Weird timing issue...

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Jon R. Pickens wrote:


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I found this:
http://tinyurl.com/gwbud
It states in the 3rd message:
"The polarity of the signal going into the HEI module is VERY important."
then...
"On an engine, a symptom of reversed pickup wires is ignition timing which is about 20 to 50 degrees retarded, and the timing bounces around a lot. When it is connected correctly, the timing is very consistent, and is close to where you set the static timing."
~jp
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and... (yes I realize I'm flooding the thread but still, this is interesting)
http://tinyurl.com/q7jzx
"One thing to watch with all these modules is to correctly phase the variable reluctor pickup. The waveform looks like this:"
/\ / \ / \ ----/ \x /------ \ / \ / \ / V
"The ignition should trigger at the zero crossing, point "x". that is the most stable point vs RPM. If the polarity of the trigger is reversed, the ignition will likely trigger on the rising edge, ***THE POSITION OF WHICH CHANGES WITH RPM***."
~jp
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wrote:

THe rising wave well not change from its trigger point regarless of RPM BUT, the fall wave relative to crank postion can because the decay rate of coil in pickup is constant over a fixed time interval so as RPM increase it will cross zero axis at a further and further point as RPM increases (relative to crank postion) and in effect, retarding the timing signal. Incorrect polarity and/or wirng could cause your problem. The key to your problem is in the pickup and its inteface with ECM.

The SnoMan www.thesnoman.com
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SnoMan wrote:

Well rock on... Here at work, I get my best thinking done out on the loading dock (smoking area). I was leaning against the wall and it hit me.
This makes a LOT of sense. That is the ONLY way I could imagine spark actually retarding with RPM increases.
~jp
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wrote:

I have put some thought into this and I agree it does add up and could explain your problem fully. There is always a cause for a problem and you need to understand it to find a solution. Your comments of the trigger signal made it cyrstalize for me as to what was going on here. It all adds up. ----------------- The SnoMan www.thesnoman.com
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Yep... basic AC voltage theory...(I'm by no means an electrician, but I know a *little*) The wave WAS running in reverse. I just walked back in the apartment not 2 minutes.
THE TIMING ISSUE HAS BEEN LAID TO REST!
Currently set to about 13 degrees BTDC @ idle with the vacuum advance disconnected, pulling about 14-15" Hg off the manifold. The mechanical advance is doing its job, advancing with engine speed... No more backfiring too. I'll take it!
Many thanks for your help, Sir...as well to anyone else who replied with suggestions.
~jp
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Eh... I mean, the wave was 180 degrees out-of-phase... :-)
~jp
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wrote:

You are quite welcome. I am here to help not to get brownie points. Your problem was curious as I never had seen one like that so I wanted to find the cause. Do not dish yourself on electrical knowledge because you knew more than most and enough to understand what was happening when I connected the dots for you. ----------------- The SnoMan www.thesnoman.com
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I can usually figure out the problem given enough time and a few decent hints.
I can't count how many good ideas I come up with on the loading dock at work, lol... more than I do at my desk, that's for sure.
Once I got a few 'keywords' down, I was able to pull up quite a bit on the subject via Google. I find it interesting that I've never heard anything about this before.
And apparently the 5-pin ignition module is uncommon enough that I'm very unlikely to find much on it. I may actually post some of this info on my site for future linking/reference.
Surely someone else will need this info someday.
~jp
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wrote:

Feel free to post a article about it on my site/forum to if you want too. I will remember this one too as I had never seen if before either (as I mentioned earlier). On a side note, unless you have a large overlap/aftermarket cam, the vacum sounds a bit low at a idle (from what you stated) . ----------------- The SnoMan www.thesnoman.com
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Well, the cam is stock to the engine, but as I stated earlier, the engine (290hp) is the same as the 260hp motor, with the exception of the cam.
Here's the cam specs: ".450'' intake and .460'' exhaust lift", and "Flat Tappet Duration @ 0.050'': 222 I, 222"....per the Jegs site.
I was never able to get a lot of vacuum on this engine. With everything plugged, and the timing and idle circuit set to max vacuum, I was able to get 16" Hg once, but that was only because I was trying to achieve max vacuum, not because it ran best that way.
What's sad is, after all this, I can now tell that the engine is running rich as ever, at least at idle. No idea how the smaller jets will affect the cruise and power mixtures yet.
I'm about to throw this carb off a cliff and get another Quadrajet... Eh, I won't do that. But the TBI swap is looking *mighty* good.
I'll post the info on your site once I've got photos taken. May not be this week, as I got packing and moving to do, but next week at the latest probably.
~jp
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In article

Glad you got it figured out Jon.
I'm a bit puzzled though...
Been a few years since I was inside an old HEI but two things come to mind; 1) aren't the terminals on the pole piece different sizes to keep reversing them from happening? 2) aren't the module terminals where the pole piece plugs in labeled 'G' for the green wire and 'W' for the white wire?
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Well...I have (what I call) a "2nd Generation" HEI. Whether it's truly the 2nd version of the HEI, I'm not sure, but it's the 2nd version I'm aware of.
This one is *supposed* to use a 5-pin module. It has 2 pins on one side for the condensor to connect to, but the other end has 3 pins, rather than just a G and W. That end connects to both the pickup coil as well as the external ESC/ECM. The connection that comes from the pickup coil has 3 pins of course, only 2 of which go to the coil. It has both female and males ends, and functions as a "pass-through" connection (that's what I call it). This basically just allows the ESC connection to piggyback onto the module after the pickup coil is connected.
If I hadn't messed with that connection, we wouldn't be having this conversation. I had figured that a 4-pin (1st generation...no ESC) module would work just fine in this distributor, despite the fact that the pickup coil connection was different. But because of the spacing of the pins in that connector, it wouldn't work. So I used the smallest flat-head precision screwdriver I had, and pushed the metal tabs down to slide the metal pins and wires out of the connector housing without damaging them or the housing.
I blew out my 4-pin module, as well as two 5-pin modules, because I didn't have the internal ground wire connected to the ignition coil. I thought when I reassembled that connector (to try out the 5-pin modules) that I reassembled it correctly. I apparently did NOT :-)
As it is, the ESC is disconnected, and although I'm using a 5-pin module, it functions as the earlier, 4-pin version of the HEI. I ended up using the ESC connector that piggybacks onto the pickup coil connection and removing the center wire, then ran a short wire between pins 1 and 3. That way there's no external harness coming out the back of the distributor. I could've used female blade connectors and accomplished the same thing. In fact, that's what I plan on doing when I document the process for others to see.
I have a spare HEI of the same vintage as mine, so I'm going to be taking some pics of the whole modification procedure to post on my site for others to see.
~jp
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In article

I hadn't realized that you had modified the harness to the ignition module, I was under the impression that someone had sent you the distributor wiring that burned up in the fire and that all you had done was jumper the 4 pin ESC connector to by-pass the knock control. I'm very familiar with the by-pass modification, was doing them 20 years ago in the dealership. Fastest way was to pull the glove box down and cut the green and black wires and splice them together. Neat, clean and protected from the elements. Of course, this assumes everything forward is in tact.
I should have had you send me some pictures of the open distributor, things would have progressed much faster.
Anyway, it's fixed and now you can move on to the transmission leak. That rates an atta boy!
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I wasn't able to locate one. I found the big connector going to the firewall at Pep Boys and the internal connector that went to the module was ok, so I made a new one from scratch. I never was able to make it run, but again, when I was using that harness I still didn't have the ground wire connected to the coil, so it was futile.

Yeah, I know it could be done pretty much anywhere... I just chose to do it internal to the distributor and eliminate the harness out of the distributor altogether. Looks cleaner. I do plan a TBI swap at some point, preferably sooner than later. The Edelbrock carb just runs way too rich and I'm sick of screwing with it. It makes NO sense, but I'm almost to the point of giving up.
The big grommett on the firewall that went to the ESC will eventually be used to run to the ECM once I do the TBI swap.

Yeah, probably... I was running myself in circles. The missing ground wire caused me to kill 3 ignition modules before I caught it. By that point I wasn't even thinking about the polarity of the pickup coil wires.

Yep...calling Mr. Transmission before lunch to talk to the mechanic and set up the deal. If everything goes as planned, I'm gonna get it towed out there today, and it'll be rebuilt by Friday.
Then I can start chasing down TBI parts and gear up for more work <sigh>.
~jp
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In article

Back fire is caused by; Late ignition timing Lean fuel mixture Leaking intake valve Worn exhaust lobe on the cam Crossed ignition wires (crossfire or plugged in wrong)
The fact that you're seeing the timing retard with your timing light makes -that- the prime suspect.
Sorry Jon, I'm not buying the "everything was fine before the fire" bit. It's been 5 months, so, a lot can be forgotten, and -something- had to be the source of the flame that started the fire when you had a fuel leak. Take the cap and rotor off, look closely at the mechanical advance mechanism. In 36 years as a mechanic, and [too] many of them as a driveability tech in a Chevy dealership, I've seen this problem more than once, and often times it traced back to something wrong in the mechanical advance. Ozone inside the cap from the arc causes rust, rust causes binding, from here it's either it's doing it because it is bound up or it's doing it because someone was in there before.
IIRC, you've had a vacuum gauge on this thing since you got it running, if the vacuum was steady, I'd rule out valvetrain problems for the time being.

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aarcuda69062 wrote:

Well, since the timing is retarding rather than advancing, (ie: later timing) that could be a problem. I did attempt to lean it out. No word on the valves or cam, but the long block is 2 years old.
It's possible that I miswired the distributor. I wasn't replacing one at a time, the wires were burned up.

Agreed.
LOL... *I* was the cause of the fire. As I said, I was trying to get it to lean out. It ran terribly rich after the new engine went in. Basically, the dude that put it in said the Quadrajet was in need of a rebuild. I needed a carb immediately, so I drove it as it for like a week, then bought an Edelbrock Performer 600cfm carb. That's when it started running rich.
When I was leaning it out (changing to smaller jets) in December, I had just driven home from work. The engine was still hot. I reconnected everything except the fuel line (Doh!) and when I tried to start it, the fuel pump caused a bunch of gas to shoot onto the hot engine via the loose fuel line that was laying on top of the intake.
When I tried to start it, it (obviously) didn't start. I heard a whooshing, boom kinda sound, and saw flames shoot out all 4 sides of the loosely closed hood.
No prior problems caused the fire. It was just me making a stupid mistake.

The mechanical advance opens smoothly. I checked the movement of the weights before I reassembled it. If that were the case, it should simply not advance right? It should retard timing should it?

Yeah, manifold vacuum is pretty steady at idle. It dumps to zero when I rev it.
~jp
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In article

When you twist the plate that the rotor screws down to, which direction makes the advance weights open up? Clock wise or counter-clockwise. Stated another way, pulling the advance weights out (as centrifugal force would do) should make the rotor (or rotor plate) move clockwise. If the advance mechanism is put together wrong, it will still open, but the timing will retard instead of advance.
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