Ok everyone, I need some advice. We have been doing some street driveability tuning, but have seemed to have developed an issue. The car has started to occasionally burp the blower when hitting the rev limiter. I'm new to tuning but I'm working with a seasoned vet. I noticed that on the factory CTS-V tune, Chevy uses fuel cut for the limiter intervention. My guy has always used spark cut. His reasoning being you don't want to create a lean situation under high load and boost (seems completely understandable). What do you guys think?

The biggest issue is when it does burp the blower, the car goes into limp mode only allowing idle until throttle re-learn is done. My guess is that the pressure turns the throttle blade which trips the safety. The first time it happened the throttle blade actually got stuck closed and shut the engine off. I had to use my thumbs to "pop" it free. This almost got me killed on the freeway yesterday! The car stayed running (sort off) rough idle only, no throttle. But I'm guessing this is because the blade didn't get stuck closed.

6500 rpm rev limit, 6400 rpm extreme resume, 225rpm hysteresis. Ignition kill active, fuel cut deactive.

 

Here are the codes.

 

Fuel continues to be injected... cyls are wet, then put the spark to those wet cyls and you can "sneeze" the blower, blower drive, belt.
Maybe spread the limits a few rpm... try maybe add 50 at a time?
Try a fuel cut and see how it behaves.

 

Fuel continues to be injected... cyls are wet, then put the spark to those wet cyls and you can "sneeze" the blower, blower drive, belt.
" I noticed that on the factory CTS-V tune, Chevy uses fuel cut for the limiter intervention".
No fuel = no load. No combustion= no boost. Chevy engineers get most things right.
Try a fuel cut and see how it behaves.

 

Yeah I've read where a lot of guys cut spark like 100 rpm before cutting fuel.

The flip of the coin is, I also read that GM cuts alternating cylinders, in the firing order. So the possibility exists you could arrive at a cylinder that is 1 of 4 combinations.

A cylinder who's cycling off fuel, but still has spark

A cylinder who's cycling off spark, but still has fuel

A cylinder who's cycling off fuel, and spark

A cylinder who's still getting fuel, and spark

So do you think setting the on/off rpms the same eliminates or exacerbates this?

 

Looks like the throttle body is getting sucked shut to me and/or running into diagnostic tests that haven't been set properly. As always without a tune actually being posted, it's just a guess. What throttle body is being used and what computer/OS?

 

Id be happy to share the tune and data logs, I didn't know if that was cool or allowed.

LS-7 stock throttle body, E67 using HP Tuners on a Panasonic Toughbook.

 

When he said computer/OS, he meant the E67 computer and whatever the Operating system number is that you are running on that E67. The OS shows up in hptuners under edit, then calibration details. However, posting the tune and datalog will show all that anyway.

 

Did I do it right? First time uploading tunes and logs.

 

That's not how it works, it never does a partial pulse for fuel it's all or nothing. A spark cut can be a lot more abusive as the fuel mix in the exhaust that was sprayed from a previous event can ignite when it kicks back on. Leave it how GM does it.

The getting stuck and having to use your thumb to pop it free is a big problem and probably THE problem. That's not normal and sounds like a throttle body problem ultimately. You do have some other problems in the tune however and I've attached a revision, you will need to do a Write Entire to make sure it uploads the slave segment part of the tune. These changes are commonly required when cranking up the boost so even though it won't fix a physically stuck throttle body blade it's a good thing to change.

 

So you are saying disable spark cut, enable fuel cut, what about the throttle cut?


Thank you! I'll put these in the compare and read through so i can learn. I'm only confident enough so far to make small changes in the timing (low octane, high octane and alcohol tables). I tried to adjust throttle followers and just got lost in the over laps.

 

post the tune. You’re likely hitting an airlflow limit.

 

Post #9 buddy.

 

Thanks for eveyones input. Switching to fuel and spark cut solved the issue. Been months with no blower burps! XD