2000 4.8 5speed, vortec v1. I just bought this truck and trying to work out the bugs. When you put the a/c it causes the motor to miss or stumble when im guessing the compressor kicks on. Its like theres alot more drag on the motor for 1 second and then it runs normal for a 30 seconds and does that little drag blurp again. Im guessing its in time with the compressor kicking on. You can actually hear the exaust sound change as if the motor had been but in to a more of a load for that brief second.
When the a/c in off i don't notice anything. Is there just too much drag on my serpentine system due to the supercharger when the a/c compressor kicks on? And thats what causes the one second load feeling on my motor. There are a few codes. One for the cat..no cat. The other is running rich in both banks. I did have a missfire in the 7 cylinder. I haven't got that code in a while though.

 

There could be something in the tuning for a/c idle-up operation that needs to be adjusted...

 

IIRC the computer pulls timing when the a/c kicks on for a sec??? my truck does the same thing and its N/A.

 

Mine does the same thing and it's not normal. It has nothing to do with the tuning. Engagement of the compressor should pretty much be transparent.

I don't know anything about A/C compressors but I figure it's slowly seizing up or something. I need to get the freon levels checked as well.

 

Well i've been wanting to get a new tune anyways. I was told by the previous owner that it had been tuned by 3 different people. Someone very well could have not known what they were doing.

 

When the ac kicks on does the truck run at the same rpm as with the ac off?

 

I'm not sure that it does change rpm. I'll pay attention tomorrow and see.

 

I checked for any rpm movement when i turn the a/c on. When i am sitting in my driveway and turn the a/c on the rpm's don't fluctuate at all. You would never have any indication the a/c was on other then cold air and the a/c light. So it doesn't idle up or anything when i turn the a/c on.

 

If you are using efi live, you need to work on the a/c airflow. What are your cam specs?

 

It has allot to do with the tuning... The PCM has tables dedicated to just this, it smoothes the transition between ac on an off. Hell a incorrect inj voltage offset table can cause that from the temporary change in battery voltage when it engages. Also the reason in the tune the idle speed can be adjusted to rise with ac engagement. I would also guess his running airflow table is off some.