Cylinder 4 Misfire

[mjonesjr84]

I've been having an intermittent cylinder 4 misfire that became perminate on a trail at Windrock this past Friday. So, since I had a spare ignition coil and injectors I swapped them out without any change. I went to the parts store and picked up new plugs (6) and put them in. The Jeep fired right up and ran good for a bit. I shut it off and let it set for a couple of hours. When I started it again, it had the misfire and dumping fuel out the exhaust. I got home late last night so this morning I pulled the #4 spark plug and it was wet with fuel. If I pull the #4 injector plug off, it smooths out the engine.

The coolant looks fine with no contamination. The head doesn't look cracked or have goop inside the oil fill cap looking down into the head. I'm almost 100% confident it isn't the 0331 head crack.

Any ideas what else this could be?

 

[JKP]

Sounds like the injector may be firing continuously. Check the injector wiring for a short to ground.

Another possibility would be the driver for #4 in the PCM is bad.

Do you have a noid light?

 

[mjonesjr84]

Sounds like the injector may be firing continuously. Check the injector wiring for a short to ground.

Another possibility would be the driver for #4 in the PCM is bad.

Do you have a noid light?

I don't have a noid light. The wiring looks fine but I know that doesn't mean anything. Would that mean a replacement PCM? How do you check that outside of swapping PCM's?

 

[JKP]

The PCM grounds the injector to fire it.

There should be a constant 12V on one wire and either a ground or open on the other one from the PCM.

I haven't tried this, but I would think you could see a constant ground from the PCM with a volt meter.

@Wranglerfix can probably fix the PCM if that is the problem.

 

[macleanflood]

You can listen to the injector clicking by holding a screwdriver to the injector and the handle on your ear.

You could move the injector and see if the misfire moves...but...I'd definitely be pulling apart the loom looking for wiring issues. Especially back of the valve cover where it turns.

-Mac

 

[Wranglerfix]

I don't have a noid light. The wiring looks fine but I know that doesn't mean anything. Would that mean a replacement PCM? How do you check that outside of swapping PCM's?

What year is your Jeep? You can send it into me and I can test it for you. Usually, I do not see misfire codes in the computer. It comes down to brand of sensor or plug that can cause your problem.

 

[mjonesjr84]

What year is your Jeep? You can send it into me and I can test it for you. Usually, I do not see misfire codes in the computer. It comes down to brand of sensor or plug that can cause your problem.

It's a 2000. Every sensor except for the O2 sensors are factory original Mopar ones.

 

[Wranglerfix]

What brand o2 are you running?

 

[mjonesjr84]

What brand o2 are you running?

Walker. They've been installed for almost 2 years.

 

[Wranglerfix]

That could be an issue. @macleanflood What is your take on Walker vs. NTK?

You can send your ecm into me and I can test it for you.

 

[mjonesjr84]

That could be an issue. @macleanflood What is your take on Walker vs. NTK?

You can send your ecm into me and I can test it for you.

Not sure how an O2 sensor would cause a single bank to misfire. I would think it would cause 3 banks to misfire since there is an upstream O2 for 1-3 and an upstream for 4-6. They are reading correct values on the Torque app I run on the double DIN radio.

I dropped it off at the Jeep shop that works on it this morning for them to fix the PSC pump and figure this out.

 

[Wranglerfix]

Not sure how an O2 sensor would cause a single bank to misfire. I would think it would cause 3 banks to misfire since there is an upstream O2 for 1-3 and an upstream for 4-6. They are reading correct values on the Torque app I run on the double DIN radio.

I dropped it off at the Jeep shop that works on it this morning for them to fix the PSC pump and figure this out.

In my experience it comes back to something basic causing your issue. Jeeps are temperamental when it comes to sensors. Sometimes the difference between working and not working is the brand of sensor on a wrangler.

 

[macleanflood]

What is your take on Walker vs. NTK?

Well my experience with Walker is 50/50 on two O2 sensors. My downstream 2001 F250 worked perfectly. My 97 TJ did the same thing as the OP and ranged slightly higher than .9v and my fuel trims were high and gas mileage suffered.

I bought a NGK and it did the exact same thing.

Sample size of three...

Interestingly enough the rusted out 2000 Sahara I'm parting out...I pulled it's unknown age NGK, installed it in my 97 and problem solved.

Shrug.

Is there something in the PCM or programming that can be adjusted to compensate for shit parts?

Just about all parts these days are crap...some exceptions like Black Magic Brakes and Wranglerfix PCMs are the rare exceptions.

-Mac

 

[por212]

Experienced a similar issue a while back. Changed just about every sensor on the engine, fuel injectors, coil, etc but did not solve the problem. Had no noticeable oil contamination or coolant lost but ended up being a cracked head. Hope that’s not your problem but I wouldn’t rule it out.

 

[mjonesjr84]

So far the noid light shows the injector firing as it should. When it's running, it's pouring gas out the exhaust and the plug is soaked in gas.

 

[macleanflood]

What's live ODB data show for the fuel trims and O2 sensor voltage?

-Mac

 

[mjonesjr84]

Replaced the ECM after tracing down and diagnostics determined that was the issue. Put the new @Wranglerfix ECM in and it purrs like a kitten.

 

[Wranglerfix]

Replaced the ECM after tracing down and diagnostics determined that was the issue. Put the new @Wranglerfix ECM in and it purrs like a kitten.

Thank you for your business and thank you for letting us know! If you should ever need me, I am always a click or a call away.

All the best,

Mark