Jump to content

v4 mode, how much vacuum

flyingfool

By flyingfool
in Troubleshooting & Recalls

Recommended Posts

flyingfool Senior Enthusiast

flyingfool

Posted
Posted

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 Enthusiast

cossack

Posted
Posted

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?

 

Thomcat Senior Enthusiast

Thomcat

Posted
Posted

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.

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Recently Browsing   0 members

    • No registered users viewing this page.

  • Forum Statistics

    250.5k
    Total Topics
    2.7m
    Total Posts

  • Member Statistics

    342,965
    Total Members
    8,960
    Most Online
    DaleB
    Newest Member
    DaleB
    Joined

  • Who's Online   7 Members, 0 Anonymous, 1,357 Guests (See full list)

  • Latest Articles

  • Posts

    • jgaudet99
      Tire psi

      By jgaudet99 · Posted

      My truck is a ¾ ton but my placard also says 80 for the rear tires, I think I might have the upgraded suspension to the 3500 series maybe.   I put my air down to 60 and the light was still on, and there was no way I was putting over 60 psi in the rear empty and not towing because I knew the actual number Toyo gave me and I didn't wanna ruin the center of my tires!   And you actually can change it in the settings from metric or is and it will show kph or mph then when you go into your tire settings it will be either psi or kpa, but it would be nice to just change it directly on the tire psi page 
    • Grumpy Bear
      Some Assembly is Required

      By Grumpy Bear · Posted

      Common Sense Assembly   Your driveline is forgiving of the occasional mistake. It will even often forgive the random serious blunder. But it will not forgive a continuous bad habit.      What? Not everything needs to be a five thousand word essay.       
    • Grumpy Bear
      Gas Prices

      By Grumpy Bear · Posted

      We drove about 15 minute east today to visit a friend and saw a steep increase in price in the same county. About 50 cents a gallon steepper. 
    • Grumpy Bear
      Wow I'm in a pickle. (Broke down truck) and a story.

      By Grumpy Bear · Posted

      Sure about that? A degree wheel and a dial indicator would lower your degree of assurance in that statement. 😉    It why we have offset keys and dialable timing sprockets. Just say'n.... I've built a few and have never seen one "On the money". 
    • Chuck FB
      Tire psi

      By Chuck FB · Posted

      I will admit I haven't experimented much with pressure drops beyond the numbers I put in and part of that is that the numbers I used are fairly low and then found out it would trigger regardless at that 35 psi. Having said that I had tried before had changed the placard pressures and being that I have a 1 ton set to 80 on the placard for the rear I believe it triggered close to 60, the front I don't recall now for sure but thought maybe it could get close to 45 from that factory 60 placard pressure. So I never did figure out if it was a number of psi from placard pressure to the alarm or a percentage of the total placard number as some figured it was like a 25% drop from placard pressure would trigger it. So as to try and answer your question, I believe I set the placard pressure on the front to 47 or so and while I run the front tires at 40, they have dipped below that some if its colder and I haven't put "winter air" in yet and never once have had the front alarm go off. I would say that the answer your looking for is no, that if you set your placard pressure to 45, you have a certain amount of room to drop below that pressure before the alarm will go off.    The pressures you decide to run in your truck, that ends up being what makes sense to you based on what your carrying in your truck or if towing, then have to bump them back up to something that will carry the load in the rear and the fronts typically left at the same pressure. It all comes down to that chart I put the link to and using an accurate roadside scale to be your guide, both unloaded and then loaded to know your minimum safe pressures.    I just wish GM would allow a person to change the readings for the tire pressures to the English system of pounds as I have to look at that goofy metric reading that will never ever jive in my head and will go over and change it just to figure out what they are if need be and then change it back. 

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...