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[allan p]

Hi I have a problem with my wife's wrangler 4.0. The engine seems to missfire+hold back and sounds like its spitting back through the inlet, if I stop and put it in to neutral and give it a couple of good revs it then drives o.k,it can then be o.k for miles. This problem can occur during the warm up phase from cold or after a short hot soak.The vehicle has had a crankshaft sensor.I wondered if anybody could help before I have to book it in for a diagnostic check.

[PtP]

...........The engine seems to missfire+hold back and sounds like its spitting back through the inlet..................

I’d look at the plug leads first. I had a very similar problem which took me a while to diagnose after replacing other parts first.

Have a look at these two threads:
http://www.birtydastards.com/frm/index.php?topic=7902.25
http://www.birtydastards.com/frm/index.php?topic=9777.0

Unless you have the Engine Management Light on on the dashboard, I don’t think a diagnostic check will throw up any error codes.

BTW you can check the error codes yourself without a scanner. And a scanner doesn’t show up any hidden codes either – I tried that!

Search on the forum and you’ll find the procedure for checking the error codes if your EML is on.

[Jonny Jeep]

Upstream O2 sensor if it's a 97-99.
http://www.jeepforum.com/forum/showthread.php?t=612880

[PtP]

.............This problem can occur during the warm up phase from cold or after a short hot soak..............

IIRC the upstream O2 sensor is not needed/read when the engine’s in the warm-up phase, so a faulty O2 sensor would not cause the misfire problem.

I wasted money on one and it didn’t resolve my problem.

[Jonny Jeep]

If you read the post I linked to the O2 sensor diagnosis is free. You unplug it and if it runs fine the sensor is the cause of the problem. No need to buy a new one unless you have to. If the problem doesn't go away with the sensor unplugged the problem is elsewhere.

If the heater circuit in the sensor isn't working the sensor isn't hot enough to be accurate when the computer starts using it to set fuel mix. When that happens the engine gets stupid rich till (stumbling, hesitating, popping) till the sensor gets hot enough to supply accurate information, at which point the engine smooths out and runs just fine.

[greggmo]

its one of the censors for sure. i would say 02 or tps.

[allan p]

Many thanks for the replies,I unplugged the 02 sensor on Tuesday night and so far it seems to be running fine,Iam going to run it a few more days then if its still ok fit a new one, anybody know who can supply after market parts?   

[Tragic]

I bought one of these on Wednesday

[PtP]

It looks like there are a couple of different ones listed on the Bosch website depending on your year. Have a look at page 224 here: http://www.bosch-lambdasonde.de/en/downloads/lambda_sensor_catalogue.pdf  The Bosch one I bought, within the last 12 months, had the plug already attached. IIRC it cost me 3x what Tragic paid though.

The link should now work

[Green Jeep]

Many thanks for the replies,I unplugged the 02 sensor on Tuesday night and so far it seems to be running fine,Iam going to run it a few more days then if its still ok fit a new one, anybody know who can supply after market parts?   

I had poor running probs on my Cherokee 4.0 Auto, turned out it was a small temp sensor confusing the ECU... more details in this topic, see last post.

Hope you get it sorted, cheers Maf

http://www.birtydastards.com/frm/index.php?topic=10561.0

[allan p]

Just thought I'd say thanks to every one who replied to my original post, i fitted a £18.00 pre cat oxy sensor and the wrangler seems to be running fine. I have re checked the emmisions and it is fine. Again many thanks.

[isle of man]

Result....We are here to help.