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Fuel injector hoses?

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Fuel injector hoses?

Post by stack633 » Sat Jul 25, 2009 3:35 am

Hi all, im currently replacing fuel injectors on my 79 633csi which uses the l-jetronic fi. I have the fuel injector rail disconnected and am ordering new injectors but I also need to replace the short rubber hoses (about 3 inches long) between the fuel injector rail and the fuel injectors themselves.

Any suggestions on how to replace the hoses and where to find them? They might as well be 30 years old so leaving them in is not an option.



Post by m6csi » Sat Jul 25, 2009 9:36 am

The new injectors will have the short hoses already fitted. All you need to do is to fit all six injectors into the fuel rail.

Having done this job replacing all the old injectors with new ones a few years back on my L-jet equipped 3.0 CSi, here are some tips that will make the installation easier and leak free.

The short fuel hoses that are oem fitted into the fuel rail and the injectors are inserted into "Christmas tree" barbed nipples on all 6 injectors, cold start valve connector and the fuel rail. The hose connections on both ends are capped with the bowl shaped brass fitting and are held with friction only, so do not crimp them. Do not use worm clamps or fuel injector clamps on these barbed nipples as these clamps will not form a perfect round seal due to their design and will undoubtedly leak almost instantly. On the single fuel feed nipple of the fuel rail, a worm clamp is all that is needed on this straight nipple so fuel leak is not a concern.

When inserting the 6 injector hoses and the CSV hose into the fuel rail, do not install them dry as they are next to impossible to insert and once they are even partially engaged, you'll not be able to pull them out. The only solution is to cut them out with a razor blade. Install a brass bowl connector into each of the nipples on the rail first, next, dip the injector hose ending into some gasoline that is contained in a small container (petroleum jelly can be used also) and push right into nipple. It should slide right in without much effort, push it all the way in until it is firmly sitted against brass bowl. When this is done with all 6 injectors, twist them one way or the other to align the electrical sockets on the injectors facing straight up.

Since all new injectors are being installed, you might as well replace all the rubber fuel hoses in the engine compartment. These hoses include the fuel feed and return line as well as the cold start valve fuel line. Recommend that you use the oem Bmw 8x13 FI high pressure hose. They are sold in 1 meter lengths, suggest getting a couple of meters. Some of the injector mounting components should also be changed, such as the nozzle tip rubber O-ring, the large rubber mounting isolator on the injector body and the ceramic liked insulators that are used for the 2 mounting screws for each injector. To remove the oval injector metal mounting plate and the large rubber ring, a circlip plier is needed. Do not lose any of the circlips as they are NLA! Here is the link for all the components listed: ... g=13&fg=15

In the future, if you need to remove and fit a new hose into an injector for any reasons, here are the procedures. Cut the hose close to the injector nipple. Next, use a sharp single edge razor blade and make repeated scores on top of nipple until hose is almost cut through then use a plier to twist out rubber hose. Don't loose the brass "bowls". Use care as you don't want to damage the nipple barbs, doing so can cause leaks down the line. Repeat same procedure on fuel rail end. Believe the original length on the injector hose is about 2 5/8". Hose installation procedures are the same as described above. When cutting the FI rubber hose, a clean and straight cut will make installation easier and lessen the chance for fuel leaks. Use one of those long single edge razor lined cutting tools--- it makes perfect, clean cuts every time.

As I recall, the rubber hoses used on the new Bosch injectors were amazingly tight fitting. Had a very difficult time in fitting them into the fuel rail even with lubrication. Ended up removing all the new injector hoses and replaced them with the Bmw hose. I don't suggest you go through this drastic route so thoroughly lubricate the hose endings prior to installation. Bosch and Bmw both use 8x13mm hoses so I suppose the fitment differences are due to different construction methods and dissimiliar rubber used in manufacturing. Both hoses had a different look and texture.

Here are some pics of the Bosch injector and its associated components.

Old injector with nozzle O-ring and large body ring installed. Missing oval metal mounting plate.

Bare injector with hose removed.

New out of the box injector should look like this.

Injector mounting parts. Reddish gasket liked insulators---2 pairs of these per injector.

Bmw 8x13mm high pressure fuel injection hose.

88 M6
72 3.5 CSi

Chris Wright

Post by Chris Wright » Sat Jul 25, 2009 4:29 pm

Nice write-up Bert! 8)

Just some interesting links:

Here is a source for cleaning and flow testing injectors:

Removing the hoses on the injectors:

A source for a reconditioned set:

Here is the FirstFives tech library, lots of good stuff for the L-Jet:

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