Re: check engine light

[Aleksander Mierzwa <alex@matrix.com.pl>]

At 02:46 22.06.98 -0600, Brooks Ellis wrote:

>>If it is the Hall sender malfunctioning, the car usually wouldn't start. 
>
>Why is a hall field sensor neccesary anyhow? To control the ignition
>sequencing in a more precise way? I'm really not very familiar with the
>newer engines (in a technical-repair sort of way). 

The timing reference sensor is located at the flywheel. The camshaft turns
at the half of the speed of the crankshaft, so the computer needs to know
the position of the camshaft relative to the crankshaft. That's what the
hall sensor is for and that's why the car won't start without the hall
sensor, but will keep running without it. Hall sensor is also used while
the engine is running for telling which cylinder is knocking in case a
knocking is detected, though.

>What's wierd, is everything has been kicking ass, and then one night, out
>of the blue it started the 'emission control system' (check engine) light
>when I exceeded 3000 rpm EXACTLY. The light would pop on right above 3k,
>and when I let the RPMs drop, as soon as the RPMs dropped below 3k, the
>light popped off. 

The distributor does not have to be precisely adjusted on these cars. The
ECU had to "see" the sensor in a specified time before firing a spark or a
fault code is generated. What happens is that the ECU "sees" the sensor
before 3K rpm, but at higher rmps when boost climbs up the ignition timing
is altered and the ECU does not "see" the hall sensor in specified time
frame, thus generating a fault code.

>P.s. What do the knock sensors look like? I couldn't locate them at a
>cursory inspection of the engine bay. 

Left side of the engine block. Don't confuse them with oil pressure
switches. Knock sensor should have red insulators AFAIK.

Aleksander Mierzwa
Warsaw, Poland
mailto:alex@matrix.com.pl
87 Audi 5000CS turbo (mine)
88 Renault Medallion wagon (mom's)
91 mountain bike (just in case both cars broke at the same time :-)