Wednesday, August 4, 2010

Bosch L-jet and BMW Bavaria notes

My friend George recently helped me convert my 1973 BMW Bavaria to L-jetronic fuel injection, replacing my troublesome carburetors.  Here are some notes that might be helpful if you're contemplating a similar project for your E3 or E9:

  • It took us one weekend to do the whole conversion, from taking off the carburetors to test-driving the fuel-injected Bavaria and adjusting the timing.  We could possibly have done it all in one day if we prepared a few parts ahead of time and weren't missing some little pieces.  Overall, this conversion isn't that difficult if you have the parts.
  • I recommend using the latest version of L-jet (called Lambda L-jet and found on the 1981 528i USA models and a few other cars) over any earlier version.  The main reasons are:
    • Simpler and more robust wiring harnesses, coolant sensors are all up front in the thermostat housing rather than below the intake manifold at the "Joules Verne" device.
    • Integrated transistor ignition module (in my car, I replaced my Crane ignition with the 528i parts, which do approximately the same thing).
    • Much safer and cleaner fuel rail design.  The later fuel rail is a once-piece solid pipe with barb fittings for the injector hoses and fuel pressure regulator located up front.  Earlier rails have multiple hoses and components as well as a fuel pressure regulator located in a rather inconvenient spot.
    • Simpler and cleaner idle air bypass parts and fewer emissions things to plug up.
    • The O2 sensor of course enables the system to run more efficiently and cleaner since it provides feedback to the ECU.  This system's O2 sensor circuit is pretty basic, there's no heater for the sensor for example, and the replacement interval is about 30,000 miles.  On the other hand, the sensor is relatively cheap and it's still better than running open-loop.
  • Be prepared to "rebuild" the fuel rail before installing it into the car.  You will need some 5/16" fuel injection grade fuel line, which you'll also use for the rubber parts of the fuel supply line.  You will need to replace all of the injector seals, otherwise the system will have vacuum leaks.  Namely you need parts 1, 3, 5, and 7 on this parts diagram and a good set of snap-ring pliers.  We used modern fuel injection hose clamps over the barb fittings in place of the BMW "cup" connectors.  There's a detailed guide about this.
  • You will need a new thermostat housing with more threaded holes for sensors unless your car already has one.  The 528i L-jet needs a temperature sensor (in addition to the one-wire sender for your instrument cluster) and thermal-time switch.  There is also a heat-actuated vacuum valve for the fuel tank evaporation via the charcoal canister and you should consider installing it.  The thermostat housing must be installed after the L-jet base manifolds are in place as there isn't enough clearance to do it the other way around.  Keep in mind that there's a front and rear base manifold, the cylinder numbers are written on them (with 1 being the front of the engine as usual).
  • We used the 528i throttle linkage rod on my car, however it was too tall when used with the Bavaria linkage pivot located at the motor mount bracket.  We shortened and re-threaded mine to work.  You can do the same or you may need the corresponding 528i pivot parts.
  • The L-jet throttle has coolant hoses running underneath it.  We don't believe that these serve any useful purpose and chose to skip them as they're not needed for making the car run properly.  To bypass that mess, simply connect the small fitting on the metal coolant bypass pipe (located toward the middle of the engine) to your block's heater fitting (located near cylinder 6) with the same kind of hose that you'd use on your carburetor chokes.  I've heard two theories for why the throttle coolant lines are there:
    • They may be part of an emissions effort: by heating the intake air, the car is forced to run leaner.  This of course is the opposite of what you want, it doesn't help to have a "hot air" intake system.
    • They may be part of an effort to prevent icing on the throttle plate in some kind of insanely cold environment.  That said, some systems (ex: Motronic on the same engine) don't have this provision so it's anyone's guess as to how well that worked out.
  • When installing the intake manifold, install the two triangle-shaped supporting brackets along with the base intake manifold.  Don't wait to install them later when you fit the "log" and C-shape runners, it's a very tight fit otherwise.
  • The E12 (or other parts car's) wiring harness winds up as part of the fuel injection and ignition harness.  You'll see:
    • Red wires with an eyelet terminal which should be bolted to your starter in the same spot that the battery cable connects.  That's your power source.
    • There's a black/yellow wire near the starter which should be connected to your solenoid terminal, it's used for the cold-start valve circuit, I believe.
    • There's a black plug with two rows of pins.  This went to the car's fuse box but on our cars the only thing we need to know is it requires ignition switched +12V at pin 2.  Simply connect your carburetor choke wires (either green/yellow or green/white) to pin 2 on that connector and you're done with that plug.  You can remove and discard the choke relay that sits on top of the brake booster bracket (I chose to install my L-jet combo relay there instead).
    • There's an eyelet connector near the alternator, it hooks up to the alternator output just like the battery does.  There's also a D+ wire there for the original car's instrument cluster (alternator warning light) which can be left unconnected if your car's wiring is already doing the job.
    • There are two eyelet terminals near the ignition coil and they connect to the coil as expected.  The ECU connector also has a gray terminal which is the "pulse" wire and needs to be connected (with a long wire that you add) to the negative side of the ignition coil.  The 528i transistor ignition harness contains its own resistor pack, you'll need to remove your ballast resistor and replace your coil with the kind used on the E12.
    • The ECU itself can be placed behind the glove box but it's a tight fit and we haven't found a good way to secure it yet.  Drill a hole in the firewall and insert the ECU harness plug through it with a grommet (the E12 uses two grommets but the E3 only needs one).  A nice trick we found is to remove the casing/shroud on the connector and reinstall it over the harness is placed through the firewall.
    • Don't forget to connect the grounds (eyelet connectors) in the injector harness, one will be near cylinders 5 and 6 and another up front near 1.  They can be bolted to the intake manifold studs or to the triangle-shaped "log" support brackets.  There's also a brown eyelet up front near the thermostat housing, that's also a ground.
  • The E12 distributor replaces your original distributor and connects to the ignition control module.  There's not much to be said about it aside from it needing only a cap and rotor for maintenance.  The cap is wider than the E3 version but the same spark plug wires fit.  You may want to replace your spark plugs with ones better suited for fuel injection, check what's recommended for the E12 528i.
  • You will need to run power for your fuel pumps.  On the E12, this comes from the combo relay which winds up near your radiator overflow tank.  You could also install your own relay off the E3's electric fuel pump fuse (and corresponding connector, located right behind the fuse box) if you wish.  I ran the wire on the driver side following the harness under the carpet at the rocker panel.  This requires taking out the driver's door threshold plate and peeling back the carpet and then taking out the rear seat as the harness curves up and under the parcel shelf.  In the trunk, it comes down the driver side wheel well and around under the tail lights.  Some fuel pump wiring tips in the trunk:
    • ground the pumps near where they sit, for example I grounded the in-tank pump at the trunk ground point for the other wires (tail lights, etc).  I grounded the second pump to the car body near where I mounted it via a self-tapping screw.  Never run power and ground wires together through a grommet, it's dangerous and there's no need, the whole car's body is ground.
    • run the external pump's power through the trunk (and a grommet) to the pump, near where the fuel line exits.
    • don't forget to grab connector pigtails for the in-tank pump and fuel level sender from a parts car so that you can solder your wiring to them.  Otherwise you need some very odd connectors and that can be cumbersome and messy.
  • You will need the right valve cover for a coupe of reasons:
    • The oil filler cap on the E3 is in the front but it needs to be in the back to get around the AFM and air cleaner assembly.
    • The 528i L-jet air bypass valve mounts to the air cleaner.
  • I couldn't find an E12 valve cover but we noticed that early Motronic covers are the same part except that the air bypass mounting holes aren't drilled and tapped.  George was able to drill and tap them so that worked out fine.  Unfortunately these later valve covers have their front bolt offset from where the original E3 bolt hole is.  You must therefore replace your upper front timing cover (and gaskets) as well.  We didn't do that on my car for now, instead we sealed up the hole (to prevent vacuum leaks) and inserted a short bolt for now.

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