I don't think that's entirely true on these trucks. PCM controls spark advance and retardation but if its not hitting the degree that the computer thinks it's hitting, then the timing would be off.

 

PCM reads crank position from the crank sensor. Turning the distributor has zero affect on ignition timing. The most you can accomplish there, is turning the distributor so far that the spark can't jump to the correct terminal. (and you may end up firing the wrong cylinder.)

Sensor in the dist only tells the PCM which cylinder should be at firing position. it switches state once every crankshaft revolution. It's only influence is on which injector fires, and when. (fuel sync)

The ONLY way you can alter ignition timing on these trucks is thru programming, or, physically moving the crank position sensor.

 

Isn't that the definition of being out of time?

I'm betting if you threw a scanner on the engine the degrees of advance vs what a timing light with advance would be totally out of sync.

 

Nope. Turning the distributor on these trucks doesn't alter the ignition event in relation to piston position. (unless you turn it too far..... then you aren't even firing the right cylinder) Ignition Advance fires the plug earlier in the compression stroke to ensure *complete* combustion, and that you get as much of the power out of it as possible. Turning the distributor a few degrees one way or the other, will alter when the injector fires, in relation to when the valve opens, but, the spark plug will still fire at the same point as it was before. (of course, altering injector timing will have an affect on how efficient combustion is, and that may have a secondary affect on ignition timing.....)

The distributor only makes sure spark goes to the correct cylinder, aside from that, it has zero control over ignition timing.

 

I'm inclined to disagree.

I believe rotor position affects advance and timing

 

Not at all. Rotor only controls which cylinder gets the spark. PCM determines when to fire the coil. It makes that determination by looking at various sensors, of which, the cam position sensor is NOT one.

Cam position only changes state once per crankshaft revolution. (have a look under the cap. It's just a hall effect switch.) It is in one state while 1, 8, 4, and 3 are in the firing line, it is in the opposite state when 6, 5, 7, and 2 are up.) All the cam sensor does, is clue in the PCM as to which injector to fire, on the next crank sensor event. It has absolutely zero affect on when the coil fires. The spark will jump to the nearest terminal, regardless of if it is + or - a few degrees to either side of it.

 

I just had this same conversation with a mechanic buddy of mine. He is an older guy and hasn't kept up with the times. I still don't think I convinced him that it isn't possible. He says if it has a distributor you can change the time. Some folks never change! How long ago was it that vehicles began being made this way? I'm guessing with the advent of direct fuel injection? or was it OBDII?

 

A fair few manufacturers STILL use a 'pickup coil' in the distributor... that triggers for each cylinder. So, on those, yeah, turning the dist will indeed affect timing. The dodge system we have doesn't work that way. Now, as more and more folks move away from the distributor altogether, using either coil packs, or the coil-near-plug systems.... there isn't even a distributor to turn.

 

Pickup coil, that is what I was trying to tell him our trucks didn't have. He was arguing that a camshaft sensor did the same thing. Got a buddy that has the new Hemi engine with the coil packs/over plug system with 16 spark plugs. Changing spark plugs on that thing got expensive fast!

 

ok well I'll just throw the distributor back in and hope that when it advances it doesnt hop to the next post cause the computer automatically compensates for rotor position.