If you haven't already, I would check the high voltage spark cables, for continuity and get a resistance value for the Front vs. Rear. These are quite vulnerable to developing internal faults. There are internal resistance elements that can fry out, and threaded connections at the coils and the spark plug caps that can open up.

One could swap the entire high voltage cabling Front for Rear. Obviously this creates an ignition timing issue, depending on how you do it.

The only other difference between Front and Rear systems, is that one side has the Fuel Pump Cutoff Relay attached to it. If the high voltage cabling checks out OK, I'd run a test with that component disconnected, and also check the wiring that goes to it for possible shorts.

There is a test for the ICM that involves using a Peak Voltage Adaptor to measure the Pulse strength feeding the coils. Page 17-2 in this manual: https://vt750dc.com/HONDA_VT750DC.pdf

A PVA (DVA) is a pretty simple gadget that lets one measure the strength of short pulses using a standard meter. Here's a video:

I believe that the Honda HEI ignition uses pulses that are between 100 and 200V DC with a negative polarity.

 

Hello Axman88. I don't know what the number 88 has to do with your handle, but I thought I'd tell you that I also own a 1988 VT1100C that I bought from a friend in the early 90's, but that bike is a whole 'nother story....

Anyway, as far as the '02 VT750DC mess is concerned, the continuity of all four plug wires checked out and were all logged in at 8.5 +/- 0.1 ohms.

I had considered the front to back spark plug cable flip-flop, but didn't think they would reach. As you know, I did flip-flop the ignition coils, and the problem remained with the front #2 cylinder, eliminating the coil as the cause, but certainly not the plug wires. So, I'll have a closer look at flipping the plug wires

Regarding the fuel cut-off relay, I already have it, the fuel pump relay and the fuel pump itself by-passed because I have the fuel tank removed from the bike and I have replaced it with a small service tank that sits on top of the frame enabling it to gravity feed the fuel line intake tee fitting, leading to each carb. I will however recheck the cut-off relay wiring to verify its condition.

From reading the Honda Service Manual for this bike I have become familiar with the use of a Peak Voltage Adapter in combination with a multi-meter for determining pulse strength into the primary side of the ignition coils. Doing so appears to be where this investigation of no spark is leading. I very much appreciate the video link that explains the simple procedure for making your own PVA so that the values can be checked against the indicated 100-200V DC range.

I'll post my results as I am able to complete the above tasks. (I do carpentry and make cabinetry and furniture by day.)

Thanks much for your welcome input axman88

 

8.5 ohms is not a familiar number.
The spark plug end caps are 5000 ohms.
The wires if still the factory wires are copper so have no resistance.
The coil primary should be about 2 ohms.
And the secondary with no wires connected is about 25,000 ohms or so.
And make sure each coil feeds 2 plugs on the same cylinder.

 

Hello swifty2014 and thanks for joining in.

I rechecked the impedance numbers:
-The electrodes on the new NGK DPR8EA resistor plugs is in the vicinity of 5,000 ohms, as we would have expected.
-The plug wires are copper strand conductors. The continuity on al'l four cables is in tact and the resistance reading is 0 ohms. (I'm using a better and newer meter than the one used previously.)
-The #1 (rear) cylinder's primary coil winding is 2.7 ohms. The #2 front cylinder's primary coil winding is 3.1 ohm
-The secondary windings on both rear and front coils is giving a reading of ZERO ohms (using the new meter) with the probes connected to the threaded spike within both coil towers. No continuity or resistance is registered on the meter, for either coil. As to why both coils are capable of firing the plugs of the rear #1 cylinder, but neither will fire the plugs of the front #2 cylinder, I can literally only guess at the moment that the ICM is the culprit.

 

Most of those readings are good.
But Did you change your meter setting to a higher resistance range, to measure the secondary,(unless it is an auto-ranging meter)?
It should be about 20,000 ohms or more.

 

Ah! thank you. I was playing with the "auto" switch and nothing was any different. That was because I didn't give the meter enough time to calculate the value, I guess. So, with some patience applied on my part I have a reading of 22,600 ohms for the secondary windings of the #1 (rear) cylinder)))))))))))))))))OOOOOOOOOOOOOOOOOOOOOOOOO)___))))))))))))))))))?(((((((((((((((++++++++++++++++++++++++++____??????????????????????

 

Excuse the jiberish at the end of my reply. My computer has issues.... Anyway, the reading on the secondary windings for the ignition coil that handles the front #2 cylinder ism 1.6 MILLION ohms. Now there's a problem, for sure!

 

I think you found it !

 

Thanks for getting me to look at that again. Much appreciated swifty.