My meter is a cheap GB meter. I would appreciate it if someone would check voltage at the coil + on their Duraspark system to compare to my 6.75 volt reading (key on, engine off).

One other thing I just happened onto when searching for a lower ohm resistor to perhaps try. This statement is from the Jeg's website in reference to a 1.6 ohm resistor. "Should always be mounted to the firewall (or another non-heated metal surface) for additional heat dissipation. My ballast resistor is mounted to the plastic inner fender well with a 1/2 inch thick washer used to lift it off the fender well for air circulation. Does anyone think this might have some bearing. I know that someone said the resistance increases with heat and I would think (dangerous I know) that a heavy load could increase the heat. I think I will move it to the firewall just to see if it makes any difference.

FuzzFace2: Spark plug gap is .045.

 

Got to thinking about the meter reading. Rather than hold out in hopes of finding a forum member with the same meter, we could probably get better results with a larger sample. Maybe we could get a half-dozen readings, just include what type of meter was used. If we get 5 similar readings with various meters, and 1 in left field, we can probably chalk up the aberration to that particular meter. I've got 3 different meters I can try, but can't get to it until this evening.

Interesting catch about the heat dissipation for the ballast resistor. I'd suspect that recommendation has more to do with avoiding heat damage to the mounting surface, such as if installed directly on a plastic surface. Obviously you wouldn't want to install it anywhere that would pick up extra heat, such as on the exhaust manifold or even on the engine block. I think as long as it's installed in free air in a relatively cool location, you should be fine. Even though under hood temps climb when the engine is working hard, I don't think the increase could act so quickly on the resistor. But who knows, I've been less correct than usual before. It wouldn't hurt to relocate it, or you could add a piece of sheet metal to the current location as a heat sink.

 

Ok, now Whisler needs to find one of those!

 

FWIW: Found the following notes in my note book:

Key off battery voltage 12.68
Key on battery voltage 12.2
Voltage at + coil, key on, motor off 6.7

Battery voltage motor running 14.65
Voltage at + coil, motor running 11.43

 

I wonder how different various DVM's read that voltage.

 

Your key off battery voltage, and key on, motor off voltage at coil + are identical to mine. I didn't check motor running battery voltage or coil + voltage. I will give it a try in a few minutes.

Out of curiosity, I moved the resistor from the plastic inner fender panel to a metal part of the inner fender. I'll see if it makes any difference. Just for clarity, all previous driving tests have been with the engine at full operating temperature. I didn't want to push a cold engine too hard. It may be frustrating me right now but I am not to the point of wanting to blow it up....yet

Gary, I do have another meter, just a cheap Cen-tech that has never been out of the box. I'm going to take some readings with it and compare.

 

I'm not in a position to check voltages right now. But, I can tell you that DVM's are geared to taking either dc voltage or ac voltsge. And the vast majority of meters expect the ac to be a nice smooth sine wave, meaning like KR showed on his portable scope:




But the voltage at the coil on the DG/Y wire, is anything but a smooth dc or ac voltage. Instead, it looks like the wave below, which I took off Rusty. The vertical divisions are 10 volts each, and ground is two major divisions above the bottom. The left side represents when the DS-II module releases the circuit, just as if the points opened. At that point the voltage goes above 50 and then rings, meaning it oscillates in a decreasing fashion until it stops at battery voltage - all the wile the spark plug is getting fire. Then the DS-II module starts charging the coil again, just as if the points had closed.

So, you can easily see that most DVM's would give a very erroneous reading since the signal is far from being either dc or ac.

 

What coil do you have in it? Once upon a time someone tried to sell me a fancy accel coil. Even though it had the buttons for the horseshoe connector it was still the wrong application for my stock DS system. I can't recall the details but I think the internal resistance of the accel coil was different than the stock coil.

Going further off road... I read somewhere the reluctor wheel inside the dizzy can somehow be altered by sandblasting or other cleaning treatments it may undergo in the recycling / rebuild process.

Re manufactured parts aren't what they used to be. I only got 1,400 miles out of the new vac advance when I replaced my dizzy. Had to replace the vac advance with my 30 year old original!

 

Brnfree: I have a new Echlin IC21 coil in it now but it still exhibited the same problem.

I tested my meters against each other, an old GB Instruments GDT-11 and a new Cen-Tech 90899 (both cheap) and got the following comparisons:
Battery, key off, GB =13.24v Cen-Tech = 13.20v
Battery, key on, engine off, (KOEO) GB =12.52v Cen-Tech = 12.45v.
Before resistor, GB = 11.74v Cen-Tech = 11.77v.
After resistor, GB = 6.83v Cen-Tech = 6.88v.
At coil +, GB = 6.86v. Cen-Tech = 6.86v.
Battery, engine running, GB = 14.70v. Cen-Tech = 14.70v.
Coil +, engine running, GB = 10.78v. Cen-Tech = 10.84v.

Whether the voltage reading at the coil + with the engine running means anything, at least my two meters agree.

Also my coil + reading (KOEO) is essentially the same as Brnfree gets and he isn't having my issue. I would like to see a few more examples of KOEO coil + readings, but it is looking more and more like the issue isn't the resistor now that it has been changed.

If I re-install the old coil and jumper the resistor and the problem isn't there, what is my next step? Running full voltage to the coil isn't a good idea, but what will the need for higher voltage point to as the root problem?

The more I test the confuseder (new word) I get.

 

Given those voltages, I don't think it is either the coil or the DS-II module. I say that because it takes current flow to create the voltage drop, an yours are like those of others.

What else is there but the pickup?

 

I am going to do the run with the jumper in place just to check the results. I am also going to check mechanical advance as was suggested. But it looks like I will have to replace the pickup and see what happens there. I just have to check my manuals to see how that is done.

 

I also had a miss under load, more of a hard bucking and sudden abrupt loss of power.

It turned out to be bad plugs.

Over the course of 4 weeks I struggled with this. I started with the fuel system, moved on to the exhaust system, then changed all the ignition stuff. I didn't change the plugs because they where fairly new... and it would have been just plain wasteful to not put some more miles on them. I even had a new set of plugs setting on the shelve.

I also don't think this is a coil or DS2 IGN module issue. But I also fail to see how the pickup in the Dist could cause a load related miss. The pickup just trips the IGN module.

Some addition voltage checks please...
KOEO... Coil positive and also Coil negative.
You can also just put the positive meter lead on the coil positive and the negative meter lead on the coil negative... to see the voltage drop across the coil.
The 6.8 volts should be dropping across the coil, well about 5.5 volts with the remaining voltage being lost in the DS2 IGN module and ground wiring. The final ground point is in the Dist.

I would change the plugs again, never hurts to have a good used set for spares.

Does your exhaust manifold have an O2 sensor?

Other thoughts and info... The coil is a step up transformer based on the ratio of turns primary/secondary. If the voltage across the coil primary is higher then the potential voltage output will be higher also... and thus a stronger hotter spark.

Jim

 

Got some readings last night with several meters. Even found a GB Instruments DVOM I forgot I had. Also broke out an old Micronta clamshell analog meter. Can't remember the last time I used it. The battery in it said "guaranteed to 2004".

All readings taken on my '84 351W, approximately 1500 RPM. Meter (+) lead on the coil (+) post. Meter (-) lead on the battery (-) post. Meter set to DC volts.

Edit: System voltage at 14.2, as measured at battery

GB GDT-190A (pictured): 11.77 VDC




Micronta 22-211 (analog): 12.1 VDC

Fluke 83: 12.1 VDC

TPI 440 Scope Plus 440 (pictured): 12.25 VDC



Sorry about that scope picture quality. The screen is very glossy and tough to photograph.

 

Jim: KOEO coil (+) = 6.86v, will check coil (-) and drop across the coil later today and post. No O2 sensor. Exhaust system should be no problem as it is new shorty headers, new down pipes with crossover, no cats, and true dual exhaust on back. Switching spark plugs sounds easier than changing the dist. coil pickup, so I'll do that first. I'll probably change spark plug wires too.

Kr98664: your GB meter reading is 1 volt higher than mine, but mine was done at idle (~800 rpm), don't know if that should affect anything. Would you mind checking voltage at the coil (+) key on, engine off with that GB meter?

Thanks to all for the time and effort.

 

I think plugs also because when changed the rpm it happens changed too.


I also had a car that would only start to move in/out of garage as needed over the years.
Went to move the car and it idled fine but give it gas to move, stick car, and it would back fire out the exh. Thinking maybe a stuck valve I took a compression test and all was good.
Plugs looked new as they had little run time on them but I did find 1 cly not firing as it should. Moved plugs around and found the non-firing moved.
Replaced the plugs and all was good after that.
I think because the carb was bad, ran lean, it hurt the plugs even if they looked new. When put under a higher load/RPM it would fail.


I say go with a different brand plug say Champion and see what happens. At worst you put the set you pulled out on the shelf till the next plug change.
Dave ----