Weird timing issue...

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I'll check... But it did work fine before the fire... When I had the distributor out, I did NOT removed, adjust, or otherwise screw around with the mechanical advance--AT ALL.
When I said "I checked the movement of the weights before I reassembled it" I meant, reassembled the distributor, not the mechanical advance. By reassembling the distributor, I mean, installed a new condensor, module, rotor, cap, button and coil, and plug wires.
But I will check it again.
~jp
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i skipped through some of the posts..lots to read...i don't know if anyone mentioned this and i don't know if it's relevant...i came across a similar situation a few times on 88-94 chevys...HUNTING timing..timing moves all over...some times runs ok till your on the gas, some times idles bad...the rector wheel with the magnets on it,on the distributor shaft was loose, and spinning on the shaft...sometimes they can move at idle and sometimes they need instantaneous acceleration, like you revving it up, to move. unfortunately there is no fix for this, you have to replace the distributor assembly...i've seen this about 1/2 a dozen times...its not that commen
let me know what happens.
redeye.racing
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Yea, been there.
I advise everyone with the 88-95 V8 chevys to dump that distrib and get the "Ready to Run" MSD distributor instead. More than worth it.
MSD-8366 Chevrolet/GMC: 1987-93 cars and 1987-95 trucks
HDS
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What happens if the two wires that go to the pickup coil are reversed? It's possible that I screwed that up. Is one side of the coil grounded? Seems like it would have to be in order for anything to happen.
~jp
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----------
Ok, I've read the other post; this is what I would do:
1. Double check that all you spark plug wires are routed correctly.
2.) Yank that thing out (Distrib), and set your motor to TDC, number one pistion.
3.) Insert the distrib, then pull it out again. Turn the rotor 180 degress, and put it back in. Each time you do this, it'll move the rotor alittle bit farter each time. Repeat untill the rotor is facing the number one spark plug connection in the cap. (you dont need to pull the distrib ALL the way out, just enough to disengage the sprockets).
4.) Hook your cap and spark plug wire up, and start it up. Set the timing at TDC, not BTDC.
hook up your vac lines...enjoy
HDS
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advance could be hooked up wrong. Take the cap off and use your mouth and suck on the end of the vaccum line, it should pull the diaphram in moving the arm in toward the vaccum pod. I don't think it is possible but maybe you ended up with a advance from some odd ball reverse motor. Stuck weights just wouldn't move, no change in timing but make sure they are free. Manifold or ported doesn't make a diffrence on which way your vaccum advance works, its vaccum no matter if its on all the time or not. Distributor position off won't cause this problem, you can put your distributor in any direction just make sure you are pointing at number one @ tdc. This isn't your problem, it is running so you aren't 180 off. Installing small blocks in vehicles not originally equipped with them you often have to turn distrubutors way off for clearance then move your wires to appropriate position. Double check your module wireing, just to make sure. Also double check your plug wires for correct order. To backfire through carb you either have severe advance allowing fire befoe intake valve closes, wrong fireing order or a bad intake valve. let us know what happens.
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David Johnson wrote:

Well the timing is retarding even with the vacuum advance disconnected. This should STILL be impossible though... All I know is, the timing gauge/tab above the harmonic balancer is marked something like "12 - 8 - 4 - 0 - 4 - 8" and says "before" on the left hand side and "after" on the right. I set timing at idle to be about 8 degress on the "before" side. When I rev it, the mark moves to the right. It's completely asinine. And I KNOW that when I timed it in the past it went the opposite way (advanced) when I revved it.

The problem is occuring even with the vacuum advance disconnected.

I concour, and they are free to move, springs are functioning too.

Again, I agree... whether it's ported or manifold vacuum should only change when the vacuum advance kicks in and whether it stays "advanced". Although, connecting to the manifold vacuum source *could* cause this (high vacuum at idle=max advance...crack open throttle, manifold vacuum drops, timing retards) but that's not the case. Again, it happens regardless of whether that vacuum advance is even connected to a vacuum source. I did try the manifold vacuum as a test--no difference.

Agreed.
Also agreed...

It's a K5 Blazer...originally had a 305. This is a 350 that was a new crate motor, installed 2 years ago.

Here is what's different about the engine POST-fire...
1) The module wiring is a mod/hack that I pulled off these here newsgroups as well as a few websites. It involves disconnecting the rear harness coming out of the HEI although and then jumpering pins 1 and 3 on the pickup-coil side of the ignition module. The pickup is connected to pins 2 and 3. Basically, either pin 1 or 3 is an "output" and the other is an "input" in a manner of speaking. The old ESC (elec. spark control/wannabe ECM) just retarded spark based on input from a knock sensor. It got the signal to spark based on the previously mentioned "output" of the ignition module and sent the signal back to the module's "input". That's the simplified explanation. Either way, by eliminating the ESC, and jumpering pins 1 and 3 together, you just create a loop that allows the engine to run.
It's a Chevy-approved mod/hack. I did this because I could not find a replacement wiring harness to go back to the ESC. The original harness was toasted in the fire. Plus I read that the ESC can cause problems when it goes south, and it's a real performance killer.
2) 5 minutes before the fire, I'd changed the jets to smaller ones. This could cause a lean condition off idle couldn't it?
When I get out of work today I'll get cracking...
Thanks,
~jp
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Just my 2 cents worth but...............
I recall the jumping of wires to eliminate the esc module, I cant remember the specifics of it but if it is what you say it is , just an input and and output then the pick up is waiting on an input from the knock sensor thru the module? basically an electrical/electronic signal? what if all you did by jumping the wires is send a signal to the pick up to retard the timing due to the signals coming into the input connector?
I am going to look for the bulletin and info on this mod.
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The pick up receives no signals, it outputs an AC voltage to the ESC box under the dashboard, the ESC buffers the signal from the pick up and sends it back out to the ignition module, when the ESC box receives a knock signal from the knock sensor, it modifies the buffered signal, retarding the timing.
By having the pick up wires reverse polarity, he altered the shape of the AC signal from this; /I /I /I /I / I / I / I / I / I/ I/ I/ I/
To this; I\ I\ I\ I\ I I \ I \ I \ I \ I I \I \I \I \I
Since the module triggers on the falling edge of the pick up signal, as RPM increased, the peak to peak voltages went up and as they did, the trigger point retarded.
Good lesson on reactance and reluctance... (apologies if my ASCI art doesn't turn out.)
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