Cold Start Cylinder Misfires

[GamblySmurf]

Hey guys. My 2001 XJ has been having trouble with cylinder misfires for a long time, but it has just yesterday become a major problem.

For a while now, it would occasionally have a misfire on a cold start, but then run smoothly after a few seconds. In previous attempts to solve this problem I have replaced the fuel pump, spark plugs, and ignition coil.

Yesterday I started the Jeep cold and it misfired all over the place, shuddered, and went into limp mode. Any subsequent attempts at starting/driving the vehicle have produced the same results.

What do you think my next step should be?

 

[lazyxj]

Any codes?

 

[Ou2mame]

Cps? By misfires all over the place do you mean multiple misfires? Codes would really help. You can get a code reader on ebay for like 7 bucks and use your smart phone to use the free app torque to read and clear codes along with other parameters. Or hit up an autozone for a free scan. But being able to do it yourself is so much better in the diagnostic process.

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[old_man]

Before throwing parts at it, let the engine cool down and then remove all the spark plugs and run a compression test across all the cylinders. If any are low, do a wet compression test as well.

This will tell you right off if you have a compression related failure.

In the mean time, I recommend running a can of BG44K through the gas. It will help any clogged injectors and get rid of combustion chamber carbon. A can every 10K miles is a good thing, especially on an older vehicle. If you can't find BG, go with Chevron Techron, which, if from what we can tell, is just a watered down version.

I give it better than a 50/50 chance the BG will clear up the problem without having to do the compression check.

Clogged injectors and low compression due to a stuck or worn out ring will present it self when cold, much more than when warm.

 

[GamblySmurf]

Cps? By misfires all over the place do you mean multiple misfires? Codes would really help. You can get a code reader on ebay for like 7 bucks and use your smart phone to use the free app torque to read and clear codes along with other parameters. Or hit up an autozone for a free scan. But being able to do it yourself is so much better in the diagnostic process.

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Sorry for the slow response, life and all that.

There was a multiple misfire code initially, but after clearing that all I am getting is a cylinder 2 misfire code.

 

[GamblySmurf]

Before throwing parts at it, let the engine cool down and then remove all the spark plugs and run a compression test across all the cylinders. If any are low, do a wet compression test as well.

This will tell you right off if you have a compression related failure.

In the mean time, I recommend running a can of BG44K through the gas. It will help any clogged injectors and get rid of combustion chamber carbon. A can every 10K miles is a good thing, especially on an older vehicle. If you can't find BG, go with Chevron Techron, which, if from what we can tell, is just a watered down version.

I give it better than a 50/50 chance the BG will clear up the problem without having to do the compression check.

Clogged injectors and low compression due to a stuck or worn out ring will present it self when cold, much more than when warm.

Hmmm, how do I run a can of BG44K with it in limp mode?

 

[Ou2mame]

I would swap the 2 spark plug with another and see if the misfire follows the plug and if it doesn't, do that with the injector.

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[Tim_MN]

Re-set the PCM with the instructions below, and follow the label instructions for the fuel injector cleaner.

Install fresh spark plugs, either basic Champion copper plugs for any Jeep 4.0L or Autolite APP-985 for the 2000-01 coil on plug ignition system. Avoid installing any single-tipped platinum plugs like the Autolite AP-985 or Champion 3034, and any Split-Fire type gimmick spark plugs.


The Powertrain Control Module, or PCM as its commonly called, stores the information for your vehicle and your driving habits in its memory. The memory is maintained by a series of capacitors that hold a charge and maintain power for the ECU when the vehicle is turned off. The following procedure will allow you to reset the memory and allow the computer to re-learn operating parameters.

This very simple procedure will erase the 1996-2001 “Adaptive Memory” stored inside the PCM and allow a new “Adaptive Memory” to be developed. After performing this procedure the 1996-2001 PCM will re-learn and store into Adaptive Memory your engines performance characteristics. Perform these steps exactly as they are written, in the order they are written. This will cause the adaptive memory in the PCM to be erased and cause the PCM to go into Fast Learn adaptive mode.

Disconnect the POSITIVE battery Terminal clamp and touch it to ground ( not the battery negative terminal ) for 30 seconds. The engine block or the A/C compressor pump will work as a ground. (This is to discharge the PCM capacitors, which maintain the Adaptive Memory).

Reconnect the Battery Cable
Turn Ignition Switch to the “On” position but DO NOT start the engine
Turn Headlight “On”
Turn Headlights “Off”
Turn Ignition Key “Off”

The PCM Adaptive memory has now been flashed, or erased from the PCM. When you start the engine it will be running off a set of pre-programmed tables that come with the PCM from the factory. When you get the engine up to operating temperature the PCM will start to collect data for the “Adaptive Memory”. The PCM will collect data for Adaptive Memory for the first 50 Warm-up Cycles.

 

[GamblySmurf]

UPDATE:

I drove the vehicle a couple of miles in limp mode, and then rechecked the codes.

It is showing 4 faults:

P0300 - Random/Multiple Cylinder Misfire
P0301 - Cylinder 1 Misfire
P0302 - Cylinder 2 Misfire
P0135 - O2 Sensor Heater Circuit (Bank 1 Sensor 1)

Thoughts??

 

[Ou2mame]

Looks like a pre cat o2 sensor which can cause all sorts of fuel mixture issues

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[GamblySmurf]

Looks like a pre cat o2 sensor which can cause all sorts of fuel mixture issues

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Would you suggest replacing both the upstream and downstream O2 sensors then?

 

[Ou2mame]

I would probably do the pre cat ones first.. I think you have 2 of them? I'm not sure on the 00 and 01s but I think there's 4. I could be wrong though. But I would start pre cat. Post cat don't really do much

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[Tim_MN]

Only buy NTK brand O2 sensors for the Jeep 4.0L.

 

[GamblySmurf]

I would probably do the pre cat ones first.. I think you have 2 of them? I'm not sure on the 00 and 01s but I think there's 4. I could be wrong though. But I would start pre cat. Post cat don't really do much

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I'm gonna start with the pre-cat for the simple reason that the post-cat sensors are seized in rocks.

The pre-cat sensors came out easily enough.

 

[GamblySmurf]

Only buy NTK brand O2 sensors for the Jeep 4.0L.

Good to know. Thanks!

 

[Dragonslayer]

Check the forward O2 sensor(s) heater(s) for continuity, resistance.

Check the O2 sensor heater fuse (in the engine compartment fuse box).

 

[Ecomike]

Do no run it in limp mode, that will burn up the cat converters running the engine rich, may dilute the oil and cause fast engine wear, the first Cats (if it is 2001?) are built into the exhaust manifold, expensive and pain to replace.

get an ohm/volt multi meter, and test the O2 sensor, and the wiring, per the O2 sensor test thread I created here about 10 years ago. Google it. It is super easy to do and will save you hours of grief and costs....

Pull the spark plugs and see what the plug wire and plug on Cyl 1 looks like verses the other 5. Post a picture link if you can?

 

[Ecomike]

Check the forward O2 sensor(s) heater(s) for continuity, resistance.

Check the O2 sensor heater fuse (in the engine compartment fuse box).

And if the fuse is good, and the O2 sensor heaters are good (there are four wires, you need to look up which two are grounds, which one is the 12 volts for the electric resistance heater in the O2 sensor and which one is the ECU data wire. Read resistance from the 12 volt heater input wire to the heater ground wire and it should read about 8 ohms.
The O2 heater wires code is a clue that it may be damaged wiring where the wiring to the O2 sensor got cut or burned by its neighbors or trail stuff.

Also check to see if plug wire 1 and 2 got criss-crossed if that is even possible on 2001? You may have two problems.

 

[Ecomike]

UPDATE:

I drove the vehicle a couple of miles in limp mode, and then rechecked the codes.

It is showing 4 faults:

P0300 - Random/Multiple Cylinder Misfire
P0301 - Cylinder 1 Misfire
P0302 - Cylinder 2 Misfire
P0135 - O2 Sensor Heater Circuit (Bank 1 Sensor 1)

Thoughts??

Check the O2 heater fuse and relay(? if there is one on that year?)wires for 12 Volts to the O2 sensor. IF the O2 heater fuse is blown, find out why first!!! Locate the short in the wires or the sensor....

 

[GamblySmurf]

Do no run it in limp mode, that will burn up the cat converters running the engine rich, may dilute the oil and cause fast engine wear, the first Cats (if it is 2001?) are built into the exhaust manifold, expensive and pain to replace.

get an ohm/volt multi meter, and test the O2 sensor, and the wiring, per the O2 sensor test thread I created here about 10 years ago. Google it. It is super easy to do and will save you hours of grief and costs....

Pull the spark plugs and see what the plug wire and plug on Cyl 1 looks like verses the other 5. Post a picture link if you can?

Yes it's a 2001 with the cats built into the exhaust.

No plug wires. The coil sits on the plugs on the 2001.

I replaced the O2 sensors. That seems to have cleared that fault, but it is still misfiring cylinder 2. And it gave me a "System Too Rich" fault on Bank 1 and 2 (codes P0172 and P0175).

The exhaust sounds louder than normal as well.

I'm ready to nuke this thing.