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Engine misfiring. Video inside. Any ideas?

cjomanche

NAXJA Forum User
Location
Orange County
Hi guys, really getting to the end of my rope chasing this issue. So far replaced o2 sensor, tps, coil, spark plugs, fuel filter, distributor cap and rotor, and did a fuel pressure test. Nothing has fixed this. It used to only do this at 2900 rpms but now it does it all over once the vehicle gets up to operating temperature. Still does well when the engine is cold. No check engine light but it has codes 12 and 35 stored. Any ideas on what I should do next?

https://youtu.be/SO3-IGeHqEc
 
Hi guys, really getting to the end of my rope chasing this issue. So far replaced o2 sensor, tps, coil, spark plugs, fuel filter, distributor cap and rotor, and did a fuel pressure test. Nothing has fixed this. It used to only do this at 2900 rpms but now it does it all over once the vehicle gets up to operating temperature. Still does well when the engine is cold. No check engine light but it has codes 12 and 35 stored. Any ideas on what I should do next?

https://youtu.be/SO3-IGeHqEc


Crank Position Sensor is a possibility. They can fail when they get warm but work when cold. They might not set a code 11 unless they've failed completely and the ECM is seeing the cam sensor going but not the crankshaft sensor when cranking the engine.

If you have a can of freeze spray you might try chilling it once the engine is warm and see if it helps. Or hit it with a hairdryer and see if it stumbles when the engine is cold.
 
Did you do plug wires as well? Can you isolate the cylinder missing? If you can you can swap injectors around and see if it follows. Throwing a vacuum gauge on wouldn't be a bad idea either.
 
I pulled my hair out for a few years trying to track down misfires on my 2001 Wrangler. Found a TSB that indicated the problem is with exhaust valves sticking open. I found that the exhaust valve seats were pitted.

I pulled the head, lapped all of the valves, and the problen was gone.

I struggled with this problem for about 5 years and 50k miles.

Sent from my SM-G935R4 using Tapatalk
 
I should also mention I replaced every single sensor, all injectors, coil pack several times, plugs of course, ran through cleaners, and nothing would fix it.

Sent from my SM-G935R4 using Tapatalk
 
Crank Position Sensor is a possibility. They can fail when they get warm but work when cold. They might not set a code 11 unless they've failed completely and the ECM is seeing the cam sensor going but not the crankshaft sensor when cranking the engine.

If you have a can of freeze spray you might try chilling it once the engine is warm and see if it helps. Or hit it with a hairdryer and see if it stumbles when the engine is cold.

We replaced the CPS last night and it didn’t make any difference, unfortunately.
 
Did you do plug wires as well? Can you isolate the cylinder missing? If you can you can swap injectors around and see if it follows. Throwing a vacuum gauge on wouldn't be a bad idea either.

We replaced all the spark plugs and plug wires. We bought some used injectors but didn’t get a chance to put them on.

We started thinking it was an electrical problem we were chasing. The dash lights would dim slightly whenever a misfire was occuring.
 
I even replaced the ECM trying to fix mine.

Sent from my SM-G935R4 using Tapatalk
 
I pulled my hair out for a few years trying to track down misfires on my 2001 Wrangler. Found a TSB that indicated the problem is with exhaust valves sticking open. I found that the exhaust valve seats were pitted.

I pulled the head, lapped all of the valves, and the problen was gone.

I struggled with this problem for about 5 years and 50k miles.

Sent from my SM-G935R4 using Tapatalk

The only issue I have with this is that if it were valves not closing, wouldn’t it be happening all the time? Like immediately after the truck started? When the engine is dead cold the truck runs absolutely perfect for a minute or two, even when accelerating into the trouble range of about 2800-3000 rpm. It’s only after the engine starts warming up does this problem present itself. Once the engine is to temp it becomes progressively worse. It just doesn’t seem like a mechanical issue based on this, but I could be wrong.
 
Check the O2 wire where it comes up the front of the motor. It can be really hard to see in places, you have to use a flashlight and look closely. Maybe even disconnect the harness from bellow and pull the section out form behind the power steering pump bracket to look at it.

I've had the front O2 sensor wire come loose from the clamp and cook on the exhaust. The O2 sensor plug oil soaked and making poor contact in the connector. The harness burnt behind the power steering pump bracket, and the rear O2 sensor wire come loose and burn on the CAT/exhaust.

On many models the O2 sensor(s) won't set a code unless it is completely toast.
 
Check the O2 wire where it comes up the front of the motor. It can be really hard to see in places, you have to use a flashlight and look closely. Maybe even disconnect the harness from bellow and pull the section out form behind the power steering pump bracket to look at it.

I've had the front O2 sensor wire come loose from the clamp and cook on the exhaust. The O2 sensor plug oil soaked and making poor contact in the connector. The harness burnt behind the power steering pump bracket, and the rear O2 sensor wire come loose and burn on the CAT/exhaust.

On many models the O2 sensor(s) won't set a code unless it is completely toast.

I was absolutely convinced I was dealing with an O2 sensor problem since the problem only seems to really happen when the truck enters a closed loop, so this is definitely something to check.
 
The only issue I have with this is that if it were valves not closing, wouldn’t it be happening all the time? Like immediately after the truck started? When the engine is dead cold the truck runs absolutely perfect for a minute or two, even when accelerating into the trouble range of about 2800-3000 rpm. It’s only after the engine starts warming up does this problem present itself. Once the engine is to temp it becomes progressively worse. It just doesn’t seem like a mechanical issue based on this, but I could be wrong.
No, the problem comes up as the rpm increase because the valves are on the seat for less time. The TSB lists the problem as a build up of carbon on the valve which causes the valves to close more slowly and only happens above a certain RPM.

When i had mine apart the valves didn't seem to have much carbon build up, or at least not enough that it should have been a problem. I did notice significant valve seat pitting though. Either way, I wire wheeled the valves and lapped them in and the problem went away.

Again, there was not a sensor that not replaced, at least once. Many I changed several times. That includes O2 sensors, TPS, MAP, CPS, Cam PS, coils, plugs, temp, etc.

Sent from my SM-G935R4 using Tapatalk
 
No, the problem comes up as the rpm increase because the valves are on the seat for less time. The TSB lists the problem as a build up of carbon on the valve which causes the valves to close more slowly and only happens above a certain RPM.

When i had mine apart the valves didn't seem to have much carbon build up, or at least not enough that it should have been a problem. I did notice significant valve seat pitting though. Either way, I wire wheeled the valves and lapped them in and the problem went away.

Again, there was not a sensor that not replaced, at least once. Many I changed several times. That includes O2 sensors, TPS, MAP, CPS, Cam PS, coils, plugs, temp, etc.

Sent from my SM-G935R4 using Tapatalk

But wouldn't this be the case even when the engine is cold? Immediately after starting the truck I can run the RPMs up as high as I want and there is no misfiring at all. As the engine starts getting warm it progressively gets worse over time. If the valve wasn't closing because of carbon buildup I don't see how heat would make a difference.
 
But wouldn't this be the case even when the engine is cold? Immediately after starting the truck I can run the RPMs up as high as I want and there is no misfiring at all. As the engine starts getting warm it progressively gets worse over time. If the valve wasn't closing because of carbon buildup I don't see how heat would make a difference.
You would think. I know with mine, if you started it up and held the motor above a certain RPM, say around 3200rpm, the CEL would start flashing after a short time.

Interestingly, you really couldn't hear any misfire from mine. The only indication was the CEL

Sent from my SM-G935R4 using Tapatalk
 
When I first got the truck it seemingly ran fine. I didn't notice anything "off" until at least a month after I bought it. I was coming back from a couple hour trip and I noticed one or two misfires on my way back while in 4th gear. I thought it was a fluke so I ignored it. Later on I discovered I could replicate this if I kept the RPMs around 2800-3000 for a little while. As long as I stayed out of that RPM range, I was fine. No issues to speak of.

A couple months ago, I changed the oil pan gasket, timing chain, oil adapter gaskets, clutch master cylinder, and front main seal. Immediately after this the misfiring problem got a lot worse, to where it is now.

What could have made it suddenly get worse in those repairs? Or could this problem have gotten worse on its own?
 
If you have a tiny head gasket leak it can cause a miss after the engine warms up and the cooling system builds pressure.

Try removing the radiator cap running it for awhile and see if the miss disappears or gets noticeably better. You might also look for any bubbles in the coolant. A quick test is right after you start up hold a white paper towel under the exhaust and catch the drips. The coolant turns to steam in the cylinder and condenses some in the exhaust. It can drip out the exhaust after a cold start and the drips may show a tint the same color as your coolant. Head gasket leaks can be tricky to troubleshoot, it depends on the amount of the leak. Another sign is having to periodically add coolant, either a tiny plumbing leak or maybe a head gasket leak. When you run it with the radiator cap off you are likely to get some overflow, I usually wad up a rag and stuff it under the overflow, it will catch most of it, then rinse the whole area down with water after you're done-

You can also check your plugs for deposits and look down the spark plug hole at the top of the piston, too clean and it may be from the steam blasting off the carbon on the piston top.

My tips are a long shot, but heck you've already hit the more common causes.
 
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I would certainly use a volt meter under the hood to see if the voltage (Alternator, VRegulator, or battery wires or grounds have an issue)

But My most recent problem has me thinking the distributor may need indexing or replacing....and indexing. More on that later.... Is this rig new to you, or has it been running great for a long time in your possession???

Now ignoring the Dizzy possibility, my first thought is a clogged exhaust, busted up or clogged CAT converter????

Or a lack of fuel supply at pressure?

Is the fuel pressure holding OK as you hit the rpm limit??? Did you test that????

Make sure there is not a dead rat or snake in the air filter box, blocking air flow, LOL

So too little fuel flow, or air flow blocked, or a timing problem (distributor indexing)
 
When I first got the truck it seemingly ran fine. I didn't notice anything "off" until at least a month after I bought it. I was coming back from a couple hour trip and I noticed one or two misfires on my way back while in 4th gear. I thought it was a fluke so I ignored it. Later on I discovered I could replicate this if I kept the RPMs around 2800-3000 for a little while. As long as I stayed out of that RPM range, I was fine. No issues to speak of.

A couple months ago, I changed the oil pan gasket, timing chain, oil adapter gaskets, clutch master cylinder, and front main seal. Immediately after this the misfiring problem got a lot worse, to where it is now.

What could have made it suddenly get worse in those repairs? Or could this problem have gotten worse on its own?

You have a timing problem!!!!! This is for sure!!!!! You need to redo the timing chain, and then index the distributor, and first make sure there is no play in the distributor shaft side to side or irrationally.

Mine had a shear pin that holds the cam gear on the Dizzy shaft going bad and it would move, slop around.....Then even the new Dizzy had to be indexed to get it in the sweep spot (Factory Cam shaft OEM errors) etc...

You could try replacing and indexing a new Dizzy or just indexing the old Dizzy first and see if that is good enough. If it was the original problem, the new timing chain may have made it worse (removed the slop that took it from marginal to worse).

But make sure there is no rotational slop or side to side play in the dizzy shaft. If there is, scrap it!!!

Once the dizzy is know to be OK and indexed, if there is still an issue I'd say the crank to Cam shaft timing must be off, maybe one tooth?
 
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