O-scope for testing ignition ????
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 2,158
Likes: 9
From: N.E. WA
O-scope for testing ignition ????
I believe that I've seen somewhere that guys are using a scope to look at the pulses of the ignition. How do you hook up the scope to 50kv? Is there a special probe that knocks down the voltage? Anyone ever done it? Thanks.
Le Mans Master
Joined: Dec 2004
Posts: 5,789
Likes: 8
From: Myrtle Beach SC
St. Jude Donor '05-'06
93Jet Jockeys thread was only measuring the input to the ICM and the output to the coil not the coil output.There are special probes for High voltage but an inductive timing light will give you enough info I believe.Either you are getting a pulse or not.Not sure if looking at a scope will show you much as the coil discharge is not a digital signal just a high voltage spike.
Looking at the output of the ICM vs. input shows how the leading edge of the signal input begins the saturation of the coil and the falling edge triggers the coil to fire.
Looking at the output of the ICM vs. input shows how the leading edge of the signal input begins the saturation of the coil and the falling edge triggers the coil to fire.
Thread Starter
Melting Slicks
Joined: Oct 2000
Posts: 2,158
Likes: 9
From: N.E. WA
The reason I am asking, is this. While on the dyno, I had a big dip in my perfomance and the operator said it looked like ignition break up to him. I figured I would need to be able to look at the output to really "see" anything. The odd part was that it happened consistently on three runs.
Safety Car
Joined: Feb 1999
Posts: 3,504
Likes: 4
From: Mexico Beach FL
There are special O-Scopes with probes/inductive-pickups designed to look at the high-voltage side of the ignition system. These probes are voltage dividing to allow the low-voltage input of the scope to be used with a high voltage signal. These probes usually have capacitive dividing instead of resistive.
I even made my own high voltage scope out of a regular scope, and it worked -- but, I don't recommend it.
The, much older, vacuum-tube-input scopes were very forgiving to an over-voltage input compared to the newer field-effect transistors and integrated circuits.
High voltage does some unexpected things -- like arcing over when least expected and destroying delicate transistors.
There are O-scopes and probes designed for this purpose.
For a trained technician, much can be learned from viewing the primary side of the coil because of reflected impedence from the secondary.
Tom Piper
I even made my own high voltage scope out of a regular scope, and it worked -- but, I don't recommend it.
The, much older, vacuum-tube-input scopes were very forgiving to an over-voltage input compared to the newer field-effect transistors and integrated circuits.
High voltage does some unexpected things -- like arcing over when least expected and destroying delicate transistors.
There are O-scopes and probes designed for this purpose.
For a trained technician, much can be learned from viewing the primary side of the coil because of reflected impedence from the secondary.
Tom Piper
Last edited by Tom Piper; Aug 23, 2005 at 09:50 AM.
Drifting
Joined: Nov 2003
Posts: 1,637
Likes: 2
From: Honeoye Ny
When I was a little kid, (and I mean 20-25+ years ago) My dad built an ignition tester from Heathkit. It was very old school, loooked like radar or sonar, but you could see dwell, waveform, coilkick back, everything that had to do with the ignition. I was probably 16 or 17 when The hink finally broke some parts that couldn't be souced anymore Too bad we couldn't get one of those things anymore.
As far as your ignition problem, once again look at the ignition control wire waveform. Thats how we found bruce's skip. It was a broked,corroded wire at the coil. But broken on the inside of the insulator. heat, vibration and an engine swap or two was the cause.
I suspect that the second Delteq box may have been unnessicary.
As far as your ignition problem, once again look at the ignition control wire waveform. Thats how we found bruce's skip. It was a broked,corroded wire at the coil. But broken on the inside of the insulator. heat, vibration and an engine swap or two was the cause.
I suspect that the second Delteq box may have been unnessicary.
Le Mans Master
Joined: Jan 2003
Posts: 8,596
Likes: 19
From: Portland Oregon
Originally Posted by ANTI VENOM
The reason I am asking, is this. While on the dyno, I had a big dip in my perfomance and the operator said it looked like ignition break up to him. I figured I would need to be able to look at the output to really "see" anything. The odd part was that it happened consistently on three runs.
If you are using a Fluke hand held scope you can purchase the ignition probe set from them. I have a Fluke 97 which is a industrial scope that I used for diagnoising AC drive systems. I use it for diagnoising problems in our C4s as well. It is especially handy when having to figure out if the cam or crank signals, and of course the dreaded opti-crap signals are OK or not.
I got my probe set from these guys a few years ago:
http://www.aeswave.com/
http://www.aeswave.com/products/Product.asp?i=64
Did the shop where you had your car dyno'd have a SUN scope there? If so he can connect the SUN machine to your car while its on the dyno and see if there is any ignition break up. That is what I use in my shop, and its extremely valuable when diagnoising problems such as what you are experiencing. I set the scope up to record the run, then make a pass on the dyne, if there is any bobble in the ignition primary or secondary circuits I can catch it with the SUN machine. It's very easy to do with the SUN machine and the dyno.
Last edited by tjwong; Aug 23, 2005 at 10:42 AM.
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Drifting
Joined: Nov 2003
Posts: 1,637
Likes: 2
From: Honeoye Ny
That's a store chock full o' goodies TJ. The meter John brought me ut to use is the fluke 199c. It quite simply the best portable I have ever used. The one's in the lab at school don't even have some of these features. Too bad John probably signed it out at work, Id tell him to pick up his car and we'd call it even. 
