Open discussion on the factory VAC boost control.... Continued**

[JMJNet]

I have gone to the TM last november 2010 and never look back. At the same time, I bought another one and give it to my Dad. He never look back.
In my case, I have a functioning vac system still but the TM is much better. MPG is relative, if you have the ghost as Tim mention, then MPG is worst than using TM.
In my Dad's case, his vac system is long gone being > 300K. He almost replaced his vac pump but I told him about TM. He drives around 50K per year and part of it in the mountain of TN, AL and GA border with a few switchback curve. He said, he is happier because he can go up the mountain easy because the boost hold up together with the transmission. Usually, when it gets to around certain speed up the mountain, the boost is gone. With TM, boost stay up there. IIRC, Tim (TD) explains that in one of the thread here and this is the actual proof of that explanation. Now, in the absence of a chip, we still hold the spring at 2.5 inches as suggested by Bill's instruction.

 

[Acesneights1]

Well CHB I see you haven't changed much in your attitudes as being cock sure on certain positions, I and a number of others are plenty capable of to diagnosing/maintaining them yet we chose to delete the vac system as you see in post 27 I got tired of repairing an aging system that left me stranded on more than one occasion, and on my burb I wanted the reliability of the TM on the family people mover, nothing worse than being on vacation than having a boost issue, minor or major or have the wife out getting groceries and vehicle won't get out of it's own way once you get used to it being able to quickly accelerate.

Im glad vac system works for you, and hope you live long & prosper with your endeavours with it, but not really a fair assesment to make the claim that those that choose to delete it are inept at maintaining it.

Oh JD (GMCTD) has no special affinitiy to the vac system, if it's more cost effective to repair it, do so, but when it gets to point ofbeing beyond economical repair he's in same camp as many of us, buy/make a TM setup.

What scenarios would constitute that IMO if the WG actuator bushing were shot and WG flapper can't seal, the WH actuator diaphragm was bad, or the vac pump itself were dead, all can be repplaced with new $$$ or used with same age issues potentially as what caused the initial failure.

All of this is moot once you go with ATT well discussed elsewhere so no need to go into that again.

Ahhh...Your BUSTED !!!!!:rofl:
"I'll call later to confirm..."
That means you have a secret pipeline to the man that inspires us all......your mission is to get him to come in on this thread now and do a famous GMCTD long way over the top colorful(and very very accurate) technical disscusion. His name has been used and he must now answer.....

 

[Matt Bachand]

I noticed a great EGT drop after installing my TM. Possibly a slight hit in MPG too. Boost comes with a cost. But I'll take lower EGT's at the slight cost of fuel, just as I'll take lower ECT's at the cost of fuel via fan clutch mod/Duramax Fan.

Around 200 degree drop climbing my main hills with 9psi boost, vs Stock boost which wasn't much.

I also like simplicity. Less things to fail the better IMO.

 

[chickenhunterbob]

Well CHB I see you haven't changed much in your attitudes as being cock sure on certain positions,

Not at all, I said a spring was a good solution for some...

When gmctd too the time to write and explain things, I thought it wise to pay attention, well, maybe someone is "busted", but may not be me, this is the text of the paper on wastegates, mechanical controllers, etc. that I recalled...

begin quote------------------->

The GM-X series turbo Wastegate is a simple flat 'flapper' valve on a flat seat.


The amount of actual control travel is minimal, as the entire port diameter is uncovered as the 'gate moves off-seat.


Most folks think full travel is required, becoming concerned when 'gate arm contacts and binds against inner exhaust elbow wall. The 'problem' occurs when installing a mechanical controller, additional 'problem' being mech controller does not allow full travel when adjusted per instructions.


Full WG travel is not necessary to regulate or dump Boost.


Attempts have been made to mechanically control Boost fade under heavy load, as up long grades, steep grades, etc., by increasing control arm length, adding stiff springs, doubling stiffer springs, etc, to little avail.


As exhaust energy - heat, volume, pressure - overcomes spring pressure, the WG does not blow open, dumping Boost - it begins to chatter, long and loud, sounding like a lawnmower engine as the 'gate comes off-seat.. As Boost drops, and exhaust energy, the 'gate seals, Boost increases, exhaust energy increases, and the loud cycles repeat.


Altho 'gate is violently chattering at that point, noone has reported 'gate damage or breaking.


Due to a deficient WG shaft bearing, the mechanically controlled turbos did suffer from early failures due to excess clearances.


Enter the PCM digital vacuum regulated Wastegate.


PCM controls vacuum to the actuator by varying the duty cycle of a pulse train to a ported solenoid valve - wide pulses = more vacuum, narrow pulses = less vacuum.


It does this based on rpm, fuel, coolant and intake air temps, Baro pressure, and manifold pressure.


~63% at idle, to ensure rapid spool-up, ease off the line, run thru the gears normally, and PCM maintains ~63% WG Duty Cycle.


Head up freeway entrance ramp, kick it, and Boost spikes up to ~10psi, WGDC drops to level needed to control at ~7-8psi - low as 20% duty cycle - vehicle moves up to speed.


Back off the pedal, hit Cruise, WGDC settles between 50-60% WGDC, exhaust energy drops, Boost settles in at ~4-5psi at speed.


Even at hard pull, Boost hung at ~8psi, WGDC at 20%, no chattering is heard, ever.


With the PCM digital control, WG is always bypassing to regulate Boost pressure.


At 15psi Boost, no chattering.


At 20psi Boost, no chattering, just smooth control. And, at 20psi Boost, Exhaust Back Pressure is outta sight, but no chattering.


Indicating minimal travel, controlled bypassing.


In 'limp-home', or backup, mode, no-to-little Boost can be achieved, indicating 'gate travel is uncontrolled.

Edited by: gmctd

 

[great white]

Alright guys.

Please, enough with the vacuum vs TM argument. That's not why I started this thread.

Let me clearly state the purpose of the thread as I intended it:

I only want to discuss how the vacuum system works (and how it goes about it) so I may better understand it.

I'm in the pursuit of knowledge here, not advice on what to do with my truck, nor why or what you did with yours.

GMCTD's quoted post is the kind of info I was hoping to draw out.

I've seen you guys go around the "TM better than the vacuum system" pole many times before.

Please don't do it here anymore. Start another thread if you wish, but please stop doing it here.

Thank you.