Tohatsu TLDI 90 surgin rough idle and sooty plugs

[slimtim]

Hi All,

I'm having some issues troubleshooting problems on my 2001 Tohatsu TLDI 90hp MD90A. Wondering if the brains of RIBnet can offer any advice. I will try and keep it brief:

Boat does not get used often. This year, turned over but didn't fire. Lots of help from the extremely good guys at Tohatsu nailed it down to all 3 (!) air injectors not working (I think due to old fuel not being run out of them after last years service). Since replacing them, it broke down again after the pipe connecting the fuel regulator to the air rail split. Fired up fine after the split section of pipe was removed.

It runs now but has two main issues. It surges around 50-100rpm at idle and also up to about 1300rpm. Idle is generally not really super smooth. Also, at a certain point just beyond engaging gear, it can almost stall unless more throttle is applied.

I have tried/checked the following:

• Checked the spark plugs. They were all very black and sooty. Dry and not oily.
• Fuel and air regulators were checked and externally cleaned, seemed ok. Not run it since.
• Air filter will be changed but I don't think that is the cause. Can run it without the filter to see if it improves the idle I guess.
• Battery is 7 years old but is smart charged regularly and voltage is 12.8 at rest and 14.6 at idle. Seems in good condition, however when new it was 680 CCA SAE which apparently might not be enough. A weak battery can apparently cause all manner of ECU issues. Will try a bigger battery if I can find one (anyone have one on the IOW I could try?!) when I get the chance but want to check all other options before buying another monster battery!
• Will check the air and fuel pressures in the rail but I think they are ok.
• Fuel is old but normally this is ok. Could it soot up the plugs? I will probably try some fresh petrol and bypass the external filter, but again, I don't think this is the reason for it running rich.

Its a 5.2m rib and I get 5000rpm at WOT (operating range is 5150-5850) with a 17inch alloy mercury prop. I have ordered a 15 inch but now wondering if with the engine running rich, it is not generating full power at WOT.

My main focus now is to figure out why there is too much fuel being burnt. Anyone have any ideas? Anything I can check before starting to spend money?

Thanks in advance!

[spartacus]

Not familiar with TLDI, but apparently can be problematic with wrong battery it seems. Been reading a few threads on US forums, almost similar with running rich, sooted up dry plugs, missing beat and excessive fuel use.

They were at the end if their tether and nearly tried a new ECU after multiple trips to different dealers. One of the fuel injector seals wasn't seated properly which helped, but when they tried the right size battery they solved it.

Can't find user manual on MD90A, but MD90C recommends 12V 100Ah/5HR, 850 (Cold Cranking Amps (CCA). If your battery is 7 years old, I'd say that's about time for replacement. Like I said, might be okay on conventional 2-stroke but not on TLDI.

Try new fuel, and if possibly run through water separator to rule out contamination. Also new sparks given they are inexpensive. Lastly is the oil you're using - specific to direct injection?

[slimtim]

Hi Spartacus,

Thanks for the reply.

Are you saying that the battery size could cause it to run rich if the ECU is out of wack?

It is hard to find a definitive statement about the battery size but burried deep in the Tohatsu US website it says 850 CCA (I assume SAE) and 1000 CCA for cold climates. I was also told this by someone over on the Marine Engine forum. It is actually quite hard to find a battery this size! I found this Numax https://www.tayna.co.uk/leisure-batteries/numax/xv31mf/ which is 800 CCA EN (around 850 CCA SAE according to https://battery-service.com/support/cca/) which should be ok so I might get this. Otherwise there is a higher capacity Numax one that is 900 CCA EN (XV35MF). I find it hard to believe the battery can make such a difference beyond the initial startup but all the posts online by experts say otherwise.

I have cleaned up the plugs so will try running those tomorrow with fresh fuel and without the air filter attached. If no improvement I will try and find a bigger battery to test or order one. The oil I am using is Quicksilver DFI supplied by my local Tohatsu dealer.

Thanks again. If you think of anything else, please let me know!

[spartacus]

Everything I've read about the engine is it needs the correct battery to energise injectors. 7 years on your original battery, then you've done well, and in real terms rules out ignition issues. I think Tohatsu tend to over spec the battery.

There's also a process of resetting ECU TPS idling speed. This is for 115hp but my understanding is it's the same across the range. https://www.manualslib.com/manual/12...age=324#manual

I just want to say I know nowt about TLDIs, but I'd try these things first. If still no success, identify a Tohatsu TLDI specialist, get it hooked up to pull any error codes, etc.

[Stevem]

I have a TLDI 50hp and have this battery, with no issues.
https://www.tayna.co.uk/leisure-batteries/numax/xv31mf/

Below is a copy from another forum written by a Tohatsu Tech.

Re: Tohatsu 50 TLDI running rough

Bob,
That battery seems to show low voltage. I would expect about 13.5v... Or at least over 13... Use a known-accurate voltmeter. Check the specific gravity with a hydrometer, if you have removable caps on the battery. If in doubt at all, get a better battery.

Tohatsu wants you to use a battery of 1000 cranking amps. If you have room for a group-31, that's pretty easy to do, especially if you opt for an AGM battery. If you only have the space for a group-27, get one with the highest cranking amps you can get. If you are above 32F, the MCA number should be at least 1000, but if you are colder than that, look for a 1000 CCA battery... relatively rare in a flooded battery, even in the group-31 size.

Arkansas is warmer than Alaska, but if it's too cold out, your marginal battery may not have the proper reserves to allow the ECU to initialize correctly while the starter is cranking. In general, Lead-acid batteries of all types cannot deliver as high an amperage when they are really cold -- they work better when warm. If/When the ECU doesn't initialize correctly, all bets are off, because if the ECU does not initialize correctly, really weird operation can occur.

Steve

[slimtim]

Originally Posted by spartacus

Everything I've read about the engine is it needs the correct battery to energise injectors. 7 years on your original battery, then you've done well, and in real terms rules out ignition issues. I think Tohatsu tend to over spec the battery.

There's also a process of resetting ECU TPS idling speed. This is for 115hp but my understanding is it's the same across the range. https://www.manualslib.com/manual/12...age=324#manual

I just want to say I know nowt about TLDIs, but I'd try these things first. If still no success, identify a Tohatsu TLDI specialist, get it hooked up to pull any error codes, etc.

I did this TPS reset procedure already and it did not help. I have also checked for error codes (on the TLDI you can do it with the tacho) and there are none stored. Even if this issue is not battery related, seems like it would be a good idea to change it anyway. Just seems a waste as the current battery is in great condition and I don't have another use for it.

Any other points I could check for a rich running engine? I will pull out the thermostat today to check it but that was replaced last year in the service because it was stuck open.

Thanks for your help.

[slimtim]

Originally Posted by Stevem

I have a TLDI 50hp and have this battery, with no issues.
https://www.tayna.co.uk/leisure-batteries/numax/xv31mf/

Below is a copy from another forum written by a Tohatsu Tech.

Re: Tohatsu 50 TLDI running rough

Bob,
That battery seems to show low voltage. I would expect about 13.5v... Or at least over 13... Use a known-accurate voltmeter. Check the specific gravity with a hydrometer, if you have removable caps on the battery. If in doubt at all, get a better battery.

Tohatsu wants you to use a battery of 1000 cranking amps. If you have room for a group-31, that's pretty easy to do, especially if you opt for an AGM battery. If you only have the space for a group-27, get one with the highest cranking amps you can get. If you are above 32F, the MCA number should be at least 1000, but if you are colder than that, look for a 1000 CCA battery... relatively rare in a flooded battery, even in the group-31 size.

Arkansas is warmer than Alaska, but if it's too cold out, your marginal battery may not have the proper reserves to allow the ECU to initialize correctly while the starter is cranking. In general, Lead-acid batteries of all types cannot deliver as high an amperage when they are really cold -- they work better when warm. If/When the ECU doesn't initialize correctly, all bets are off, because if the ECU does not initialize correctly, really weird operation can occur.

Steve

Hi Steve, good to know about the battery, thanks. I have read that post already, describes the battery issue quite well.

[slimtim]

Did some checks today. Wrote a post for another forum so just copying and pasting here incase anyone can give any input:

- Checked the air and fuel pressures. My digital gauge reads about 74psi for the air rail and another, analog gauge (sacrificed for the purpose of measuring the fuel pressure but not accurate because the needles wiggles around) was measuring about 10psi higher for the fuel side.
- Removed the air filter while running and it made no difference to the surging. Not sure if this means anything. I guess the filter would need to be really blocked to change anything.
- Measured voltage across the battery while starting and it drops to 11.7v so I guess this is an issue if it needs to be above 12. Trying to source a battery at the moment. Not so easy with the varying CCA standards and also the fact that regulations were brought in not so long ago forcing companies to report more realistic CCA numbers meaning some batteries are now rated lower than they previously were, even though they remain unchanged. Best I have found so far is this: https://www.tayna.co.uk/leisure-batteries/numax/xv31mf/ which is 740 CCA EN or 925 MCA, which just falls short of the 850 CCA SAE requirement (bit hard to convert). This option https://www.varta-automotive.com/en-...se/820-054-080 is 800 CCA EN and 1000 MCA but this is still short of the requirements!
- Tried to check the resistance of the water temp and throttle position sensors to check against the values in the service manual, but could not get a good reading. They were only showing something like 2kOhms which doesn't make sense (for the WTS it is supposed to be 2.45ohms at 20 degrees).
- Checked for fault codes again, still nothing. Is there a chance there is something preventing fault codes being logged or preventing the RPM counter reading them?
- I carried out all these checks using fresh fuel purchased today.

[slimtim]

I have found that I can get the Ah and CCA requires from a car battery as opposed to a marine/leisure battery. For example: https://www.halfords.com/motoring/ba...ee-174049.html

By searching on here, it seems a few people use car batteries without any problem. Biggest risk I see is that I must keep it well charged when I am not using it. The additional requirements (on top of starting) for my battery are very minimal - a fish finder (sometimes used when the engine is not running. Nominal 0.8amps) manual bilge pump (used mostly only when the engine is on) and a switch to turn the lights on behind the gauges (that I never use).

Any comments on the use of a car battery as opposed to a specific marine/leisure battery? Some sources say that marine batteries are strong to resist vibration, but I am dubious of this unless you can a very expensive high quality marine battery.

[Amidas]

Having had tohatsu tldi
Always use 85 amp battery and lot of faults come from using battery isolators that get dirty connections inside
If you have one miss out and try going direct to battery
Tohatsu tldi rev counter can give fault codes by using key to bring them up to diagnose any problems

[babbot1]

I have a 40 tldi that had the same issue. Replaced the injectors 2 seasons ago and was fine until last season and it started again but not as bad. I always used an external fuel filter but I put a lower micron filter (25 micron) on this year and didn't have an issue all season. It's not the smoothest thing but it doesn't stall anymore and the surging is very minimal if at all.

Not sure what you can get for a batteries over there but Interstate has a group 27 1000mca battery that seems to be okay. Mine is 3 years old and seems fine without a maintenance charger and it runs the bilge pump. Optima makes a group 27 1000mca agm that's pretty small as well just more $$.

[slimtim]

I'm bringing this thread out from the archive. A year has passed and I have finally managed to get home again to check the engine. I have replaced the fuel regulator (I suspected it was faulty), had the injectors cleaned professionally and checked a few other things but I still have sooty plugs suggesting it is running rich. I need to get it on the water to see if I still have some surging issues.

Any ideas?!

[babbot1]

This is not much help but replace all the fuel filters if you haven't done so in a while. Maybe water or debris in the tank. On mine there is a high pressure filter on top, one low pressure on the side, and there is an aftermarket spin on filter right in front of my engine.

It sound like a sensor or computer issue to me. Have you gone through the computer diagnostic? Check the manual on how to run the diagnostic. I haven't done it but you don't need any special tools. It uses the gauges on the dash and you look up the meaning in the manual.

[slimtim]

Hi, thanks for the reply.

I've changed or cleaned all filters apart from the high-pressure fuel filter, however, I don't think that is the problem. I have also run the diagnostics several times and throughout this whole time, it has never thrown a code. I checked the TPS and water temp sensors with a volt meter and they seem ok.

Right now I have a few avenues of investigation:

1. I changed the battery to make sure this was not causing any issue but I still have the old 16mm2 battery cables from my old 70hp non-TLDI engine. I am wondering if these are too small and I should upgrade to 35mm2. Problem is, I have no idea how many amps the engine draws while cranking so don't know how big I need to go with the cables. Can anyone give any pointers? I assume I cannot simply take the starter motor amps (83A)?

2. When I measured the air and fuel pressure with my £10 amazon gauge, it fluctuates considerably by about 10psi and in time with the engine cycle. Every video I can find of a pressure check on an injection engine (no TLDI's but I found a couple of Opti videos), the gauge is much more stable. I'm wondering if this is a problem and something is causing the fluctuation, perhaps a damaged reed valve in the compressor or fault air regulator. Does anyone know if the pressure should be stable? The compressor is a piston which obviously pressurises cyclically, so I am not sure.

[babbot1]

From my experience I doubt it's the air compressor but it's possible. Mine rusted and broke, the engine died and wouldn't start. After replacing it would still surge.

Where did you check pressure? Before or after the regulator? If you replaced the regulator my assumption is either the fuel pump or the cpu telling the regulator to surge.

A perfect battery has always been the answer other people give to questions with these motors. Needs to be 1000mca. Good clean cables too.

[slimtim]

I checked the rail air and fuel pressures from the schrader valves on the air rails. Tonight I had the bright idea of using a bike suspension pump to pump up the air-rail to verify that the air regulator vents at 75psi which is a bit low but just within the spec tolerance. My air-rail pressure test was averaging at this same pressure so now I am fairly confident the compressor is producing enough pressure. However, when I took the air regulator out, there was some milky slime which may be water in the air from a leaky gasket in the air compressor. I will replace these and inspect the reed valve at the same time.

However, I am not sure how any of these issues relate to sooty spark plugs! Plus I still don't know if I should change my battery cables or not!

I have attached pics of the milky slim for reference.

[babbot1]

I would think water would restrict the air flow from the regulator creating a richer mixture. The only thing is if the water gets passed to the chamber water is good at cleaning internals.
Sorry I guess I am not much help on this.