Ignition scope results

Stevehose

Stevehose

Well-Known Member
Site Donor $$
Messages
13,396
Reaction score
6,194
Location
Sarasota, FL
I bought a vintage Heathkit ignition scope (1972) recently and hooked it up tonight:

Scope.jpeg



My first test run gave this wave form:

Before.JPG


Note the upper left hand side of the trace, it starts off chaotic (this is the plug firing-it is supposed to be flat in between the spikes and not this high up according to my noob knowledge level) before going down to the first flat line (coil dissipating excess voltage). The second flat line (after the build up) is the recharging of the coil (dwell).

According to the stuff I've read, the plug firing stage looks like this because of high resistance in the 2nd stage, possibly from wires, cap/rotor, fuel mix, and/or plug gap. Since my other ignition components are new and I recently bumped my gap up to .030 I decided to start there and backed the gap down to .024 and got this trace:

After.JPG


The second trace is tighter and more uniform with less voltage spikes and the spark line is flat, lower, and longer like the books show. The dwell looks more uniform. The idle is smoother and it revs nicely although I haven't taken it out on the road yet. Pretty cool stuff.

My question is, when the owners manual says the gap should be .024 +.004 does this mean plus or minus .004 or does they mean the range of .024 - .028 and not .020 - .028?

Any other comments on the trace images from the experts that might reveal other issues? Would the trace moving back and forth (slight wobble) indicate a worn distributor?
 
Steve that's very cool. My blue service binder has a lot of scope pictures.

Did you get the assembly and calibration manual with it?
 
Yes it came with both which is helpful for calibration etc.

I've been pushing the limits on plug gap thinking that wider is better and taking Pertronix' suggestion to open them up a little. In my case it's evident that this is not a good idea even though my ignition components are all new and now I suspect our cars with non-CD boxes and old wiring etc. may respond better to smaller gaps.

This visual confirmation is helpful and I will be experimenting with different caps and rotors this weekend.

Any idea on the acceptable range of the gap? The reason being this trace looks better than the one I did at .028 too and am wondering if even lower would be beneficial. Until I can drive it however it is staying at .024.

It also shows the parade view of each cylinder (doesn't photograph well due to the crt refresh) which is helpful for tweaking mixtures and checking individual cylinders:

photo%25201.JPG



And the primary side which I have no idea how to interpret at this point but it looks pretty crisp:

photo%25202.JPG




Luis A. said:
Steve that's very cool. My blue service binder has a lot of scope pictures.

Did you get the assembly and calibration manual with it?
Click to expand...
 
Last edited:
Stevehose said:
I bought a vintage Heathkit ignition scope (1972) recently and hooked it up tonight:

Scope.jpeg



My first test run gave this wave form:

Before.JPG


Note the upper left hand side of the trace, it starts off chaotic (this is the plug firing-it is supposed to be flat in between the spikes and not this high up according to my noob knowledge level) before going down to the first flat line (coil dissipating excess voltage). The second flat line (after the build up) is the recharging of the coil (dwell).

According to the stuff I've read, the plug firing stage looks like this because of high resistance in the 2nd stage, possibly from wires, cap/rotor, fuel mix, and/or plug gap. Since my other ignition components are new and I recently bumped my gap up to .030 I decided to start there and backed the gap down to .024 and got this trace:

After.JPG


The second trace is tighter and more uniform with less voltage spikes and the spark line is flat, lower, and longer like the books show. The dwell looks more uniform. The idle is smoother and it revs nicely although I haven't taken it out on the road yet. Pretty cool stuff.

My question is, when the owners manual says the gap should be .024 +.004 does this mean plus or minus .004 or does they mean the range of .024 - .028 and not .020 - .028?

Any other comments on the trace images from the experts that might reveal other issues? Would the trace moving back and forth (slight wobble) indicate a worn distributor?
Click to expand...


If no number either plus or minus is mentioned, than it it is assumed to be zero. So, in the case of .024 +.004, that could be written as- .024 +.004/-.000. The resulting range is- .024-.028
 
I use a bosch MOT 251 ... allthough much newer!

When you lower you gap, burn time will usually get a little longer, and spark voltage will get lower - especially on old ignition systems!

New ignition system is so poworfull that you can break the tip of the sparkplug off and it will still run perfect! But if you compare burntime with a normal gapped plug, its where you will notice a big difference. It can be shortened down to about 0,5 ms from 2ms

If you coil was powerfull enough, you would have a normal spark with just a slightly shorter burn time.
 
Nice, I can see DQ installing a scope instead of the center speaker for drive time optimizations.
 
Digital Storage Oscilloscope

deQuincey said:
really cool

no way to get one of those traveling over the pond...:-(

does anyone know an alternative european brand for those ?
Click to expand...

I recently bought a DSO on Ebay for about 100 Euros. It's a Hantek 1008c 8 channel with Automotive software. It comes with an ignition pick up cable.

http://www.ebay.co.uk/itm/Hantek-10..._Measurement_Equipment_ET&hash=item2c71656a35

It really is a cheap way to get into ignition analysis and other electrical wave forms found on cars but you need some knowledge of how to use a DSO.

The Rolls Royce of auto DSOs is PICO and if you go on their site there is lots of useful info as well as being able to download the software for free which gives you the opportunity to use the software in trial mode. It leads you through the connections you have to make and gives examples of waveforms that you should be seeing. http://www.picoauto.com/software-picoscope-automotive.html

I bought the Hantek to get a feel of using a DSO but hope to eventually get a Pico.

Hope this helps

Peter.
 
steve, can we compare the curves ?

Stevehose said:
After.JPG
Click to expand...

secondary curve:



theoretical curves:





what can you tell ? it seems that we are talking about what they call the "secondary" curve

yours seem pretty good shape, according to the theoretical ones, i mean

mine is a bit strange, first if talking about the "spark line" (#5) it is not horizontal, but a bit up slope, and what worries me more is that i can see a Little but clear "v" that breaks the line, what does this mean ? i dont know

then is more about the length of the closing time, it seems that it takes too long to reach the horizontal after (#6), i dont know if this is due to the resolution of the image,...

do you have "primary curve" images as this one ?




BTW, what you said is your primary looks pretty much upside down to me, so probably wrong conections ?...
 
Your upward slope spark line could be too wide a plug gap, check this first-what are your gaps now? This is first thing to change. Narrowing them could level the line. I found my waveform had better pattern closer to .024-.026.

Your recover to #6 is normal for points, mine is sharper because electronic ignition (Pertronix) provides a quicker recovery.

Other than that, yours looks very healthy.

I will check primary...


deQuincey said:
secondary curve:

what can you tell ? it seems that we are talking about what they call the "secondary" curve

yours seem pretty good shape, according to the theoretical ones, i mean

mine is a bit strange, first if talking about the "spark line" (#5) it is not horizontal, but a bit up slope, and what worries me more is that i can see a Little but clear "v" that breaks the line, what does this mean ? i dont know

then is more about the length of the closing time, it seems that it takes too long to reach the horizontal after (#6), i dont know if this is due to the resolution of the image,...

do you have "primary curve" images as this one ?




BTW, what you said is your primary looks pretty much upside down to me, so probably wrong conections ?...
Click to expand...
 
Last edited:
You must log in or register to reply here.
Back
Top