Can I repair my Air Mass Sensor?

Since inventing the automotive “Hotwire” air mass sensor in the early 1980’s, Bosch has implemented many improvements in design and manufacture of these complex and critical engine sensors. Earlier design sensors used a fine platinum wire for the sensing element while later versions use minute temperature sensors mounted on a ceramic wafer only microns wide.

During the manufacturing process, Bosch uses the latest OE build specifications and materials to ensure all replacement air mass sensors meet the original system specification. Once manufactured, calibration of the air mass sensor is undertaken, a complex and exacting procedure requiring laser trimming of internal calibration resistors via special calibration points as well as ensuring the alignment of the sensing element in the housing. These procedures are vital to ensure the correct performance of the sensor across its’ entire operating range.

Many “reconditioned” air mass sensors suffer from various calibration and design issues, possible problems include flat-spotting during cold start/run also leaning out at high engine loads, possibly resulting in engine damage due to detonation or knocking.

Fuel pump → fuel pressure regulator compatibility

Whilst it has become common practice to fit high flow competition type fuel pumps to standard road cars, it is important to consider whether other system components are suited to this modification. The function of the fuel pressure regulator is to maintain system operating pressure at a preset factory value. This regulator can only do this within its’ nominated return flow specification, an abnormally high fuel flow may exceed the regulators ability to control fuel pressure as it cannot recirculate the fuel back to the fuel tank quickly enough. This situation will result in an abnormally high fuel pressure and/or erratic control.

What can cause cracked coils?

Modern ignition systems operate with high primary ignition current levels, typically between 6 to 10 amps. This high current is required to produce the secondary ignition energy to meet modern engine demands. Current flow at this level will generate a great deal of heat, the modern ignition coil is designed to be able to withstand this providing it is correctly applied and not exposed to abnormal environmental conditions.

It is important to note that when replacing an ignition coil, the correct specification coil is used for the application. Incorrect specification may result in abnormally high coil current resulting in the overheating of the ignition coil and consequential cracking. Other defects may also occur including damage to the ignition module or power transistor unit.

Note that measurement of the primary and secondary coil resistances only are not a reliable guide for coil selection, always use the manufacturers recommended application data. 

Can I remove the non-return valve?

Many Bosch fuel pumps utilise an external threaded non-return valve most of M12 x 1.5mm specification (i.e. pump number 0 580 254 044). These pumps were originally applied to vehicles that use a “banjo” style fuel line connection system and hence have the threaded non-return valve connection used in conjunction with a banjo fitting, copper washer and cap nut. The purpose of this valve is to prevent fuel returning back to the fuel tank when the fuel pump is shut down.

This non-return valve must not be removed from the fuel pump, removal will result in fuel system pressure loss as soon as the fuel pump is shut down. If the fuel system cannot retain a certain amount of pressure after shutdown, fuel vapourisation may occur in the fuel lines and rail resulting in difficult hot start characteristics.

The non-return valve is a serviceable item in many older style fuel pumps and is therefore removable for this purpose only. Consult the Bosch Engine Management Components catalogue for a listing of relevant non-return valve to fuel pump applications.