A Different Misfire Question: Specific Circumstances

[phil04]

01 XJ 4.0 Auto 4x4 178k
I have read countless misfire threads but none seem to address the situation I have:

From start up rough idle, though it seems to get more rough as the vehicle warms up (it will actually move you).

When in closed loop, if I allow the vehicle to decelerate while in drive, either through just taking my foot off the gas or applying brakes, for around 8 seconds I get a flashing cel. Start giving it gas and the light stops flashing after a few seconds. Occasionally it goes into limp mode after and I have to restart the car.

I have been throwing it into neutral as I come to stops or have a prolonged deceleration to avoid the flashing cel. Anyone have a good idea of what this might be?

Codes: Misfire cyl 1, 4, 6. We drove it with the code reader and most misfires detected were from cyl 1. It actually just kept counting while driving normally.

I did replace my transmission about 2 months ago and a mechanic mentioned the possibility of a bent flex plate window for the crank sensor but i'm not sure the symptoms fit.
I have also tried two different crank sensors with no change.
New plugs and thermostat.
Fuel pressure was good and passed leak down test.
Mechanic never checked vacuum because he was confident it wasn't a potential cause, but I am not so sure since during deceleration you are at your highest vacuum and that is when I get enough misfires to get the flashing cel.

Thanks so much for any help! This is driving me crazy and the mechanic at jeep let me know he would be happy to throw parts at it but has no clue what the cause is. Luckily I managed to get about 2 hrs worth of "troubleshooting" for 50 bucks.

 

[phil04]

This is driving me crazy!

 

[Talyn]

Have you checked cam sensor synch? Possibly a coil rail problem.. 1&6 share a coil. Have you checked compression? What plugs did you use? What about your O2 sensors?

 

[heyhar]

TPS? Some of your symptoms match. I've replaced it in my '96, trying a few from the JY, and a new one (it was the happiest with a used one), and have done a few lately for friends, different models, but all 4.0 JEEPS. Different problems, but replacement seems to cure them. At eleven years, pushing 200k, it wouldn't hurt.

 

[phil04]

Thanks for the info! I was going to check on the cam sensor and see if there is any play for starters. I didn't know 1 and 6 shared a coil and was wondering how the coils were distributed so that is very helpful, thanks. I will try to hit the jy this morning and see if there are any tps's I can snag. Does anyone find it strange that I get the flashing cel only under deceleration? It has plenty of get up and go when I give it gas. I don't detect any hesitation or misses when accelerating.

 

[phil04]

Oh, I just replaced the plugs with basic NKG's and the 02 sensors are working per the mechanic but my cat is completely gone.

 

[Talyn]

are you saying your cat is gutted?

 

[heyhar]

are you saying your cat is gutted?

Or clogged? Maybe the ceramic honeycomb is broken? Try to get the mechanic to be more specific. If the cat is not doing its job, the CEL is possibly being generated by the second, or downstream O2 sensor, alerting the computer that the cat's not working.

 

[phil04]

gutted. However, the secondary 02 is just for emissions purposes and should not affect driveability. Also, as mentioned, i only get the flashing cel after continuous decelration/coasting for more than 8 seconds. I can literally count to 7 and give it gas and no flashing cel. All injectors are firing, though whether they are clogged or not is still tbd but it is strange that i have plenty of power on acceleration, no hesitations or anything. I would think a faulty spark or injector would have some affect on that?

 

[phil04]

Oh, I also went ahead and started unplugging sensors to see what happens. With the tps the engine revs up and then goes back to idling poorly as it was. Unplug iac and no change. unplug cps and no change.

 

[phil04]

corretction, unplug camshaft position sensor, not cps

 

[heyhar]

Unplug iac and no change.

Is the IAC chamber clean? Take it apart, get all the carbon deposits out of the ports, make sure the pintle seat is clean, and if it's still acting up, maybe a new IAC is in order.

 

[Talyn]

The flashing light is probably from the cat being gutted. The engine is going slightly rich when you let up on the gas and the after cat o2 sensor is seeing that thinking that the cat it getting too much fuel through it. However that wouldn't cause the misfires.

Also, do you have the cali emissions package or the federal? 3 cats and 4 o2s or one cat and 2 o2s?

 

[phil04]

2 O2's.

 

[phil04]

Also, why would it take 8 seconds for the light to flash? Oh, and I noticed it only happens in closed loop.

 

[Dcoy1283]

Also, why would it take 8 seconds for the light to flash? Oh, and I noticed it only happens in closed loop.

Have you ever figured this misfire issue out? I have a 2000 with the same problem.