Very perplexing tuning dilemma..........

[FreddyG]

I had an A&A Vortech SQ V2 blower kit put on my 2001 Corvette and here's a quick description of my problem. I hope that you guys can help. My tuner is using HP Tuner, so I can't view the file yet.

The car is going fat at 3400 rpm with 18° of timing, but when it runs with
16°'s it's fine. It's going from commanded 12:1 to 11.3:1 at 3400 rpm. He said that he'll probably leave it at 16°'s and just command the AFR to 12.1:1 to make up for the lost 2°. At 3400 rpm/18°, he said that he was getting 2° kr, which I thought was weird because wouldn't getting more gas stop knock? He was still getting slight knock at 16°., Does this make sense to you guys?

I hope that I explained it well enough, but if I didn't, Please tell me.

Thanks in advance!

[dfe1]

Something really strange is going on-- either the tuner doesn't know what he's doing or the data being logged isn't correct. Not even HPT is that far off.

[FreddyG]

Something really strange is going on-- either the tuner doesn't know what he's doing or the data being logged isn't correct. Not even HPT is that far off.

The tuner definitely knows what he's doing, and as far as I know the data is correct, but I can't figure out why changing timing effects AFR.

Either way, I agree that something strange is going on.

[Biggsy]

The tuner definitely knows what he's doing, and as far as I know the data is correct, but I can't figure out why changing timing effects AFR.

Either way, I agree that something strange is going on.

I have read your first post a few times now and still don't quite know what you are saying

Is the change of timing affecting the AFR or is he changing the AFR to compensate for the timing? (chicken or egg?)

Cheers,

[11sprocket]

A few weeks ago, I had a problem where the commanded AFR would spontaneously drop to 10.x. There was nothing in any tables which should have caused this, but eventually I guessed it might be the catalytic converter protection kicking in. I raised the cat protection temperatures and the problem seems to have gone away. I'm not totally convinced, though, but it might be worth a try.
Someone else may like to explain how the cat protection works and what it does (please).

[FreddyG]

I have read your first post a few times now and still don't quite know what you are saying

Is the change of timing affecting the AFR or is he changing the AFR to compensate for the timing? (chicken or egg?)

Cheers,

Hi Biggsy,

I apologize because sometimes I have a hard time putting my thoughts into words, and this would definitely be one of those times. Your last sentence is the question that I'm asking, but would like to know what is causing the AFR to change because it doesn't make sense to me. Timing shouldn't have an effect on AFR should it?

A few weeks ago, I had a problem where the commanded AFR would spontaneously drop to 10.x. There was nothing in any tables which should have caused this, but eventually I guessed it might be the catalytic converter protection kicking in. I raised the cat protection temperatures and the problem seems to have gone away. I'm not totally convinced, though, but it might be worth a try.
Someone else may like to explain how the cat protection works and what it does (please).

Thanks for the reply 11Sprocket!

I'll ask the tuner if he looked at that or maybe I'll just throw on my off road pipes and shut COT off.

From what I understand (and Please correct me if I'm wrong) is that COT works like this:

Your cats must heat up to do their job, but can get too hot. So to compensate for this, the computer throws extra fuel in the tune (fattens it up) to cool the cats down. This is because a richer mixture runs cooler because the extra fuel slows down the burning process. Once again, this is how I understand it. Maybe one of the More knowledgeable members can/will correct me if I'm wrong.

[Biggsy]

Ahhh now I understand your first post! "fat" meaning "rich", makes sense to me now
If one of my mates said his car was running fat today, I would think he was saying "running really well" or "running its best". Same word meaning different things!!
Cat protection is a possibility.
Engine or piston protection mode will make it run richer.
There are some PE modifiers based on IAT and ECT, being supercharged these might have been hit.

As for timing having an effect on AFR, I don't really know. It shouldn't affect the commanded AFR but as to the actual AFR, mabe detonation can gives a less complete burn causing a richer measurement (Just a thought).

Cheers,

[FreddyG]

Ahhh now I understand your first post! "fat" meaning "rich", makes sense to me now

Cat protection is a possibility.
Engine or piston protection mode will make it run richer.
There are some PE modifiers based on IAT and ECT, being supercharged these might have been hit.

As for timing having an effect on AFR, I don't really know. It shouldn't affect the commanded AFR but as to the actual AFR, mabe detonation can gives a less complete burn causing a richer measurement (Just a thought).

Cheers,

Thanks for the input Dave! I Appreciate it!

This has me stumped and I'm pulling what little hair that I have left out!

Which PE modifiers are you talking about hitting with the blower?

Thanks again!

[Biggsy]

{B3617} PE Modifier based on coolant temp
{B3641} PE Modifier based on Intake Temp

I was thinking, because supercharger is compressing the air, that generates heat (how much is dependant of the efficiantcy of charger and the amount of boost, and if you have an intercooler) so the intake temp will rise.

Also, because the motor is under more load than usual and working harder, the engine coolant temp will rise. Also depending how long he had been runing it on the dyno beforehand and how good his fan is setup infront.

Cheers,

[Biggsy]

I edited post 7 too