VVT Start Stall?

Could a bad VVT system cause a start stall, from my understanding VVT is only valve overlap so while it might reduce power I have never seen an engine not run due to bad actuators. Has anyone ever seen a car not run due to bad VVT. I'm dealing with 2009 Chevy traverse with 3.6 gdi man I can't get to anything in this car it's all covered up

Does it run if you tap the throttle as it starts? These electronic throttle body are very sensitive to carbon buildup and a good carbon cleaning cures the stalling on startup (sometimes it will need to relearn to idle correctly after cleaning)

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I can't keep it running more than couple seconds, I'm thinking timing is off, I haven't done Cam crank but injectiin timing compare to in cylinder pressure was dead on

To fully answer no matter what I do I have tried giving throttle, no throttle, tapping throttle, nothing I do will make it run more than 5 sec Max, usually it dies real quick (start stall), it has a compression problem as relative compression had High and low peaks

Hmm well to answer your question I don't believe the vvt system is causing your problem I've had them run verry verry bad but not a start stall . How does it run for those couple moment that it does start is it misfiring real bad? Have you disconnected the maf sensor to make it load factory spec fuel tables?

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I didn't disconnect MAF as most of the time it's a crank no start, and it u crank on it long enough u get get it to start stall, it runs rough have misfires on 2,3,4,5 cylinder tell if that ain't weird, and relative compression was all over the place some high some low so definitely low compressiin problem I didn't think VVT would cause a no start/ start stall, with this gdi it's a pain to take coils out the front , I'm done Cam crank correlation Thursday and incylinder pressure,

Actually it's easy enough to get plugs put of those motors there's only a hand full of bolts holding that upper intake down (I think 8 total) and there all easy to get to

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I hope you are referring to the gdi when you say it's easy to pull the plugs I'll do it tnite, does anyone have a Cam crank correlation waveform for 3.6L

Yes the 3.6 gdi is easy to remove upper intake I believe it was 8 bolts 2 of which are down low by the throttle body but all are easy to get to, it takes 10 mins to get intake off then coils are easily removed to get to plugs , I'll check and see if I have a known good in my modis tomorrow if not Tyler may have 1 hiding in his files to compare to

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I'll see if I can dig up a known good cam/crank. In the mean time, any codes? These are usually very good about setting correlation faults if the chains jump/stretch/fail. Likewise, if you had an actuator stuck, you'd get a code.

Ben wrote: Hmm well to answer your question I don't believe the vvt system is causing your problem I've had them run verry verry bad but not a start stall .

Totally agree. Even vehicles with stuck solenoids or actuators will still start and idle with a little throttle work. I'd be very interested to see the relative compression waveform, as it sound like one bank is completely dead. :ohmy:

This video is definitely relevant, if you haven't seen it already:

The only other codes were O2 heater codes and cat codes maybe I have plugged exhaust, I only ran basic test Tuesday and it's been to cold lately, I watched that video below but it isn't the gdi or it's just old as the crank is analog and this 2009 traverse is digital, ill get ya the answer, or more waveforms if I don't solve it Saturday.

Check out the post of codes and let me know how you would go about this does the O2 codes give you any direction in a start stall

Personally, I'd ignore the O2 and codes for now. I wouldn't be surprised if you found a bad sensor, or the wiring to it, but you can chase that later. The catalyst code might suggest a problem IF the catalyst has broken up or plugged.

I'd suggest checking the history misfires next, in the Misfire data list. See which ones have high counts, and which ones are just getting incorrectly counted by the monitor. Knowing that might help you put together a better picture of the problem.

I'd also suggest revisiting the relative compression waveform. Disable the fuel so it doesn't attempt to start, otherwise you'll get wacky waveforms. I'm thinking you're gonna see three low cylinders.

The red relative compression is inverted. All three of them look different, I wonder if the Cam actuator locking pin broke and it's flopping around.i really need some know good cam crank waveforms.

Also check how the timing changed from being slightly retarded to slightly advance on those 3 cylinder pressure waveforms that's a square wave so firing event