My 1988 LFX F40 build. (Page 35/68)
Daryl M MAY 31, 01:45 AM
If that pump is sufficient to run brakes on an Impala full time, why did you bother using engine vacuum at all?
Joseph Upson MAY 31, 09:32 AM

quote
Originally posted by Daryl M:

If that pump is sufficient to run brakes on an Impala full time, why did you bother using engine vacuum at all?



It's not likely intended to do that full time. Without researching it, I'm pretty sure it's there to assist under circumstances where commanded camshaft angles produce potentially insufficient vacuum for extended periods where a situation can occur, for braking to appear frighteningly insufficient. Recall in most cases, the EGR effect is a result of the VVT, dependent upon the appropriate angles commanded. Cam angle tables can be pretty intimidating in terms of how they work in the programming, (there are at least 4 in the Bosch PCM system) and more so when it comes to figuring out which cam angle table the PCM is reading from to set the desired angles.

msweldon MAY 31, 11:44 AM

quote
Originally posted by Joseph Upson:


It's not likely intended to do that full time. Without researching it, I'm pretty sure it's there to assist under circumstances where commanded camshaft angles produce potentially insufficient vacuum for extended periods where a situation can occur, for braking to appear frighteningly insufficient. Recall in most cases, the EGR effect is a result of the VVT, dependent upon the appropriate angles commanded. Cam angle tables can be pretty intimidating in terms of how they work in the programming, (there are at least 4 in the Bosch PCM system) and more so when it comes to figuring out which cam angle table the PCM is reading from to set the desired angles.




The first part of what Joseph just said above is an accurate paraphrase of what is stated in the FSM for the Cadillac ATS with the LFX/LGX and even somewhat more so with the ATS-V LF4 TT. As a matter of fact the LF3/LF4 have an additional mechanically cam driven vacuum pump in the opposite head of the HPFP for wastegate and BOV operation.

[This message has been edited by msweldon (edited 05-31-2020).]

Daryl M JUN 01, 02:39 AM
I am having a hard time getting a schematic of the vacuum hose routing for the 2013 Impala, and don't know where on the engine they get vacuum for the booster from. Does anyone know where I can get that info?
Thanks

[This message has been edited by Daryl M (edited 06-01-2020).]

La fiera JUN 01, 08:38 AM

quote
Originally posted by Daryl M:

If that pump is sufficient to run brakes on an Impala full time, why did you bother using engine vacuum at all?



The pump is more than sufficient for my application. It doesn't run constantly it comes on and off
on demand and keeps the vacuum right at 15inhg. When vacuum drops to 10inhg it turns on and brings the vacuum back to 15ingh.
I have it wired to a relay and an adjustable pressure sensor.
msweldon JUN 01, 05:34 PM
Eautorepair.net has been invaluable with helping me in my swap especially since FSM's are still so pricey for late model engines.
Joseph Upson JUN 02, 04:17 AM

quote
Originally posted by La fiera:
The pump is more than sufficient for my application. It doesn't run constantly it comes on and off
on demand and keeps the vacuum right at 15inhg. When vacuum drops to 10inhg it turns on and brings the vacuum back to 15ingh.
I have it wired to a relay and an adjustable pressure sensor.



I'm not sure how often and for how long the pump is cycled on in the applications it was designed for, but my concern here would be the absence of a backup system in the event it failed to operate at some point. The funny thing about these situations, is that when there's a potential setting for something to really go wrong, it's just a matter of time before it does.

In addition to this pump in its OE arrangement, my booster also receives a vacuum signal from the intake plenum on an LLT motor. I've never bothered to trace the pump tie in. I don't recall how difficult it was to stop the Fiero without power assist, but imagine it's not an end of the world moment, however, you only need to tap the car in front of you to have your insurance company sued for a substantial amount, or worse if it involves a bit more than a tap.

I believe it's wiser to make an access point for a traditional vacuum signal and be better safe than sorry, or use two pumps.
La fiera JUN 02, 07:42 AM

quote
Originally posted by Joseph Upson:
use two pumps.



Yes, I'm getting another pump and another source of vacuum storage because I though about the same thing. In my case is very important to have a back up
I track the car more than I drive it on the street. Thank you for the reminder Joseph!
Daryl M JUN 02, 03:11 PM
I was able to determine that the vacuum for the booster does come from two sources, the intake plenum and the electric booster pump. They use a few check valves to insure there is no bleed back from one vacuum source to another. The check valves are part of a pre-made vacuum hose . I am trying to source them individually now, but have not found them yet.
mender JUN 02, 05:23 PM

quote
Originally posted by Daryl M:

I was able to determine that the vacuum for the booster does come from two sources, the intake plenum and the electric booster pump. They use a few check valves to insure there is no bleed back from one vacuum source to another. The check valves are part of a pre-made vacuum hose . I am trying to source them individually now, but have not found them yet.



A vacuum pump probably isn't needed for your application. The main reason that the factory added one is that the new cars are set up to run at low rpm with high throttle openings for efficiency with the resultant low vacuum. That usually means less than 2000 rpm at highway speed.

A car that successfully used only manifold vacuum with a 2.8 should have no problem doing the same with a 3.6. I won't be running the vacuum pump on my Fiero track car with the LFX.