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Tohatsu 2002 MD50A, why is it running so bad?

MrRob

New member
Let me start. I have a 2002 Tohatsu TLDI MD50A that is acting up. I bought this outboard recently at a good price because it would not start, well; it was firing briefly but did not stay running. Was supposed to work as late as this spring when it suddenly stopped.
“-I can fix this.” I thought to myself. O boy was in for a ride. Little did I know what I was getting myself into. TLDI is definitely not a “tree shade mechanic” engine.
After reading some, well most, of the threads here and doing some research I found out the usual suspects: Battery and CCA power. Compressor/pressure in air rail, fuel delivery, TPS resetting. Ground cables.

Did a visual check and no obvious problems. Hooked it up to a brand new battery with 100Ah 860 CCA. New gas and tank. New pressure bulb. Fuel filter cleaned. Sure enough, it fires up as it would start, but that’s it.
Hooked up shop air to the Schrader valve (as mentioned in a post) and got it to stay running. The compressor is bad!
Took apart the compressor. The cylinder and piston looked good, checked reef valves and changed the gaskets. Installed it again and reset the TPS.
Now it started but was running very poorly. Dies at idle and misfire. Hard to start sometimes but goes if I help with some throttle. Checked the pressures on the rail and it is now ok. 80 psi air and 90 fuel.
Now the real troubleshooting begins.

- Changed to a DFI oil in the system as I did not know what kind of oil was in there.
- Got brand new recommended spark plugs.
- Cleaned out the VST clean and float/needle all looked fine.
- Cleaned out the FFP and changed the rubber seal.
- Compression test.
- Tested the low-pressure pump, diaphragm and seals good.
- Air intake reef valve looks good.
- Adjusted the gap on the CPS.
- Took apart the air rail and cleaned the air- and fuel injectors and checked the regulators. Tried to get the injectors professionally cleaned and serviced but there is no one doing that in my country.
- Measured resistance of all electrical parts mentioned in service manual.

The self-diagnostic do not give me a clear error message.

What am I missing? I suspect that the engine is running rich. The spark plugs are sooty and often wet after I check them. Bad air/fuel injectors? TPS fault even if measuring doesn’t indicates that? God forbid the ECU?

I have the service manual and by now I know it from cover to cover. Searched all over Internet for TLDI information, forums, videos etc. Hell, I even learned about the Optimax trying to find out what could be wrong.

Here is a video of the engine:
https://youtu.be/6JPI8vkWbP0


Sorry for the wall of text. This is my last resort. Thanks!

/Robert
 
Are you running too much oil? Check the pump rod setting. That could cause that.

Thanks for the advice! I will check that.
Actually there was a lot of oil in the base at the power head when I got it. Also the air-box had quite much oil in it. So might be an oil issue.

/Robert
 
Update!
I checked the oil pump and it was adjusted accordingly and don't seem to over-oil.
But all of a sudden when i was doing some troubleshooting on the stand i got it to idle good, no misfires and started every time. So, happy i went on and tried to run in a big water barrel... It stalled as soon as i put it in gear, so no power.
I tried over adjusted the idle position (10-15 mm from stop bolt) and that really improved the power and i could put it in gear and run it in the barrel with no problem. It also made the startup really smooth not revving up when starting like it did before, even when warm.
Well, this almost fixed the problem. What came with that is the TPS sensor sends a fail code. "TPS 1 and 2 idle position error". Darn!

What i can assume from this is that when i adjust the idle position i let more air in to the throttle house and that made the engine run better.
So it is running rich and want more air. But then the ECU detects that the TPS sensors are way off (from stop bolt) and say no no. I tried to reset the TPS position in this state but it did not let me. Got a fault code straight away.
I also assume that this is not the correct way it should be set up so i guess it is just getting to much fuel?

Any thoughts about this?

Ragards
/Robert
 
I have done all the measuring on the TPS sensor and readings seems all to be in spec.

Sensors seen from back:

TPS.jpg
Supply is 5.04 V

A-C = 5.304 kohm
D-F = 5.322 kohm

A-B = Idle 0.84 kohm WOT 5.36 kohm
D-E = Idle 0.87 kohm WOT 5.49 kohm

Back-probing:
B-C = Idle 4.6V WOT 0.4V
D-E = Idle 0.46 WOT 4.8V

I also checked for "dead-spots" on the TPS but all seems good.

Should the engine run good with the throttle linkage pushed against the stop-screw? Or is the throttle plate supposed to be a little bit open at idle? There are holes in the throttle plate I guess is for idling.


Thanks!
/Robert
 
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