BMW Bosch L-Jetronic Fuel Injection - Strip-Down / Maintenance Guide + Diagrams [E30, E21, E28]

Throttle Housing:
1. Disconnect the cables (1, 2 or 3) as applicable - Fig. 1.
2. Pull off the vacuum hoses, the coolant hoses (1 and 2) - allowing the coolant to drain - and the air hoses (3 and 4) from the throttle housing - Fig. 2.
3.Remove the vacuum hoses (1 and 2), and the air hose (3) and pull off the multi-pin plug (4) - Fig. 3.
4. Remove the fixing nuts and take off the throttle housing. Do not separate the throttle switch from the housing, as a special gauge will be required to adjust it when refitting.
5. Refitting is a reversal of removal. Use a new gasket and bleed the cooling system.

Throttle Vacuum Control:
1. Pull off the hose (1), release the nut (2) and remove the vacuum control (3) - Fig. 4.
2. When refitting, adjust dimension (B) to between 32.8mm and 33.2mm (1.291" and 1.307") using screw (4).
3. Adjust dimension (A) to between 2.6mm and 3.0mm (0.102" and 0.118") using screw (2) - Fig. 5.

Control Unit:
1. Open the glove compartment and pull the pins from the retaining straps.
2. Remove the screws and place the glovebox cover to one side.
3. Depress the retainer (1) and pull out the multi-pin plug (2) - Fig. 6. Remove the control unit.

Air-flow Sensor:
1. Release the clamp and pull the duct from the air-flow sensor.
2. Disconnect the multi-pin plug, unscrew the fixing nuts and withdraw the sensor.
3. Refitting is a reversal of removal. Renew the seal if necessary.

Temperature Time Switch:
1. Pull off the plug, then unscrew and remove the switch.
2. Refit the switch using a new sealing washer.

Coolant Temperature Sensor:
1. Pull off the plug and unscrew the sensor. Refit using a new sealing washer.

Cold Start Valve:
1. Pull off the plug (1) and disconnect the fuel line (2) - Fig. 7.
2. Unscrew the mounting bolts (3 and 4) and withdraw the valve.
3. Use new seal when refitting.

Fuel Injectors:
1. Unscrew the four injection tube bolts and push the tube upwards until the fuel injectors have cleared the guide in the intake manifold.
2. Pull off the plug (1) and take out the circlip (2) - Fig. 8.
3. Take off the fuel injector.
4. Refitting is a reversal of removal; use new O-ring seals.

Throttle Shaft Return Springs:
1. Disconnect the throttle, kick-down and cruise-control cables. (The latter two where applicable.)
2. Remove the retainer (1), washer (2) and disconnect the linkage (3) on the lever (4).
3. Raise the lever and turn it to relieve the spring tension.
4. Remove the lever.
5. Remove the spring.
6. Disconnect the spring (1) and unscrew the nut (2) - Fig. 9.
7. Remove the washer (1) and lever (2) - Fig. 10.
8. Remove the sleeve (1) and spring (2) - Fig. 11. - also the wave washer.
9. Reassemble in the reverse order to dismantling and adjust in the following way - Pull off the tamperproof lock (1) and loosen the screw (2) until the lever (3) no longer rests on the screw - Fig. 12.
10. Place a finger on the lever and tighten the screw until the lever just begins to move. Turn the screw a quarter-turn more and refit the tamperproof lock.
11. Adjust the throttle, kick-down and cruise-control cables (where applicable).

Injection-system trouble-shooting guide here - https://www.beemerlab.org/2020/12/bmw-bosch-fuel-injection-system-trouble.html

Bosch L-Jetronic injection-system overview / diagram here - https://www.beemerlab.org/2019/11/e30e28e34-bosch-l-jetronic-fuel.html

E21/E12/E28: Bosch K-Jetronic Fuel Injection System Diagram / Explanation

Two types of fuel injection system are fitted. E21 3er 323i models are equipped with the Bosch K-Jetronic system, whereas E30 3er 320i and 325i models are fitted with the Bosch L-Jetronic system. This article covers K-Jetronic injection for E21 models, also injected E12 and early E28 5er. For L-Jetronic in E30 models, also later injected E28 5er, see THIS ARTICLE.

K-Jetronic Operation:
Fuel is drawn from the fuel tank by an electrically-operated pump and is then fed, via a pressure reservoir and filter unit, to the fuel distributor-unit. The fuel is then pumped direct to the fuel injectors which are located near the inlet valves, but mounted in four induction-manifold branches. The system is continuous acting type and the amount of fuel admitted to the injectors, by the fuel distributor, is governed by a pivoting baffle-plate mounted in the air-intake. Air drawn into the engine lifts the baffle-plate and this action moves a metering shuffle-valve in the fuel distributor. The ratio of air to fuel is thus controlled to a fine degree. After the mixture is drawn into the cylinder, the normal four-stroke combustion cycle takes place.

The fuel is maintained at a constant pressure by a pressure-regulator incorporated into the fuel distributor-unit, excess fuel being diverted through a return-line back to the fuel tank.

For cold starting, a solenoid valve injects fuel into the air-intake for a period determined by the coolant temperature. In addition, a temperature sensitive (warm-up) regulator, working in conjunction with an additional air slide-valve, is connected to the fuel distributor-unit and has the effect of increasing the amount of fuel delivered by the injectors. Later models are fitted with a throttle bypass-valve in place of the additional air slide-valve. On some specific versions this valve is coolant-heated.

A normal type throttle butterfly-valve, mounted between the baffle-plate and the cylinders, is connected to the accelerator pedal linkage. These constant flow injection systems work in a similar manner to a carburettor, vaporising fuel in the inlet-manifold and metering it into the engine.

E30/E28/E34: Bosch L-Jetronic Fuel Injection System Diagram / Explanation

Two types of fuel injection system are fitted. E21 3er 323i models are equipped with the Bosch K-Jetronic system, whereas E30 3er 320i and 325i models are fitted with the Bosch L-Jetronic system. This article covers L-Jetronic injection for E30 models, also later injected E28 and early E34 5er  For K-Jetronic in E21 models, also injected E12 and early E28 5er, see THIS ARTICLE.

K-Jetronic Operation:
In fuel injection systems of Bosch L-Jetronic type, the volume of air drawn in by the engine is measured.

Each cylinder has its own independent injector.

An additional air slide-valve bypasses the throttle butterfly stub pipe and controls the additional air volume required when the air is still cold. When the engine is warm, idle speed airflow control is by means of another bypass around the throttle butterfly.

Fuel supply and pressure is provided by an electric pump with an inline filter and pressure regulator.

The volume of air drawn into the engine is measured by the air flow meter and this is converted into an electric impulse and transmitted to the control unit. A calculation is made to determine the quantity of fuel to be injected (based upon the engine running speed) into each cylinder.

Automatic cold-start and warm up devices are incorporated into the system with corrections made to the amount of fuel delivered for idle-speed and full-load by contacts in the throttle butterfly switch. When the engine is on the overrun and throttle is closed, due delivery is shut off completely.

The electronic control unit processes information from the various engine sensors and sends an impulse to the electromagnetic fuel injectors, telling them to open for a precisely defined period and deliver a set amount of fuel for each ignition. This is how most modern fuel-injection systems (with the exception of direct-injection systems) work.

E39 Audio: On/Off Switch for the Amp/Subs

The system remote shuts off with the ignition [see: Getting a Remote Signal for the Amp], so I've no worry about getting a flat battery, but it would be nice to have a manual On/Off switch inside the cabin so I can mute the subs while driving if I need to, without having to cut out the rest of the speakers.

While I had the back seats out I ran a wire through the bulkhead into the o/s rear footwell [see: Adding an On/Off Switch], so I got hold of a beacon-switch from a tipper at work to fit inside the cabin. The plan was to run the wires out from the middle of the seat and under the carpet on the transmission-tunnel, then fit the switch inside the armrest-compartment. Neither of these panned out. Running the wires under the carpet is doable, but to lift the carpet [and the sponge backing] up enough involves completely removing the armrest console, as well as all the side trim and clips, so I've taken a shortcut for now and run the wires under the trim below the o/s door, then under the driver's seat and through a gap in the side of the console. The wires are exposed, but they're well hidden and I've made sure to keep them well away from the seat-runners.

As for the placement of the switch, which is over an inch deep with the wire terminals on, it turns out there's just no room for it inside the centre-console. The base of the armrest-console is a solid steel tray with an electronics-module right under it and the storage-tray below the armrest angles up to fit flush with it too. I don't want to go further forward on the dash and mess up the wood so I've fitted it in the storage-slot under the rear air-vents. The plastic slot was missing anyway and the vents were hanging loose, so at least it looks complete now even if it's a pain to reach. Not a problem for people in the back though and that might not be such a bad thing if one is screaming we've missed our turn-off and we can't hear over the drum and bass. I just used a piece of thin plywood for the panel, covered in the leftover vinyl wrap from my ScoobyLab stickers. It's a bit shiny, but the vinyl gives it more of a trim look than black paint.