vacuum hoses connected to fuel injectors?!?

[BLINGMW]

ok, someone 'splain me this please:



On this 318ti I got (and apparently all e36 318s), there's a hose coming off the rubber intake tube, connected to a little 4-way thing, and then smaller hoses connecting to each fuel injector. What possible purpose could this serve? :?: :?: :?:

another pic I found:

[.RJ]

Returnless fuel system?

[Dave]

That's pretty wild. 13 & 16 look like your feed/return hard lines. Some hypotheses, although I don't think any of them are right:
-Injectors squirting tiny amounts of fuel into the intake
-Injector needs some kind of vacuum for functionality (whats the point of EFI?)

[Steve85]

there's a hose coming off the rubber intake tube

Before or after the throttle body? I know the title is "vacuum hoses" but it never hurts to ask the explicit questions to figure this stuff out. On 99% of cars I have seen the TB is connected directly to the manifold and the intake tubes (from filter to TB) are therefore generally positive pressure areas.

[BLINGMW]

yeah it definitely has a regular return and regular looking FPR with its own vacuum control....

-Injectors squirting tiny amounts of fuel into the intake
-Injector needs some kind of vacuum for functionality (whats the point of EFI?)

good ideas, but maybe this helps. The hoses are cracked, the large hose wasn't even connected to the intake, and the car runs fine. "fine" being hesitating a little when cold, I would assume due to the extra air being pulled in past the MAF, hence running lean, but once it gets into closed loop, it runs perfect. Now if it's a little down on power or something, I wouldn't know, but I'm pretty temped to just remove this squid of hoses if it's some minor, emissions related thing.

So yeah, if they were squirting fuel into the intake, I'd have fuel everywhere, and if the injectors needed it to function... well... they aren't getting it. :dunno:

Before or after the throttle body? I know the title is "vacuum hoses" but it never hurts to ask the explicit questions to figure this stuff out. On 99% of cars I have seen the TB is connected directly to the manifold and the intake tubes (from filter to TB) are therefore generally positive pressure areas.

Good questions. The system is tapped into the large boot that connects the TB to the MAF. And you may be on to something when you put vacuum hoses in quotes, because it's not vacuum line type thin little hoses, the small ones are fuel line size and the big one that taps off the boot (#17) is maybe an inch in diameter. It would seem to me that the boot area between the filter and TB would be slightly less than atmospheric pressure = vacuum, but I'd love to be educated on that if I'm wrong. I just don't see how it could be positive unless it's boosted.... well, I guess unless you're going pretty fast and have a "ram air" system.... :dunno:

[ViPER1313]

The area between the throttle body and MAF is at a very low vacuum, unlike past the throttle body / intake manifold. If I were to take a wild guess, I would say it is some sort of fuel vapor recovery system or some form of air cooling system for the injectors.

[BLINGMW]

some form of air cooling system for the injectors.

hmmm.... that's an interesting thought.

My only other idea was that it's an over the top safety system. Like, if the injector seals started leaking, this would pull that fuel into the intake instead of just notifying the owner with fire. Maybe BMW thought a lot of these engines would be a top choice for airplanes. :lol:

[Steve85]

Filter to TB should not be vacuum unless the filter is a restriction. and despite what K+N wants us to believe, for 99.9% of cars in their normal operating range, it isn't. The size of the hose was also suspect, it is definitely feeding air to the injectors.

Now MAF to TB should not be vacuum either unless the MAF sensor is flowing less than the engine desires, again typically not the case. I'm not saying it isn't or can't be, but it shouldn't if the system was designed properly. The MAF that came on TPI 350s that peak at 245hp@4500 rpm have fed 600+hp 434's. Resolution is lost but the flow is there.

I do agree with Adam though, it is most likely a secondary cooling method (the fuel is supposed to cool injectors) or possibly some sort of way to improve atomization.

[CaptainHenreh]

It's German engineering. Why use 1 part when 12 will do the job?

[ViPER1313]

Filter to TB should not be vacuum unless the filter is a restriction. and despite what K+N wants us to believe, for 99.9% of cars in their normal operating range, it isn't. The size of the hose was also suspect, it is definitely feeding air to the injectors.

How is this? In the picture below you can see a tube run from the bottom right of the front valve cover to the intake tube between the airbox / throttle body. It is used to suck crankcase fumes from the block back into the intake for emissions purposes. I imagine that even though the airbox / filter doesn't introduce much restriction, it does introduce a little, and that is enough to create vacuum (minimal, minimal vacuum.)

[Steve85]

That tube looks to be providing the fresh air side of the PCV system. Fresh air from the intake tube into the crankcase, then sucked into a port aft of the TB (vacuum) to suck the air out.

Just above the oil fill cap there is another tube connected to the valve cover. Does that tube run to the back of the manifold (vacuum)?

If that tube your talking about is designed to pull air out I would say it does it through a combination of crankcase pressure pushing and a venturi effect of air rushing past the opening, not vacuum in the intake tube.

I just don't see how a MAF with an opening 2.5 in circumference could force a vacuum between it and a blocked, smaller passageway (TB with blade 99.9% of the time more closed than open) The MAF has to flow more than the TB to work properly.

[Dave]

I'm voting stupid emissions crap. Cap off the injectors and intake piping and put the vacuum squid on the shelf...

[Steve85]

Another point to the above pic...that would also not be a proper design because the air from the crankcase would be introduced to the engine, unmetered. It is on purpase that the PCV system takes air after the filter and sensor, but before the TB. Air diverted into the crankcase should nearly equal air coming out and into the manifold to ensure all the air going in the engine is accurately accounted for.

[D_Eclipse9916]

Another point to the above pic...that would also not be a proper design because the air from the crankcase would be introduced to the engine, unmetered. It is on purpase that the PCV system takes air after the filter and sensor, but before the TB. Air diverted into the crankcase should nearly equal air coming out and into the manifold to ensure all the air going in the engine is accurately accounted for.

ECUs already account for this in their engineering (or should, even DSM ecus account for this "air". :thumbup: You are correct in the fact that between filter to TB there should not be "vacuum" in the sense of the meaning we are using it.

The breather line, (whats it is called between a hose after the MAF and into the engine) is used to feed fresh, filtered air into the engine at idle/light load conditions. This is because the PCV valve is using manifold vacuum to pull crankcase gases. However when you get into the throttle, boost closes the PCV and pushes out the breather hose into your intake, this is why you have crap in your intake as well.


Many foolish people (including me before I learned) simply pop off the breather to the air.

This effectively created two problems
1. It breaths in, therefore your getting non-filtered air into your crankcase.
2. The ECU has calculated for this, so even though it is a small amount, it is calculated for, effectively reducing the ability of your ECU to compensate for changes.

The proper way is to have it all hooked up, its not just for emissions, partly is though. The correct way would be to have 2 catch cans for both the breather hoses, and the PVC. However, you want pretty strong vacuum, so many racers have actually put vacuum pumps in to help get rid of crankcase pressure, making more power.

[BLINGMW]

so I blocked it off this morning and the car starts, idles, and runs *much* better in open loop. Seemed the same once warm too. So.... whatever this connection does.... it's not much. :dunno:

[BLINGMW]

wow, someone on 318ti.org finally posted the most perfect answer ever. Air shrouded fuel injectors:

<!-- m --><a class="postlink" href="http://www.motortraders.net/groups/group.asp?group=1&menu=88">http://www.motortraders.net/groups/group.asp?group=1&menu=88</a><!-- m -->

So that's that, I'm not going to spend money fixing an obvious kludge that they could have done with the ECU. I'm blocking it all off ASAP. :thumbup: Unfortunately, since the ECU knows about this system, that means I'll likely run a little rich at idle and low load conditions. I can honestly understand them doing it for the M42, but when they started using the M44 in '96, why wouldn't they have done away with that?!

[Steve85]

So they are simply leaning out the mixture at idle and low rpm. Seems to me reducing injector pulse width and increase IAC valve "counts" would have served the same purpose. All this could be done in the ECU quite easily. Maybe I'm wrong but a lot of cars pass emmissions with out air shrouded injectors...

It's German engineering. Why use 1 part when 12 will do the job?

ding ding ding

[BLINGMW]

Apparently they put the new guy on this one. I guess the ECU firmware guy was on strike. Cause they certianly didn't do it in any of their other cars, and figured it out on later models too. :dunno:

[ViPER1313]

Word.....

Why not leave it hooked up though - vacuum hose is cheap and it will make you car get better fuel mileage...

[Maengelito]

It's German engineering. Why use 1 part when 12 will do the job?

ding ding ding

lol, as soon as I read Channing's answer, I imediately thought "ding ding ding, Rex is the winnAr!" I'm glad I'm not the only retard on this board that was thinking literally the exact same thing. :bow: