Hot Rods Question for you electronic experts

I'm using a Tach, Dwell and Cylinder Inhibitor analyzer to tune the woodie. I understand the benefits and usage of the cylinder inhibitor function and I understand how to conduct the test, what I don't understand is how the unit is able to short the individual cylinders or multiple cylinders when trying to balance the idle circuit.
There are three leads on the unit 1. power lead attachs to the positive terminal of the battery and a ground, this one powers the unit. 2. this lead attaches to either the - terminal on the coil or the tach terminal on an HEI distributor cap and is the source of the tach function. 3. this lead is an inductive clamp that goes on the plug wire to the number 1 cylinder.
So with only these three leads how is the unit able to short out individual cylinders or groups of cylinders, I don't get it

 

It must be able to identify the cylinders based on the switching going on at the coil caused by the points (or HEI) and ground the required cylinders though it's attachment to the coil primary. I assume it has a switch for number of cylinders.

That's my guess, until an expert comes along..

 

If it shorts the tach signal to ground, while that cylinder should be firing, then that cylinder will not fire. It gets it's timing information to this from the tach signal, and the #1 pickup cylinder.

 

I guess I don't understand how it's able to differentiate the tach signal from one cylinder over another with no regard for the firing order

 

I can't see the machine you're talking about...but I expect it lets you select which cylinder in the firing order is disabled...not which actual cylinder is disabled. What does the instruction book say?

 

It always knows which cylinder is #1
It knows when each successive cylinder in the order is going fire.
You know the firing order.
Maybe you need the secret decoder ring to cancel the third position in the firing order, not necessarily cylinder #3
Just a WAG

 

The instrument is a Snap-On MT-460, I have downloaded the manual it explains the why but not the how. You must be right about selecting which cylinder in the firing order is shorted, I thought it was telling you to select the actual cylinder number. That makes more sense, I need to quit over thinking things and just accept it on faith.

 

Did it come with these. There are 16 of them with various firing orders on both sides. (32) and they are placed over the dials. I haven’t used mine in years.


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Rich, No it didn't and in fact I was just scouting around on the web trying to find a set of them. The two engines that I use this thing on are an SBC in the woodie and an AMC 360 in a Jeep Wagoneer. Luckily they have the same firing order which is on the Code B overlay card. Is there a chance I could talk you into photographing that card and posting it so I can download it and make a card for it?

 

No problem, I ‘m in a meeting all day tomorrow, but Friday I’ll copy them (both sides) and send them to you.


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Here’s B. I’ll Pm you the rest of them Friday.


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You're a good man, thanks so much. I can print them and put them on card stock, it'll work just fine

 

I have not heard of one of these in many years. I remember in a chevy dealership we had a test machine and it would short out cyls and record the rpm drop to pinpoint weak cyls to test overall engine condition. Forgot all about it. Can't remember what brand machine it was though. You just hit the switch and away it went automatically. Lippy

 

And that’s the secret decoder ring

 

Interesting....now we all know.

 

Yeah it's that "automatically" that had me stumped.

 

41woodie, check your PM/Mail