Last summer I was having HOT STALL, car would not restart until
it had cooled down some
I've read that it may be the Crank Speed/Position Sensor
http://www.ipdusa.com/Volvo-200/Engine/Engine-Electrical/Crank-Speed-Sensor/p-69-258-335-3946/
I replaced that sensor today, the one I pulled out had three cracks in the
insulation cover, one at each end and one closer to the center of the wire.
I sure hope that this was the HOT STALLING fix.

What is the function of the Crank Position Sensor and the function of the
knock sensor?

I am also having HOT STALLS on my 1983 240 during summer, but it does not have the
Crank Position Sensor? Is the Hall Sensor what was replaced with the Crank
Position Sensor? How would I replace the Hall Sensor if possible?



Joseph in NM

The CPS (crank position sensor) is used in place of the sensor that used to be used in the distributor to inform the CPU or ECU of the position of the crankshaft, in order to determine when to fire the ignition coil.

On the older cars, the sensor in the distributor was also linked to a system of weights and springs as well as a vacuum diaphragm to incorporate changes in timing (advancing or retarding) based on engine speed (hence the centrifugal weights) and load (based on manifold vacuum). However, with the incorporation of the CPS, these determinations of appropriate advance/retard is determined by a "map" algorythm in the ECU -- it's all software, and the distributor is now empty of such pieces, and consists solely of the rotor, just to direct the secondary (high voltage) current to the respective sparkplug. In fact, you cannot adjust ignition timing anymore by rotating the distributor -- timing is entirely ECU controlled.

As for the knock sensor, it simply reacts to engine knock (it can be simulated by rapping a hammer against the engine's head) to signal the ECU to retard ignition timing. Knock can occur because of lower octane fuel, high temperatures, and a heavy load, or any combination of these factors. In fact, for your (our) cars, fuel that is an A.K.A. (formerly "(RON+MON)/2") of 91 is recommended to avoid having the car's timing retarded due to knock, which will reduce mileage and power output, although it will run adequately on fuel as low as 87 albeit with occasionally retarded timing (and lower mileage) as required by conditions.

The function of the crank position sensor is to tell the ignition system what degree the engine crank is at so it knows when to fire off the coil. The knock sensor detects detonation in the cylinders that causes a "knock", when the ECU detects said signal, it backs off the timing in order to prevent engine damage by reducing cylinder temperature.

jorrell
--
92 245 291K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently taking names and kicking reputations!

Hi Jorrell,

Thank you for sharing your knowledge.

"when the ECU detects said signal, it backs off the timing in order to prevent engine damage by reducing cylinder temperature".

What is meant by "backs off the timing" and how is engine temperature reduced?

Thanks,
Joseph in NM

re: "...What is meant by "backs off the timing" and how is engine temperature reduced?...

This means that the timing is retarded -- the ignition spark occurs a little later in the cycle of the piston going up and down. "Advanced" means that it occurs earlier. These timings are all in reference to the moment when the piston is at the top of its stroke.
The exact timing affects the efficiency of the combustion -- consider that, as a major oversimplification just to explain it, you might want the spark to begin to ignite the fuel/air mixture in the combustion chamber a little before the piston reaches the top of the stroke, so that, by the time the flame front from the spark spreads over the chamber, the piston will be at the top of the stroke and ready to be pushed downward by the explosion. However, this advanced timing requires a fuel that resists preignition (the measure of octane or A.K.A. value).

Engine (actually combustion chamber) temperature is affected by ignition timing (the more advanced, the hotter), and you want to avoid excessively high temperatures. BTW, in case you were wondering, this is not the same as engine coolant temperature that is indicated on the temperature gauge.

What Ken said in great detail, but to provide a more simple explanation, the knock sensor system will prevent you from melting or shattering the pistons in their respective cylinders when temperatures get too high.

I ran a boosted 4 cylinder engine beyond its limits on low octane gas. When I removed what was left of the pistons after the engine died, the pistons looked like molten tennis balls, and yes, I heard the "detonation" but ignored it. My bad.

jorrell

--
92 245 291K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently taking names and kicking reputations!

My understanding was that it senses the shaft spinning and acts as a master "everything is ok" switch. In the event of a collision, the shaft stops and the CPS kills everything, including the potentially deadly flow of fuel.

A pain in the butt to change and not robustly built as one would hope, but cheap and keeps you from maybe blowing up.