[hbbrewer]

The car has a miss between 40 and 50 MPH, where to start looking. 76,000 mi, going to change fuel filter.

 

[godsdiablo]

Check engine light flashing? Could be coil pack or spark plug

 

[hbbrewer]

no lights at all, just got the miss..

 

[godsdiablo]

Then how do you know it's miss firing? You feel it at 40-50 spuddering?

 

[hbbrewer]

Yea, that's what its doing.

 

[godsdiablo]

Coil pack, which one I'm not sure. The check engine light usually determines that, maybe someone on here can shine some light in on this I haven't ran into that problem on my CTS yet

 

[hbbrewer]

Well I finally got to drive the car, It is not a studder or a miss, It is like a klunk, it does it just ever now and than, and the times it done it was on a hill, kind of like when it would downshift. Drove it about 150 mi sunday and it done it twice. No CEL' at all. Give the car to my Grandson, about two months ago. And he was the one telling me what it was doing. But the car runs and shifts smooth, just has the klunk sometimes. When he called me he was worried about it, and quit driving it till I drove it. Does anyone else have this noise sometimes??? thanks!!

 

[CTSM]

If you scan for diagnostic codes and non are returned, I would start by inspecting the drive train.
What's the mileage on the car?
What's the state of the front differential bushing? When it fails it usually results in a clunk upon downshifting or WOT downshifting.

Upon failing the items below usually cause a vibration not a clunk per say but worth checking anyway while under there just in case.

- The rubber flex disc couplers front and back of the drive-shaft, look for cracking and tearing at the bolt locations.
- The drive-shaft carrier bushing and bearing, inspect the rubber condition.

Also this might be a good time to check the diff fluid and change it, if the old fluid is 8 years old in there might be a good time for it.

Those are the easiest things to check first. If all of the above look OK without cracking or disintegration, only then I would turn my attention to the trans and engine.

Speaking of trans and engine, it's not a bad idea to change the trans fluid and filter if that never was done before and the car is at 100K+
And if the car is high on miles and still on the original plugs, it's a good time to change the plugs and inspect the coils and coil boots.

And concerning the fuel filter, well it's not like the engine was starved of fuel, then it would have most probably stalled or something. I change mine every 60K miles, however the fuel filter in the CTS can easily last much longer before needing a change.

 

[cswimc]

Well I finally got to drive the car, It is not a studder or a miss, It is like a klunk, it does it just ever now and than, and the times it done it was on a hill, kind of like when it would downshift. Drove it about 150 mi sunday and it done it twice. No CEL' at all. Give the car to my Grandson, about two months ago. And he was the one telling me what it was doing. But the car runs and shifts smooth, just has the klunk sometimes. When he called me he was worried about it, and quit driving it till I drove it. Does anyone else have this noise sometimes??? thanks!!

I had the same exact problem with the car making a 'Thud' or a 'Klunk' and it was the Rear differential bushing (front). I was able to diagnose it by taking my car over to my buddy's house to check it out. He has a car lift in his garage (not the norm), and we we able to shift gears and watch the rear differential 'pop' up and down when shift from drive to reverse. I bet this is your problem as the front bushing is known to wear out. This isn't my video, but it may give you a good starting point:

If it is this, and the front rear differential bushing is worn out causing the klunking noise, you can get a replacement here: http://www.revshift.com/product-p/dbf-cts.htm

 

[Static1120]

I had the same exact problem with the car making a 'Thud' or a 'Klunk' and it was the Rear differential bushing (front). I was able to diagnose it by taking my car over to my buddy's house to check it out. He has a car lift in his garage (not the norm), and we we able to shift gears and watch the rear differential 'pop' up and down when shift from drive to reverse. I bet this is your problem as the front bushing is known to wear out. This isn't my video, but it may give you a good starting point:

If it is this, and the front rear differential bushing is worn out causing the klunking noise, you can get a replacement here: http://www.revshift.com/product-p/dbf-cts.htm

I think this is the best shot, and I also think this is the issue you are having. My car aswell clunks and kicks when changing gears from park to reverse and drive. Sometimes the kick is so hard it feels like I got rear ended. I need to take a look at these bushings soon.

 

[hbbrewer]

The car has 78,000 mi, will check the bushings this week end, And get trans filter and fluid for change. And also check the drive shaft. Will put it up on stands this weekend, and check it out.