Fuel

To keep your E30 moving, it needs fuel. Since the majority of E30s use petrol injection engines, "Fuel" here is a synonym for "Petrol".

For Diesel engines, jump to the Diesel section of this page.

For M10 engines and other carburettor systems, please refer to the M10 page.

Overview

The fuel system on E30 engines M20, M40, M42 and S14 is a petrol injection system. Pressurised fuel is delivered from the tank to injectors, which squirt fuel into each cylinder in turn, at times controlled by the ECU. It is then ignited by the ignition system, and turned into lovely lovely horsepower.

Components

Fuel Tank

The E30 range benefited from two different fuel tanks; a 55L and 62L. Tourings and facelift M20-engined cars will have the larger tank.

Both tanks are fitted with a pump housing, to which are mounted the fuel pump itself and a level sender.

Because of the low placement of the fuel tank into the floor pan, a central channel was required to allow the prop shaft to travel under the car; this channel effectively separates the tank into two halves.

The 55L tank has a pipe connecting the two halves together at the bottom, so the level in each side is always the same, except after long corners, and so is only fitted with a single level sensor.

The 62 litre tank has a much more sophisticated internal syphon system to transfer fuel from the Left side to the right, which results in the levels in the two halves not being the same. For this reason, the 62 litre tank has a sensor in each half, connected in series, to give an average level for the fuel gauge.

Learn more about replacing the fuel tank.

Filler Pipe

The primary source of fuel delivery into your tank.

Fuel Pump

The fuel pump is a relatively simple construction comprised of three components; the pump housing, the pump itself, and a fuel-level sender.

Because of the two types of tank, there are two types of pump housing. A 55L pump housing will have two pipes on it, while a 62L pump housing will have only one.

A two-pipe housing can be used on a 62 litre tank, provided the second pipe is blanked off, and the pipe that was connected to it re routed to a stub pipe on the side of the 62 litre tank. If this pipe is not re-routed, you will only be able to use the fuel in the RH side.

A single pipe housing cannot be used in a 55 litre tank, as there will be nowhere to connect the return line from the fuel rail, although the basic pump can be swapped between the two types.

The actual pump is rigidly fixed to the housing, and its electrical connections soldered in place. It also has a detachable filter mounted to its base. This pump is interchangeable between housings.

The level sender is held to the fuel pump housing by four screws, and must be removed before attempting to remove the pump housing from the tank. Learn more about replacing the fuel pump.

Fuel Level Senders

While all pumps are equipped with a level sender, 62L tanks contain a second level sender on the left side of the tank, wired in series with the first. The construction of each sender is a basic float, which bridges two lengths of resistive wire. When the float is at the top, the wires are bridged close to their terminals, and thus read a low resistance. As the fuel level drops, so does the float, moving the bridge down the wires and thus increasing the resistance. In this way, each level sender works as a 60 Ohm resistor, reading zero Ohms for a full tank and 60 Ohms when empty.

Therefore the gauge for a 55 litre tank needs to read empty when in series with 60 ohms, but for a 62 litre tank gauge, it must read zero when in series with 120 ohms. Both need to read full when in series with zero ohms. This is why there are two types of fuel gauge available for the E30.

A 62 litre tank can be used with just a single level sensor, but the indicated level will vary, depending on the respective levels in the two halves.

Fuel Filter

As fuel leaves the tank, it passes through a standard canister fuel filter. The filter is mounted to the car body with a simple jubilee clip, and connects to the fuel lines using two lengths of fuel hose, again joined with jubilee clips. It is a service item, and should be replaced regularly.

Fuel Lines

Two steel brake lines run from the fuel tank to the engine bay, delivering and returning the flow of fuel. These fuel lines are attached to the floorpan of the car, and run the length of the sill, terminating at the bulkhead just underneath the brake servo. From here they connect to rubber fuel hoses.

Fuel Hoses

The fuel hoses connect the fuel lines to the main fuelling system of the engine. They are made of 8x13mm rubber, and run below the air intake in the engine bay. They are the common source of all leaks in the fuel system, and must only be replaced with genuine BMW fuel hose.

Fuel Rail

The supply hose delivers fuel to the fuel rail; a metal tube into which are screwed the fuel injectors. It is basically a pressurised reservoir, ensuring that all the injectors a given a steady supply of fuel at a constant pressure.

Injectors

The injectors are the exit point of the fuelling system. They are electrically-operated solenoids which, when activated, squirt fuel at such high pressures that it atomises into a fine mist, which is the most efficient form for it to burn. The injectors are considered one of the most important components in a well-running engine, and one of the best ways to get more power from your old engine is to get the injectors back into good working order by cleaning them, and fitting new pintle caps if necessary.

Injectors do not need to be upgraded, and there is no benefit in fitting bigger injectors to a standard E30 engine.

Fuel Pressure Regulator

To keep the injectors squirting as they should, a constant pressure needs to be maintained which is above the pressure inside the engine. If the pressure was lower, then fuel would be blown back down the pipes to the tank when the injectors opened, so the Fuel Pressure Regulator (FPR) self-regulates the fuel pressure in comparison to the manifold.

The FPR is mounted to the end of the fuel rail, closest to the radiator. It has a small rubber tube connecting it to the top of the intake manifold, and also connects to the returning fuel hose. It is a simple diaphragm valce, sucked and blown by the intake manifold pressure to open or close the fuel flow. Failure of this diaphragm can result in rich running, lumpy idles, poor fuel economy and even engine failure. Despite this, the FPR does not have a reputation for unreliabilty.

Carbon Canister

To meet increasingly stringent emissions regulations, later engines were fitted with a Carbon Canister. This small brown container sits in the engine bay and is bolted to the inner wing. It captures fumes from the fuel tank venting system, filtering them through a self-contained carbon filter and releases them into the throttle body. Utterly redundant, it causes more problems that it solves and is recommended to be removed if found, or at least disabled.

Controlling

The injection system is the main function of the ECU, be it L-Jetronic or Motronic. The ECU reads data on the engine from the Crank Position Sensor, and activates the fuel pump via the Fuel Pump Relay. This provides power directly to the fuel pump through Fuse X,

The pump is controlled by the ECU, based on information it receives from the Crank Position Sensor, and is activated by the fuel relay.

Common Problems

Fuel Smell (Inside)

A strong smell of fuel inside the vehicle is normally attributed to leaks around the fuel pump housing. The simplest cause of this is a perished rubber O-ring that fits between the pump housing and the tank, and is replaced easily. The second cause will be the pipes connecting to the pump housing, and the braided rubber vent pipe connected to the tank. The ends of these pipes perish and split over time, but usually an inch can be cut from the end of these pipes and still leave enough to re-attach to the tank.

A more serious cause of the smell would be rust of the tank itself, most notably at the joint with the filler pipe. Unfortunately this necessitates a removal of the tank, and a repair or replacement. Learn more about removing the fuel tank.

Fuel Smell (Outside)

A fuel smell outside, either around the engine bay or the rear wheel arches, is indicative of a leak in that area.

Upgrades

None at this time.

Diesel

The 324d and 324td were Diesel versions of the E30, and thus employed a standard diesel fuelling system.