1988 Johnson 110 intermittent misfire

[AEROCOOK]

My 1988 Johnson 110 (J110TLCCA) has been plagued with an intermittent misfire for the last 2 years and I'm hoping someone can help me diagnose the problem.
The motor idles perfectly at 800 RPM but as I accelerate, it starts to shudder, if I continue to advance the throttle, it will eventually hit on all 4 cylinders and take off. The same shudder occures when I back off the throttle from high speed to half throttle or less.
Suspecting that the cause was ignition related, I took my timing light with me on my last outing and here's what I discovered... The 2 starboard cylinders provided a good consistent strobe with the timing light pick up clamp loosly fitted over the plug wires but the 2 on the port side wouldnt strobe unless I physically held the plug wires tightly against the metal pickup on the clamp. Given these results, am I safe to assume that I have weaker spark signal on the 2 port cylinders? If so, would coils be a likely culprit? I have the factory manual for the motor and it states that you need specialized equipment (Merc-O-Tronic or Stevens) to properly test the coils, but before I even go there, do you think I'm on the right trail?

 

[racerone]

Take the 2 coils from the one side and install them on the other side.---See what happens.

 

[emdsapmgr]

Those coils are usually pretty reliable, but I would do the test Racerone suggests. Unfortunately, your engine has the newer, single power pack. Before you just go out and replace it, you may want to test the timer base and the stator first. You can find some excellent troubleshooting info at this website: cdielctronics.com. They go into detail regarding doing a cranking volt output test for both devices. If those two test ok, and the coils do also, then it's probably a bad pack. You will need a special "peak reading" voltmeter to test for the volt outputs. All of these electronic components are fairly pricey, so some time spend testing will save you $ in the long run.

 

[AEROCOOK]

Thanks for the replies and suggestions, I will swap the coil positions and see if the weak spark follows, I would have done this while I still had the boat in the water but the wife was with me and she was already annoyed with my timing light procedure lol.
So do you concur that I do have weak spark based upon my timing light test?

 

[emdsapmgr]

If you do see weak spark on the light from the gun, it is an indication of a problem in the system. The timing light test is a good test, but the spark-gap test is even better. The timing light will pickup even weak signals and show it's firing. When you get the plug at high rpm's and under load, a weak spark may not be enough to continue to fire the plug under that scenario. There is a huge difference of the spark plug voltage at idle vs 5000 rpm's.

 

[AEROCOOK]

Well I tried doing a power pack cranking output test on the motor today but the results just confused me. To begin with, I had a buddy build me a DVA adapter so that I could measure peak outputs. I then followed the test procedure in the factory manual but the meter read only 15 to 18 volts on the 2 starboard coils and 8 to 10 volts on the port coils. My first thought was that I had the meter set wrong but as it turns out, it wasn't, I confirmed this by plugging the 2 leads of the DVA adapter into a wall socket and it read 167 volts DC. Am I doing something wrong? Would the motor even run if the true peak voltage at the coil primary leads was less than 20 volts each?

 

[AlTn]

household current, U.S. anyway, is AC..~ 120 v. or 220 v. at the wall outlets....from the cdi chart 150 v. DC minimum. should be reaching your power pack from the stator...same voltages out to the coils...these measurements are with the coils attached to the power pack....minimum cranking rpm is 250 while testing...you may be getting some misleading readings by attempting the procedures given in the factory manual for use with another tester

 

[durban]

I just do a simple test cost 50 cents buy a o.5 v neon light it will tell you if your hall sensor is working or not & you can see when it misses the light don't flick on & off

 

[AEROCOOK]

household current, U.S. anyway, is AC..~ 120 v. or 220 v. at the wall outlets....from the cdi chart 150 v. DC minimum. should be reaching your power pack from the stator...same voltages out to the coils...these measurements are with the coils attached to the power pack....minimum cranking rpm is 250 while testing...you may be getting some misleading readings by attempting the procedures given in the factory manual for use with another tester

This is what I was thinking as well, I was using a fluke meter set at the highest DC voltage setting (600v) along with the home made DVA adapter whereas the manual makes reference to "Junction boxes for peak-reading voltmeters" available from Merc-o-tronic, Stevens and Electo specialties. I just assumed these were DVA adapters? I was also reading the trouble shooting info from CDI, same test procedures as the manual. Anyhow, I 'll take another crack at it tomorrow with a different meter and see what happens. Is there any way to test a DVA adapter? I'm sure mine is good but knowing for sure would be reassuring.

 

[emdsapmgr]

As long as you are doing cranking voltage tests, consider checking the output from the timer base also. CDI shows two different cranking voltages, depending on year. either 0.3 volts or 0.6 volts. Must be at least that to be considered good. If both the stator (150 volt minimum) and timer base check ok, then you could have a bad power pack.

 

[AEROCOOK]

As long as you are doing cranking voltage tests, consider checking the output from the timer base also. CDI shows two different cranking voltages, depending on year. either 0.3 volts or 0.6 volts. Must be at least that to be considered good. If both the stator (150 volt minimum) and timer base check ok, then you could have a bad power pack.

That's good advice. I'll test all of these components and post results. In regard to the timer base output spec, the sheet I printed from the CDI website for 1988 110hp states 0.5 v minimum but the 1988 factory manual, says 0.3 v minimum??

 

[emdsapmgr]

See what your timer base cranking voltage actually reads, it may not be a problem. Along with the 4 coils, these are pretty reliable components.

 

[AEROCOOK]

​Well, I have a couple of updates and a couple of questions.
My home made DVA apapter does work, this was confirmed when I tested the stator and got a reading of 155 volts DC.
I then checked the resistance on the timer base pins and got readings of around 43 ohms for each (spec is 40 - 50) Next I tested DVA voltage at the same pins and got 1.3 - 1.5 volts on each, spec is at least 0.5 v which makes me wonder if 1.5 is too high?
Last, knowing that my DVA adapter was in fact working, I tested the output of the power pack again and the 4 readings were all below 20 v so it looks like I need a powerpack unless someone can chime in on somthing I've missed.
I do have one last question, given the power pack output readings of less than 20 volts when spec is 150+ is it normal for the motor to run so well at idle? also, spark jumps 1/2 inch and is bright blue.

 

[emdsapmgr]

These engines will seem to idle just fine, when running on just 2 or 3 cyls, esp when running on the trailer. Hard to tell by your feel, or by your hearing. The true test is when the boat is floating normally in the lake and it's in forward gear. (under load-that's when you need all 4 cyls firing)

 

[AEROCOOK]

Well I finally installed the new power pack and headed for the lake for a test, the results were disappointing. The idle seems pretty smooth but the motor is sluggish and took too long to get on plane. Also, the motor would only rev out to 5200 RPM with the same 17 pitch prop that used to allow 5800 RPM. Top speed used to be 65 km but is now down to 54 km I also have the same annoying stutter that has plagued the motor for the last few years. Back to the drawing board (and bank) I guess.

 

[AlTn]

your timing light and coil swap test would seem to be a valid starting spot

 

[AEROCOOK]

I just found a 1990 88 Special with bad compression on 1 cylinder, picked it up complete with controls and power trim for $250. The stator and timer base are the same part numbers as my 88 110 but coils and power pack are different. I'm wondering if the power pack and coils could possibly work on the 110 if swapped over together? Either way, I figure I'll make money on the 88 special just by selling the lower unit and power trim system.
One other question... Can I assume that the conventional fuel pump from the 88 will supply enough fuel for the 110? I already premix and I'd like to do away with the VRO pump if I can.

 

[AlTn]

the fuel pump part no.'s are the same...BRP 0438556....or Sierra 18-7352...don't know about the ignition component question

 

[AEROCOOK]

Good to know, I'm going to swap the pump tomorrow.

 

[emdsapmgr]

I have a dealer-type peak reading voltmeter. (a Stevens Instrument) version. Was confused by a reading and thought the meter needed to be sent back for the factory to re-calibrate it. Called up Stevens and told their tech up there that I was seening 160+ volts from my household AC outlet. He said that is a normal reading and that the instrument was working fine.