Misfire 2 & 6

[Bowhiker]

Hello everyone sorry posted this on the wrong section so re posting it. I’m new to the forum and eager to learn. I have a 2002 jeep liberty 3.7 that starting throwing P0300,P0302 and P0306 with a flashing check engine light. By doing a hard reset by disconnecting the battery it will throw the codes again with flashing check engine light on the third drive cycle start up.

Little back history. Started burning coolant and found passenger side head was cracked between two and four. Replaced head and started having this issue. During diagnosis, I have swapped injectors, coil packs, new plugs were installed with head replacement and replaced injector connectors. I’ve tried a different pcm with the same outcome. I have done some research and from what I have learned is a hard misfire will shut the injector driver module down on misfiring cylinders. Fuel pressure test good per Mitchell pro demand. I have also removed front timing cover to verify timing is correct. I have not performed a compression check to verify compression, but vehicle runs strong and good with no misfires during drive cycle one and two. This leads me to believe that it is not a mechanical issue. I was thinking wiring, but I’m kind of lost at the fact it’s on the third drive cycle start up each and every time. I am hoping that somebody can enlighten me with something that I don’t know or give me a direction to look. Thank you in advance.

 

[ikuo78]

Are the 2nd and 3rd times a cold start or a hot start?
There are certainly some car models that shut off the injector of the problematic cylinder when there is a problem with the ignition coil.
In that case, if you unwire the coil while idling, the misfire will still occur even if you wire the coil again.
The temporary disconnection of the ignition coil may have led to a series of misfires.
But why it only happens the third time is a mystery.

 

[Bowhiker]

3rd start up is cold. Using a noid light during running 1st and 2nd start up coils and injectors fire. When removing connectors there is a change in idle due to the misfire caused by removed connectors. During 3rd startup check engine light immediately and starts flashing and 2&6 injectors quit firing but coils still fire. Once I disconnect battery all runs good until third cold start drive cycle once again.

 

[ikuo78]

If you turn the key on and off several times before starting the car, will it no longer misfire?

 

[ikuo78]

What is the long term fuel trim value?

The head gasket comes out.
→A large amount of water vapor is emitted.
→The O2 sensor is damaged.
(O2 sensor is sensitive to moisture)
→Fuel trim goes out of order.
→ Trim returns by resetting the ECU.

 

[Bowhiker]

If you turn the key on and off several times before starting the car, will it no longer misfire?

No difference iby cycling the key. Has long crank on 3rd start. I thought about that of possibly being a fuel pump or leak down.

 

[Bowhiker]

What is the long term fuel trim value?

The head gasket comes out.
→A large amount of water vapor is emitted.
→The O2 sensor is damaged.
(O2 sensor is sensitive to moisture)
→Fuel trim goes out of order.
→ Trim returns by resetting the ECU.

I will have to report back on fuel trim on freeze frame don’t remember off the top of my head. O2 sensors replaced along with cat on leaking head gasket. Had issue before O2 sensor and cat swap but I had a bias O2 sensor after head replacement so I figured coolant had ruined it so I also replaced cat for fear of coolant ruining it as well.

 

[ikuo78]

Although it may have been replaced,
the altitude value measured by the MAP sensor is also recalled from memory at startup.
I'm not sure if there was any other memory to accumulate.
It seems that some accumulated memory is inappropriate on cold start.

If the O2 sensor is not genuine, it is better to check by reading the waveform.
If the ignition coil is not genuine, it is a good idea to perform a leak test.

 

[Bowhiker]

I agree that its accumulated data causing the issue I have not checked the MAP. I didn’t know it accumulates data. I got home late tonight and won’t have time to check fuel trim. Hopefully I will get off tomorrow at a decent time if not I will report back on Saturday morning. Thank you for the input of something else to check. I will report my findings as soon as I get a chance.

 

[Bowhiker]

ikuo78 Thank you for making my mind go back though everything in my head. Tested all the wiring this morning and found a bad spot in one of the wires barely hanging on. Must have disturbed it more while doing the head replacement which caused my issue after the replacement. I have only made it through one drive cycle but it already seems to run much better than before and fuel trims seem to be where they should be. If you don’t hear from me again then it made it through the 3rd drive cycle. LOL Thank you again.

 

[ikuo78]

ikuo78 Thank you for making my mind go back though everything in my head. Tested all the wiring this morning and found a bad spot in one of the wires barely hanging on. Must have disturbed it more while doing the head replacement which caused my issue after the replacement. I have only made it through one drive cycle but it already seems to run much better than before and fuel trims seem to be where they should be. If you don’t hear from me again then it made it through the 3rd drive cycle. LOL Thank you again.

I'm glad it's going well.

 

[Bowhiker]

Well took the Liberty out for another drive cycle and this time it set the P0306 code with flashing MIL while under acceleration. I have always just cruised during my drive cycles but figured I would get on the throttle a little bit and it bucked once set the MIL and started flashing. So I have not found my problem. Here’s a pic of the freeze frame. My son still has my good scanner so I’m using my cheap one. I am happy to say all the O2 sensors were reading good though

You must be registered for see images attach

 

[ikuo78]

Does it feel like it's actually misfiring?
If compression is low, the piston rings or liner may be damaged.
Depending on the circumstances when the gasket was damaged, they may be damaged.
In the worst case, if water hammer occurs, the connecting rod will also bend.

 

[Bowhiker]

Does it feel like it's actually misfiring?
If compression is low, the piston rings or liner may be damaged.
Depending on the circumstances when the gasket was damaged, they may be damaged.
In the worst case, if water hammer occurs, the connecting rod will also bend.

It only feels like a misfire once the CEL flashes that is when the injector cuts out so then a definite misfire.
I have not checked compression as I was thinking not mechanical due to running fine until flashing CEL but will check to verify
When I replaced the head due to the crack the cylinder looked good but obviously can't see the rings or the rod. I know it doesn't take but a few thousandths of a bend to create issues. The cylinder was also cracked between #'s 2/4 so that takes it away from #6. I am also going to due another fuel pressure check since 6 is the furthest away from fuel inlet. I am wondering if I have a fuel volume issue since 6 is the last to see the fuel flow.

 

[ikuo78]

Checking fuel flow is a good idea.

Certainly, if #6 is actually misfiring, there is little doubt that it is due to the sliding resistance of #2 and #4.
I don't know if there is a possibility of injector shutoff due to false misfire judgment.

The following are additional points that are likely to be overlooked.
・Secondary air intake due to intake manifold gasket deterioration or damage
・Valve closing failure due to intermittent sticking of the rocker arm lifter (if the used head ASSY has been stored for a long time)

 

[ikuo78]

The translation is strange.
The meaning is as follows.

If #6 is actually misfiring,
It is very unlikely that it is due to the sliding resistance of #2 and #4.