and the ground, to see if it operates like described in the testing O2 sensors thread.

I am getting for sure up to 2 volts on my 4th wire. And I dont know if my DMM is picking up some kind of feedback or something but when I have the black lead on the battery negitive and touch the red lead to the 2 grounds ( while the jeeps running ) I see about .25 volts either one? and this is on both upstream O2's...... I will try to borrow an analog meter from work to see I get different readings.

 

[Dcoy1283]

Check for vacuum leaks.

Also, I chased a misfire on a TJ 4.0 for weeks. It would only misfire at highway speeds and would always cut injectors and make the jeep not go past 50mph, but after a restart it would be fine. Changed injectors, plugs, coil, ect just like you. What I ended up finding was that someone had previously installed the crank position incorrectly. The air gap/adjustment was done incorrectly and the cardboard/paper spacer was still stuck on the tip of the sensor. This caused the PCM to incorrectly detect a misfire and would cut injectors making us think it really had a misfire.
Might be worth checking....

Hey thanks for the info, but I replaced the crank sensor myself and althou it wasnt an OEM sensor im getting the same exact problem that clears up with a simple restart of the engine, and only happens a mile after I leave somwhere and only when the engine is cold.

 

[Ecomike]

I am getting for sure up to 2 volts on my 4th wire. And I dont know if my DMM is picking up some kind of feedback or something but when I have the black lead on the battery negitive and touch the red lead to the 2 grounds ( while the jeeps running ) I see about .25 volts either one? and this is on both upstream O2's...... I will try to borrow an analog meter from work to see I get different readings.

That sounds like bad grounds, and a wire shorting out?

We need some late year, 2000, O2 sensor wiring troubleshooting experts here now!!!!!

Try posting the measurements you have on the wires on that link I gave you below, to the long O2 sensor testing thread!!!! Be sure to post the year, etc!!!