Question about cam position sensor and spark timing
Thread Starter
Safety Car
Joined: Sep 2003
Posts: 3,558
Likes: 2
From: Cape Coral FL
Question about cam position sensor and spark timing
This is something I have been wondering about. Last year I installed a set of AFR 205's and a 224/228 .581"/.588" 112LSA at +2 advance dot to dot. About 3 months ago I redegreed the cam to 0 advance using a Cloyes hex adjust. In doing this the cam position sensor has been retard by ~2.5 degrees, the amount I retarded the cam to get a 0 degree advance. Have I retarded my spark timing by doing this? If so, should I bump the appropriate spark tables in the PCM by 2.5 degrees to get back my timing? There is absolutely no KR at this time. My PCM has 28 degrees of spark advance at WOT in the high octane table. I don't want to go higher than this unles I am actually at 25.5 degrees of spark. Is this thinking correct?
Drifting
Joined: Oct 2004
Posts: 1,384
Likes: 8
From: Southwest Virginia
The cam position sensor has nothing to do with the ignition timing. The ignition timing is derived from the crank position sensor. The cam position sensor is used to tell the PCM if the engine is on the exhaust or intake stroke. The engine will still run without the (or with a bad) cam sensor. The PCM know exactly what position the crank is in from the crank sensor, but don't know where the cam is without the cam sensor. If the cam sensor is not working the PCM has to hunt for the correct position making a longer cranking cycle. I don't think the cam position accuracy is very important to the PCM, it only changes state once per engine revolution.
Thread Starter
Safety Car
Joined: Sep 2003
Posts: 3,558
Likes: 2
From: Cape Coral FL
That's what I thought SpeedyZ! Thanks for the clarification. It's not like the old SBC where the distributor gear is driven by the cam gear. I know about the crank reluctor, I was just wondering if the cam sensor played a more significant role in determining absolute timing. 
