or other mods for instance, but keeping ECM.

I have a 99 5.9.
How do timing chain or cam manufacturers, and DIY hot-rodders handle fuel sync/distributor timing?
Seen any advice from adjustable timing sets?
Any from cam manufacturers?
(Do they grind in at zero for the distributor gear so it doesn't matter? Most seem to claim some 'advance'...)
I have a unique situation I'm trying, but I knew I needed to retard the distributor to even-out a recent startup.
Sure enough, when I got done, I had a 1391 code from my first attempts to start that has not repeated.
I'm very tempted to just move to the two extremes to trip both sides of 1391, and clock back to the middle.
Does that as much sense as anything else?

 

The middle between the extremes should work just fine, or set the #1 cylinder to TDC/valves closed and align the rotor with the mark on the distributor housing. As I harped on many times on this forum, "fuel sync" merely tells the PCM which cylinders are in the intake phase and which ones are firing. All timing is derived from the crank position sensor.

 

That is exactly what I did: no-valve TDC, oil drive to 1 bolt, rotor to mark on plate.
Which would be great, unless one changes cam position or installs aftermarket parts.
I knew to retard the distributor, but there should be a process or a limit on doing it right.

Best I understand, fuel sync is really the 'agreement' between the crank sensor and cam sensor.
All parts and positions factory should be great, but what if they're not?

Let's say Dodge had a good reason for timing fuel to cam, like valves were perfectly positioned for the squirt.
Makes sense. Moving cam sensor with the cam here would maintain this relationship. But it alters the rotor / cap relationship and the crank/cam relationship. One or other will soon be a problem - but when?

 

P1391 Intermittent Loss of CMP or CKP
If i understand you correctly you want to degree the cam(advance) and want to set the fuel sync? If you advance the cam you will need to set the distributor the same way. Advancing the cam will move the rotor position the piston will still be tdc. Not sure how this will effect performance with a stock tune.

 

Oh, I did advance the cam, set everything up by the book, and had to fudge exactly the way I thought I would.
My rough calculations show the distributor (in it's job of ignition position switching) has about 30 degrees (dist degrees) of play where parts should still connect.
CmPS will match lobe as before.
My particular mod was 12 crank degrees, so 6 cam degrees, so within MOE.

But, what do cam manufacturers suggest to 'comp' for their advance?
Is it built in (gear NOT indexed, just lobes)?

 

You don't really hear of people degreeing a cam on computer controlled cars but it's done to move the power band one way or the other. It's done by getting offset keys or some timing gear sets.
https://www.lunatipower.com/how-to-degree-a-cam

 

It bears repeating "fuel sync" is not providing any sort of timing, look at the "hat" in the distributor and it changes the cam sensor output once per revolution. Not exactly conducive to exact timing needed for fuel injectors. Both fuel injection and ignition timing are controlled by the PCM based on the crank signal which triggers 8 times per revolution. If you want to adjust fuel injection timing for the cam the PCM mapping needs changed.

 

Cam sensor simply tells which end of the firing order the engine is in. Needs to be fairly accurate, it has a tolerance of plus/minus 7 degrees before things start getting weird, although, one member had his 180 out, but, the engine still ran decent. I figure that the higher the RPM, the less it matters, as the fuel doesn't sit there for more than a couple milliseconds in any event. It's important for STARTING the engine though..... I do believe cam sensor is more about WHICH injector to fire, more than WHEN to fire it.

 

Hey - I could love that theory.
I looked at the flywheel sensor ring, and no difference for any position.
So at speed, it would only know a cylinder, a cylinder, etc.
The cam sensor, correctly positioned could locate which cylinder.
For discussion, since cylinders are about 90 degrees apart, why such a tight tolerance?
I wanna' think that the cylinder is id'd AND the fuel spray coordinated for full valve lift, max air speed, or something else logical sounding tied to cam position.
I do know 4 tads (the smallest amount I could move the distributor) changed how my truck runs - maybe 4 mm at the circumference.

I wanted to know if anyone knew exactly what cam or timing pros did (or instructed) after say, working on hundreds of these...

I'm gonna':
make a scale along the left fender (probably a yard stick mounted),
stick a stick in the terminals for a pointer,
and measure the limits for my truck between 1391 codes.

I would then test a few positions on the road and narrow it down.

I would also like to know if anyone can confirm that existing/moving CCW at the dist is considered + (and thus moving CW would go through 0 to -).

 

Distributor rotates in a clockwise direction, looking down at it from the front of the truck. (yeah, like you would be able to see it...... )

I *suspect* that the PCM pays attention to the relationship between when the crank sensor triggers, and when the cam sensor triggers. (so, as cylinder 1, or cylinder 6 are coming into firing position.) Keep in mind the amount of time the valve is actually open at say, 5000 RPM, is friggin' tiny. So, the difference a couple degrees either way determines if the injector fires before the valve closes........ So, some precision is necessary. Purpose here being, the injectors are still timed right, even as the timing chain stretches over the years/decades the chain is in there. (and the morse style stock chains are prone to stretching....)

Going on just general principles, I would expect that the PCM wants to fire the injector just as the valve starts opening, or VERY slightly before, so the fuel is injected into the air stream when it is moving its fastest. (takes time for the fuel to travel from the injector, to the valve....) Keep in mind, we are talking about events that are taking place in MILLISECONDS here...... So, a couple degrees either way, DOES make a difference.