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Old 11-02-2011, 12:26 AM
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bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
Join Date: Mar 2008
Posts: 25,236
Mein Auto: 02 BMW 525i M54 auto 130K
How does the BMW E39 sucking jet pump (aka suction jet pump) work & how does it fail?

EDIT: It's a vacuum multiplier, which provides more than manifold vacuum could alone, to the brake booster where behind the master cylinder. The air flow goes from the brake booster to a hose at the top of the SJP, to your intake manifold hose on the bottom of the SJP & at the same time to the upper snorkel tubing at the F connector from the middle of the SJP where the venturi effect multiplies manifold vacuum to the brake booster.

Originally Posted by Fudman View Post
I believe this is how the SJP works:
a) The F connector is not a vacuum (negative pressure) source. It a supply (positive pressure) source, providing access to filtered air flow.
b) The SJP is a vacuum multiplier of the intake manifold negative pressure. See below.

a) The check valves are needed to prevent airflow from reversing direction back into the brake booster. Two valves are needed to cover both entry points back into the booster. Since the pressure in booster is now lower than the intake manifold (due to the SJP effect) side and the F connector side, air can flow into the booster if there were no check valves.
b) The venturi constricts airflow in one channel, causing the airflow to accelerate (think of a wing with the straight channel below the wing and the venturi above the wing surface). Just like a wing, you get a reduced pressure above the wing (venturi side). The negative pressure at the venturi (where the two yellow lines join) is greater than the negative pressure at the intake manifold, thus air flows from the booster into the SJP, creating more vacuum. This is the net effect of the multiplication factor of the SJP.
This sucking-jet-pump specific thread was prompted by new information today:
- E39 (1997 - 2003) > Different scanner. New code

By the title, you'd never know there is good information therein about the "SJP", and, a thread with that title on another forum is rather sparse; so, I figured we'd give it its own detailed thread on Bimmerfest. As always, this is to edify the tribe as a whole, and to server as a reference in the future, long after we're gone.

Here is the diagram for the 2002 M54 sucking jet pump:
- Engine => Vacuum control => Vacuum control - engine

Note: In the 2002 M54, it seems the following is the case:
1. The top hose appears to go to the brake booster
2. The bottom hose appears to go to the intake manifold on the M54 (or to the CCV on the M62TU)
3. The center venturi tube (despite the diagrams) goes to the F connector on the intake snorkel boot

Please note that the diagram is wrong in quite a few ways. One error is the "L" elbow is actually an "F" connector in the M54. (Apparently BMW didn't update the diagram between the M52 and M54 when they moved the fuel pressure regulator and CCV valve hose connection to the F connector on the intake snorkel).

Another error is the number of hoses & tubes on the sucking jet pump (only one hose and one tube are shown but there are actually two hoses and one tube attached to my M54 suction jet pump).

Here is a picture of my 2002 M54 sucking jet pump in situ (but with the tube to the F connector removed):

Here's that same picture only zoomed out so you can get an engine-bay perspective:

Note: In this picture above, the F connector vacuum tube has been removed; the two hoses (one at the top, and another at the bottom of the sucking jet pump) are in place.

The question for this thread, is:
Q: How does the BMW E39 sucking jet pump (aka suction jet pump) work & how does it fail?

See also this rather ambiguous thread (from another forum):
- What is the purpose of the "Sucking Jet Pump"?

And, view this nice PDF from RDL which explains the sucking jet pump operation on page 12:
- 03 E85 M54 Engine.pdf

Suction Jet Pump:
The suction jet pump ensures the necessary vacuum in the brake booster so that the braking force is retained for a certain period even after the intake system vacuum depletes. Two non-return valves are integrated in the suction jet pump for brake power assistance.
1. Connection to intake boot
2. Suction jet pump
3. Connection to intake manifold
4. Venturi pipe
5. Connection to brake booster

The suction jet pump works according to the Venturi principle: generation of a pressure difference by increasing the flow speed. This means that the suction jet pump creates a higher vacuum for the brake booster than that already present in the intake system.
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Last edited by bluebee; 11-09-2011 at 06:30 AM. Reason: Fixed the use of 'hose' and 'tube' where, technically, a hose is a single material whereas a tube is multiple materials.
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