Cam Sensor Frequently Asked Questions
Tom Chou 
Cam Sensor Basics
If we're discussing a DIS on a TR, well after 10 years I'm surprised there's still confusion.

1. Setting the cam sensor has NOTHING to do with initial timing.
2. Moving the cam sensor a few degrees does nothing to the ignition timing. If the car runs, (and the 3x trigger on the balancer is mounted correctly by the factory) then your ignition timing will be EXACTLY what's in the spark map of the chip regardless of where the cam sensor is set.
3. I say if the car runs, because for ignition timing, all the cam sensor does is tell us which cylinder is #6. After the cam signal goes LOW, (stock spec is 25 deg ATDC of cylinder #1) the next RISING edge of the CRANK pulse will occur exactly 10 deg BTDC of cylinder #6.
4. Therefore, if the cam signal wasn't there, you would never know which crank pulse signaled #6 (or any other cylinder for that matter).
5. Once we have this info, cylinder #6 and #3 will fire. Remember this is a waste spark system (but I'm sure everyone knows that by now) so #6 will be on compression but #3 on exhaust, whose spark is wasted. It takes very little energy to fire a plug that's not under compression, so it's no big deal.
5a. Note also that the current goes through and fires one plug the "normal" way (center electrode to GND electrode), through the block, and fires the other plug "backwards" (GND electrode to center electrode).
5b. This being the case, if you switch wires on the SAME coil (6&3, 1&4, 2&5) it won't make a bit of difference to the car - the plug that was "backward" firing before will now be "normal" and vice versa.
5c. So you can see, on crank up and during limp-home mode, spark advance is 10 deg BTDC since the rising (active) edge of the crank signal occurs 10 deg BTDC of every cylinder.
6. So, moving the cam sensor within the window where the next rising crank pulse is the #6 cylinder has absolutely NO effect on actual ignition timing. Ignition timing calculations are based off the CRANK sensor, which cannot be adjusted short of modifying the balancer or retapping the crank sensor mounting location!
7. So what happens when you move the cam sensor beyond that window and the next crank pulse is either #1 or #5 (depending on the direction you moved it) and not #6? You guessed it, the #6/3 coil will still fire, but the #6 won't be anywhere near TDC and the engine will either kick back or just not run. Regardless, if you get the cam sensor out of adjustment enough to affect ignition timing, it'll simply be out of sync so much the car won't run. That's why if the car is actually running, you can bet the ignition timing is dead on.
8. This brings up some more points. (Might as well be thorough) What happens if you set the cam sensor 180 degrees out? For ignition, nothing. The plug that was supposed to be on compression will now be on exhaust, and vice versa. The car doesn't care! Ignition will be perfect. Fueling, on the other hand, is a different story. More on that later.
9. What happens if you unplug the cam sensor while the engine is running? Nothing. A malf code will set, but as long as you don't kill the engine it'll keep running perfectly (assuming the crank sensor is good.) Once you kill it though, it won't start again.
10. What happens if you move the cam sensor while the engine is running? Every two revs, the cam sensor info is checked. If the cam sensor signal is present, it updates and resyncs. If not there, a malf code is set and the previous sync is used. See #9. For ignition, moving the cam sensor within that window where it syncs correctly does nothing. Move it outside that window and you'll backfire like never before, as you'll fire the wrong cylinder at the wrong time. Trust me, I had it happen. My cam sensor lost it's tab for the keyway on the shaft and started moving on it's own. Exploded my mufflers. I wrote a note about 2 months back about that.
11. So, I hope everyone's convinced that adjusting the cam sensor has absolutely no effect on ignition timing, but can only cause a no-start or tremendous backfire & stalling if running.
A stretched/slipped timing chain therefore also has no effect on ignition timing.
12. HOWEVER, adjusting the cam sensor has a tremendous effect on FUELING, as the SFI syncs off the cam too. I don't know much (yet) about the fueling specs, but it apparently has a much narrower window than ignition in order to sync to the wrong cylinder. This is why if you have the cam 180 deg out the car will run terribly because the fueling is all messed up. Basically it'll be in a SFI mode where fuel is puddling for 1 rev before being sucked in.
13. This is where any performance gain/losses will occur. MAYBE advancing the cam sensor a bit might help a big cam engine that opens the intake sooner, I don't know.
It definitely affects idle quality having the cam sensor out of adjustment. In my opinion I can't see how advancing the cam will help as you're practically in a batch fire mode at WOT where the injector is on practically the whole time. I can't see how a few msec sooner is going to have a great effect. SFI has it's greatest effect at idle & part throttle, and a misadjusted cam definitely can be felt here.
Actually, the fueling can only sync off the crank signal too, with the cam telling it which crank pulse corresponds to which cylinder, so it you're off, you're off by a whole cylinder. It'll be a step function. Within a certain window, you'll be fueling the same cylinder, adjust some more, and you'll step into another one. I can't believe fueling the wrong cylinder can help performance no matter what cam you have.
14. I think that's it. Sorry, didn't mean to write a book. Isn't this info in the FAQ list or something? If not it needs to be. Too much misinformation out there. I should copyright this and charge! Now that it's posted on the list, everyone will be an expert on this and can claim "Oh yeah, I knew that stuff 10 years ago!" Yeah, right. But that's what this list is for, to educate Buick owners and admirers about their cars, so that they don't get ripped off by mechanics and such, right Scott?

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