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How does the BMW E39 sucking jet pump (aka suction jet pump) work & how does it fail?

169K views 82 replies 25 participants last post by  RJay.86 
#1 · (Edited)
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.

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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#2 ·
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.
 
#4 ·
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).

The sucking jet pump is not a "pump" at all
Now that's interesting!

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'?

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?
 

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#3 ·
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/Hydraulic_brake#Power_brakes
 
#5 · (Edited)
(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)

 
#6 ·
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.
 

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#12 · (Edited)
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

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.do?model=DT62&mospid=47546&btnr=34_1129&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?
 

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#14 · (Edited)
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!


Here is mine, which is only one piece.
 

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#19 ·
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.
 
#20 ·
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.
 
#21 ·
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?

 

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#33 ·
Pretty sure you have the arrow from the intake boot connection drawn in the wrong direction and to the wrong end.
It should be pulling air from the intake boot F- connector to the intake manifold port on the rear of the CCV.
Once the manifold evacuates all of the air from the booster it needs to keep drawing air thru the valve (from the F-connector port) to increase the vacuum inside the booster.
 
#22 · (Edited)
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)

 
#23 · (Edited)
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...
 
#27 · (Edited)
=
in your diagram, to "vacuum manifold port" goes to the PCCV valve on the back of the M62TU.
Now 'that' is interesting!

  • On the M54 CCV, the vacuum port is closed off with an endcap!
  • On the M52, the vacuum port of the CCV goes to the fuel pressure regulator!
  • Are you saying on the M62, the vacuum port of the CCV goes to the bottom of the SJP?
Note: Details on the M54 and M52 (but not the M62) are here:
- Clarification on how the M54 CCV vacuum port works on the M52 CCV valve connection to the fuel pressure regulator connection (1)

 

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#44 ·
Bluebee, there is always air flowing thru the F connector (at least on the V8's), never played with the I6 one.
The F connector that is ahead of the throttle body only has a slight vacuum while the throttle is open.
It is an almost open path to the outside atmosphere, thru the MAF and air filter box.

Most of the vacuum for the booster comes from the back of the CCV (in the 540).
When you step on the brake, the throttle closes, the vacuum level inside the manifold increases.
At this time the throttle closes and more air goes thru the F connector to help keep the vacuum in the booster low.
 
#48 ·
You can put your hand on the hose and follow it back to the connection at the manifold. The electrical terminal that connects the starter is close, so be careful.

Sent from my DROID2 GLOBAL using Bimmer
 
#49 · (Edited)
Does BMW use the term "sucking jet pump" for two totally different components?

I'm really confused by the following exchange today.

QUESTION: Are there TWO different things called the 'sucking jet pump'?
a) The 'vacuum multiplier' attached to the driver-side rear of the M54 engine (aka sucking jet pump)
b) A fuel pump siphon apparently attached near the fuel tank itself (aka suction jet pump, & sucking jet pump)

It all started today when someone posed symptoms of fuel starvation at half tank indication on the fuel gauge:
- E39 (1997 - 2003) > Fuel supply failure

... where the OP indicates a fuel starvation at half tank indicated value ...

My e39 5 speed manual 97 on getting to half tank on the fuel gauge, just stops and refuses to start. Have already changed the fuel suction pipe in the fuel tank three times can seem to get a solution
In response, cn90 pointed the user to a similar problem:
Search forum for "sucking jet pump".
Always keep gas tank above 20%-25% level. When it gets down to below 1/5 or 1/4 of the tank, refill it.

http://www.bimmerfest.com/forums/showthread.php?t=547280
Going to that cn90-referenced thread:
- E39 (1997 - 2003) > Gas Pump Reading

I do see a somewhat similar problem being discussed (the fuel starvation occurs at a different level though):
when my car reaches around 70ish miles left to the tank without the car having its reserve light come on, my car feels sluggish and to the point where it shuts off as if I ran out of gas...when I finally pour gas from those portable red gas cans the car fires up
To which cn90 recommended:
Search forum using keyword "siphon pump".
Which was further clarified by bimmertech, using the words 'sucking jet pump' (but which don't sound, to me, like the sucking jet pump at all):
CN90 is talking about the "sucking jet pump" that transfers fuel from one side of the tank to the other, if it's not working properly you will have gas stuck on the side of the fuel tank with no pump.
Furthermore, bimmertech pointed the user to a TIS, which seemed to support his terms completely:
OP-what CN90 was originally referring to is what BMW refers to as the "sucking jet pump" see below for removal/replacement.

http://tis.spaghetticoder.org/s/view.pl?1/01/40/76
In that TIS (see below), what BMW refers to as the "sucking jet pump" is indeed, in the fuel tank!
- BMW TIS Home => 5' E39 => M5 (S62) Saloon => Fuel supply system => fuel pump => Replacing sucking jet pump

Now 'this' sucking jet pump in the fuel tank doesn't look or act anything like the sucking jet pump attached to the driver-side rear of the M54 engine. Is BMW using the same name for two wholly different components?

The last post of that thread ends with cn90 providing the following diagram which, again, refers to the 'suction jet pump' as being in or near the fuel tank.

Thanks bimmerteck for the clarification of the terminology.

O.P., the gas tank in many RWD cars have this saddle shape to accommodate the driveshaft.
(I used to have an E23 1983 735i, whose gas tank is behind the Rear Diff, so no saddle shape, no "suction jet pump").

In the E39 (compared with E23), the gas tank is moved forward. Perhaps it is safer this way in case you get a bad rear end, the tank is further in the car. Placing a gas tank further in requires it to have a saddle-shape, thus the need for the "suction jet pump" to transfer fuel from (L) to R) side.

The main fuel pump is #2. The "suction jet pump" is #4.
Whatever it is, to keep life simple, fill it up once you hit 1/4 tank for now until you sort things out.

Looking in Realoem for my particular 2002 525i, I find both called the "sucking jet pump":
- 2002 525i => Engine => Vacuum control => Vacuum control - engine
- 2002 525i => Fuel Supply => Fuel feed => Fuel pump and fuel level sensor

Here is the former:

Here is the latter:


I must admit I am thoroughly confused:

Are there TWO suction jet pumps on the E39?
a) One which is a vacuum multiplier???
b) The other which is some sort of fuel balancing mechanism???

EDIT: I can come to only one conclusion - which is that BMW 'is' using the same term for two wholly different components!
I suggest we call the "sucking jet pump" bolted to the engine the 'vacuum multiplier' and maybe even find a better name for the 'sucking jet pump' that is bolted to the fuel tank (maybe a 'siphon pump")?
 

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#50 ·
Yes there are two sucking jet pumps.

One is attached to the brake booster and is used to increase vacuum during periods of low intake vacuum.

The other is in the fuel tank and is used to transfer fuel from the right side of the fuel tank to the left side of the fuel tank.

Maybe brake booster SJP and fuel tank SJP would help differentiate the components.
 
#51 ·
Yes there are two sucking jet pumps.
Either that, or one of them is mis-named in the engineering diagrams (I'd suspect the vacuum diagram since it is already known to be wrong in other areas).

One is attached to the brake booster and is used to increase vacuum during periods of low intake vacuum.
Hmmm... a 'vacuum' SJP.

The other is in the fuel tank and is used to transfer fuel from the right side of the fuel tank to the left side of the fuel tank.
Hmmm... a 'fuel' SJP.
 
#52 ·
I think the name should actually be suction jet pump. It was poorly translated from the German.

The term "jet pump" describes a device that uses a venturi to move fluids, like shallow well pumps.

The BMW design engineers used the same type of device to solve two different problems. I think the term is appropriately applied to both the brake booster SJP and the fuel tank SJP.
 
#53 ·
Wow, this thread has really taken off. I have been trying to hunt down the cause of my PO171/174 codes. That is where the thread "Different Scanner , New Codes" originated.

The other day I decided that I would go ahead and cut the clamps to the SJP and inspect it. The pump itself appeared to be fine. However, the hose from the intake to the pump had somehow wore itselfdown to the inner linnings. I went to Napa and had a new hose cut to replace the worn one out.

This did not work because of two reasons - 1. The OEM hose is form fitted to allow the brake booster hose and the vacuum line from air boot to line up correctly (On the 540). The new hose was not strong enough to handle the curving requiered. This made the hose pinch.

2. The same hose is flared out so it can connect to the jet pump correctly. I managed to get the hose on but damn near developed a case of carpil tunnel.

I ended up buying the correct hose from EAC which should be here today or tomorrow . Another problem I encountered was the line to the brake booster. It was showing its age. When I tried to reconnect the jet pump back on, the hose just started splitting. So I ordered a new hose for the booster as well. I just hope I dont break the fitting to the booster while trying to remove the old hose.

I will report back today or tomorrow to confirm that my codes have been resolved.
 
#54 ·
Steve530, over here today, found an excellent picture of the sucking jet pump elusive connection to the intake manifold in the back of the M54 engine:
- For all to benefit, WHERE are the ends of these hoses in our beloved E39s anyway?

I was browsing and found a nice photo of the back of a M54 intake manifold with hoses attached. I edited and annotated the photo to show the location of the attachment of the fuel tank breather (purge) valve and the suction jet pump.

For the crosslinked record, here is the original picture, un-annotated and shrunk to 640x480 pixels.
 
#55 ·
Here's more information just now from Steve530 on the location of the manifold vacuum to brake booster suction jet pump:

I didn't notice the CCV end cap until I zoomed in on the photo. I've added labels for that cap, the SAP one-way valve, and the SJP for clarity.

Note also that this photo shows the older style tube that connects the CCV to the dipstick tube. The newer style has a 45 degree bend instead of the 90 degree bend in this photo.

 
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