v4 mode, how much vacuum

[flyingfool]

i just did some testing with my obd2 scan tool  and monitered my vacuum in v4 mode while going down the highway. Was wondering what the factory manual calls for being in spec?

 

i'm producing 3-5 inchec of vac at 60 mph on 4 cyclinders. i can see if you had a bad check valve in the brake booster that you can easily loose all brakes going down the highway.  : 0

 

any gm techs on here know if this is correct  or do I need a new vacuum pump?

[cossack]

If the vacuum is driven off the belt, why would it matter how many cylinders are turning that pulley?

And doesn't vacuum only reduces the bake pedal effort?

 

[silveradosid]

intake vacuum has nothing to do with your brakes, the vacuum pump provides the vacuum for the brakes

[It's Tim]

Playing with your OBD2 scan tool while driving 60 mph... wait for it....

[Thomcat]

Had one in my '16.  All DI engines including the one in my '18 Traverse and '19 Silverado exhibit low vacuum that is insufficient to supply brake vacuum levels. A mechanical belt driven pump and electric backup supply sufficient vacuum under all conditions.

 

The belt driven vacuum pump in the former gen Silverado was under a TSB for premature failure, not a recall fix (may have been a recall in Canada?) Claim was made that lack of oil changes accelerated pump wear. GM would replace the pump only if a problem was encountered and if not replaced had continued coverage  to 100K miles. But, GM has amended it to a formal recall in the US to rectify the possible loss of vacuum assist; however, instead of continued replacement of the mechanical pump,  now GM recall calls for a kludge software fix by reprogramming the secondary electric vacuum pump to run more frequently to compensate for a weakening/failing mechanical pump. That was all the excuse I needed to say bye bye to my '16. No recall to the new systems employed in the new gen.