now this here is by far the best and biggest help ive seen for setting these dist. thank you, good sir. as luck would have it, apperently i muffed up somehow. im throwing the 1345 also, did the process of turning the dist one tooth, and yet im stuck. as the truck runs, and the rotor points *just* before cyl1 at TDC. cam retard shows 20*. i retard one tooth, and at the same cap position the cam retard shows -28*
Greetings drifterwanb666,
Glad you found my explanation helpful. My target audience are those who are both
new to the GMT400 hobby and also wish to learn how to be a more self-sufficient
DIY owner. Thanks for the positive feedback, it's appreciated.
****
Before performing any of the following, please make sure that you have already tried to
rotate the distributor per the info in @east302's reply above (#10) and you can't get
the CMP measurement to 0° before the distributor is prevented from turning any further
due to physical interference.
****
OK then. If you are reading this I'm assuming that you find yourself stuck just like many others
have also been. BTW, good job with your clear description of the distributor phasing issue
that you are experiencing.
The problem description is:
Installed distributor is showing a +20° offset.
Retard distributor *1* tooth, now -28° offset.
OK. This is a very specific failure footprint. In order for all involved to be able
to reason through how we can fix this, I first need to do a little quick math.
First, in one full revolution of the distributor shaft the rotor travels exactly 360°.
Now here is the trick. If you pull the distributor out & count the number of teeth
on the gear, you should find an odd number: 13. (Take your time, I'll wait here. :0)
Now why do we care? Well, if they had made the tooth count an even number
(ie: 12 or 14) then when the gear was installed onto the distributor shaft, you
would end up with the same relative phasing between gear teeth and shaft no
matter which way the gear was installed.
But with 13 teeth, IF the gear is installed 180° out, then we are going to end up
with one distributor stuffing that's too far positive, and then when we retard it
1 gear & restuff, it's now too far negative?
So how much of an offset are we talking about? Well, 360° divided by 13 teeth
= just shy of 28° per tooth. And again, because we are dealing with an odd
(asymmetric relative to the roll pin) number of teeth, by removing the drive
gear, spinning it 180°, and reinstalling it, we will now have shifted the phasing
by roughly 1/2 a tooth.
And when you reinstall the distributor, now the phasing will be such that you
should be able to physically swing the distributor either positive or negative
as needed for a CMP reading of 0° *before* running out of room to rotate
the distributor assembly.
Here's the illustration in the FSM showing the gear removal/installation:
You must be registered for see images attach
And how does the distributor gear get installed wrong in the first place? We aren't sure,
but as I mentioned in my previous reply it seems that this assembly error is being
missed during the QA process by whoever is making/remanufacturing these distributors.
Another way this happens is during a camshaft change, where the new camshaft is
installed, and at the same time a new (compatible metallurgy) distributor gear is also installed
by the mechanic...but unfortunately they phase it 180° out. Followed by the P1345 code.
Fudge!
****
Listen, while we are in here looking for trouble, let's quickly discuss one more issue
having to do with these distributor/cam gears. Simply put, some people pull the
distributor out, and the teeth are worn to almost a knife edge. (Refer to 1st attachment.)
Some people know to look for this, find it, fix it, and away they go. But it's the other
folks who don't know to check this out, don't realize that this is a problem, and put
this back in, and experience all kinds of wiggle-waggle/spark timing scatter/weird
misfires, etc.
Since mom said I'm not supposed to identify a problem without also proposing a
solution, I have included the 2nd attachment showing what a new, spiffy, unworn
distributor gear looks like.
****
And that's a big-picture overview of the most popular issues surrounding the
cam drive/distributor driven gears. IF you get the phasing correct, AND your
gears are not worn, then there should be a near 100% chance of you being
able to adjust the distributor within the tight confines of where it lives.
Hope this shed some light on the misunderstood '96+ Vortec distributor setup,
especially when the CMP<>CKP signals are out of sync, and the distributor
is physically blocked from rotating far enough to make the adjustment.
If you have any follow-on questions about this please don't hesitate to ask.
And not if but when you clear the P1345 fault please report back here with what
it took so that other folks trying to sort out similar issues can benefit from
your experience.
Best of luck --
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