BMW 733i E23 Fuel Rail Information

My 1984 BMW 733i has been sitting, parked, for several years and it’s safe to say the fuel system is suspect. I drained the fuel tank, and cleaned out the crud at the bottom of the fuel tank as well as I reasonably could without removing the tank.

I swapped out the fuel sending unit and in-tank fuel pump with more-likely-to-be-reliable units. The replacement in-tank fuel pump ended up being dead too. These pumps are hard to find in good working condition. Without them the car will run but it’s vulnerable to vapor lock, typically on hot days.

I replaced the main (in-line) fuel pump and fuel filter.

I also removed and tested the fuel injectors, which involves removing and replacing the fuel rail.

My first step was to remove the 13mm bolts and nuts that attach the two struts (one in front, one in back) that connect the valve cover to the intake manifold, and make it impossible to remove the fuel rail while they are in place. The back strut has two sensor wire plugs attached. The front strut has a diagnostic plug attached. It’s not necessary to remove either of these. I just moved them out of the way.

My next step used a pick tool. This is sort of a smallish screwdriver with a not-quite-straight pointy tip like an awl. I used that to loosen the metal retaining rings that lock the plastic electrical connectors into each of the fuel injectors. The plastic was brittle and I found it impossibly hard to slip the little wire clip off each connector without breaking something. With the little wire clips off each connector, each connector and its attached wire could each be slid off its injector.

The next step involved using a flat-headed screwdriver to loosen the clamps around the fuel lines that attach to the fuel rail, then using a Vice-Grip to move the fuel line back and forth, and then using some combination of these tools to get the fuel lines slid off the fuel rail. There are three lines: the inlet line at the back, the return line that is attached to the fuel pressure regulator that’s at the front of the fuel rail, and then another line somewhere near the back and towards the bottom. I’m guessing that this is the line to the cold-start injector.

Next, I pulled the vacuum hose off the fuel pressure regulator.

The next step involved removing the four 10mm bolts that attach the fuel rail to the intake manifold. This freed up a slew of intimidating-looking brown ground-wire ring connectors.

At that point, I could remove the fuel rail and move it so that it is clear of the throttle body, and able to slide out the front. To loosen the injectors from their respective holes in the cylinder head, I tried to rock the rail back and forth. I tried to pull up on one side of the fuel rail and then the other. I tried to pry it up with a steel bar. Some combination of this worked.

The wiring harness tends to get in the way, but moving it aside isn’t a problem. Then, you can remove the fuel rail, and at the end of the exercise, you have a fuel rail with six fuel injectors in your hand.

If you have my sort of track record, you’ll notice that some of the O-rings that seal the injector to the head came with the fuel injectors and at least one didn’t. At the time, I worried about this a lot, and I raided a 1987 535i fuel rail that I had handy, only to find out the injectors are different. I then raided my 1983 733i and found the injectors to be the same, so out of twelve injectors I chose the sex best-looking ones for the fuel rail to be re-installed. I focused on which ones didn’t have O-ring damage. Later, I learned that NAPA sells replacement O-rings at very reasonable prices. I plan to buy some.

I tested each injector by putting 12V over it and listening for a “click” and seeing it spew liquid when I pressurized the fuel rail.

I have an informal test-bench set-up that uses rubbing alcohol instead of gasoline. The alcohol evaporates quickly so I don’t have to worry about it leaving a residue on the parts, and it’s not as much of a fire hazard as gasoline is.

I removed the old O-ring(s) that stayed behind in the little holes in the cylinder head. I next lubricated the O-rings on the to-be-re-installed injectors using a thin layer of white grease.

I then moved the newly-tested fuel rail back into position, and pushed it down firmly so that the each injector seated into its little cylinder-head hole.