Damn Crank!

[qwknuf6 jr]

If the cam sensor moves out of adjustment (more than alittle ) while engine is running the ignition timing will be way off , hence the big backfire . the cam sensor is referenced evey 2 engine revoloutions in relation to ignition timing , fuel puddling is not the cause of the backfire.

 

[RmvBfrFlght]

With a cam signal present the ignition module will re-sync each time it sees it. But it doesn't have to re-sync, it just does.

On a running engine, if the cam signal just "goes away" the engine will stay running. However, it won't restart as the ignition module needs the cam signal for the initial sync up during cranking.

What happens when the cam sensor tab moves is that the ignition module will re-sync to the wrong cylinder. Now the timing is way off, this is when things get bad.

RemoveBeforeFlight

 

[TurboDave]

OK, I'll eat my "humble pie".

 

[Ed Valvo]

I think what TurboDave meant was a degree or two adjustment on the cam sensor does not alter the ignition timing a degree or two. Some old fashion guys think it was like an ignition distributor.

Ijames, do you know how far off on the cam sensor you have to be for the ignition to be 120 degrees off?

 

[jasjamz]

Any of you guys that think a bad cam sensor changes timing have a data log to support your claim? I have seen guys using starting fluid cause backfires. Fuel in the cylinder at the wrong time. Timing wasn't off fuel was...

 

[qwknuf6 jr]

Incorrect
No soup for you

 

[qwknuf6 jr]

This is a well written explanation for the uneducated Buick V-6 owners

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. 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 your IGN WILL 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.

No data log needed

 

[ijames]

No data log really possible, either, because the ecm has no clue what is going on. I and a mechanic friend witnessed the timing jumping with a timing light, with the mark on the balancer going from the timing tab to somewhere under the turbo when the timing chain stretched just enough to move the cam sensor to the next crank window. Ed is correct, which is why I said Dave H. was correct but didn't go quite far enough - the cam sensor in normal operation has no effect on ignition timing until you get so far off you sync to the next window, at which time all h!!! breaks loose.

 

[Blazer406]

No data log really possible, either, because the ecm has no clue what is going on. I and a mechanic friend witnessed the timing jumping with a timing light, with the mark on the balancer going from the timing tab to somewhere under the turbo when the timing chain stretched just enough to move the cam sensor to the next crank window. Ed is correct, which is why I said Dave H. was correct but didn't go quite far enough - the cam sensor in normal operation has no effect on ignition timing until you get so far off you sync to the next window, at which time all h!!! breaks loose.

Which would also be supported by the fact that you can put the cam sensor in 180 deg out...... and the car will barely run if at all (mine wouldn't.... but tried to hit a time or two).

 

[jasjamz]

Incorrect
No soup for you

What's incorrect?

 

[qwknuf6 jr]

Timing wasn't off ...

That Part.
At least as is relates to the OP cam sensor failure , I dont think I understood your post after rereading it

Mark

 

[bison]

A broken cam sensor ring will throw timing off , as it rotates out of postion it will cause a major backfire .

The connecting rods are likely all bent.

 

[Mad_Trbo]

Dream86

I have a 3.8 block I took out when I started building my 4.1.

I sourced a whole short block assembly from Weber Racing. I ran it for somewhere in the neighborhood of 2000 street miles while trying to figure out why I had such a bad blow by issue.

This block has their steel caps and will require cylinder work. Blow buy was due to incorrect ring gap hence the need for cylinder work. Let me know if you are interested, I think I saw where you were looking for a block.

I also have a crank for sale in the for sale section.