Strange misfire>>>> please help!!

[Ecomike]

Have you actually replaced, and or tested the front O2 sensors yet? Also, could there be a clogged pre-Cat?

 

[Dcoy1283]

Have you actually replaced, and or tested the front O2 sensors yet? Also, could there be a clogged pre-Cat?

Not 100% sure on how to test them, I checked the grounds on them but that's all I know. I have unplugged them to see if I there was any change but have heard that's not an accurate way to find out. I do realize that with 144k on it that all 4 should be replaced but never wanted to spend the dough. May be time thou. Now I'm also not sure what a pre-cat is? I know what cats are just never heard of a pre-cat. It your talking about the cats I have 2 of them and I have no idea if they're clogged but always thought clogged cats got worse with heat, my issue gets better with heat. Any was to see if ones clogged?

 

[Ecomike]

Here is the O2 sensor testing how to thread:

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

Precat is a mini Cat Converter closer to the engine located in exhaust header after three tubes merge, right after the first O2 sensors, it is part of the exhaust manifold in most newer vehicles, and I think the 2000, 4.0 had two Pre-Cats, and then the 2 larger main Cats, and then final O2 sensors to verify the last Cat worked.

I am not sure why Jeep used the PreCats, perhaps regs. In my 2001 Saturn the Precat heats the O2 sensor, and eliminates the need for 2 extra wires and 12 volts feed to the O2 sensor. Jeep still used the 2 extra wires and heater in the sensor.

PreCats can be clogged, carbon fouled, no longer working, or burned out shells.

Try installing one new O2 sensor only, on the pipe that cylinder #4 operates on, before pulling the head, and reconnect the O2 sensors.

Your buddy with the scanner may be able to get live O2 sensor data for you!!!!!

 

[Jnida63]

Ok, if the vehicle seems to have plenty of power when it isn't missing it most likely isn't the cats, if the cam sensor is out it can set a number 1 and number 4 misfire code. you need to find someone with a DRB III scanner to check the correlation, the cam sensor sets the injector timing and if it isn't at zero you could have a problem there.
I still vote for the front 2 02's

 

[Ecomike]

Ok, if the vehicle seems to have plenty of power when it isn't missing it most likely isn't the cats, if the cam sensor is out it can set a number 1 and number 4 misfire code. you need to find someone with a DRB III scanner to check the correlation, the cam sensor sets the injector timing and if it isn't at zero you could have a problem there.
I still vote for the front 2 02's

Interesting idea, X2 on that for sure! I think he said he replaced it, but is set properly?

 

[Dcoy1283]

Replaced to cam sensor and checked the index, it was set perfectly.

 

[Dcoy1283]

Interesting idea, X2 on that for sure! I think he said he replaced it, but is set properly?

Im going to pick up the front 2 o2's, just because I know they should be replaced no matter what, but cant grasp why it still acted up after I unpluged them and reset the ECU?

 

[Dcoy1283]

I have another interesting thing to add, Sunday I used a can of throttle body cleaner on it while it was running, to clean it and maybe clean up some internal carbon. Ever since then my jeep will still flash the engine code at the same time as before but doesn't miss or sputter or anything else???????

Didn't have a chance to use my buddies high tech scanner yet but should be able to tomorrow.

No o2 sensors yet but did grad a MAP sensor while at a junk yard today.

 

[Jnida63]

Anytime the check engine light flashes it means it is showing that serious gasses like raw fuel is in the exhaust that will damage the cat. (or at least it thinks it is seeing them).
A screwy 02 can cause that thinking it is really rich or really lean when it isn't.

 

[Ecomike]

I agree, so its back to O2 sensors or sticking fuel injector, or both.

 

[Dcoy1283]

I agree, so its back to O2 sensors or sticking fuel injector, or both.

She acted up this morning, so tomorrows pay day so im going to pick up the front 2 O2's and throw them in and see what happens.

 

[Ecomike]

Suggestion, the next time the CEL is flashing, disconnect the fuel injector electrical on #4 and see if it stops flashing?

 

[Dcoy1283]

Suggestion, the next time the CEL is flashing, disconnect the fuel injector electrical on #4 and see if it stops flashing?

It was flashing on the way home from work so I pulled over to disconnect #4 but found out that it stops flashing when I stop for afew seconds....

 

[Dcoy1283]

One positive thing with the jeep today...... found that my evap leak was in the line that runs from the charcole filter to the gas tank...it was rusted through in a few spots

 

[Dcoy1283]

I got a live data scanner off a friend but I'm not sure what I should be looking for. I did notice that my STFT for bank 1 and 2 are always jumping around between -1.5 and 2.3, but always pretty close to each other but my LTFT is always about 7 to 9 difference between them with bank 1 being the higher of the two ( ex. Bank 1 at 7.3 and bank 2 at 0, or bank 1 at 12.4 and bank 2 at 3.4 ) Any thoughts?

 

[Jnida63]

You add the 2 together on each bank, should be under 10 for each bank, should be around 0.
Say bank one is 12.4 and 7.3, that equals 19.7, that bank is seen as way to lean.
If your trims are on the positive side that means it is adding fuel to compensate.
Bank 2 looks really good, i would say the bank 1 sensor 1 O2 is bad

 

[Dcoy1283]

You add the 2 together on each bank, should be under 10 for each bank, should be around 0.
Say bank one is 12.4 and 7.3, that equals 19.7, that bank is seen as way to lean.
If your trims are on the positive side that means it is adding fuel to compensate.
Bank 2 looks really good, i would say the bank 1 sensor 1 O2 is bad

So i replaced my o2s ( both upsteam ) and still have the issue... Me and a few friends where pondering an idea, i had and fixed the normal heat soak issue on #3 and also wrapped # 4 just cause, but has anyone ever heard of a heat soak issue in the fuel rail? After thinking this I drove my jeep for alittle bit in the 93 degree heat then let it sit for a few minutes then opened the hood and used an infrared thermometer on the fuel rail, i got temps from 180 up to 210 on it. Any thoughts?

 

[Dcoy1283]

Suggestion, the next time the CEL is flashing, disconnect the fuel injector electrical on #4 and see if it stops flashing?

Why would a fuel rail temps get to 180 to 210 degrees? and could this cause a heat soak issue similar to the common # 3 injector problem?

 

[Jnida63]

One last suggestion from me, if #4 is the problem and you switched injectors and problem stayed, unplug the injector and look at the connector, the pins in the connector may have spread and not making good contact with the injector, the tangs inside the connector should be touching opposite side, if you can see air thru it then it needs to be tightened up or replaced.
I tighten mine by using a small dental pick and get behind the tang and pulling it out

 

[Ecomike]

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?