So when EFI came along, you now had two things to fire- the spark plugs and the fuel injectors. The crank trigger system worked fine for the plugs, but now you had to fire injectors, which use a completely different timing map, since they fire while the intake valve is opening, and their position DURING the intake valve opening changes with pulse width. For this to work properly, the PCM needs to know where the camshaft is.

So in a perfect world, you have a crank sensor firing the spark plugs and a cam sensor firing the fuel injectors. Of course, nothing can be that simple.

So now we have a PCM determining where the cam is, where the crank is, how far the can has moved due to timing chain stretch (and thus how the rotor phasing has changed), what timing map to use based on conditions, where to fire the fuel injectors during the IVO (Intake Valve Opening) event, among other things.

So now we have meaningless crank and cam positions, with the ignition and fuel injectors firing based on the phase angle of the cam and the crank.

So yes, it is a form of timing. But totally different from old school timing.

If you didn't turn the motor while the distributor was out, and you clocked the distributor shaft correctly into the teeth on the can as you dropped it in, then you should have gotten within one tooth of where it should be...technically it should be right dead in place. So you just need to get your rotor phasing in, and that should get your fuel sync angle back close as well. But if you are a tooth off on the cam gear and have the rotor indexed to the distributor body, then everything will be off however many degrees a tooth is, even though the shaft and body are lined up.

 

Can't say it, or explain it, any better than what Magnet posted. Yes it is a form of timing but not in the traditional sense since it applies to fuel AND ignition.

You do need a scan tool to set it correctly.

 

well when you build your own engines and work with people that grind their own cams, you tend to learn how to explain this stuff. :P

 

Wow! In hindsight I wish I had just cut the grass instead of trying to install a new cap and rotor. I also have a 1989 V6 Dakota 4x4 that is so easy to work on which is why I bought the used '98 recently. Anyway, I do have a scan tool but not real sure how to use it as the two of you suggest. I'll go online and found out how. Yesterday I did install all new plug wires and a new cam position sensor. It still ran bad at acceleration so I rotated the distributor until it smoothed out on acceleration and quit backfiring. But I want it to be right so can you briefly tell me how to use the scan tool to gat everything right?

 

Is it a scan tool or a code reader? You need to see live data.

It should display the fuel sync.

 

Dan it will show/read live data.

 

Does it display fuel sync? Not all do.

Snap-On has the MT-2500 that makes it easy.

 

I'm not sure. I will check and get back to you....

 

I just hooked the scan tool up and set it on "Live Data". Fuel sync was not an option on this tool and I guess the closest thing was "Spark Adv (degrees). Spark adv measured 14 to 17 degrees at idle and when I would rev up the engine it would read from 40 to 65 degrees. Am I in the ballpark? I also cleared the previous "Check Engine" light several days ago and asked it to read stored codes and also pending codes again today and it did not find any. So what do you think? Should the spark adv read 0 degrees at idle (600 rpm) or is the 14 to 17 degree correct?

 

Fuel sync is independent of the ignition timing. The camshaft position sensor in the distributor is used for the fuel sync.

Your symptoms, including the loss of cam/crank position sensor codes are consistent with the distributor being turned.

I know I sound like a broken record.

You need to correct the fuel sync, not the ignition timing. It really should only take a few minutes at a good shop with the proper tools. Note: fuel sync is not set at idle. It's set at about 1000 rpm to reduce valvetrain fluctuations. The Snap-On scanner I mentioned will bring the RPM up for the test.