The BMW 2002 tii was introduced into the US Market in 1971. It is simply a further modification of the 2002 carburetted model, employing fuel injection as a means of getting gas to the engine.
It is basically just the same as other 2002's: the engine has a slightly higher compression ratio, the suspension system is somewhat stiffer, and the brakes are larger. The major difference is the fuel system.
This was the first year BMW featured fuel injection. The system incorporated a Kugelfischer Mechanical Fuel Injection Pump. A list of components and their operation will be found in the next section, along with a wiring diagram and schematic of the system.
The components are: The fuel tank with a filter screen in the pick-up; a high-pressure fuel pump; an expansion jar; a fuel filter; the injection pump with a Warm-Up Transmitter and Auxiliary Air Valve; fuel delivery and return lines; the injectors; and a ColdStart System.
The electrical components are the battery, starter fuse box, instrument panel components, fuel pump, ignition switch, and the Cold-Start System Components: the Cold-Start Valve, the Time Delay Relay, and the Thermo-Time Switch.
The following diagram is a schematic of the electrical system of the 2002 tii with all components labeled.
Fuel Supply System
The fuel supply system begins in the fuel tank, which incorporates a separate fuel pickup and gauge float. Since fuel injection systems are very sensitive to contamination, there is a fine mesh screen in the pick-up.
Next is the fuel pump. It is a high-pressure, `Roller Cell' type similar to those pumps on current fuelinjected models. As soon as the ignition is turned on, the pump puts the system under full pressure approximately 2 bar. There is also a fine mesh screen in the pump's inlet.
Next is the expansion jar, which is mounted together with the fuel pump. It acts like a muffler to dampen noise.
The fuel filter is mounted in the engine compartment on the left side of the radiator. It contains a paper element and a lint trap. If you have to remove this filter, make sure you put it back in the same way you took it out. It's advisable to change it during every major service.
From the fuel filter, gas flows directly into the inlet of the injection pump. There is also a fine mesh screen in this inlet. This screen, plus the screens in the fuel pick-up and fuel pump, should be serviced every 40,000 miles.
At the rear of the top of the injection pump is a pressure regulating valve. It maintains fuel pressure at approximately 2 bar, and allows excess fuel to return to the tank.
The injection pump is a Kugelfischer Model PL O Mini Pump. It's interior is very much like a small engine.
There is a camshaft which drives tappets. These, in turn, drive plungers which are pushed back down by springs. When these plungers move down, suction valves are pulled open and gas is sucked into the cylinders of the pump.
Pressure created by the upward stroke of the plungers forces the suction valves closed and the delivery valves open. Fuel is pushed out into the delivery lines and through the injectors. The pressure generated by the injection pump is quite high 35 to 38 bar.
The amount of fuel injected into the engine is controlled by the stroke of the plungers. Their travel is limited by a regulating lever inside the pump. The position of this lever is controlled two ways.
One side rides on an irregular cone; the other is mounted on an eccentric hinge which is controlled by the warm-up transmitter.
The irregular cone controls lever movement two ways: backward and forward movement of the cone is directly connected to the throttle linkage; rotation of the cone is related to engine speed.
A magnetic pick‑up inside the pump's camshaft transmits engine speed, through a set of gears, to
the cone. The cone then rotates, much like a speedometer, in time with varying camshaft speeds. These movements raise or lower the regulating lever, varying the amount of fuel injected into the engine.
Fuel delivery lines run from the delivery, or pressure, valves on the pump to the injectors. Inside each injector is a spring‑loaded valve in a tapered seat. When pressure from the injection pump reaches 35 to 38 bar, the springs are overpowered and the valves are forced open, spraying fuel into the intake.
The final part of the injection system is the Warm-Up Transmitter, which incorporates an Auxiliary Air Valve. The Warm-Up Transmitter is located on the back of the pump and provides a richer mixer for warm-up.
It is connected, via linkage, to the eccentric hinge on the back of the pump's regulating lever. When the engine and warm‑up transmitter are cold, the hinge is rotated to its lowest position. This lowers the rear of the regulating lever and increases the amount of fuel injected.
As coolant temperature increases, a heat-sensing element in the warm-up transmitter expands, pushing a rod out of the unit's housing.
As the rod extends, the eccentric hinge for the regulating lever rotates upward, gradually returning the lever to its warm-operating position and leaning off the mixture.
Additional air is necessary to maintain a stable idle, so an Auxilliary Air Valve is incorporated in the Warm-Up Transmitter. It is simply a valve on the upper end of the warm‑up transmitter rod. A rubber hose connects this valve with the air collector on the intake manifold. As the rod extends, the valve is gradually closed, shutting off the extra supply of air to the intake.
The pump is lubricated by oil from the crankcase under pressure. Excess oil is returned through a line near the dip-stick. The pump comes from the factory dry, so oil must be added before the engine is started. A warning tag is attached to new or rebuilt pumps as a reminder.
Some changes were made to the pumps between the first models in 1971 and the later years up to 1974. Do NOT interchange pumps from different model years. Be sure to check the part number for the model year you're working on. Additionally, in 1974, a vacuum limiter was added to the system for deceleration control.
Later models had a re-designed throttle housing, which made CO adjustments much less sensitive.
The Cold-Start Valve, which provides the additional amount of fuel necessary for cold starting, is controlled by two electrical devices: the Cold-Start Relay and Thermo-Time Switch. When the engine is cranked, current flows through the Relay to both the valve and the Thermo-Time Switch. On a warm engine, the contacts in the switch are open, and the relay provides power to operate the valve for only one second.
On a cold engine, the bimetallic strip in the ThermoTime Switch causes the valve to remain powered for a longer duration, causing more injection.
For example, injection duration is 8 seconds at 00 C, 4 seconds at 20° C, and one second at 350 C. Above 350 C, the bimetallic strip in the ThermoTime Switch has been heated enough to interrupt current flow; the points open and the cold-start relay loses its ground, which interrupts current flow to the valve and ends injection. But the valve will always inject one second of extra fuel, no matter what the coolant temperature of the engine is.