Cylinder 7 Misfire

[Nicnak26]

I have a 2006 Hemi 5.7L (210K) started with a cylinder 7 misfire, changed the plugs (it was needed) didnt clear the code, tested the coils, they are good. Spoke to a mechanic and truck did have the infamous Hemi tick. Replaced the lifters, cam, head gasket, timing chain, etc.

Still has a cylinder 7 misfire. Checked the fuel injectors, swapped 7&5, still coming back cylinder 7.
Checked compression, all cylinders have compression.

Its running rough and shuddering. At a loss on what else it could be. Any ideas?

Thanks

 

[Dean2]

Did you check the rail pressure at 5 and 7. You may have some crud plugging up the pipe to the 7 injector. Single cylinder misfire, if the plugs and coil are good, and you have already done valves, cams and lifters, then it can only be caused by fuel issues to that cylinder. Have you run some cleaner like Seafoam through the fuel system.

 

[Dean2]

Pull the valve cover for #7 cylinder and check rocker arm travel, may be cam and lifter time!!!

If you read his first post and I mentioned it it mine too, those have all, already been done. Easy to miss the comments but unless the mechanic that did them didn't bother doing the valves at the same time I doubt that is the source of the issue.

 

[Nicnak26]

I did all the work myself, i have worked on cars my whole life with my dad who was a mechanic. That being said, i have never checked the rail pressure before. How do i do it? Thank you for the info. Unfortunately my Dad is no longer with us and he was always my go to when i had questions. This is the first time i have ever been stumped lol I also have not ran seafoam through it, i do have some and was planning on doing that next.

 

[Dean2]

I did all the work myself, i have worked on cars my whole life with my dad who was a mechanic. That being said, i have never checked the rail pressure before. How do i do it? Thank you for the info. Unfortunately my Dad is no longer with us and he was always my go to when i had questions. This is the first time i have ever been stumped lol I also have not ran seafoam through it, i do have some and was planning on doing that next.

I would just run the sea foam first. You need a pressure gauge and a couple fittings is all, to check the rail pressure. Easier to see it than type out the procedure. Once you have seen it done once it is pretty easy. There are youtubes that show how to do it.

 

[Wild one]

I did all the work myself, i have worked on cars my whole life with my dad who was a mechanic. That being said, i have never checked the rail pressure before. How do i do it? Thank you for the info. Unfortunately my Dad is no longer with us and he was always my go to when i had questions. This is the first time i have ever been stumped lol I also have not ran seafoam through it, i do have some and was planning on doing that next.

Are you sure you have all the pushrods properly seated,it's pretty easy to have one out of place.Did you try moving #7 injector to another cylinder. If you move the injectors around and it still has a misfire on 7,it's probably time to pull the valve cover off and check to make sure all the rockers are moving the same distance

 

[Daily Driver44]

try and pull the push rods for that one cylinder. could have swapped a exhaust for an intake pus rod. or maybe bent a push rod.
i always make sure i can't wiggle it left or right but that it will still spin in its seat when not under a load. it shouldnt be real loose but enough to spin it

 

[Nicnak26]

Did you check the rail pressure at 5 and 7. You may have some crud plugging up the pipe to the 7 injector. Single cylinder misfire, if the plugs and coil are good, and you have already done valves, cams and lifters, then it can only be caused by fuel issues to that cylinder. Have you run some cleaner like Seafoam through the fuel system.

Seafoam cleared it up. Running great! Thank you. I was so stuck on it being something with the repairs i just did, i didnt even think of a fuel issue. Appreciate it

 

[Dean2]

Seafoam cleared it up. Running great! Thank you. I was so stuck on it being something with the repairs i just did, i didnt even think of a fuel issue. Appreciate it

Yep, always go after the easiest fixes first. Think through the sequence of events. In your case you had a misfire on 7 BEFORE you did a whole bunch of repairs. Misfire was still there after the repairs and even after replacing plugs, swapping injectors, and checking the coils, you still had a misfire on 7. It tells you that none of the stuff you did caused or fixed the misfire. Only leaves fuel.

 

[JWehr]

Nicknac26 how much sea foam did it take to clear the issue? I have a cylinder 3 miss fire. Swap coils still cylinder 3, replaced plugs still cylinder 3. It idles rough but no issue while driving. Only on normal idle. As it doesn't idle rough at high idle. Thanks