IHADAV8.com - Turbo Buick Tech, and Nonsense
Tech Area => General Buick Tech => Topic started by: Steve Wood on March 02 2012, 11:20:15 PM
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This week, I had two emails from people with a miss at part throttle and intermediate boost. And, we have Keith over here which makes three.
All three sound (ed) like compressor surge but not everything added up.
One guy from tbs was asking for him and said someone had told him to unplug the cam sensor to see how it ran. He was seeking reassurance that it would not do any damage to drive it that way.
I told him to try it and if that did not help, it sounded pretty much like compressor surge if everything else added up. His scantool numbers looked okay.
So, he unplugged it and it ran much better. He cleaned out the cap and that seemed to help a little as well. I told him to rotate the cam sensor about 1/8" CCW and that seemed to finish it off.
I asked him to left up on the reluctor and he said it moved about an 1/8" vertically.
My new cam sensors seem to have about 0.045" vertical play in them. We used to suggest shimming the shafts to something closer to 0.20" to be more like a good distributor.
We have seen a few people in recent years that have shimmed the cam sensor cap upward by placing some washers between the cap and the housing and it seemed to cure odd misses.
This is what I think is happening. The excess play in the shaft is causing two problems. One the reluctor window in the cam sensor is rising up too high and messing up the signal because it does not interrupt the magnet properly. Second, it may allow the reluctor to rotate more from its desired position in the window which then puts it in a place that it may be screwing up the fuel timing at part throttle.
Now, moving the cam sensor setting further CCW may keep it in the right window beyond helping with longer duration carms as we have projected for many years.
Beyond the additional rotation from the set point as I always suggest, it may help to use some distributor shaft shims (Mr Gasket 2820) and get the clearance down to 0.45-0.050".
I have not heard back from the other guy yet.
Keith, I suggested you check this in your thread in case it might fix your problem. I don't mind being wrong...got lots of experience in that. :icon_eyes:
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I will check it Steve Thanks
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Steve I unplugged the cam sensor at idle and it started running rough so i didnt go for a ride, it is raining out here so i would not be able to test anyway
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it should not run rough. I have seen it before, tho. That makes me wonder. When the weather gets good, try it...just for the heck of it, go ahead and rotate it about an 1/8" counterclockwi se.
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Okay, the second guy's problems went away when he rotated the cam sensor....so, that leaves you, Keith! :D