It's hovering around -12°. What does it mean?

 

It means your distributor needs to be loosened and turned 10 to 12°. 0° is ideal with a + or - 2° allowable variation.
The cam retard angle should only be read above 1000 rpm's. Any reading below that won't be correct and should be ignored.
The name cam retard angle is actually a misnomer because the VCM/PCM/ECM uses that signal for injector timing and if it is off the injectors will be firing at the incorrect time.

 

Which direction do I turn it?

 

IDK. With your scanner hooked up turn it whichever directions lowers the number. It may help to have an extra body to hold the revs above a grand and read the scanner while you turn it.
Last time I set one, my Tech2 has a long enough cord so I could let it set on the front of the windshield and I stuck a small wood shim in the throttle linkage to keep the rpm's up.
Loosen the distributor bolt a little before starting it and be careful there are a bunch of moving parts under the hood that can bite.

 

My experience:

I removed the distributor, took off the stock hold down bracket and replaced it with the Mr. Gasket 1009 adjustable hold down. Note that the gasket that comes with this kit does not fit on the distributor shaft. I had to carve out the inner diameter with a knife. While I was at it I replaced the distr gear with GM part 10457356. You pound out the pin, take off the gear/washer/backing plate and do the reverse. Drifting CMP retard is apparently due to a stretching timing chain and worn distr gear. Before removal tap the starter with the distr cap off until the rotor is pointing towards the firewall and mark its position. Then mark the body of the cap to the distr body. If you lose track of these two positions you will have more work.

Note that CMP retard is very sensitive, you don't move the distr body very much so get the hold down bolt just loose enough to need some force to turn the distr so it stays put when you tweak it and more importantly when you tighten it down because its hard to tighten without bumping the cap or wires. A short 10mm ratching articulating box wrench works best. CCW to make CMP retard less negative and CW to make it less positive. It does change slightly when you fully tighten the bracket so don't go for zero or you will be chasing your tail.

George

 

A word of caution to anyone replacing a distributor gear, it has and odd number of teeth and if you install it 180° out you won't be able to get the distributor installed correctly.
Some of the aftermarket cheap aluminum distributors have come with the gear 180° out.

 

Excellent feedback gentlemen. Looking forward to applying all this as soon as weather and health permit. Sick+cold+raining for days=misery.����

 

Good tip. This can be important when using the stock hold down clamp.

 

Lots of people don't understand that turning the distributor does not affect the engine timing on this system. Timing is determined solely by the crankshaft sensor and the PCM (along with it's other sensor inputs).

However, turning the distributor itself (or the shaft inside) does change where the rotor is pointing inside the cap at any given time. Know there is an optimum relative rotor position that will best handle the range of spark advance that the PCM will send to the coil.

This system also has sequential fuel injection that times fuel pulses to the intake valve event. So the PCM needs to know exactly when to fire that injector pulse for the most power and efficiency. It is the function of the cam sensor in the distributor (along with the crank sensor) to let the PCM know exactly where in the firing order the engine is at the moment.

The distributor is designed for both the proper rotor position and the cam sensor to be lined up inside, when distributor is dropped in on the correct tooth and locked in place with the factory hold down clamp (non-adjustable). As timing chain stretches or distributor gear wears, the cam sensor retard goes negative, and so does the rotor position.

Having the injector pulse a little bit late is not a huge problem, but if the rotor position is too negative - the spark has to jump further to reach the proper terminal inside the cap. If rotor position is really out or if the cap/rotor is marginal, the spark can actually jump to the wrong terminal or to ground at times and cause a misfire. This is why good quality cap/rotor is advised and is reported to fix misfires.

If cam sensor retard exceeds around 360°/13 teeth = ~27° then a code P1345 will set (cam/crank correlation). Note that the engine will still run even with a cam sensor unplugged, as the P1345 set will trigger the PCM to pulse the injectors in banks (instead of sequentially).

So in the end the cam sensor retard is effectively the measure of where the rotor is pointing (in relationship to the distributor design). It should be set to 0° ± 2°. The ability to adjust it is quite important on higher mile engines, as the timing chains stretch over time. Any wear in distributor gear and gear at a minimum should be replaced.

Also FYI when I installed my $45 Skip White all-aluminum distributor, I switched over the Delco cam sensor, Delco cap, and Delco rotor from my old distributor. I figure a $45 distributor has to have the cheapest ones possible. If you do this make sure the cam sensor clears the windows completely before installing. I found my cam sensor had to be seated slightly differently. Still a good bargain part and the screw hole won't strip out again like the original plastic distributor.

Make sense?

 

Superb. I figured there was some way for the system to compensate for age/wear of timing components. You have explained it with clarity. Much appreciated!