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I have a 2015 PM 3500 Gas with about 78k miles on it. It has been shuddering and idling rough when the engine is cold, and P303 showed up. The shop replaced the spark plug, coil, and injector. The problem went away for about 1,000 miles but now it is back.

Has anyone else seen this problem? Once the engine warms up fully the shudder goes away.
 

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Discussion Starter #2
So, I brought it back to the same shop and they said the new injector had already gone bad. Fortunately the replacement was covered under warranty, so I didn't have to pay anything for a new one. Has anyone else had a replaced injector go bad so quickly? Any ideas what could cause that?
 

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Perhaps damaged during a ham fisted replacement job? A bad rebuilt unit? Could be a number of things. Mine have been fine so far. Hope they nail it for you this time.
 

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Mike....i had same code on pmc about every 4000 miles.....i would delete code and run next 4000 miles....usually on trip....only mine did not run rough except cold weather start for about a minute....after about 6 time I had dealer replace spark plugs....they come with something around them at part goes into motor....big $$$ just to change spark plugs....have not had code come back knock on wood....have probably added 10000 miles since work done
 

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I have a 2015 PM 3500 Gas with about 78k miles on it. It has been shuddering and idling rough when the engine is cold, and P303 showed up. The shop replaced the spark plug, coil, and injector. The problem went away for about 1,000 miles but now it is back.

Has anyone else seen this problem? Once the engine warms up fully the shudder goes away.
Mine would do it when it got hot at first then it will when ever it wants to had it to dealer 4 times so far and no luck. They have replaced just about everything. Done replaced the motor. I can make u a list of problems I have had with it. I'm trying to get my boss to sell it. Mine is a nightmare.
 

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It’s unlikely to be an injector. The injector works when it’s warm, so it works.

You need to do a compression check. So far as I know, drivetrain is still warranty to 100,000. Watch this video. You can do the plugs on cylinders 1,3, and 5 without pulling the intake, so you can do a compression check on those cylinders too. If the compression check comes back bad, you are in the pickle. PM me if so.

 

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2016- (IIRC) the powertrain warrantee went to 60,000Miles down from 100,000 on gassers but stayed 5 years/100,000 on diesels.
 

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Wow Kip! I never get the honor of adding to a post of yours as- You The Man!
 

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Hi I have a 2018 promaster 2500 high roof
check engine light came on yesterday autozone checked the codes and it's cylinder 3 misfire
My spark plugs is due also
Should I replace all the coils?
Any advice on tools needed and how to get to the plugs is greatly appreciated
🙏
 

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Get one coil and replace all the plugs if they are due which is 100K miles. If that doesnt fix it you need a compression and leak down test. That will tell you if the valves or pistons are leaking pressure. Hope for the coil to fix it.
 

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Yes I am doing the spark plug change
So no need to replace all coils?
I had cylinder 5 misfire at 80000 mi and now cylinder 3 at 120000

Big thanks and stay save!
 

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Coils either fail or don’t- at 120K it may be your plugs. Change them and you can test the coil by moving it to another cylinder. I would replace that one only. You didn’t say the #5 misfire was a coil but I am assuming it was?
 

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Thank you for the advise
I replaced the sourk plugs and a coil on cylinder 3 only
It seems to fix the problem but I feel small hesitations
It's just me but it drives me crazy 🤪
 

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We need a picture of the plugs to comment further.
The engine learns so give it a few more days and drives to reset the injection. Clear the codes and reread after a few restarts.
 

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I am being patient but it seems like it's getting worse
Noticed my coolant reservoir is small Crack right on the lower level
63568
 
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