Thunderbolt IV ICM Testing

[OldAmerican]

Think I have read practically every post on the internet about testing the Thunderbolt IV ignition module but have not found a method for actually testing the functionality of the unit. I went through the troubleshooting flowchart for a no start condition and got to the bottom where it said replace the module. Given the cost of a new one (not interested in used) I am loathe to shell out that kind of cash without having actually done some kind of test to verify the module is bad. I asked a local shop about testing it and they said you just need an ohm meter and test light but no offer to tell me how to use them--bring it in and we'll fix it for you!! Cheaper to just buy the module. Regardless, anyone out there know of a way to actually test the module? Barring that, wondering about the wisdom of just doing a complete remove and replace using the Delco kit that has a new distributor/module/wires/etc and costs less than just the Merc replacement part.

 

[alldodge]

The way you check if the module is working is with the troubleshooting guide. If done exactly according to the guide, it will indicate what needs replacing. The modules are expensive, and for me personally I would not have an issue using a used on so long as it worked.

In any case, if I needed a TB 4 or 5 and was looking at buying new (around $400), I would just change out the whole thing with the Delco EST and go boating. The one below is for a 350, but they make them for other motors.

http://www.michiganmotorz.com/delco-voyager-marine-electronic-distributor-p-119.html

 

[OldAmerican]

Thanks AllDodge. Yeah, the flowchart says replace the module but like I said, I would feel more comfortable doing that if I had a way to test the module alone. The flowchart basically eliminates the other components as the problem and then draws the conclusion that the only thing left is the module so that has to be the problem. Maybe, maybe not. The boat was working great when I pulled it out of the water and a couple weeks later no start. Electronic components typically fail during use, not while powered off. Just feel uneasy about the whole thing. If I can't do a positive test of the module will go with the Delco replacement. Found one at wolfiesenterprises.com that fits my engine and seems like a good price. Definitely cheaper than the MSD unit.

 

[RobertThoreson]

Kind of a long shot but could you find some way to test it on another motor or find one you can "borrow" for a bit? I have 0 experience with those modules so idk how feasible that would be.

 

[Fun Times]

Did you not get spark out of the coil while striking the White/Green wire?

There should be two other tests that you could try performing to see if the module is producing a switching signal.

1. Connect the alligator clip of a 12 V test light to the positive (+) battery terminal. The ignition coil can be connected to its electrical connector or not. (Gray wire in this case needs to be touched) Next touch the coils negative post terminal with the test light tip (or gray wire if disconnected from coil).
2. When ready, have your helper crank the engine while you observe and hold the test light in place.
3. Your 12 Volt test light should either,
4. 1.) Flash On and Off very quickly while the engine is cranking 'Indicating the module appears to be working/Controlling.
5. 2.) Not flashing On or Off 'Indicates the module appears to be Not working/Controlling.
6. Test # 2 to try,

   If you set your meter to dc volts and connect the positive to the negative side of the coil and the negative side to a good ground, with the ignition "on" hold the white/green wire from the module to ground for a few seconds, if the voltage drops to 7-9 volts, then returns to 12, the module is good. http://forums.iboats.com/forum/engin...76#post4719776

7. If interested in an illustration, There a some pretty good videos online if you search How To Test An Ignition Module With A Test Light.

 

[OldAmerican]

Thanks Fun Times. If we ever get above freezing and the foot of snow melts off the boat, I will have to give your suggestions a try. And to answer your question about getting spark while striking the White/Green wire to ground, no spark. Although I didn't buy a new coil and test that, I did ohm the coil I have and it is well withing specs.

 

[OldAmerican]

Well, the weather has warmed up significantly and the urge to get the boat in the water has returned. Now if I can just get it running. I got to run the tests that Fun Times posted but got mixed results. Using the test light (made from a 12v automotive turn signal bulb) method, when I first connected it the bulb lit up but then began to fade and eventually went out. Assume it was a capacitor in the circuit discharging. Anyway, when I cranked the engine, the bulb did flash on and off which indicates the module is working. Then I went to the voltmeter test. Hooked things up as indicated and got a reading of 12v. But when I touched the White/green wire to ground, no change. That apparently means the module is bad. I think I need a tie breaker test.

 

[alldodge]

But when I touched the White/green wire to ground, no change.

Disconnect the wire and ohm it out, there may be a bad connection

 

[OldAmerican]

Why didn't I think of that??? I did check for continuity through the micro switch on the throttle/shift linkage to make sure that silly thing wasn't my problem. All seemed to work, at least I got continuity through the switch in one position and no continuity in the other. If it doesn't rain tomorrow, will try to get out there and check the wire. Thanks.

 

[OldAmerican]

Well, the good news is, the wires check out fine. I did notice some corrosion on the wire from the coil to the distributor which I cleaned up (doubt it is the source of my problem but clean connections are always good) and while I had it off decided to check its resistance. Ohmed out at 6.5kohms which seems high for a 6" wire. I know it is resistance wire but can't find any specs on it to know if that is acceptable. Anyone know?

 

[alldodge]

None of the TB ignitions use a resistance wire, that was for points systems

 

[OldAmerican]

Now that is very interesting. No doubt in my mind that I have a TB4 breakerless system. And that wire is definitely not a solid wire core. I can't remember for sure at the moment but the wire was marked as either resistor or suppression and with the 6.5K resistance reading it definitely has resistance. Makes me wonder if the prior owner replaced the wires at some point and got the wrong ones? Doesn't explain why I have no spark at all after having run the boat as it is for several years. Must admit it didn't like to start easily but always attributed that to a gas problem. Beginning more and more to think I would be better off to just put in the Delco kit which replaces the whole mess.

 

[alldodge]

Beginning more and more to think I would be better off to just put in the Delco kit which replaces the whole mess.

With all the crud your running through I would be really looking at that, but then again I try never to let something beat me. It has dine it, but hate to admit it