QM600 cam in 2008 Z06 wants to come back to life after shutoff

[DSteck]

Fuel trims wouldn't support that though, and there is no degradation of idle quality that is usually present with a vacuum leak.

I'm finding it hard to believe it isn't directly related to the blade opening back up to 20%. Ive gotten reports from other people that have had this same issue pop up. I'm mostly looking for a way to control the blade during shutdown. I haven't seen this issue on 06s which makes me question if something is different between 06 and later operating systems. I don't have access to an 06 right now to test this though.

[IDRIVEAG8GT]

Oh! So (pardon my ignorrance) You want the throttle blade completely closed upon shutdown until the next key on cycle? Try the thumbnail:
This may be a crude method to control it but if the TB slams shut fast enough it will be more effective in making it die before the TB opens back to default.

[DSteck]

The throttle blade is shut to 3% the second the key is turned off, so I don't know if adjusting the final airflow table would really do anything. Bottoming out the minimum idle airflow table is not what I want to do, especially if the owner accidentally bogs the engine with too quick of a clutch release or something.

[IDRIVEAG8GT]

Just coming up with ideas....

[DSteck]

I hear ya. I'm just explaining my response to them.

The big kicker is 06s don't do think. There has to be control somewhere regarding the throttle blade position during shutdown and how long it stays at that position. These are all very high static compression cars with DCR around 9:1.

[IDRIVEAG8GT]

What if..... You simply idle it down a bit.

[DSteck]

Then the car will have poor vacuum at idle and recovery issues. I don't want to bandaid what's happening. If I idle something at 1200 I should still be able to shut it down.

[IDRIVEAG8GT]

I know that, but here we are dealing with High Compression and a big cam. Because I have never heard of a plausible solution to this I can only come up with relatively crude solutions. Unless, again, you reduce the timing a bit down low.

[IDRIVEAG8GT]

Hey Steck, can you set the throttle opening limit at 3% for the low low number Kpa on the MAP sensor when its dying? Therefore the throttle can't open at all at super low Manifold Pressure until you key it on and the TB would go back to default.

[DSteck]

MAP shoots towards barometric pressure pretty quick after turning the engine off, so I think that's out.

[IDRIVEAG8GT]

:/ I once saw a table in the T/C section that you could control ETC opening versus RPM, and it would most likely work if edited but when dying the T/C light would illuminate.

[imaboa]

I've got the exact same problem with an 07 Z06. Stock Intake, Stock Airbox, Stock TB, Stock Injectors, and a decent size cam.

I've been racking my brain for days trying to figure out whats causing it.

[imaboa]

I'm wondering if it has anything to do with the decel fuel cut off.

The log says the injectors are operating a a 1.9-2.0ms pulse width while the rpms are coming back down? Is that info in the log valid, or will it not show a 0ms pulse width?

Fuel has to be coming from somewhere in order for it to keep firing. It wouldnt matter what the throttle plate position was if there was no fuel in the cylinders.

Any thoughts?

[DSteck]

Show me what PID it is in the list and I'll see what I can do.

Despite showing a pulse width, I'm pretty sure the injectors do indeed shut down. The fuel that's in there is pooled up from idling. Like I mentioned, if you stab the gas pedal and immediately shut off, it will not rev back up when the throttle opens again.

[IDRIVEAG8GT]

dsteck or imaboa can you log the L-terminal?. if so i would like to look at that.

+1 Great idea.

[DSteck]

The MAF calibration is not bad. We can take that off the table.

[IDRIVEAG8GT]

Can you control the fuel pump when idling down on this Z06? You know, variable state?

[Christian GM]

I'm also interested in this issue.
I'd like to know what solution you will find out

bye

[DSteck]

FYI, worked on a cammed Procharged Z06 yesterday... The car is a 2006. When you shut it off, the throttle stays closed.

[IDRIVEAG8GT]

Can you please post up this tune for reference (If your customer doesn't mind?)