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2005 CTS 3.6L
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59 Posts
Discussion Starter #1
Cylinder 1 on my 05 CTS 3.6 is misfiring

I've changed the following:
Spark Plugs
Coil
Injector
Injector Wire​

After changing all of this and still seeing the problem, I tried swapping the coil and injector with another cylinder to see if the problem shifted, but it's still misfiring on cylinder one.

Now I'm thinking it might be ECM. While the car is running I can sometimes hear the misfire through the intake. This leads me to believe that the computer is just firing that cylinder at the wrong time.

Has anyone had any experience with an issue like this? Is there anything else I can try before buying and programming a new ECM?
 

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2005 CTS 3.6, 2016 Malibu 1.5T
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359 Posts
My knowledge is very limited but, maybe try checking the grounding? I know when my car had misfire problems it was a recommendation I got to check out, you have gone trough the list, give the grounding a try.
 

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2005 CTS 3.6L
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59 Posts
Discussion Starter #3
Yep, everything looks good as far as I can tell.

Still going to go over it again to make sure though.
 

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629 Posts
Do a compression test on 2,3 then check one and compare to number one. Also if you have a volt meter make sure your injector and coil are getting the right voltage. Like mentioned above a bad ground could be the cause, check all the wires though. There should be constant power, ground, and signal wire. Theres probably a few more wires and I'm not sure how many because it's raining and I don't want to go look, but you'll have at least three. And checking those grounds with a meter for continuity is your best bet.
 

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2004 CTS luxury package
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300 Posts
Try this: There is probably at least one gas station in your area that sells gas with NO ethanol in it. Run a tankful of it in your car
and see what happens.

It has made enough of a difference in my '04 CTS that despite the significantly higher fuel costs, I will not
put gas in my car that contains ethanol unless I have to as I'm not near a no ethanol pump when I run low, and even then
I will only put enough of that garbage gas into my car to make it to the good stuff.

I had a persistent failure to fire on cylinder 3 which absolutely disappeared with the first tank of good gas.
Even when forced to run garbage gas briefly since then, the misfire has not reoccurred.

There is also a substantial difference in overall performance. I'll never go back to ethanol gas.
 

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2005 CTS 3.6L
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59 Posts
Discussion Starter #7
Thanks for the suggestions guys. I took it to a shop and they put a smoke machine on the intake and blew smoke through the engine. No leaks. They also hooked up a scanner and said everything looked fine.

They said they jiggled around all of the wiring harnesses and when they started it, it wasn't misfiring, so it might just be a bad wire somewhere. I've driven it a few times and it hasn't misfired, so if it happens again I'll have to bring it back and see if they can find the bad wire.

They also said it's still possible that the ECM is bad but I'm hoping it's just a bad wire/connection somewhere.
 

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2005 CTS 3.6L
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59 Posts
Discussion Starter #8
Another update. The misfiring came back. I said F*** it and bought an ECM and had a local shop program it. It's been a few days and it hasn't misfired once.

ECM was the issue!
 

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2004 CTS luxury package
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300 Posts
Don't toss out the old ECU if you still have it. There are places that rebuild them. You might want to have the original rebuilt, and returned to you,
to have on hand as a drop-in replacement if the new one fails. One you wouldn't have to reprogram.

What WERE they thinking when they decided that bolting a heat-sensitive computer to the side of a freaking ENGINE would be a good idea? Electronics last longest when they're kept cool!
 
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