Chasing Rough idle

[davidxthree]

I’ve rebuilt the engine in my GN a couple of years ago and have been chasing a rough idle ever since. Have read all the blogs pertaining to rough idle and have done all checks. Scan master numbers are great.
Am wondering if inconsistent compression could cause this? Numbers are:
1-185
3-180
5–180
2-175
4-170
6-160
Cam is 206/206 roller. 62/62 turbo
55#low z injectors.

 

[Mr. Michael]

Just an opinion here, but your widest spread is still only 13% (185-160) In general you want that to be better than 16% (which yours are) so I dont want you to assume that you have something wrong in there. No doubt that 13% is a wide margin, but its not terminal. Your average of all six by the way is pretty strong.

Now... Would it affect idle characteristics on a six cylinder?.. Perhaps.

 

[Chuck Leeper]

55#low z injectors.

??
Not with a stock ecm unless it has the driver mod.

 

[davidxthree]

Yes it has the drivers added
I guess if it’s come to the point of really not knowing what else to check I’m going to pull the head and have it decked and a valve job. Possibly it can smooth it out some or might not.
If not of course the idle is livable but annoying. A friend of mine said let it growl. Maybe he’s right.

 

[Chuck Leeper]

Before you tear it apart run a leak down.

 

[davidxthree]

Pulled the head and found slight combustion leak on #2 and #6. Replaced head gasket RJC did retorque but no difference at idle. Compression in the cylinders matches the other side now. Guess I’ll just have to let her growl.

 

[TTA308]

Did you deck the heads when you rebuilt the eng ?

 

[davidxthree]

I had machine shop do a valve job

 

[davidxthree]

Are there any Buick GN in guys willing to take a look within the Houston Galveston area?

 

[davidxthree]

Just an update. I’ve since replaced the 10” 2800 to 3000 torque converter and gone back to the larger stock converter. With my set up the lag is a little more than I’d like. But the idle is a little better—liveable.
I guess this must point to quite an imbalance in the rotating assembly. So performance is a little tamer on initial WOT but guess I’ll have to live with it for now as I’m not sure where to go with it from here.

 

[jckcolarusso]

Get your injectors flow tested

 

[greeneyegi]

I'm a novice compared to the pros here
But maybe the fuel pressure at idle can be adjusted higher or lower for different results?
My car seems to idle much different at different settings.
what plugs and gap are you using?
One last idea is the maf,
I've been through every type and they all seem to have different idle characteristics.
The 85mm z06 with translator seemed to give me the best idle until I went SD.

 

[dynoman]

davidxthree , put your cars mods in your signature so we don't have to ask a million questions on what you have , and I'll say it again .... it will help us help you !!