I think a lot of the confusion comes from not knowing exactly what the fuel/ignition timing terms are as opposed to what fuel sync is and how the term "fuel sync" gets used generically for something it really isn't.

On our engines, the distributor and oil pump is turned by a gear connected to the camshaft. The camshaft is connected to the crank via the timing chain, which in turn connects the crank to the flywheel. In the flywheel there are 8 notches that are read by the crank position sensor. The crank position sensor and the cam position sensor work thru the PCM to tell the coil when to fire the spark. When the engine is set correctly, the crank sensor tells the PCM when the engine is at TDC of the compression stroke and to fire the coil. The cam sensor tells the PCM when to fire the injectors to deliver the fuel load, but this event is also based of crank position information as well, and can only be adjusted in very minute amounts.

When the timing gets off, either by installing the timing set incorrectly or by incorrect orientation of the oil pump gear onto the camshaft gear, engine timing events are affected. The oil pump gear has only 18 teeth, so one tooth off too early or too late translates to 20* of improper timing, which means that the spark fires as the piston is still compressing the A/F mixture (very bad), or piston is going down and the exhaust valve is opening as the spark is delivered, causing glowing headers as the fuel is burning in the exhaust tubes, (Also very bad). I did this once on a cam install and about pulled my hair out trying to figure out what I did wrong.

At the timing set, a small incorrect placement of the crank gear relative to the cam gear can be beneficial in small increments, but bad in larger doses. The crank gear moves at twice the speed of the camshaft so a slight bit of advance or retard is possible for various effects. Too much out though, and the crank sensor's interpretation of the crank's position in relation to the cam sensor's reading of where the cam is cause a sync issue between the two. The engine will either run poorly, or not at all. This is because the crank and cam events are not lining up as they should on a properly running engine. They are not in sync.

This is not FUEL SYNC, however. Fuel sync as Chrysler defines it is actually set at the PCM level and can only be adjusted with a tuner or an OBD-III tool capable of altering Chrysler PCM stored data. It is essentially changing the relationship of the crank and cam interaction within the PCM. It is only advisable to do so if you know exactly what the hell you are doing.

You can cause the ignition to fire just a bit early or late by slotting the mounting holes on the crank sensor and moving it slightly left or right to adjust how much earlier or later it reads the notches on the flywheel. At most, you'll gain about 4* of ignition advance or retard, and it's not worth the effort IMHO.

Fuel sync as most of us lay-people use the term is that very minute control of exactly when the injector fires relative to the valve timing events. Twisting the distributor very small amounts clockwise or counter-clockwise can make the injector spray a little early or later than the standard set of 0. The cam sensor fires the injector relative to the position of the brass groove on the inside of distributor as it passes through the "gate" or "pick-up" on the underside of the cam sensor (which is commonly referred to as a Pick-Up sensor). If you twist the disty a tiny bit right or left, this makes the cam sensor read the firing a bit early or late depending on which way you twist it. If the injector fires a bit early, this usually leads to a small gain in performance for most naturally aspirated vehicles as the valve on that particular cylinder is still closed and the fuel hits the backside of the valve and vaporizes a bit more as the valve will be hotter than the surrounding cylinder head chamber. It also causes a bit rougher idle on a cold engine, as the valve isn't heated up yet and the fuel kind of sits on the backside of the valve and "pools" as it is waiting for the valve to open. Retarding the timing a bit shoots the fuel as the valve is opening and usually nets a small increase in performance on a boosted application, and at high revs. The extra pressure from boost is sufficient to atomize the fuel and you want as much of it as you can get in the cylinder for firing. The timing events become faster and faster as the revs increase and the time to pack the cylinder and fire it decreases significantly.

At about +10 and -10 the cam and crank sensors start to notice something is not quite right and you usually get an out of sync CEL. I have found that a +2 setting works best on my engine for a decent idle and a tiny boost in performance, though I am currently running 4 hole injectors that better atomize fuel anyway. It's also good to note that our stock injector design shoots a 1 hole pencil beam type shot of fuel, so it's conceivable that they are better suited to more advance (maybe even +6 or +8) and better than 4 hole injectors for a mildly boosted application, depending on fuel delivery needs of course.

 

This might help...

dizzy10.jpg?t=1290755361

 

your crank turns twice for every 1 rotation of the cam so it might look like you have the distributor in right but it could very easily be wrong.

 

that was a good read aim4squirrels

 

Aim does a very good job of explaining some of this technical stuff.
Even this old man understands it some times.

 

Thanks again to all. Truck is up and running. Going to dealer this week to set sync. Was thinking about having them set it to +4.

Great write up Aim for Squirrels, learned alot from it. I'm sure it'll help others too. Hopefully all of this will. As I found during my searches this is actually a common issue. There are many people out there that don't fully understand this system and have many questions. At the same time there doesn't appear to be very much detailed information out there and much of it is contradictory, many different opinions and it just makes it more confusing.

I didn't realize the link was to a free download at first, but have since downloaded it.

I did know about some but not all of the marks on the intake manifold, etc., and I did know that the dist rotates 2:1.

Much of the information brought up here I already knew, but there's much I didn't know as well. Of course even having 99% of the knowledge on how to do something isn't enough to complete the job, so once again thanks to all for contributing your part.

 

So was it 180 out or just not lined up properly?

 

Understanding aim4squirrels would make me go stark raving naked.

 

I think I'm having this same issue. I just dropped in a fresh salvage rebuilt engine (I rebuilt) and cant get the damn thing to fire. (On my dads truck, its a 99) its got fuel and spark but just turns over and over with occasional back pressure blowout. The distributor is set properly and I have check my wiring multiple times.

So I take it from this that my timing cam is off? Can't use a timing light cuse the damn thing wont fire. Gettin pretty f'in frustrated.

 

A timing light won't do jack anyway. I assume you have tried rotating the rotor 180 ?