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Discussion Starter #1
Hey y'all I have an 07 Colorado (automatic I4, Z85 i believe) and out of nowhere it developed a miss after about ten minutes of driving it. We brought it to the "talented" gents at O'Reilly and sure enough, cylinder 4 misfire. So we unplugged the battery overnight and it was gone for a few days but then came back. so next we pulled it apart and I replaced the coil pack. Now it starts missing as soon as it starts (rather than waiting ten or so minutes like before). So I pull it back apart and check the spark plug but it looks just fine. So just to be sure I swap the coil pack off cylinder 1 and still the same. I just went and bought a new injector but I have yet to find any threads about replacing them. I'm just trying to find some advice or see if anyone else has had this issue. I miss driving my yellow lady! Thanks in advance!
 

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What is the check engine code?

May be helpful before you keep throwing parts at it.

You need to read the code after swapping the coil pack to know if the misfire is following the coil or staying at the cylinder.

It is least likely the injector is faulty.

How many miles on the plugs? Do you know what plugs are in there?
 

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I would check the compression in that cylinder and never assume a spark plug is good just from a visual inspection as the resistors can short out inside the top insulator.
 

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Not sure if this will work for you but. I had a p300 code and thought I will try the easy fix mechanic in a bottle.

Well one bottle of redline gas treatment and 50km of driving light went out and has not come back on. That was 2 years ago now at each oil change I just add a bottle.

Just throwing it out there may or may not work for you.
 

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what codes are you getting?
 

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Discussion Starter #6
What is the check engine code?

May be helpful before you keep throwing parts at it.

You need to read the code after swapping the coil pack to know if the misfire is following the coil or staying at the cylinder.

It is least likely the injector is faulty.

How many miles on the plugs? Do you know what plugs are in there?

They didn't let me see the code or tell me they just said "cylinder 4 misfire".

Will it hurt to drive the truck all missing like that? That's the only reason I haven't taken it back was fear of causing even more harm.

the plugs are auto-lites, nothing special just some replacements, and have about 2,500 miles on them.
 

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Discussion Starter #7
I would check the compression in that cylinder and never assume a spark plug is good just from a visual inspection as the resistors can short out inside the top insulator.
Okay I'll have to look and see what it costs to loan one from o'reilly and test it. Thanks for the help.
 

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I'm having misfire problems as well on number 5 just did a relearn on computer waiting to see if the light comes back on. Been driving around for two days.

Took it to the dealership they were not much help.

Got a second opinion at local shop they got their scanner to hook up to the truck said everything looked fine so they just did a case relearn.
 

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They didn't let me see the code or tell me they just said "cylinder 4 misfire".

Will it hurt to drive the truck all missing like that? That's the only reason I haven't taken it back was fear of causing even more harm.

the plugs are auto-lites, nothing special just some replacements, and have about 2,500 miles on them.
Okay, that's at least something. Each cylinder is assigned a code number. I feel it is more than a guess at this point. But having the code read after moving the coil is important to know if the code changes to a different cylinder.

The plugs aren't old enough to be worn out and if it has been good until recently then you are probably still good. A spark plug is not ruled out from that theory though. But should not be the first/likely cause.

As long as you CAN drive it it won't be a problem get it back and forth to the store for code reading. Sometimes they are so bad that you can't drive too well and get yourself into traffic, etc.
 

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Discussion Starter #10
Okay, that's at least something. Each cylinder is assigned a code number. I feel it is more than a guess at this point. But having the code read after moving the coil is important to know if the code changes to a different cylinder.

The plugs aren't old enough to be worn out and if it has been good until recently then you are probably still good. A spark plug is not ruled out from that theory though. But should not be the first/likely cause.

As long as you CAN drive it it won't be a problem get it back and forth to the store for code reading. Sometimes they are so bad that you can't drive too well and get yourself into traffic, etc.
Okay then tomorrow i'll drive it up and let them read it again. I guess i should hope that it moves so maybe it's just a bad new coil pack. I'll get back to you tomorrow.
 

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Discussion Starter #11
okay just got back from O'Reilly and unfortunately the misfire has stayed on cylinder 4. Code was "P0304-generic code misfire cylinder 4" or something close to that realm. So coil pack i believe can be removed off the possible failure points, now what?
 

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How long would it take for truck to throw misfire code?

The other shop reset the computer but its not throwing any codes. Truck seems about the same.

might do my own compression test , mabey the dealership is full of krap,lol
 

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So I took the truck to the dealership to have them look at it. Injector looks good and flows as it should, everything electrical seems fine. Nothing came up on diagnostics. So they're thinking its a mechanical issue but they don't know what it is. So they want to charge ten hours to pull the engine and see what is wrong. Needless to say I won't be doing that (with them) so it seems it's time to call my mechanic friend and bribe him because no way in hell am I gonna pay $1200 just for them to pull it apart not including parts or outing it back together/in. Sounds like Charlotte will be at a standstill for a while :(


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So did they check the compression and perform a cylinder leakage test to determine its an engine mechanical issue?

Maybe your engine is covered by the extended 100,000 mile powertrain warranty?
 

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Yeah that's same price they wanted to charge me. it was 3 times that to have them replace the head.

They couldn't even get their scanner to hook up to my truck so they wasted my 1hr on trying to get it to read my truck.

had to pay for another 1hr for compression test.

leak down 55% cyl number 5 air heard thru intake manifold.

Then after that i took it to a local shop which their scanner connected an showed them if the truck was misfiring.

They said everything was fine so they did a case relearn on computer which i thought was the same as leaving the battery cables off... idk No codes yet.
 

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Discussion Starter #19
So did they check the compression and perform a cylinder leakage test to determine its an engine mechanical issue?



Maybe your engine is covered by the extended 100,000 mile powertrain warranty?

They did do a compression test and said it was great in that regard. And I didn't buy the truck new or anything can I still being up their warranty?


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