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.
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.
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
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
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
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
This doesn't even seem mechanically possible. There is no way a vaccum
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.
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
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...
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.
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/
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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