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-   -   How does the BMW E39 sucking jet pump (aka suction jet pump) work & how does it fail? (http://www.bimmerfest.com/forums/showthread.php?t=578766)

bluebee 11-02-2011 12:26 AM

How does the BMW E39 sucking jet pump (aka suction jet pump) work & how does it fail?
 
4 Attachment(s)
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.
http://www.bimmerfest.com/forums/att...1&d=1320816243
Quote:

Originally Posted by Fudman (Post 6430206)
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
http://www.bimmerfest.com/forums/att...1&d=1320219136
http://www.bimmerfest.com/forums/att...1&d=1320218907
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):

http://www.bimmerfest.com/forums/att...1&d=1319781947

Here's that same picture only zoomed out so you can get an engine-bay perspective:
http://www.bimmerfest.com/forums/att...1&d=1319781945
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

Quote:

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.
http://www.bimmerfest.com/forums/att...1&d=1320218700

Fudman 11-02-2011 05:08 AM

Quote:

Originally Posted by bluebee (Post 6415806)
The question for this thread, is:
Q: How does the BMW E39 sucking jet pump (aka suction jet pump) work & how does it fail?

BB:
RDL's .pdf file gives a good explanation. The sucking jet pump is not a "pump" at all but just a fitting that creates a vacuum for the master cylinder to boost braking power. This is a feature on all power assisted braking systems. In this caes, once the engine starts, the intake manifold vacuum draws air from the intake bellows through the fitting (jet pump). The fitting constricts the air flow, increasing airflow speed which creates a venturi effect, which then causes a pressure drop. The angled fitting connection (which is attached to the brake master cylinder) is exposed to this pressure drop which creates a vacuum in the line. This vacuum is used to boost the brake master cylinder.

Q: Why not attach directly to the intake manifold? There is probably insufficient vacuum (pressure drop) at the intake manifold to directly attach to the master cylinder. Hence, the engineers use this "pump" to increase the pressure differential to increase the brake boost without adding an electrical pump. Very clever!

Q: How does vacuum increase braking pressure? Beats the hell out of me. Haven't a clue. Start another thread. :)

Q: How does it fail? Since there are no moving parts to the "jet pump", failure would seem highly unlikely. One mode could be caused by clogging. Since it is downstream from the air filter, it does not seem likely that contamination will come from the air box side. Another failure mode could be material failure, but again highly unlikely given the lack of mechanical loading. Hence, the pump appears to have high reliability.

edjack 11-02-2011 08:59 AM

How does vacuum increase braking pressure?
 
Vacuum from the engine on one side of the diaphragm in the brake booster (that large tank mounted to the brake master cylinder; you know, the one that fills with water and freezes up in the winter?) allows atmospheric pressure to push on the master cylinder. Nominally 14.7 psi X surface area of the diaphragm, so, for a 6 inch booster, you'd get as much as 418 lbs of boost.

My Shelby GT-350 had 11 inch front disc brakes, and no booster! I had to really stand on them to stop, but they worked great!

Read all about it: http://en.wikipedia.org/wiki/Hydraul...e#Power_brakes

bluebee 11-02-2011 09:19 AM

1 Attachment(s)
Quote:

Originally Posted by Fudman (Post 6415902)
RDL's .pdf file gives a good explanation.

I had trouble understanding their explanation (but not yours). It troubled me that their hoses and tubing (E85) were in different places than ours are (E39).

Quote:

Originally Posted by Fudman (Post 6415902)
The sucking jet pump is not a "pump" at all

Now that's interesting!

Quote:

Originally Posted by Fudman (Post 6415902)
just a fitting that creates a vacuum for the master cylinder to boost braking power.

That description makes it sound more like a 'valve' than a 'fitting'?

Quote:

Originally Posted by Fudman (Post 6415902)
manifold vacuum draws air from the intake bellows through the fitting (jet pump). The fitting constricts the air flow, increasing airflow speed which creates a venturi effect, which then causes a pressure drop. The angled fitting connection (which is attached to the brake master cylinder) is exposed to this pressure drop which creates a vacuum in the line. This vacuum is used to boost the brake master cylinder.

Wow. I just realized, reading your explanation, that the big fat drum that is in 'most' cars for power brakes, doesn't exist in the E39!

Does the SJP take the place of that thing?
http://www.bimmerfest.com/forums/att...1&d=1320250713

bluebee 11-02-2011 09:22 AM

Quote:

Originally Posted by edjack (Post 6416330)
(that large tank mounted to the brake master cylinder

I can easily picture that large tank in a big ole' American car; but I just can't picture that 'large tank' in my mind for the E39 (I'll have to look for it but I don't remember ever seeing it).

If someone has handy a good picture pointing to that 'large tank', that would be useful to many reading this thread (including me).

Here is what I have handy (from this thread):
- Identify all unknown parts in the engine bay (1)

http://www.bimmerfest.com/forums/att...1&d=1277709589

Steve530 11-02-2011 09:39 AM

1 Attachment(s)
You can see the hose that runs from the top of the sucking jet to the brake servo in Bluebee's photo. The hose from the bottom of the pump connects to the bottom of the intake manifold, just above the starter motor. The brake servo is under the cabin filter housing.

Steve530 11-02-2011 10:43 AM

1 Attachment(s)
Quote:

Originally Posted by bluebee (Post 6416378)
I can easily picture that large tank in a big ole' American car; but I just can't picture that 'large tank' in my mind for the E39 (I'll have to look for it but I don't remember ever seeing it).

I found this posted a few months ago on this forum. I added the labels.

Fudman 11-02-2011 10:56 AM

Quote:

Originally Posted by bluebee (Post 6416374)

That description makes it sound more like a 'valve' than a 'fitting'?



Wow. I just realized, reading your explanation, that the big fat drum that is in 'most' cars for power brakes, doesn't exist in the E39!

Does the SJP take the place of that thing?

It is literally a fitting, like the F connector. It is not a valve because it does not open or close. It is always open. However, instead of a smooth inside channel of consistent diameter, the fitting has a nozzle like constriction. This causes the airflow to accelerate to squeeze through a smaller opening. The faster airflow causes a pressure drop (much like faster airflow above a wing surface causes a pressure drop and lift to occur). The SJP doesn't replace anything and draws a vacuum on the "big fat drum" which does exist. See Steve's post for the picture.

bluebee 11-02-2011 02:25 PM

2 Attachment(s)
Quote:

Originally Posted by Steve530 (Post 6416585)
I found this posted a few months ago on this forum. I added the labels.

Ah, I see, said the blind person. It was hidden BELOW the cabin air filter!
My bad.

In the annotation below, do I at least have the direction of molecular flow correct?
http://www.bimmerfest.com/forums/att...1&d=1320269299


Quote:

Originally Posted by Fudman (Post 6416614)
It is literally a fitting, like the F connector....it does not open or close. It is always open.

Ah, yet again. I see. It's not a valve. It's a fancy fitting. Thanks!
Sorry for being dense.

The good news is that newbies can now even more easily follow in our footsteps in the future! :)

Steve530 11-02-2011 03:06 PM

1 Attachment(s)
Quote:

Originally Posted by bluebee (Post 6417088)
In the annotation below, do I at least have the direction of molecular flow correct?

Yes, that is the flow.

Brake boosters (or servos) have long been connected directly to the intake manifold as a source of vacuum. The suction jet pump is supposed to supply additional vacuum to the servo.

My understanding of the suction jet pump is that the lower hose connects to the intake manifold. This is a good source of vacuum which evacuates the servo through the top tube. The vacuum from the manifold also pulls air from the intake boot between the air filter and throttle body through the smaller fitting that is angled from the main body. The air in this stream goes through a venturi that creates a lower pressure area that actually pulls more air from the servo than the manifold vacuum alone.

I found a picture of a suction jet pump that was partially cut on a VW Passat forum. It appears to be similar to the ones used on the e39.

bluebee 11-02-2011 08:25 PM

Quote:

Originally Posted by Steve530 (Post 6417179)
actually pulls more air from the servo than the manifold vacuum alone.

Thanks for explaining and for the pic.

Based on that, to me, it's neither a valve nor a fitting.

It's a vacuum multiplier!

http://www.bimmerfest.com/forums/att...8&d=1320271537

bluebee 11-03-2011 07:22 AM

3 Attachment(s)
For the record, this 530i MSport thread implies the SJP top vacuum hose goes to the "firewall" in some engine bays (which I find odd, if it turns out to be true):
- E39 (1997 - 2003) > help identifying hose

Quote:

Originally Posted by gibo58 (Post 6418046)
Sorry people, forgot to 'search' first, just saw Blubee's thread on the sucking jet pump.
Mine seems different as it goes to the firewall not to the brake booster. Would the hose be one of these:
http://www.realoem.com/bmw/showparts...29&hg=34&fg=27

Attached are the pics (shrunk to 640x480) from that thread just today.

Does anyone else have this type of upper SJP hose?
http://www.bimmerfest.com/forums/att...1&d=1320330449

Steve530 11-03-2011 08:32 AM

Right hand drive car.

bluebee 11-03-2011 09:09 AM

2 Attachment(s)
Quote:

Originally Posted by Steve530 (Post 6418530)
Right hand drive car.

Oh. I hadn't thought of that. [hides embarrassment with hands]

Here is the OP's initial realoem reference diagram (notice the two hoses to the brake booster, one of which we can presume, based on what the OP stated, starts at the firewall, apparently at the #10 location).

BTW, I do NOT see that vacuum endcap that I see in the OP's picture!
http://www.bimmerfest.com/forums/att...1&d=1320336843

Here is mine, which is only one piece.
http://www.bimmerfest.com/forums/att...1&d=1320336843

Steve530 11-03-2011 09:53 AM

1 Attachment(s)
Looks like they missed that piece. But the connector is shown with a vacuum port.

MightyShilling 11-08-2011 02:08 PM

My sucking jet pump came apart.... just replaced it...

it was on the car like this, barely pressure fit together. think this would cause an issue?

http://www.bimmerfest.com/forums/att...5&d=1320788035

Steve530 11-08-2011 03:07 PM

Quote:

Originally Posted by MightyShilling (Post 6428930)
My sucking jet pump came apart.... just replaced it...

it was on the car like this, barely pressure fit together. think this would cause an issue?

http://www.bimmerfest.com/forums/att...5&d=1320788035

Did you put it back in the car or replace it with a new suction jet pump?

MightyShilling 11-08-2011 03:39 PM

Quote:

Originally Posted by Steve530 (Post 6429072)
Did you put it back in the car or replace it with a new suction jet pump?

Replaced with a new oem unit

Steve530 11-08-2011 03:50 PM

Good.

If the SJP was apart when it was installed, it might cause a vacuum leak which I would think would have set a lean mixture code. It certainly would have caused a problem with the vacuum assisted brakes. I'm sure you would have noticed that. My guess is that the vacuum would tend to hold it together.

I don't think it would have caused any real damage, if that's what you're asking.

Glad you got it fixed.

MightyShilling 11-08-2011 04:15 PM

Quote:

Originally Posted by Steve530 (Post 6429162)
Good.

If the SJP was apart when it was installed, it might cause a vacuum leak which I would think would have set a lean mixture code. It certainly would have caused a problem with the vacuum assisted brakes. I'm sure you would have noticed that. My guess is that the vacuum would tend to hold it together.

I don't think it would have caused any real damage, if that's what you're asking.

Glad you got it fixed.

I did have it installed in that condition (put together the best I could) for about a week. No ses light, no issue with the brakes. I however was told to look for a intake leak for a cause of my smokey starts with a new ccv. I'll report back if this fixed it, because it'd definitely be an intake leak.

bluebee 11-08-2011 04:18 PM

2 Attachment(s)
How on earth did you realize that the SJP was broken?

BTW, I've never seen one outside the vehicle - and I only noticed mine about a week ago ... so ... may I ask ...

Did I get the annotations and orientation correct below?

http://www.bimmerfest.com/forums/att...1&d=1320797883

bluebee 11-08-2011 04:39 PM

Is it just me ... or is this BMW diagram upside down from reality in the E39?
And, are the numbers all wrong (for the E39)?

Seems to me, on 'my' E39, the following is different from this E85 diagram:
a) The side tube angles UPWARD (not downward as shown below)
b) The side tube is connected to the intake boot (not to the brake booster as shown below)
c) The connection to the intake manifold is on the bottom (not on the top)
d) The connection to the brake booster is on the top (not on the side arm)

http://www.bimmerfest.com/forums/att...1&d=1320218700

MightyShilling 11-08-2011 04:45 PM

Yup. looks good to me (your diagram with the arrows). Basically, in your diagram, to "vacuum manifold port" goes to the PCCV valve on the back of the M62TU. I replaced the PCCV valve searching for a smoking condition. while replacing, the SJP just came apart into 2 pieces. I put it back together and forgot about it. a couple weeks later, I'm still chasing the smoking. I replace the PCCV valve AGAIN with an OEM part. also reseal the manifold and various other vacuum parts because a friend who's a BMW Master Tech is convinced it's a vacuum issue. while re-sealing the manifold, this damn thing came apart again... I remember to put it on my needed parts list. start the car today, damn things smokes. I get pissed. call my master tech friend, he's convinced I screwed something up, tells me to smoke it and look for a vac leak. In the mean time I order this. when looking at the diagram as to how it's installed, I realize it hooks up to the manifold, and is a source of a vac leak. so we'll see if it's the cause of my smokey start. Here's to hoping...

bmw330pp 11-08-2011 04:45 PM

Could this "sucking jet pump" be a possible cause of a P0174 code (Running lean on bank x)?

Steve530 11-08-2011 04:56 PM

Quote:

Originally Posted by bmw330pp (Post 6429269)
Could this "sucking jet pump" be a possible cause of a P0174 code (Running lean on bank x)?

Yes, but I think you'd notice the lack of vacuum assist on the brakes right away if the SJP was broken or disconnected.


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