Before getting into it, here is some background:
1.) Over time, the injector O-rings just like almost any rubber, will deform, loose elasticity, change some its properties. Some effects are deteriorated mpg (for some), or fuel leak for others. The lower mpg (I experienced it too) is due air geting sucked in - just like a vacuum leak. This can be tested with a COLD running engine (in the morning, first key) and some carb cleaner - spray it around the fuel rail, and if there is a rpm surge, you found it. Very simple. When the O-rings are gone, one is responsible for a lean condition, the other one will leak fuel (I thought I had the latter, but it wasn't true). If fuel leaks, or if you lose mpg due to injectors absorbing air (lean situation), new O-rings are the cure.
2.) For the M54B30 (applies to e39 530, e46 330, X5 3 liter, z3/z4 3liter)engines manufactured I believe up to 2006, there is another issue. It's the injector himself. It seems that the batch of Siemens VDO injectors for this particular engine will deform over time (ever so slightly), allowing the fuel to mist under the hood through the fuel rail, when the car is started in cold weather. The condition is a cold engine and temperatures below -20°C (the car does not need to be parked outside, it's enough if the garage has the temp around 0°C - 2°C). Raw fuel smell will waft into the cabin a few minutes after starting to drive under these conditions. I witnessed myself the fuel mist/vapours coming out of the fuel rail. It's scary, because the engine has all kinds of electrical gizmos, and a small spark can be the end of the car's life (and maybe the driver too). I tried changing the O-rings, but it did not do the trick - I still had the raw fuel smell at cold starts and cold ambient temps. The mpg started to get back to normal though. Then I found out that BMW had an internal bulletin concerning those injectors, and there is a new batch of Siemens VDO injectors that apparently do not exhibit the deforming issue. This happens only when it's real cold, and the z series is driven mostly in warm weather, and until not too long ago, even the e39 were stored during winter (not me). More 330 had this issue, and lately the X5 with the i6 engine.
So here we go:
If you have a lean situation (mpg will start going down ever so slightly, but steady), you will need O-rings:
If you live where it's cold in the winter, and the O-rings didn't help, you need the improved Simens VDO injectors:
Remove the beauty cover (10mm). You will see the O2 sensors wires, just pull them out from the clip, set them aside, then pull the retaining clip out:
The next step is to take off 2 electrical connectors - one in front (vanos side), and one in the middle:
Now, you need to take off the long electrical connector box. This is where I had trouble, because the retaining clips are upside down, and very hard to take them off. After about 3-4 unsuccessful attempts, I figured it out. This is how they look:
Just slide one end/hook of the clip down (you don't need to take the whole clip out - that's the ticket)- here:
The last 2 electrical connections (close to the firewall), you have to slide the back side of the clip, the front side is in the way of the fuel rail skate where the screw is attached. And finally the electrical box comes out with a slight tug:
Now, before you take the fuel rail off, you need to relieve the gasoline pressure. There are 2 methods:
One is to use compressed air (if you have a compressor), set the compressor to about 30 psi max and give a short burst of pressure inside the front valve (take the cap off, and it will look similar to your tire valve stem - and works the same).
Another method is to use a small screwdriver and press the valve - fuel will come out, but not too much. Just wrap some rags around to contain the little gasoline that comes out - below are the pics:
Now you are ready to remove the screws. A good idea would be to use a magnet, because they can slide out, and fall in the engine bay, and not retrieve them anymore:
Once the screws are out, pull up on the fuel rail, and there she goes:
To take out the injectors and either replace them entirely, or only the O-rings (I would also go to a specialized shop and re-calibrate them. About 140-150 bux for 6 or 180-200 for 8. Including new O-rings, new filter and cleaning - with a detailed report), you need to pry off the retaining clip:
There is enough room on the fuel rail without needing to pull it out from the fuel line, so just pull out each injector. Here are side-by side new and old. They have different numbers stamped on them, they are very small (on the other side though):
And once an old one is out, replace with a new one:
I also cleaned the injector receptacle - it was really dirty:
Make sure you don't loose the q-tip inside the fuel chamber. Then align as close as possible the new (or old and serviced) injectors and push them together with the fuel rail in - start at the cowl (firewall) end, and work your way to the front of the engine. You might need to slightly use some force (short, sharp shock with the fist on top of each injector) to slide them in. The rest is the same as removal in reverse sequence.
Have a fire extinguisher handy, and I am sure you know you are responsible for your own doing.
Good luck
P.S. I forgot to mention: tightening torque of the bolts to the fuel rail is 10 Nm or 89 inlbs.
1.) Over time, the injector O-rings just like almost any rubber, will deform, loose elasticity, change some its properties. Some effects are deteriorated mpg (for some), or fuel leak for others. The lower mpg (I experienced it too) is due air geting sucked in - just like a vacuum leak. This can be tested with a COLD running engine (in the morning, first key) and some carb cleaner - spray it around the fuel rail, and if there is a rpm surge, you found it. Very simple. When the O-rings are gone, one is responsible for a lean condition, the other one will leak fuel (I thought I had the latter, but it wasn't true). If fuel leaks, or if you lose mpg due to injectors absorbing air (lean situation), new O-rings are the cure.
2.) For the M54B30 (applies to e39 530, e46 330, X5 3 liter, z3/z4 3liter)engines manufactured I believe up to 2006, there is another issue. It's the injector himself. It seems that the batch of Siemens VDO injectors for this particular engine will deform over time (ever so slightly), allowing the fuel to mist under the hood through the fuel rail, when the car is started in cold weather. The condition is a cold engine and temperatures below -20°C (the car does not need to be parked outside, it's enough if the garage has the temp around 0°C - 2°C). Raw fuel smell will waft into the cabin a few minutes after starting to drive under these conditions. I witnessed myself the fuel mist/vapours coming out of the fuel rail. It's scary, because the engine has all kinds of electrical gizmos, and a small spark can be the end of the car's life (and maybe the driver too). I tried changing the O-rings, but it did not do the trick - I still had the raw fuel smell at cold starts and cold ambient temps. The mpg started to get back to normal though. Then I found out that BMW had an internal bulletin concerning those injectors, and there is a new batch of Siemens VDO injectors that apparently do not exhibit the deforming issue. This happens only when it's real cold, and the z series is driven mostly in warm weather, and until not too long ago, even the e39 were stored during winter (not me). More 330 had this issue, and lately the X5 with the i6 engine.
So here we go:
If you have a lean situation (mpg will start going down ever so slightly, but steady), you will need O-rings:
If you live where it's cold in the winter, and the O-rings didn't help, you need the improved Simens VDO injectors:
Remove the beauty cover (10mm). You will see the O2 sensors wires, just pull them out from the clip, set them aside, then pull the retaining clip out:
The next step is to take off 2 electrical connectors - one in front (vanos side), and one in the middle:
Now, you need to take off the long electrical connector box. This is where I had trouble, because the retaining clips are upside down, and very hard to take them off. After about 3-4 unsuccessful attempts, I figured it out. This is how they look:
Just slide one end/hook of the clip down (you don't need to take the whole clip out - that's the ticket)- here:
The last 2 electrical connections (close to the firewall), you have to slide the back side of the clip, the front side is in the way of the fuel rail skate where the screw is attached. And finally the electrical box comes out with a slight tug:
Now, before you take the fuel rail off, you need to relieve the gasoline pressure. There are 2 methods:
One is to use compressed air (if you have a compressor), set the compressor to about 30 psi max and give a short burst of pressure inside the front valve (take the cap off, and it will look similar to your tire valve stem - and works the same).
Another method is to use a small screwdriver and press the valve - fuel will come out, but not too much. Just wrap some rags around to contain the little gasoline that comes out - below are the pics:
Now you are ready to remove the screws. A good idea would be to use a magnet, because they can slide out, and fall in the engine bay, and not retrieve them anymore:
Once the screws are out, pull up on the fuel rail, and there she goes:
To take out the injectors and either replace them entirely, or only the O-rings (I would also go to a specialized shop and re-calibrate them. About 140-150 bux for 6 or 180-200 for 8. Including new O-rings, new filter and cleaning - with a detailed report), you need to pry off the retaining clip:
There is enough room on the fuel rail without needing to pull it out from the fuel line, so just pull out each injector. Here are side-by side new and old. They have different numbers stamped on them, they are very small (on the other side though):
And once an old one is out, replace with a new one:
I also cleaned the injector receptacle - it was really dirty:
Make sure you don't loose the q-tip inside the fuel chamber. Then align as close as possible the new (or old and serviced) injectors and push them together with the fuel rail in - start at the cowl (firewall) end, and work your way to the front of the engine. You might need to slightly use some force (short, sharp shock with the fist on top of each injector) to slide them in. The rest is the same as removal in reverse sequence.
Have a fire extinguisher handy, and I am sure you know you are responsible for your own doing.
Good luck
P.S. I forgot to mention: tightening torque of the bolts to the fuel rail is 10 Nm or 89 inlbs.