Tohatsu MFS9.8A3 ignition problem

[Ticketeeboo]

Our outboard was bought in 2009. It is a 2008. MFS 9.8 A3 3V2 Ser:054787XH.
It's probably run less than say 20-30 hours since we bought it and is only used intermittently on our tender. During last 2 years, from time to time it has given us some problems, noticeably it could be difficult to start when warm and seemed to flood, which could be overcome by pulling a few times full'ish throttle. Towards end of last season when running couple of friends a mile or so away at fairly high revs the engine almost 'died' then 'picked-up' then almost 'died' again and this continued to happen until I settled for a very modest speed to complete our journey. The engine problems persisted, sometimes being difficult to start, not able to run continuously at high revs, cutting-out at tick-over revs. Basically troublesome! I have removed the carb and cleaned it thoroughly. I have had the two jets out, using carb cleaner some surface dirt was evident and I have made sure each and every orifice is perfectly clean. I am satisfied the carb is perfectly clean as well and the float chamber kept full to the correct level. Now, having had the carb on and off and re-checked it, I have now switched attention to the ignition system and find there is no spark on either of the two plugs.
Symptons now:
# Increasingly difficult to start.
# When does eventually start will run at high rpm in neutral - runs under load at low rpm but sometimes dies and dies immediately if attempting high rpm under load.
# With plugs removed and new plug held against block, no spark can be seen at all.
# Red warning lamp flashes when attempting to start.
# Oil pressure switch is fine. (Wiring across switch makes no difference).
# Stop switch is fine. (Wiring across stop switch makes no difference).
# Voltage changes across Pulser Coil when rotated. (digital meter unable to measure actual voltage accurately *)
# Voltage changes across Exciter Coil when rotated. (ditto *)
# Voltage changes across LT input to Ignition Coil when rotated. (ditto *)
# With everything re-assembled and I work hard enough to get the engine started (very hard) it will first 'back-fire' then eventually even start and run as described above!

I now believe our CD Unit CU7256 or our Ignition Coil IG3796 is faulty. I have checked all electrical connections and they are fine.

Are there any specific tests I can carry out to determine which component is at fault?

Any further advice to help is most appreciated, please.

 

[TOHATSU GURU]

Re: Tohatsu MFS9.8A3 ignition problem

You have to have the factory service manual as it provides the values and test procedures...By the way, if the engine does not have spark it will not start at all, so I suspect you do have spark.

 

[Ticketeeboo]

Re: Tohatsu MFS9.8A3 ignition problem

Hi Elvin.
Appreciate your prompt reply, thanks. Unfortunately I don't have a service manual with this info.
I don't have a spark, which can be seen although if I persist long enough the engine appears to back-fire once or twice and then ultimately I can get it to start (after much work!). It appears the CD unit has the ability to kick itself into 'limited' life. If there is a way of temporary getting the engine operating I would like to know. Unfortunately I do not have a service/repair manual but will obtain one next time home UK. In meantime am on our yacht and would dealy like to get our outboard working, even in a limited way if possible. The Tohatsu dealer in Menorca does not hold spares stock.
Any info will be much appreciated on:
#How to independently test the CD unit?
#How to independently test the HT coil?
Thank you.

 

[pvanv]

Re: Tohatsu MFS9.8A3 ignition problem

The ignition tests are too involved to list, so it would be best to have the Factory service manual for the 8/9.8 A3 handy. As that's not an option, I can offer the following:

90% of problems with the epa-rated 4-strokes are fuel problems.
Of those, 90% are carb-related.
Proper cleaniing requires a 4-hour soak in real carb dip; spray is inadequate to dissolve the organic deposits.
If it runs at all, there is spark.
Many of your symptoms may be related to an over-full crankcase. It should be about 1/2 way on the dipstick, and never even a drop over full. Over filling the oil could even lead to a sheared magneto key, which can throw the timing off.

FWIW, you must use an analog (not digital) meter, preferably with DVA capability to test the ignition system.