cutting out under load. (archive)

This is a "typical" description of a malfunctioning waste gate control setup. It is usually preceeded by a grin inducing burst of hard acceleration followed by that disconcerting fuel pump / engine cut. The engine cut lasts until the manifold pressure drops below atmospheric.

The wastegate "electro-valve" functions somewhat like the electronic idle air control valve on the later Motronic cars.

When I measured the wastegate control circuit voltages, there was no voltage except when the boost went over 6 psi. At that point the voltage would vary from 3.x to about 7.x vdc. The higher the boost level the higher the voltage, and logically the more controling air was sent to the wastegate to open it wider as necessary to maintain the boost at 6 psi. The engine cutting out is indicative of 10 psi fuel pump shutdown commanded by the Motronic.

To trouble shoot, first ensure the 3 air control lines and the 2 check valves are inplace and functioning. There is one self-relieving checkvalve above wastegate in the knock control line, and another between the HVAC vacuum air pump line and the engine.

Regards

John Stein
85 745 15 + in boost and 225 000 miles

Hey Kelvin,

Sounds like you may have the same problem as me. Mine cuts out under load. The problem I think is caused by a faulty wastegate control solenoid. Try to apply 12v to yours and see if you get anything from it. Mine was dead.

Scottie

Follow Ups:

Re: cutting out under load. oldmaddog 23:28 11/11/2001 (0)
Re: cutting out under load. Scottie San Jose CA 84_745i 85_535i 16:19 11/05/2001 (0)

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