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I would probably not do it just to prove a point, but I do believe the VVT has problems.

Interestingly, the MAP sensor may well be culpable. It's new role in the LLY, is as a feedback sensor. It was never intended for this role, and tolerances may well a real issue for various LLY's.

Can 21 vs 25 psi be the difference between overheating, and not overheating? Yes.

I took one overheating LLY vehicle that was running "too much" boost, and fixed it by removing the boost enhancement, no other changes. Then I started thinking:

What if many vehicles were overboosted?

I have read about a few instances where the guy who had an edge attitude (LB7) was reporting 10 psi on the display. Then found it was actually 21 psi (normal), turns out the MAP sensor was bad, heat damaged. But other than noticing the display was off, on the LB7, there were no consequences, and were it not for the Attitude, he never would have had cause to investigate.

LB7: The MAP sensor is a simple reporting sensor, no induction related ECM decisions are made with it. The boost is designed by turbine gas flow, and merely capped by the wastegate. It's compressor innefficiency is hardware limited.

On the LLY (VVT), by contrast, this is not the case. If there is a MAP sensor anomoly, it appears the VVT will just produce more boost till the desired MAP sensor return volatage is achieved. The reading on the attitude display (or any scanner for that matter) will be no help in identifying the problem, because it will always read 21, even if actual boost is 40 psi. This is unlike the LB7. Plus, there is no software efficiency degradation limit, and certainly no hardare limit, the wastegate is gone. In fact, the VVT has, in my opinion, serious efficiency erroding feedback loops, and nothing to safeguard against them.

If you have a LLY MAP sensor damaged by heat, and it is reporting 10 psi when the plenum is seeing 21, guess what? That 21 psi reported in the attitude display, might actually be 32 or more, which the turbo is glad to produce unchecked. AND THAT IS AN OVERHEAT, the stack cannot handle that much heat, as much as (5) five-bedroom heating and cooling units worth, from the CAC alone. Reports of unusual or constant fan without load is also an indicator, there is heat, but where from? The CAC.

I started thinking more. "isn't there LLY comparator tables that issue a MAF code, if mass air flow doesn't mate with boost, correlated within certain tolerance parameters?" There is. And I adjusted them so that the ECM would expect to see really low MAF numbers when boost was high. For example, I set it to read 20 lb/min of air when boost was 25 psi (in actuality, 25 psi produces around 50-60 lb/min of air, so there is a clear mismatch). To my surprise, I got NO codes, after running around for 20 minutes. Then again, you need 100 occurences of failure to set the code. I can change that to 1 and retry

I started thinking more. "if no code results from overboost conditions due to a bad MAP sensor, then all these LLY's might be overheating, without the telltale cause showing up".

Then from a different angle "what if MAP sensor voltage scaling changed with sensor temp itself?" IOW, what if, as the sensor itself heated up, it's scaling became unreliable with too low a return voltage? We would never find the problem, because it would fix itself every day.

I am still playing with this, but more can be found about this and other real VGT forced induction issues HERE.

I really like the VVT for its other virtues. I have finally gotten Ross to fix the ECT boost issue (thank you again Ross), that allows us to use boost as an artificial load, and I am able to warm up the truck much quicker in the winter, for example, and have that boost disappear at 170 ECT.
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