Finally fixed my P0170/P0173 problem in my '01 750iL

[NotEnufGarage]

Those two codes (P0170 and P0173) had been dogging me for a while. After taking a broken injector apart, I found the cause of the problem.

The 5/97 to 2001 M73N 750's use a "Air Assisted Injector", which gets manifold vacuum through the pintle cap. Under the outer cap that has the vacuum nipple on it there is an inner cap that is locked onto the injector by a U shaped clip. On the inside of the inner cap there's an O-ring to seal it and the U shaped clip provides tension to get it to seal. On the outside of the inner cap there are two more O-rings that seal against the outer cap. Here is where the problem lies. These O-rings get hard and brittle over time. They will stay sealed if they are never disturbed, but if you have to replace any injectors with ones that have been used, repositioning the vacuum nipple is enough to break the seal and the will probably not seal again on their own. I had to replace several injectors because of broken pintle caps that made it impossible to get the lower O-rings on the injectors to seal.

I fixed them by running a very fine bead of RTV silicone on the joint between the lower cap and upper caps on the injectors, creating a new seal. After letting them set up, I put the car back together and took it for a drive. No codes set and it passed 8 of the 9 of the inspection monitors within about 20 miles of driving (all except heated catalytic converter which ran during a subsequent drive).

I took some pictures that I'll upload later.

[ryanpeter]

Awesome. That's good to hear.

[Clintjebmw]

Nice

[Binjammin]

Hopefully the RTV you used won't dissolve in fuel.

[NotEnufGarage]

Hopefully the RTV you used won't dissolve in fuel.

The seam between the inner and outer caps is on the outside of the injector so it won't be exposed to gas, except for fumes. To be safe, I also wrapped a few layers of black tape around them to hide and protect the RTV.

In retrospect, if I had to do it again, I'd used clear nail polish or something similar to seal the seam. RTV is too messy to use on small parts.

[Binjammin]

The seam between the inner and outer caps is on the outside of the injector so it won't be exposed to gas, except for fumes. To be safe, I also wrapped a few layers of black tape around them to hide and protect the RTV.

In retrospect, if I had to do it again, I'd used clear nail polish or something similar to seal the seam. RTV is too messy to use on small parts.

Clear nail polish will be hard, and crack almost instantly as the injector heats and cools down. You want something that's fuel safe and flexible.

[Cubehacker]

Those two codes (P0170 and P0173) had been dogging me for a while. After taking a broken injector apart, I found the cause of the problem.

The 5/97 to 2001 M73N 750's use a "Air Assisted Injector", which gets manifold vacuum through the pintle cap. Under the outer cap that has the vacuum nipple on it there is an inner cap that is locked onto the injector by a U shaped clip. On the inside of the inner cap there's an O-ring to seal it and the U shaped clip provides tension to get it to seal. On the outside of the inner cap there are two more O-rings that seal against the outer cap. Here is where the problem lies. These O-rings get hard and brittle over time. They will stay sealed if they are never disturbed, but if you have to replace any injectors with ones that have been used, repositioning the vacuum nipple is enough to break the seal and the will probably not seal again on their own. I had to replace several injectors because of broken pintle caps that made it impossible to get the lower O-rings on the injectors to seal.

I fixed them by running a very fine bead of RTV silicone on the joint between the lower cap and upper caps on the injectors, creating a new seal. After letting them set up, I put the car back together and took it for a drive. No codes set and it passed 8 of the 9 of the inspection monitors within about 20 miles of driving (all except heated catalytic converter which ran during a subsequent drive).

I took some pictures that I'll upload later.

Can anyone give me more details about how to fix this problem?
Iam suffering about this problem since over 1 year and even
The bmw dealer here in germany couldnt fix it.