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

Originally Posted by Steve530

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

I did and do notice my brakes are acting funny. I already replaced the hose (it was sucked in), and one way vacum valve going into the brake booster...

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Originally Posted by MightyShilling

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)

Originally Posted by bluebee

=

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)

It goes to the large port on the back of the PCCV. the 2 smaller vac ports, one goes thru a solenoid to what I think is the secondary air pump (I'll find out if I research it a bit) and the other goes to the fuel pressure regulator. and of course there is the part that connects to the pipe that runs up to the OSV.

Blue asked me to cut open my dead SJP so the inside could be seen. Ask and ye shall receive.

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Nice pictures. I've made notes on the first photograph.

Originally Posted by Steve530

Nice pictures. I've made notes on the first photograph.

Very good. Glad I can help. Note: M62 engines, the pipe marked F connector connects to the intake pipe on the filter side of the throttle body, down stream of the MAF sensor

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Originally Posted by MightyShilling

Very good. Glad I can help. Note: M62 engines, the pipe marked F connector connects to the intake pipe on the filter side of the throttle body, down stream of the MAF sensor

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That's where the "F" connector is on the I6 engines - on the upper intake boot downstream of the MAF. I should have made that clear.

So the air going through the SJP is filtered and metered.

Originally Posted by bluebee

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?

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.

Here's a photo of the SJP i n place with the connections to the brake servo and "F" connector on the upper Intake boot.

Originally Posted by Steve530

Here's a photo of the SJP i n place with the connections to the brake servo and "F" connector on the upper Intake boot.

Your arrows are showing the correct air flow routes.

Originally Posted by JimLev

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.

Agreed. I was looking at it between customers, took a quick glance when I said it was correct. Upon further review, Jim is right.


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Originally Posted by MightyShilling

Upon further review, Jim is right.

I'm confused. But I understand what Jim, Steve530, & MightyShilling are saying.

You're saying the direction of air molecules is from the F connector to the sucking jet pump.

I'm not so sure of that. But I'd need to test it by pulling the hose off and feeling for suction to be sure.

"My" reasoning would be twofold:
a) The F connector is a vacuum source (i.e., air moves into it not out of it)
b) The sucking jet pump is a vacuum multiplier (so why would reducing the vacuum at the venturi be a good thing?)

But, for two reasons, I'm not really sure about that:
a) The sucking jet pump apparently has two red one-way flap valves; why would you need that second red flap valve if no air went through it?
b) I don't really understand 'how' the SJP venturi multiplies vacuum; perhaps it 'does' use two passageways of air going in the same direction to 'multiply' the vacuum???

Either way - we'll need confirmation of the actual direction of air flow in the SJP angled pipe with physical tests.

My yellow lines below on MightyShilling's most excellent pictures (thanks!) are what I think Jim, Steve530, & MightyShilling are saying is the direction of air flow. Right?

Originally Posted by bluebee

You're saying the direction of air molecules is from the F connector to the sucking jet pump.

I'm not so sure of that. But I'd need to test it by pulling the hose off and feeling for suction to be sure.

"My" reasoning would be twofold:
a) The F connector is a vacuum source (i.e., air moves into it not out of it)
b) The sucking jet pump is a vacuum multiplier (so why would reducing the vacuum at the venturi be a good thing?)

But, for two reasons, I'm not really sure about that:
a) The sucking jet pump apparently has two red one-way flap valves; why would you need that second red flap valve if no air went through it?
b) I don't really understand 'how' the SJP venturi multiplies vacuum; perhaps it 'does' use two passageways of air going in the same direction to 'multiply' the vacuum???

A great cross sectional picture to describe the workings of the SJP.
BB, 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.

Originally Posted by bluebee

I'm confused. But I understand what Jim, Steve530, & MightyShilling are saying.

You're saying the direction of air molecules is from the F connector to the sucking jet pump.

I'm not so sure of that. But I'd need to test it by pulling the hose off and feeling for suction to be sure.

Actually, you need to hook a vacuum gauge to it, and then measure the vacuum at the intake port. That 7mm capped vacuum port on the intake manifold would be a good place to take a reading. What you'll find is that the manifold is operating at a higher vacuum than the "F" connector.

You should be thinking in terms of pressure differentials. Higher vacuum is lower pressure. Air moves from an area of higher pressure to areas of lower pressure.

The intake manifold will have the lowest pressure and everything upstream of it will be higher. Let's assume the pressure in the intake is 15, the pressure at the "F" connector is 25, and atmospheric pressure is 30. With the SJP connected, air flows from the "F" connector through the SJP into the intake because the pressure is lower in the intake manifold(15) than the "F" connector(25). But if you remove the tubing from the "F" connector, air from the atmosphere will move into the "F" connector because atmospheric pressure (30) is higher than the pressure at the "F" connector (25).

Originally Posted by bluebee

"My" reasoning would be twofold:
a) The F connector is a vacuum source (i.e., air moves into it not out of it)
b) The sucking jet pump is a vacuum multiplier (so why would reducing the vacuum at the venturi be a good thing?)

a) See above.
b) As I uderstand it, the venturi side of the SJP operates during periods of low manifold vacuum. So when the pressure differential between the brake servo and the intake manifold is insufficient to evacuate the brake servo, the venturi in the SJP lowers the pressure.

Originally Posted by bluebee

But, for two reasons, I'm not really sure about that:
a) The sucking jet pump apparently has two red one-way flap valves; why would you need that second red flap valve if no air went through it?
b) I don't really understand 'how' the SJP venturi multiplies vacuum; perhaps it 'does' use two passageways of air going in the same direction to 'multiply' the vacuum???

Either way - we'll need confirmation of the actual direction of air flow in the SJP angled pipe with physical tests.

a) No, you would not need the second check valve if no air went through it. Air does go through it.

b) I don't think it multiplies vacuum, but it creates a lower pressure (higher vacuum) than sometime exists in the intake manifold.

Looking at the photo, it is not clear whether the two chambers are separated at the top. If they are separate, that would explain the second check valve. But I think it's clear that air only flows through the check valves when the brake servo operates. And it's clear that air always flows from the intake boot through the venturi into the intake manifold.

Originally Posted by Steve530

You should be thinking in terms of pressure differentials.

I don't disagree; yet, to be honest, I'm having (conceptual) trouble with the direction of molecular flow. Mainly I'm slowed down simply because I find it hard to conceptualize the stated directions of flow.

For example, the M54 F connector small hose is already said to be a vacuum source for the fuel pressure regulator; so I found it conceptually odd to consider the adjacent large hose a (perhaps slight) pressure source for the SJP.

However, I fully understand the difference in pressure is what matters when considering it a pressure or vacuum source (just as with a voltage source or a current source).

So, it is conceivable that the F-connector small hose is a vacuum source while the adjacent large hose (connected to the same F connector) is a pressure source.

Once I get over the hurdle of the same F connector containing both a vacuum source and a pressure source only a millimeter away, then I can focus on re-reading (a few dozen times) the explanations above to understand how the SJP creates a lower vacuum for the brake booster than that at the intake manifold.

EDIT: I must repeat, I 'understand' what you are saying. I understand fully. I just never 'believe' in my heart anything anyone tells me until I believe it myself - and then I can move on. So there is no need to further explain (except to clarify perhaps); I'll just first convince myself that the two F-connector hoses 'act' differently with respect to the direction of air flow ... that's all.

BTW, this earlier picture seems to imply that the two check valves are separate.

Originally Posted by bluebee

Once I get over the hurdle of the same F connector containing both a vacuum source and a pressure source only a millimeter away, then I can focus on re-reading (a few dozen times) the explanations above to understand how the SJP creates a lower vacuum for the brake booster than that at the intake manifold.

EDIT: I must repeat, I 'understand' what you are saying. I understand fully. I just never 'believe' in my heart anything anyone tells me until I believe it myself - and then I can move on. So there is no need to further explain (except to clarify perhaps); I'll just first convince myself that the two F-connector hoses 'act' differently with respect to the direction of air flow ... that's all.

Go figure it out, then come back and explain it to us.

The 2 check valves are indeed separate. One path thru the venturi and one thru the normal Channels.

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Originally Posted by MightyShilling

The 2 check valves are indeed separate. One path thru the venturi and one thru the normal Channels.

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Thanks. That sheds some light on the operation of the SJP.

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.

Originally Posted by JimLev

...Most of the vacuum for the booster comes from the back of the CCV (in the 540)...

On my 530 (and other I6 engines, I suspect), the SJP is connected to the intake manifold just above the starter.

Originally Posted by Steve530

the SJP is connected to the intake manifold just above the starter.

It would be nice to have a picture or diagram of exactly where the SJP bottom hose connects to the intake manifold.

Given Steve's hint above, I tried looking in Realoem around the starter ... but ... failed to find anything more than 'just' the starter.
- E39 525i => Engine Electrical System => Starter


If someone has a picture or diagram of WHERE the SJP lower hose connects to the intake manifold, that would help us better understand how the engine is designed.

Blue I can get a pic of the M62TU if you'd like...

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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.

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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 ...

Originally Posted by kaynoe39

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:

Originally Posted by cn90

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/sho...d.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):

Originally Posted by Sixfiggaz

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:

Originally Posted by cn90

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):

Originally Posted by bimmerteck

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:

Originally Posted by bimmerteck

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.

Originally Posted by cn90

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")?

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.