L322 2007 Super Charged
Vacuum pump

Does anyone have ideas as to;

When the Vacuum pump will operate?
Under what conditions the pump will operate?
Where the pump gets the signal to operate from?
Where is the Vacuum sensor located?

I dont see anywhere in the W/S manual answers to any of these questions.
The pump seems to be a back up system to my way of thinking, should your engine stall while underway as your brake booster will loose engine vacuum and obviously you will loose power assisted brake action.

I have disconnected the vacuum line at the engine side to see if the pump is triggered, NO
No indication comes up in the message centre when you do this but you do get a P2525 DTC
So obviously if the system is inactive due to a fault the driver would be unaware.

Last edited by RR P38 on 27th May 2020 8:57pm. Edited 1 time in total

Hi, I recently discovered that my vacuum pump on the 4.4 jag engine is disconnected (wires cut) when I was replacing spark plugs. I don't know why anyone cut the wires in the past (car has lpg instalation so maybe lpg shop did that?)
The most interesting thing is that the car don't have any fault or warning message about brake system.
I would like to know if I am in danger if I continue to drive like that? And also all this questions that RR P38 sad, I didn't found in the workshop manual when the vacuum pump triggers? RR HSE 4.4 2006 LPG

Just looked at the workshop manual and there is quite a detailed description of how the system works in the chapter "Power Brake Actuation"

A small quote from the manual..

"Operation of the vacuum pump is controlled by the engine control module (ECM), which uses the vacuum pump relay in the battery junction box (BJB) to switch power to the vacuum pump. The ECM controls the time for which the vacuum pump is energized and also features built-in safeguards to protect the pump from overuse." Range Rover 4.2 Supercharged 2006
Ford Focus EcoBoost 1.5 2017
MG TF 2003

Previous Cars of note
Land Rover Discovery 2
Jaguar Mk2 3.8 - Company car
MG Midget 1974 - Concours

I have read the manual several times previously, and again today.
I still see no detail regarding when or why the Vacuum pump would be activated other than as it states in the manual "Operation of the vacuum pump is controlled by the engine control module (ECM), which uses the vacuum pump relay in the battery junction box (BJB) to switch power to the vacuum pump"
I am assuming that there is some reason we have a Vacuum pump, as a back up system possibly, since we have constant Vacuum applied when the engine is running I can only think there is a need for its existence from a safety perspective.

Possibly the ECM operates the Vacuum pump periodically on a timer basis. If you disconnect the plug for the VP no fault is logged and no message displayed on the message centre. If you disconnect the vacuum line at the booster end of the system and allow vacuum to escape you will log a DTC (but the driver gets no warning) as already noted by Maric995

There has to be a sensor in the system but where?
The check valves maintain the vacuum even when the engine is off for lengthy periods, does the ECM trigger the VP periodically to ensure a constant vacuum?

Sorry missed the sensor bit..

Reading between the lines I am guessing that the ECM switches the pump on when the brake pedal is pressed it then controls the time it's on and protects from overuse.

That way no sensor is required it just provides extra vacuum when required.

You've got me wanting to try and test that theory but that might be difficult if it only runs when the car is moving. Range Rover 4.2 Supercharged 2006
Ford Focus EcoBoost 1.5 2017
MG TF 2003

Previous Cars of note
Land Rover Discovery 2
Jaguar Mk2 3.8 - Company car
MG Midget 1974 - Concours

The reason Im asking these questions is that under normal driving conditions the brakes are great.

Pushing the RR to its limits on a twisty down hill run brake fade comes on, which surprises me with the Brembo brake pack, i have also installed cross drilled and slotted discs and flushed the system with Dot 5.1 fluid so everything is pretty well new.

I know the booster is fine as it holds a vacuum for hours after shut down.

The fade is not related to the VP questions Im pretty certain of that now, Im just intrigued as to why there is even a VP in the system and exaclty how and why it operates ?

One line in the manual "the electric vacuum pump supplements the main vacuum supply from the engine manifold"

So I guess LR thought there may be some conditions where the extra vacuum would help but I agree it does not say why.
I wonder if the ECM receives a signal from the ABS detecting the pressure being applied and switches the VP on at a certain level.

Because of the lockdown I've not had the opportunity to push the brakes to the limit but like you I'm surprised that you get some brake fade I was rather relying on the Brembo's getting me out of trouble as its a lot of metal to bring to a halt. Range Rover 4.2 Supercharged 2006
Ford Focus EcoBoost 1.5 2017
MG TF 2003

Previous Cars of note
Land Rover Discovery 2
Jaguar Mk2 3.8 - Company car
MG Midget 1974 - Concours

There is stacks of vacuum available from the inlet manifold
The only real reason I can think of for its existence is in the event of an engine outage while driving and you require multiple applications of the brakes to stop........you exhaust the reserve of vacuum in the booster and you will get a very hard pedal.
But with a Vacuum pump in electric guise you are going to be fine.....one would hope.
As yet I have not found a way to trigger the VP, yet, I know it works as I have removed and bench tested it.

Surely with a supercharged or turbo'd engine the inlet manifold has a positive pressure rather then a vacuum as per normally aspirated engine? BMW i3 Electric Car
2012 Full Fat RR 4.4 TDV8 (now gone)
2006 VW Touareg 3.0 TDi V6

"Surely with a supercharged or turbo engine the inlet manifold has a positive pressure rather then a vacuum as per normally aspirated engine?"
On the intake side of the super/Turbo charger, no
Or they can utilize a venturi system

I would disagree, in a throttle closed situation a normally aspirated engine creates maximum vacuum i.e. when braking just when you need it, a turbo or supercharged engine will have very little vacuum on the inlet to the turbo / supercharger, there's no airflow, theyre effectively open to atmosphere or have I got that wrong? A venturi system would only work with airflow and of course causes a restriction in the airflow which is exactly what we want to avoid by turboing or supercharging an engine. BMW i3 Electric Car
2012 Full Fat RR 4.4 TDV8 (now gone)
2006 VW Touareg 3.0 TDi V6

"A venturi system would only work with airflow and of course causes a restriction in the airflow which is exactly what we want to avoid by turboing or supercharging an engine."

Basically if there is something coming out the exhaust, there must be something coming into the engine, ie its running.
I ran a bench test on my VP with a vacuum gauge and achieved 2 inches of mercury, negative, pretty much instantly through a 0.5mm orifice.
There are two check valves in the system prior to the booster, 1 is at the manifold side the other is upside of the VP.......the booster has a significant reserve of vacuum on its side of the two check valves.

Obviously there would be times, very briefly where there is a near equalisation of atmospheric pressure within the induction system regardless of it being natural, Turbo or super charged, it would be pretty briefly though.

Then go for it,m remove the vacuum pump and connect onto your alternative vacuum source. Supercharged I dont know enough of the details, turbo I would say youre wrong, the inlet side of the turbo is open to atmosphere pretty much. BMW i3 Electric Car
2012 Full Fat RR 4.4 TDV8 (now gone)
2006 VW Touareg 3.0 TDi V6

Supercharged engines definitely don't generate as much vacuum at the inlet manifold as a normally aspirated engine.

Although RRP38 measured a "reasonable" vacuum through a 0.5mm orifice, you wouldn't get anywhere near that through the 5mm or more likely 8mm bore opening that the brake booster would need to supply the throughput if you pump the brakes hard a few times.
The vacuum pump on the RR SC (& also on a few very high performance normally aspirated engines) is there to increase the vacuum level upto a better level to support maximum braking with a fully laden car.
The disadvantage of the vacuum pump is that although they can generate really low pressure levels / high vacuum, most can't generate much throughput - that's why you can exhaust the vacuum assistance on turbo diesels so easily by a few repeated hard presses on the brake pedal and why you can wait for assistance to build up when the engine starts.

You can probably run without the vacuum pump on a SC, but I wouldn't like to find out what max braking was like in an emergency fully laden. Paul,
2001 Discovery 2 TD5, 211,000 miles & climbing
2006 FFRR TDV8 Vogue 151,000 miles & now sold
Member of Midland (Land) Rover Owners Club, www.mroc.co.uk

AJGalaxy2012 wrote:

Then go for it,m remove the vacuum pump and connect onto your alternative vacuum source. Supercharged I dont know enough of the details, turbo I would say youre wrong, the inlet side of the turbo is open to atmosphere pretty much.