Troubleshooting 1993 Force 150

[HotTommy]

Given the recent problems with this forum, I'll summarize my situation. Last winter I bought a 1993 Force 150, 2 cycle outboard that was known to be damaged and partially disassembled. With help from forum members, I've replaced a damaged piston, fixed a leaky head gasket, rebuilt the carburetors, fuel pumps and water pump, replaced the thermostat and fixed some other incidental problems. I managed to get it running and tested it on the lake only to discover it running mostly on three of the five cylinders. I'm trying to figure out what to fix/replace next. Here are some random facts in search of a diagnosis.
- When I first determined that the engine was not running on all five cylinders, I tested the spark and found cylinders 4 & 5 weaker than the others. I obtained and installed new coil packs and spark plugs wires on those cylinders. That did not solve the problem.
- The last time I tested it on the lake, I ran the engine at full throttle for about ten seconds before abruptly shutting it off and coasting to shore. When I pulled the spark plugs, the top three showed black residue from burned fuel. The bottom two were clean with no black residue. I took that as confirmation that cylinders 4 & 5 were not running.
- Later, I ran the engine at idle and played with a range of idle mixture settings (from fully in to three turns out) on the bottom carburetor that feeds cylinders 4 & 5. It had no apparent effect on how the engine ran. I took that as further confirmation that cylinders 4 & 5 are not firing.
- Following my FSM procedures I attempted to test the trigger resistance with my ohm meter. It didn't surprise me that the reading for trigger 4 was zero rather than the spec 1100-1400. It did surprise me to find that ALL the triggers showed zero ohms. The FSM did not consider that as a possible outcome and offered no guidance. Not fully understanding the principles behind the operation of the triggers, I was left wondering whether my testing procedure was faulty (the picture in the FSM was not very clear), or whether some faulty triggers can still function adequately. Not having a clear idea of whether or not that test had been completed, I was reluctant to go to the next one.

Bottom line is I'm running out of ideas and patience. If I could take this thing to a professional and get it back in less than a month, I would. But this time of year, I'd be lucky to get it back by Halloween. So I'm grasping for ideas and understanding. I will deeply appreciate advice or suggestions from anyone who can help me figure this thing out.

 

[HotTommy]

Correction: resistance on the trigger test was infinite, not zero.

Also, the spark tester indicates there is a spark going to #4 & 5, just not a strong one. Which components might cause this?

 

[pnwboat]

I would suspect the Switch Box may be the problem. I would measure the voltage while the engine is idling on the wires that go from the Switch Box to the coils on all five cylinders and compare the readings between 1,2,3, and 4,5 to see if there is any major difference.

To measure the trigger resistance, you use the White/Black wire as the common. Measure from White/Black to Yellow, the White/Black to Black, then White/Black to Brown etc. Make sure the wires are disconnected so nothing else in the harness will interfere with your readings

 

[HotTommy]

pnwboat,
We may be on to something. The PO told me he had replaced the "CDI" at a cost of $300 because he had damaged the original when he inadvertently reversed the poles on the battery. Perhaps he was referring to the switch box. It's the only ignition part I see with a price in that range. If he did get a replacement switch box, he got a used one, because the one on my motor is not new. .... To test the voltage at the coils as you suggest, do I simply test the DC voltage across the two terminals on the back of each coil? ..... BTW, when I tried to test the trigger resistance, I thought I was doing it as you described. If the trigger acts primarily as an on/off switch rather than a source of power to the coil, then a weak spark would indicate it is working. Is that how it works?

 

[HotTommy]

pnwboat,
We may be on to something. The PO told me he had replaced the "CDI" at a cost of $300 because he had damaged the original when he inadvertently reversed the poles on the battery. Perhaps he was referring to the switch box. It's the only ignition part I see with a price in that range. If he did get a replacement switch box, he got a used one, because the one on my motor is not new. Perhaps the replacement was not really good. .... To test the voltage at the coils as you suggest, do I simply test the DC voltage across the two terminals on the back of each coil? ..... BTW, when I tried to test the trigger resistance, I thought I was doing it as you described. If the trigger acts primarily as an on/off switch rather than a source of power to the coil, then a weak spark would indicate it is working. Is that how it works?

 

[pnwboat]

Yes the DC voltage across the two terminals on the back of the coil. It's pretty high voltage, not sure how much, so be careful The black wire on each coil goes to ground. Check and make sure each one is making a good ground connection.

Each trigger is a small coil of wire imbedded in the trigger assy. There is a magnet around the center hole of the flywheel. Each time the magnet passes the trigger coils, it generates a pulse which is sent to the Switch Box which then sends DC voltage to the appropriate coil. If you're getting spark, most likely the trigger assy is good.

The way your ignition system is as follows.
1. 12VDC is fed to the Battery Converter Box.
2. The Battery Converter Box takes the 12VDC, steps it up and converts it to AC voltage, and feeds it to the Switch Box.
3. The switch box takes the AC voltage and converts it to DC voltage to charge a capacitor.
4. The trigger signal tells the Switch Box which coil to fire by discharging the voltage stored in the capacitor.

If the Battery converter Box is bad, you usually get no spark on any cylinder. That's why I would suspect the Switch Box. Make sure all of the ground wires from the Switch Box, Battery Converter Box and coils are making good contact. Don't do a visual inspection. Either measure with your OHM meter, or disconnect them, clean and re-attach.

 

[HotTommy]

Thanks for the insight. I'll check further and see what I find.

 

[HotTommy]

I found an interesting related thread on this forum that referenced a troubleshooting guide published by CDI Electronics. It helped with my understanding. But it raised the spectre of needing a DVA meter. Any opinions on whether or not I can run this problem down without one?

 

[pnwboat]

I purchased a DVA adapter for my meter about 7 years ago. Only had to use it once, so I think there's a good chance that you won't absolutely have to have one. A process of elimination and the knowledge from some of the folks on this Forum I think should be good enough.

 

[pnwboat]

You could also swap the trigger wires on the Switch Box and the corresponding wires wires between the Switch Box and coils. This would be essentially be swapping the ignition circuity inside the Switch Box that fires say #4 and #5 coils to say #1 and #2 coils. If the problem moves, then I would say it is the Switch Box.

If the problem stays the same, then there might be a mechanical problem affecting the bottom two cylinders. First thing that comes to mind is the exhaust cover gasket leaking some water.

 

[pnwboat]

Also make sure all the gaskets for the bottom carburetor and reed block assy are in place and not leaking.

 

[Jiggz]

Correction: resistance on the trigger test was infinite, not zero.

Also, the spark tester indicates there is a spark going to #4 & 5, just not a strong one. Which components might cause this?

If this diagnosis is accurate, I can only think of two components that can cause such a thing, faulty ignition coils or CDI modules. However, since the coils are independent of each cylinder (4 & 5), but are probably commonly fed by a single CDI module, I would start by switching the CDI between that of #1 & #2 cylinders first and see if the problem follows. Unfortunately, unlike Prestolite systems which are easily accessible, the switchbox makes it a little complicated when switching components. Just make sure you take note of the original wiring configurations and pictures before starting the switching. Remember, if you switch CDI's the trigger wires should also follow unless you physically moved the CDI position or location.

In addition, you can also take the coils out of the equation by switching #4 with #1 ignition coil, if the problem persists, then you know it is not the coils.

 

[HotTommy]

Let's regroup. My comments about which cylinders were firing and how strong the sparks looked were based on observations that were subjective. What I can say for sure is that the engine does not sound like it is consistently running on all five cylinders when above idle, and #4 and #5 appear to be ones that were not firing some of the time. That is why they got new coil packs and spark plug wires. However, when I hook up a timing light while the engine is idling, the light indicates all five cylinders are getting spark. .... Here is some new information. I checked the DC voltage on the leads going to each coil pack at idle. The factory spec calls for 150-250 volts. Mine showed about 90 volts on all five coils. Based on that test, the FSM says I should replace the Switch Box ($300). ... I then tested the triggers. The FSM says the resistance between the lead from each trigger to the common lead should be 1100-1400 ohms. Every one of my trigger leads showed infinite resistance. The FSM says I should replace the trigger assembly ($200). I have not tested the converter box because I do not have a DVA meter.

If both the trigger assembly and the switch box are faulty, I'm baffled that the engine runs at all. If all five coil packs are getting the same input voltage, why would some cylinders fire and the others not? I don't mind paying to replace a faulty part, but I'm not not confident I actually understand what is happening. Does it look like I am seeing the result of the coincidental failure of two independent parts, or is there a single problem that might account for all the symptoms?

 

[Jiggz]

The specs for the switch box (SB) output voltage, I believe is peak voltage and not rms as indicated by a regular voltmeter, it would seem you are within specs and I am assuming you are reading a little more than 90VDC or at least 100VDC. And this is the reason the motor is still running.

As for the trigger resistance, the common wire is the white/black wire. All resistance readings should be paired with this wire, i.e. yel, blk, vio, wht and brn each paired with the wht/blk wire for resistance reading. Note you need to disconnect all wires from the SB or terminal board so they are totally isolated from the rest of the system (except obviously from the trigger unit). My manual indicates the resistance spec at 1200~1350 ohms. And if you happen to have a DVA adapter for your voltmeter, the trigger voltage output should be 4V+ (peak). And as in the resistance reading this has to be taken from each wire paired with the common wht/blk wire. The only difference is you can take voltage reading without isolating the wires.

 

[HotTommy]

Jiggz - For the trigger test, I disconnected all six wires coming from the trigger assembly to the switch box. I paired the end of each wire coming from the trigger assembly with the black/white wire from the trigger. All showed infinite resistance. I take that to mean the trigger assembly should be replaced. ... if my voltage reading at the coils is not too bad, I'll wait until the trigger assembly is working correctly before I decide on replacing the switch box. ..... Regarding the trigger assembly. I have not removed the flywheel to get a good look at it. Is it a remove and replace item only, or is there a chance the problem could be something fixable? If this were your engine, would you go ahead and order a new trigger assembly, or wait until you got a good look at the old one?

 

[HotTommy]

Jiggz - For the trigger test, I disconnected all six wires coming from the trigger assembly to the switch box. I paired the end of each wire coming from the trigger assembly with the black/white wire from the trigger. All showed infinite resistance. I take that to mean the trigger assembly should be replaced. ... if my voltage reading at the coils is not too bad, I'll wait until the trigger assembly is working correctly before I decide on replacing the switch box. ..... Regarding the trigger assembly. I have not removed the flywheel to get a good look at it. Is it a remove and replace item only, or is there a chance the problem could be something fixable? If this were your engine, would you go ahead and order a new trigger assembly, or wait until you got a good look at the old one?

 

[pnwboat]

When you were checking the trigger wires, did you happen to try reversing the meter leads? Is your meter auto ranging or do you have to select the range manually? I'm pretty confident that the trigger assy. is good, but you never know. Also I wanted to mention that since this is a battery powered ignition, the battery and all cable connections need to be in good operating condition.

Trouble-shooting the Thunder Bolt Switch Box system is fairly easy. Since there are no CDI modules and associated wiring, the wiring is pretty much straight forward. I would try switching the #1 and #2 trigger leads and coils leads at the Switch Box with #4 and #5 and take it for a spin and check the plugs.

One other thing to check is your voltage regulator. What kind of voltage are you seeing at 2000RPMs and higher?

 

[Jiggz]

If this is my motor, nope, I will not order a trigger unit at this time. The fact, that there is spark on all cylinders at idle and only weak sparks on #4 & #5 above idle, it tells me the trigger unit is good to go. A trigger's function is to provide a positive signal to one of the gated diodes (most likely an SCR) in the switchbox to discharge the charged capacitor as an output of the SB and an input to the ignition coils. In short, a trigger signal is either yes or no or go or no go when it comes to discharging the charged capacitor in the SB. There is no such thing as weak trigger signal instead it is either there or it is not.

Since the misfiring seems to be speed related, the problem I believe will be in the charging of the capacitor in the CDI modules. Since the CDI's are sealed units, that means the entire CDI unit will have to be replaced. In short, I will try to switch things around to validate that the CDI is the faulty component before buying anything new.

 

[HotTommy]

The mystery just got more interesting. (The forum managers could have picked a better time or a better contractor to install their new system.) As I couldn't see the forum this morning, I went ahead and pulled the flywheel off to take a look at the trigger assembly. The attached pictures show what I found. ... The underside of the flywheel has two magnets firmly attached to it plus the remains of part of another magnet. The stator has most of three magnets plus pieces of another attached to it magnetically I'm guessing this is not the way things are supposed to be. ... The trigger assembly appears intact with no visible signs of damage. So now what?
1. Do I need a new flywheel?
2. Do I need a new stator?
3. Is it possible/likely that the ignition problems I've experienced were a result of this newly found condition?

You may have to cut and paste to see these photos.
https://lh3.googleusercontent.com/-...gjGB4gfk/w576-h432-no/2014-06-02+08.19.58.jpg
https://lh4.googleusercontent.com/-...AAA8g/bTfXbHCG9xU/w385-h373-no/stator+150.jpg

 

[HotTommy]

Disregard.