2007 Tohatsu MFS 9.8A3 Ignition problem, died at WOT and only 1500 rpm now

[swiftability]

Hello guys!
Hope for an advice...

I have Tohatsu 9.8 four-stroke outboard. It is 2007 model named MFS9.8A3. I like the engine and use it on my inflatable boat for some fishing trips. I bought it new and it has 150 hours on it. It did its job perfectly until last week. I was running over a lake at almost WOT when it suddenly died. It sounded like no gas in a carb. I checked a fuel line and it was not bent, the rubber pump was firm as well. Kill switch was ok, too.

The motor started easily but did not respond to a throttle, dying if I opened it more than 1700-1900 rpms. I checked and changed spark plugs right on spot with no effect on the erratic rpms. Everything else looked ok. I was pretty far from a ramp so it took me a while to get to shore at 2 miles/h. If I tried to open a throttle it died immediately but started at a first pull. At some point I decided to open a choke and the motor began working normally so I finally got to a shore. Later I checked the spark plugs and found them extremely dirty.

Next day I brought it to a mechanic at a local marina. I explained what happened and asked to do a tune-up because I never did anything with the motor except oil change and winterizing procedures.
This morning I got a call and was told a CDI block needs to be replaced and all-in-all would be $400. I didn?t believe my ears because I bought the motor after reading about its reliability and didn't expect such a repair after 150 hours... I take a good care of it and maintain it properly. Same time I feel the mechanic doesn't really want to look into the problem and there is no guarantee the CDI is a reason of it.

So guys, what would you advice? I will definitely take the motor back home as-is because I doubt it is a real reason of the problem and want to be sure everything else is eliminated before going to the costly repair. Unfortunately there is only one Tohatsu service nearby and I need to drive for 150 miles to another one.

Would be also obliged for the part number and price if anyone knows it...

 

[pvanv]

Re: 2007 Tohatsu MFS 9.8A3 Ignition problem, died at WOT and only 1500 rpm now

Odd. It could be the CD, but that's rare. if you do need one, the proper cd module depends on your serial number. 031096XD~ calls for 3AA060600M C.D. IGNITION UNIT (CU7256), $152.04.

Before condemning the CD, I would check the magneto key to see if it is damaged or sheared. Then do the resistance tests on the CD.

 

[swiftability]

Re: 2007 Tohatsu MFS 9.8A3 Ignition problem, died at WOT and only 1500 rpm now

Thank you, Paul!

Ordered some parts from you some time ago and had nothing but very positive experience. You helped me a lot then.
I'll try to check what you recommend and if nothing helps will order the part.

 

[pvanv]

Re: 2007 Tohatsu MFS 9.8A3 Ignition problem, died at WOT and only 1500 rpm now

Glad it worked out for you so far. There is a Factory service manual specifically for the F8/9.8A3, and it has a good section on testing the CD. To do the tests, you will need a good analog (not digital) ohm meter. I like the Triplett products; you can also get a very accurate one through your Tohatsu dealer. That ES-branded meter also has DVA capability, so you can get readings on the ignition pulses without needing a oscilloscope.

Remember: Diagnose before just changing out parts randomly.

 

[swiftability]

Re: 2007 Tohatsu MFS 9.8A3 Ignition problem, died at WOT and only 1500 rpm now

Alright, yesterday I began my own repair with carb disassembling and cleaning following Paul's recommendations at this forum. I opened it up and found a piece of dirt sitting right in a main jet. I put it out with a needle, assembled the motor and it began running like knew. So simple!

It is unbelievable how the mechanic at authorized Tohatsu centre was unable to determine the problem and even didn't look at the carb to check the obvious reason. He proclaimed the faulty CDI was the reason and was repeating that all the time convincing me to order one. And he noticed several time that he had had 20 years of experience and in my particular case it was a CDI.
I wrote the shop management a letter about this and asked for a refund because was charged $130 for such "comprehensive diagnostics".

I am just wondering how the piece of dirt could get there. Could it be through air intake because there is only a mesh? I can't believe it went through the fuel filter....

 

[pvanv]

Re: 2007 Tohatsu MFS 9.8A3 Ignition problem, died at WOT and only 1500 rpm now

Glad you got it fixed. I had my doubts that the CD was bad. I don't understand why the "mechanic" was so convinced you had a bad CD. Clearly he didn't diagnose the issue. Since over 3/4 of problems with EPA-rated outboards is in the fuel system, your problem is in line with what I would expect.

In the future, be very careful using any stiff wire of any sort near carb jets. It's very easy to scratch the jet, which can give weird mixtures at some speeds.

A bit of debris could have come from anywhere. While the filter element is very fine, any little bit of stuff could have made it into the fuel system during manufacturing (or any time a gas line downstream if the filter was disconnected), eventually making its way into the carb bowl. Or for that matter, a rupture in the filter could allow a bit of junk through. From there, it could slosh around in the bowl, literally for years, without being an issue. But... given the right conditions (coming off a wave, etc.), it could then get drawn into the jet. I have never seen anything enter the carb bowl through the air intake. After all, manifold vacuum draws fuel out of the carb, so any debris would have to go against that vacuum in order to get into the bowl. The screening in the air box is primarily a backfire arrestor, btw.

 

[swiftability]

Re: 2007 Tohatsu MFS 9.8A3 Ignition problem, died at WOT and only 1500 rpm now

Thank you, Paul!
I wrote a letter to the shop asking why I faced such an attitude from an authorized Tohatsu service and what was the nature of brass drillings in the motor housing under the carb. I got a following response:

• The mechanic checked your spark plugs, they were fouled so he replaced them with new.
• Next he checked the carburetor as it was obvious that this unit never had a pre-delivery inspection performed on it. The air screw located under the welch plug which had never been drilled out was only turned out ? of a turn not 2 full turns not allowing the engine to idle properly.
• He then checked the valves to see if they needed adjustment and they were fine.
• He was able to get the engine started however it would die out at high RPM’s. It would re-start but again would die at high RPM’s. Diagnosis is common as a bad CDI unit.

There was no need to check your fuel line as the same issue was happening with our fuel line. Although this is not a common issue we have seen a few of these in the past two years and wonder if it was a not so great batch of CDI units from the manufacturer.
You had stated that the engine would start and run for a while before dying out. This is the same situation we had when we ran your engine. Your carburetor did not have an effect on this issue.

We stand by our diagnosis that your CDI unit is not functioning properly.

And doubt there was a need for the drilling because I have never had any problems with idling since I bought the motor...

 

[TOHATSU GURU]

Re: 2007 Tohatsu MFS 9.8A3 Ignition problem, died at WOT and only 1500 rpm now

1) If they drilled to get to the air mixture screw they knew you had a carburetor problem.

2) If they drilled to get to the air mixture screw they do not know how to clean a carburetor as you never have to adjust that screw.

3) If the air mixture screw was only 3/4 of a turn out the engine would never have run correctly.

4) The engine was test run at the factory so the screw was set correctly

5) The technician, the dealer principal or both lied.

 

[pvanv]

Re: 2007 Tohatsu MFS 9.8A3 Ignition problem, died at WOT and only 1500 rpm now

As usual, Elvin is spot on.

I suspect that they jumped to conclusions; Many a mechanic will try to skip diagnosis, because "that symptom is always caused by X". Diagnostics take time, but it is usually time well spent. Clearly, they did not test the CD. CD failure on these is extremely rare. Likewise, slightly excessive valve lash (uncommon on a 9.8 with your number of hours) might limit maximum power and top speed, but would not -- could not -- cause the motor to stall at higher RPMs.

So they guessed. Wrong. Thrice. Not a CD problem... Not too much valve lash... and Not idle mixture.

They were close when they guessed that there was a mixture problem, but again, they did not disassemble the fuel system and diagnose that problem. They tried to use a "band aid" of richening the idle mixture. That probably was not necessary (the mixture is set by instrumentation at the factory), and setting it too rich may lead to slightly more fuel consumption, possible increase in oil dilution ("making oil"), and plugs fouling more easily (at idle speeds)... Yet it will not -- can not -- correct a high speed stall. Yes, I have found a couple of these motors that idled a little better when slightly richened, but that's rare.

I agree with Elvin 100%. Someone... either the technician, the dealer spokesman, or both... are not being truthful, either through ignorance (likely), or malice (maybe). And now they want/need to "justify" what they did (or didn't do) when working on your motor.

 

[swiftability]

Re: 2007 Tohatsu MFS 9.8A3 Ignition problem, died at WOT and only 1500 rpm now

Thank you very much for your inputs, gentlemen!
You helped me a lot to solve the problem and make the engine back to life. I even made a short video about my test-drive on the lake and sent it to the shop to prove there was nothing wrong with CDI and the carb was a problem. They refused to refund anyway, even partially.

These guys call themselves a "Largest Tohatsu dealer in Ontario" and I did not expect to meet such an unprofessional attitude there. I feel I have a moral right to disclose that I was dealing with PISCES MARINE from Oakville, Ontario and that is the place I will never come again.
I sent the story to Tohatsu N.A. as well, by the way.

 

[rotocopter]

Re: 2007 Tohatsu MFS 9.8A3 Ignition problem, died at WOT and only 1500 rpm now

Hello Gentlemen,

Great forum! I am new here and appreciate your experience.

This year in Croatia I had the EXACT same problem with my brand new 2012 Tohatsu MSF4, after only 15 hours running!

Damn! it spoiled a couple of days of my vacations, until suddenly it started working again. The engine ran properly for another 10 to 15 hours and then again the problem appeared.

I did demount the carburator and cleaned it (but there was no dirt whatsoever). As expected, this did NOT solve the issue.
The engine is now stored in my garage, awaiting for me to have the time to take care of it.

Honestly I don't really know what to do, and I would appreciate any suggestion/advice.

Somehow I believe that the fuel might play a role here... I had a small tank (5 liter) which I was refilling every couple of days at different gas stations. In Croatia it might happen that they sell you E10 or E20 fuel as pure gasoline...

 

[pvanv]

Re: 2007 Tohatsu MFS 9.8A3 Ignition problem, died at WOT and only 1500 rpm now

You really have a different issue, with a different model, so your posting should actually be in a new thread. But...

Firstly, you are in warranty, so your dealer should be able to help you. If you prefer to do the work yourself, follow the proper procedures:

As I stated in an earlier reply, and this applies to all outboard repairs, you must... must... Diagnose the problem. Guessing... and then replacing random parts is the least cost effective, and often the slowest, way to repair an outboard.

In order to be effective, you need decent tools, average mechanical abilities, and the Factory service manual. Then review the running conditions of the motor... Was it broken in properly? Was the carb run dry at the end of each and every day? Is the oil level even a drop high? If the motor was operated properly, then start reviewing and diagnosing the fuel, electrical, and mechanical systems (in that order, since that is the order of probability for problems). Use the Factory service manual as your guide. Diagnosis will uncover the problem, which will then allow you to repair it. If the oil is high, or the carb was not run dry at the end of each and every day, look at correcting those issues first.

What method did you use to clean the carb? Did you verify float height? What does the spark plug look like? Have you run the ohm meter tests (with an analog meter) on the ignition system?