AFM and injector swap

Around July/August of 2001, I decided to attempt the "big six" AFM swap. People often spoke of this swap, but no one that I talked to seemed to have actually done it, or had specific information on what was involved. I decided to go through with the swap, documenting both the procedure as well as the results. This way people would know exactly what is involved in the swap, as well as what they should expect as far as performance gains.

I purchased an M30 AFM (from an '86 535i), and another M20 AFM ('86 325). I figured it would be better to modify these two, leaving my existing AFM intact in case I run into problems. This will also leave my original system intact, so that I could dyno the car with both setups for comparison.

I removed the electronics board from the M30 AFM, which was not particularly easy. First, note how much tension is on the gear, when you take the retaining wire off. The gear will probably only move 3 or 4 teeth positions. Once the arm and plug is out, remove the steel screws which hold the circuit board into the aluminum housing. I am not sure if it is due to the different types of metals, or if the manufacturer puts some form of thread lock on the screws, but they are not easy to turn. One of the screw heads stripped. Since this is the M30 AFM, my concern is getting the screws out, not the circuit board. I bent the board up and back until the corner broke off. I removed the remaining corner of the board, then had enough room to use some pliers on the screw (which did finally come out).

Since the housing is aluminum, I decided to clean it up using a foam sanding block and steel wool. I did this for both the outside, as well as the areas inside that I could reach. It was pretty easy, and looks *so* much better!

At this point I removed the electronics from the donor M20 AFM. Again, 2 screws came out with a little work, but the 3rd stripped (different location than on the other AFM). Since on this AFM my concern is the circuit board, I took a hacksaw blade, and slowly cut a groove through the top of the screw. I cut almost all the way through the head, then used a flat blade screw driver to twist it. The screw head broke off, which was fine.

Here are a few pictures at this point, which show the difference between the two:

Air filter

Since my existing K&N cone air filter will not fit, I needed to purchase a new one. Unlike the M20 AFM (which requires a mounting flange), the M30 AFM has a 3 1/8 inch (o/d.) flange which you can clamp a cone air filter to. I took some measurements in the engine well, then checked out what was available. I ended up ordering K&N part number RC-3250 from Martel Brothers Performance. Now that I have the filter, I can position the assembly in the engine well, and see how and where I will mount it.

Fuel system

Since I will be changing the amount of air getting into the engine, I figured that it would also probably be a good idea to increase the available amount of fuel as well. Apparently the stock injectors are barely adequate for a stock motor, and tend to lean out drastically at higher rpms.

The 325i uses Bosch 0 280 150 715 injectors, which have a rating of 149cc/min.
The 535i uses Bosch 0 280 150 203 injectors which have a rating of 185cc/min.
I ended up purchasing Bosch 280 150 556 which have a rating of about 200cc/min. They are the Mustang injectors (Ford part# FOTE-D5B).

Realizing that I have no means to see what is happening as far as the air/fuel ratio, I purchased an Auto Meter Z series 2 1/16" electric air/fuel ratio gauge (2675) from Summit Racing, which I installed in the console. I wanted to keep the console pocket, so I decided to remove the ashtray and create a custom panel for 2 gauges. I am not sure what the 2nd gauge will be. For now I just needed the one gauge in.

I installed the gauge, which was pretty simple. There are 4 wires on my O2 sensor, 2 white, 1 gray and one black. The diagram in the Bentley manual showed the signal wire to be the gray one. I hooked it up this way and the gauge was only reading lean. I used a volt meter and checked the output at the O2 sensor, and it turns out that the signal wire is the black one.

The next step is to add an adjustable fuel pressure regulator and fuel pressure gauge. Apparently you need to ease the ECU into the larger injectors, by first installing them, but using a lower fuel pressure (2.5 bar). Once the ECU has adapted by reducing the duty cycle of the injectors, you can return the pressure to the stock level (3.0 bar), and the ECU compensates by further reducing the duty cycle of the injector. After looking for an adjustable fuel pressure regulator which would work for this application, I decided to go with the kit that BMP sells. It seems expensive, but to find a different regulator and gauge, then fittings/connectors to replace the existing regulator (on the fuel rail) with the new one, the price will be close. Since the BMP kit comes with all the necessary hardware, I decided that would be much easier.

I received the BMP kit, and I can't say I am all that impressed. Several hardware pieces were missing (the rubber mounts as well as some of the bolts/nuts). The 2 hose fittings appear to be glued in, and actually look as though they have been used before. There were also a couple of pieces which were not connected (for no reason) which meant I would need to pick up some thread tape before I could assemble them. They include new fuel and vacuum lines, but both were far too short (the included vacuum line was less than 12" long).

I checked to see how I would mount the regulator in the car, and was quite surprised to find out that there is little to no room to mount the regulator! Here are a few pictures of the left side of the engine well. You can see the regulator on top of the coolant reservoir for size reference:

Since the regulator has hose fittings on 2 sides and the gauge on a third, I decided that it was not going to fit like this. I checked to see if the gauge could be mounted somewhere else, and it turns out that there is room to mount it on the fuel line adapter (where the existing regulator is now). I went to remove the existing gauge, and could not turn it with a wrench. In a moment of utter stupidity, I thought I could hit the wrench with another, in order to get the gauge to begin to unscrew. Well, the shock from the impact of the two wrenches was enough to cause the gauge needle to jump to 20psi and stay there. I put the regulator in a vice (protected with a rag) and easily removed the gauge, but since this gauge would no longer give me accurate readings, I was going to have to order a replacement before I could continue. I ordered a chrome with white face, 1.5" VDO 60psi pressure gauge (part #153-005) from egauges.com for $25.50. This is essentially the same gauge the regulator came with, except a different color, and I chose one with the maximum psi of 60 not 100. Since I will not be exceeding around 45psi, I figured this gauge would be easier to get an accurate reading from. Here are the two gauges for comparison:

While waiting for the gauge to arrive, I stopped at a hardware store and picked up the fittings that I would need to mount the gauge to the fuel line adapter. I bought a 1/8 MPT tee (female on all sides), a 1/8 MPT to MPT hex nipple and a 1/8 plug. This will allow me to mount the gauge between the base and the hose fitting of the fuel line adapter. The plug will be used to cap the hole in the regulator where the gauge was previously mounted. Be sure to use thread tape when connecting the fittings.

The next item on the list was replacing the injectors. First, the electrical plugs need to be disconnected. Some cars (like mine) have the injector electrical connector wires running through a plastic tube. This needs to be removed in order to get the injectors out. You also need to remove the small manifold bracket in order to make room to remove parts. Remove the clips that hold the electrical connectors to the injectors. This takes a small screw driver and some patience. Once these are out, remove the plug on the drivers side of the engine. The injector wiring can now be pulled out.

I removed the bolts which hold the fuel rail to the intake manifold and pulled the assembly up to separate the injectors from the head. Next, I removed the clips which hold the injectors to the fuel rail, and pushed the injectors out. I put a little clean oil on the new injector O-ring before inserting them into the head. Once they were in, I connect the fuel rail, the electrical connections and bolted everything back down.

I started the car, set the fuel pressure to 2.5 bar and let it idle. The air/fuel ratio gauge was reading rich for a few minutes, then began reading normally. In the morning, I took the car for a quick drive, then set the pressure back to 3 bar. After a few minutes the ECU again adapted to the change and adjusted the injector cycles accordingly. I took the car for a nice long drive, and it ran great. I am not sure how to explain it, but the car just seemed to run better. It just seemed to run stronger and more smoothly.

With the fuel system now ready, I was able to start building the brackets to install the AFM. I bought some 3/4 inch steel strips, which I used to make the brackets. Since the angle and position was correct, I left the existing aluminum bracket (which came with my cone air filter kit) installed, and found a way to attach the new AFM to it. The problem is that the bolt holes for the M20 AFM are on the left side and the bolt holes on the M30 AFM are on the top, 2 along the right side and one on the left. What I ended up doing is making two brackets which go from the holes on the top right side, over and down the right side, then underneath the AFM to the aluminum bracket. I drilled two holes in the aluminum bracket, and bolted the new brackets to it. I also bolted the end of the brackets to the holes in the AFM. I then made a small bracket to connect the one hole on the top left side of the AFM to the aluminum plate. Once I get a chance, I will pull out the brackets and make a diagram of them which shows the shape. I will also list the hardware needed to assemble this. Here are some pictures which show the M30 AFM installed:

Since the new AFM is mounted in almost the same position as the old one, there was just a small gap between the intake bellow and the AFM. I did find a place which said they could make a 3" aluminum tube to connect the AFM to the throttle body, but that won't be for a couple of days. The rubber bellow is too small to connect to the AFM, but I decided to use duct tape to connect the two pieces, so that I could see if the car would actually start.

I turned the key, and the car started right up! I took the cover off the AFM, and could see that the components were working normally. The air/fuel ratio gauge also seemed to be reading normally, so I took the car around the block (a couple of times :-)

I was not really hard on the acceleration, since I was just trying to make sure that everything was working ok. I will say that the car felt stronger, and the intake had a deeper sound. I am really excited about getting the car on the dyno and getting it tuned, as well as graphing the difference between the different AFMs.

Here is a general breakdown of the project:

Reference articles:

Fuel Injector Flow Rates
E30 Fuel Injector Upgrade Information
Fuel Injector Technical Information
Air Flow Meter Adjustments