So what's the deal with the vaccuum/air connection at the fuel injectors?

[ecpreston]

No other BMW I've had has had this, and searching here and google, I can't find an explanation. So what's the deal with the hoses connected to that 4-way splitter and then to the intake boot?


not a pic of mine, stolen from elsewhere in this forum:


Mine were split, cracked, and letting a bunch of false air into the intake, so it hesitated a bit until warm when it got in to closed loop operation. But what was that connection supposed to accomplish? I disconnected and blocked off the hole at the intake boot this morning out of curiosity, and sure enough, it ran *much* better when cold, no apparent change when warm.

Is it a cooling system for the injectors?
Safety system so if injectors start leaking, it goes into the intake instead of just everywhere?
Do these injectors adjust something individually based on pressure?
Emissions related thing when coasting?
Does any other car other than the E36 318 (i/is/ti) use this? My '91 M42 318 sure didn't. I'm pretty temped to leave it blocked off and remove that squid of hoses.

[b.u.ti-ful]

http://www.motortraders.net/groups/g...roup=1&menu=88

[ecpreston]

Wow. That's like, the most perfect answer I've ever received. Thanks!

And yeah, I'm probably not going to spend money fixing that system. That looks like a pretty ghetto way to do something that could have been done by the ECU.

[b.u.ti-ful]

I guess if you blocked it off and it runs good it's probably fine.

I replaced the cracked hoses on mine - the parts were not expensive and it's an easy job.

[ecpreston]

it is fairly easy, and fairly cheap, but I'd rather not bother. I guess since the ECU expects the system to be there, it'll probably run a little on the rich side during low load, low RPM conditions, but this car isn't going to spend much time doing that. I'll likely dyno it in a few months and make sure the AFR is good to go.

Just so others might find this while searching, they're called "air shrouded fuel injectors". YEAH.

[MPWR]

The air intake line for the injectors is taken downstream of the MAF. So if you securely block those air hoses, you shouldn't have any mixture issues- all the air passing through the MAF is still going into the engine.

The only issue I can think of with running without it is fuel atomization. If those injectors are designed to spray the fuel into the airstream from the hoses, if the airstream is removed the injectors might not spray optimally.

I'm getting ready to replace them on mine- I know they're leaking which means the engine is probably running a tad lean. I'm going in to do the plastic coolant pipes, but it seems silly not to do these also.

I'd be curious to hear if you get a dyno (or emissions) difference running without them.

[pdxmotorhead]

Hilborn, Kinsler, Lucas Mechanical injection have a similar air bleed to help fuel atomize at idle and smooth out performance, it also helps power a lot at high RPM. (Better Fuel Atomization?) Any way when they plug up on a sprint car teh performance tanks...

Dave

[CirrusSR22]

Here's the work I did on those which I included in my cooling system write-up. It has seemed to fix all issues I had last winter with cold starts.

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Last winter I started having trouble with very cold starts with my ti. I think I tracked it down to a vacuum leak somewhere, so I just did work to fix that. Since it involves taking the engine apart, like doing the cooling system, I highly recommend replacing the following parts while you're in there as they are rather cheap.

The goal for this project was to replace every vacuum hose and o-ring that could lead to a vacuum leak in cold weather.

Parts:
• Fuel Injector O-Rings: 13641743377 (4x)
• Fuel Line O-Ring (replace, as long as the fuel rail is off): 13531247953
• DISA O-Ring: 11611437690
• Vacuum hose between the intake boot and injector vacuum hose "Tree": 13411247782 (no ASC part#)
• 3' of Goodyear 5/16" (7.9mm) Fuel/Emission Hose, Auto Zone. Approx $1.19/ft.
http://www.goodyearep.com/productsdetail.aspx?id=10526

• 1' of Goodyear 5/16" (7.9mm) Fuel Injection Hose, AutoZone. Approx. $3.39/ft
http://www.goodyearep.com/ProductsDetail.aspx?id=5144
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I replaced the roughly 3" segment of fuel-rail hose with the Goodyear Fuel Injection hose. As you can see from the link above, it's a special high pressure, specially lined hose just for fuel injection supply. Do not use the standard fuel hose. That's for the vacuum work.

The top hose is the higher quality injection hose and the bottom is the emission hose.

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Here's the new Goodyear injection hose on the left next to the little segment that connects to the fuel rail. This is an optional step, but it's worth it when you're in there. I think this hose can also be used when replacing your fuel filter. I know the hose at my fuel filter connections is in bad shape.

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Next I replaced the fuel injector o-rings that seal the injector to the manifold. Surprisingly my injectors are MUCH cleaner at 185,000 than they were at 158,000 when I did the orginal project. I've been using the new BP gas with Invigorate a lot lately. Maybe that actually works?

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Old, squished O-ring.

--

New, fresh o-ring, lubed with brake caliper grease. I hear that's a good choice for injectors since it's rubber safe.

[CirrusSR22]

Next I tackled the injector vacuum "tree" which is getting notorious for hard, brittle hoses that crack. See elfhearse's picture above! Mine were not as bad, but were definitely starting to crack. They were also getting extremely hard.

Following elfhearse's advice, I found the Goodyear 5/16" (7.9mm) fuel/emission hose to be a perfect fit. I suggest slicing the old hoses off with a razor.

Cut replacement hoses from your 3' section of emision hose and reassemble the tree. You'll need no more than 2' of the Goodyear emission hose which will be under $2.50. You can also buy a new tree assembly from BMW for about $26. Replace the larger vacuum hose that runs from the tree to the intake boot as well.

Orginal tree.

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Hoses removed

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New hoses fitted. The tightly bent hose is a little finicky because the factory hose is molded to that curve, whereas the emission hose kinks a bit when you bend it that tight. It takes a little squeezing/working of the hose to remove that slight kink. That's the only downside I can think of by using the Goodyear emision hose vs. a new factory tree. Thankfully you can make the curves of your replacement hose larger than the factory hoses as there's no need to make an EXACT reproduction of the factory hose. All this is doing is carrying a little vacuum.

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After that, I used the remaining portion of the emission hose to replace the section that runs from the throttle body to the "fuel tank breather valve". Not sure what this valve does, but it's electrically controlled and it sits between this vacuum hose and the carbon filter.

The hose in question:

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Simply replace this hose with the remaining emission hose. The original hose is molded to keep it from touching the alternator. I found I needed to use a little electrical tape and attach it to the bottom of the intake boot to provide clearance from the alternator.

While everything was out, I also replaced the o-ring that seals the DISA valve to the lower intake manifold. Just remove the three bolts holding on the DISA valve, use a pick to remove the old o-ring, and install the new one using some synthetic caliper grease. Make sure you clean the bore the DISA valve goes into first with a clean rag.

Also, use a pick and replace the tiny o-ring that's in the hard fuel rail connection. Probably not necessary, but might as well as you have everything apart.

[pdxmotorhead]

Nice pics and writeup there guys!

The tank valve is also called the purge valve it opens to evacuate the vapors out of the fuel tank. It allows the vapor to be sucked through the charcoal canister and burn through the engine. If this is not working its pretty common to have odor in the car...

Dave

[ecpreston]

thanks CirrusSR22, I had posted this in your thread but didn't get any replies. Good pics though thanks!

[ecpreston]

So, going on three weeks with the system removed and capped off at the injectors and intake boot and no ill effects, no apparent change in fuel economy, cold or hot driveability, or ECU codes thrown or anything. I ended up having to remove the top of the manifold to really get in there, but that wasn't hard and gave me a chance to inspect a few things, clean and adjust throttle and such.

[ssimms]

This isn't that difficult to get to so I will just rebuild the tree with vacuum hose when necessary. I have found over the past 28 years of BMW ownership that BMW did a pretty good job of engineering things and the cars themselves are better off left to the expert engineers. I just do the labor and leave the fixes and parts to BMW.

[atlanta318ti]

nice writeup

[6speed ti]

My hoses were cracked when I replaced the injectors at 200,000 miles. I went to a local auto parts store and purchased some hose and made up my own lines. BMW does sell the entire hose and fittings as one assembly if you want to go that route. The injectors on the M44 engine use air to better atomize the fuel coming out of the injector. So replace the hose(s) if they are worn or cracked. Do Not block them up. They are there for a reason.