[Gmecm] erratic 3.8L Cam sensor alarms

[Scott Feaver]

I had my magnet come out of the sproket at about 130k miles.   Its held in a 
plastic retainer and it disintegrated.    Maybe its starting in your case, 
and its position drifts slightly back where the sensor wont pick it up..

Scott
----- Original Message ----- 
From: "Ron Drew" <rjdrew at adelphia.net>
To: <gmecm at diy-efi.org>
Sent: Sunday, October 08, 2006 10:09 AM
Subject: [Gmecm] erratic 3.8L Cam sensor alarms


> Has anyone experienced problems with a GM 3.8L (1989 with 122K miles) 
> missing cam position pulses? More specifically, the pulses generally begin 
> to miss when the car has been driven for a while on warmer days; and it 
> only seems to trigger the alarm at lower speeds.
>
> This what I have done:
> - I replaced the ECM with a known good spare which did not help.
> - I've tried a couple of different brands of sensors, which did not help 
> (they all behave the same).
> - The crank sensor works flawlessly; the cam sensor shares the same '+ 
> volts' & 'ground' with the crank sensor, so any problems with the '+ 
> volts' and 'ground' would need to exist on a very short run of wiring 
> between the Crank and cam position sensors.
> - I have not yet scoped the sensor line going back to the ECM.
>
> I suspect the problem may be with the position indicator mounted on the 
> cam sprocket. I don't know if this is a permament magnet or a normal piece 
> of metal. As far as I can tell there is no magnetism in the position 
> indicator. BTW I may go weeks and not see an alarm, so the problem can be 
> very erratic.
>
> I thought I'd check here and see if nayone has experienced this or has any 
> ideas.
>
> Thanks
> Ron
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