Ideally it works all the time, yes. The point of my post was that once the engine is running in later models, the cam sensor doesn't do anything. So issues like hesitation, no power, misfires, bad idle etc. can not be solved by messing with "fuel sync".

The older SBEC needed both signals all the time, I'd think that when Chrysler switched to the new JTEC in 1996 they didn't want to do too many changes at once. I used to work in a somewhat similar environment of hardware and software development and typically brand new HW would initially run "known good" older SW until all the kinks were worked out.

 

I wonder if the computer learns the initial cam sync and uses that after the engine is running rather than relying on the cam sensor? If that is the case, then it seems that if the cam sync is not set correctly it would still not run right even though the cam sensor is not being used after the engine starts. In other words, if you need to be set at +4 and the sync is actually running -8, it would still run at -8 after the engine starts keeping the engine from performing correctly.

 

That seems perfectly reasonable.

Another problem I could see cropping up there, is if the crank sensor misses a window. (failing/bad sensor, or just a cheap one) Fuel sync is instantly out the window, as the PCM is firing the wrong injector at the wrong time.

 

The misconception here is that "fuel sync" provides some sort of critical timing info. It doesn't, all timing for fuel injectors and ignition is based on the flywheel notches which are picked up by the crank sensor. What fuel sync provides is which injectors are to be fired, not when. Think of it as synchronizing the fuel injectors with the correct cylinders that have their intake valves open.

 

That is true for older SBEC systems, and possibly the first year JTEC (no hands-on experience). The later ones, as the video demonstrates, keep track internally of where in the 4 cycles each cylinder is once the engine is running.

 

Yeah, and it does that by reading crank sensor signal....... So, miss a signal, and everything is out the window. Sure, it will run with the sensor unplugged, but, will it run RIGHT?

Quite frankly, I think the only way to be able to say for sure would be to either talk to an engineer that designed it, or, have a look at the code.

 

The way I understand it is the fuel sync is set at a range to determine when the injectors are to spray in sync with the timing. That is why it has a negative to positive range when you set it with a scanner. Currently mine is set at +4 for example. Maybe I am misunderstanding what you are saying...lol

 

Technically, it doesn't control WHEN (in relation to ignition) an injector fires, so much as WHICH injector to fire. All the PCM really needs to know is which cylinder is up next in the firing order, and it determines when to fire the injector, and coil.

That seems kinda strange though, given some of the oddities I have seen when folks fuel sync is way outta whack. (more than 10 degrees....) Maybe trying to compensate for timing chain stretch?

 

I see what you are saying, it does let the pcm know the cylinder that is getting ready to fire, but if you don't have the sync set to 0 wouldn't that manipulate the timing of the injector spraying (earlier or later depending on which way you rotate the distributor)? (Not arguing, just trying to understand...lol).

And in reality, if you are way off in the distributer location that would affect the rotor hitting the terminals on the distributor cap causing performance issues that the fuel sync may be getting blamed for.

 

So long as the cap as mounted properly, the rotor shouldn't hit it.

As for fuel sync being off a bit, I have no idea if that affects injector timing or not. Don't have the tools to test that theory either....... Supposedly, it does..... but, theoretically, so long as it is close, it shouldn't matter....