Black8Banger

The car is a 2003 Z06 with a fender mount twin turbo setup that is SD tuned.

I made a test hit from a 60mph roll. After the hit, I let off the gas and the car shuts off. It restarts no problem but will not idle at all. The boost gauge usually reads about -10 but was now reading in the -2 range. I’m thinking no biggie, probably just blew off a vacuum connection somewhere. I limp the car home and start checking it out but I cant find a thing. The next morning I come out and start the car, it starts just fine. Soon as I backed out of the driveway, idle tanks and the car tries to shut off, just as it was the day before. Over the past few weeks I have checked everything I can think to check.

I pulled apart all the vacuum connections and checked them, bought a smoke machine to look for leaks, used parts cleaner to check for leaks (while someone kept the car running), went through a series of disconnecting and blocking off different, and at one point, all vacuum connections at the intake manifold and have found zero leaks.
I tested the BOV to make sure the diaphragm wasn’t busted, checked all the couplers on the cold side piping (just in case), checked the fuel injectors with soapy water to see if they were leaking at the o-rings, checked TB, intake manifold and exhaust manifold gaskets, replaced the TB (thought maybe the TPS was bad) and the MAP sensor….and after all of this still no change. Also there are no codes or SES light.

I don’t think its relevant but since most people ask, the boost controller setup is as follows: line from compressor side of each turbo to the bottom side of respective waste gate. Top side of each wastegate goes into a T and then to 1 port on the boost controller. The middle port vents to atmosphere and the 3rd port receives CO2 from a bottle in the trunk.

I did log the car on startup. Cold starts normal with AF around 15, boost gauge reads -10. It runs fine for about 30sec-3min and then BOOM, idle tanks, boost gauge goes from -10 to -2 and the car tries to shut off. In the log you can see the MAP value go from about 53kPa and jump to a max of 94kPa. I can make the car idle by forcing into closed loop and it will eventually idle on its own but the boost gauge still reads about -6 with MAP kPa settling around 73kPa.

Of course I don’t want to keep throwing money at guesses on different parts so I need someone with a better understanding of this car than myself. I’m convinced that it is not a vacuum leak. At this point my last guess is something electrical but I don’t know where to start. I cant think of a sensor that would cause the issue other than the TPS or MAP sensor. I have replaced both and the issue remains.

Anyone have any guesses?

romandian

not sure how it can idle at 73 kpa.

Black8Banger

Haha, "barely" is how I would say it idles at 73 kPa.

ysb02

So it idles fine cold but not after it warms up?

Milan

idle airflow table...go multiply the whole thing by 1.10 and let me know if fixes it....sounds like you need to run russ k idle config...search for it

Black8Banger

For the most part yes.

Its really odd to me this all started after a WOT pull. The car has been running fine so I struggle to say its in the tune but on the other hand, I cant find any mechanical issue with the car.

Milan

You are right...it's probably not the tune. Keep checking everything you already checked until the car fixes itself. That's the approach I would take...

Some people just can't be helped

Black8Banger

No need to be a dick. I was just about to post that I tried your suggestion and it didn't work, but thank you for your input.

ysb02

If it ran fine long before and only started to do it after a pull it's probably mechanical. Can you bypass the boost controller and just run without it? Just need to start ruling things out

Black8Banger

I thought same but the way my setup is, the only thing the boost controller does is regulate CO2 to the top side of the wastegates.

Black8Banger

I logged the car again this morning. The log didn't record everything correctly so I had to reset the log shortly after starting. The car started just fine.
After the car had been running for a good minute or so I stopped recording fuel pressure and started recording the AF gauge and boost gauges inside. While doing this, the issue presented itself! You can see it in the log when the MAP value jumps up, vacuum tanks to -2 and STFTs go to crap. The car saves itself from shutting off but the vacuum reading on the boost gauge ends up back at -6 (opposed to -10 when normal)

Maybe someone with more knowledge than myself can find some clues in this video and corresponding data log??

Not the best video but it corresponds with the attached data log file

ysb02

Did you try running it in open loop yet to see if there's a difference in behavior?

Black8Banger

It doesn't stay in OL very long on the initial cold start but in this case it ran fine OL and was fine for a while in CL. When I go to restart it now, after the motor has gotten warm and the issue has presented itself, the issue will continue in OL.

It only starts fine on a true cold start, as in sitting over night. That iron block holds in the heat for a long time!

Here are how the codes were set from the tuner (I skipped a few that don't apply):

stevieturbo

With so many errors, that would shout as a wiring issue, whether a sensor ground, 5v supply, break/short of something related to those.

Investigate that, and test/monitor all sensor feedback as you check through the loom.

Possibly a faulty sensor on that circuit could affect everything else on same wiring.

Vetteforplay

I would do a compression test on the motor to rule out somthing internal.

Black8Banger

stevie, my thoughts are leaning towards a wiring issue as well which is a nightmare as electrical is an area of weakness for me. I do notice that in my log, the very first reading to start going crazy was the MAP sensor reading. Since I just put a new MAP sensor in, I don't think it would be the sensor itself. That may be the wiring I need to check first.

vetteforplay, I will try this before chasing down any electrical issues.

Black8Banger

Did a compression test this morning...

8: 145 7: 150
6: 145 5: 150
4: 90 3: 145
2: 135 1: 145

I'm gonna do a leak down test on #4 this afternoon and see what I come up with.

Also going to check the torque on those head studs since a shop just replaced the head gaskets for me.

Black8Banger

Pretty sure I found the issue!
Did a leak down test and the I couldn't even get #4 to pressure up. Took the valve covers off the check around again. I must have missed it the first time but the outer spring on the intake valve of #4 cylinder was broken.

Going to order new springs and see if that was indeed 100% the issue.

Z06PSI

Hope that was it Josh.

stevieturbo

Strange one that it would cause an intermittent problem...and so many errors ?