98 DT 115 intermittent power loss

[Solarman]

Am glad you're back up together. Am a little surprised that loss of compression didn't show up in that leaking cylinder. Usually compression loss shows up if water gets in?
Just glad you found your problem.
Am very familiar with the sandpaper on glass method for making sure head is level and smooth for good head gasket seal.

Good luck happy boating.

[Mlkurtz]

Jumped the gun...

Success was short lived.

Same running results as before. Started missing soon after it left the ramp and performance still same at 4600 top rpm.

Pulled the fourth plug again and water is still present with each stroke.

On to the exhaust covers and the broken bolt (I believe you told me this already...). At least I ordered the gasket seals with the last order so I have them on hand.

I managed to shear a few more of the exhaust cover bolts (six) <insert curse word> in the removal process, and the original broken one was in fact covered in silicone, broken flush with the surface and covered in rust. They didn't leave me much to work with.

Overall surface seal area looks good, obvious corrosion and gasket breakdown in the area of the original broken bolt. Separator shield appears to be in good condition, obvious difference in residue between the top two cylinder chambers, and the bottom two (bottom looks nearly spotless, perhaps from the steam clean).

Due to location it looks like I am going to have to pull the powerhead to get the bolt repair done right replacing that seal in the process, ie limited space and access between the cowling and the bolt location, not to mention a second broken bolt next to this one. Hopefully those bolts aren't seized too...

<Insert stronger curse word>

[Solarman]

Yes, I think it would have saved many hours for mechanics if stainless threaded studs were used for these areas where bolts corrode in the threads. By using nuts and washers on the studs, could just cut nuts off, and replace. Another thing is if they made left hand drill bits (bits that drill CCW), then as you're drilling bolts out, they may unthread add they get hotter? Bet many would just unscrew.

Anyway, sorry for all the problems. While power head is off, check the water and exhaust passages between midsection and head.

Good luck. Post back what you find when able.

[Mlkurtz]

6 weeks later...

I finally got the powerhead back from machine shop #2. I'll save you from the long story. Still very reasonable from a cost perspective but may have been as much trouble as it was worth.

All frozen/broken bolts removed and retapped, all but two held. Retapped one 1/4-20 and the other took a longer M6 40mm. Replaced exhaust gaskets, mid section gasket, cleaned all surfaces and reset powerhead. Crankshaft was stuck after 6 weeks in open air, took a little coercing, but finally (and gingerly) got turning manually with oil and without plugs in. Rewired ECU, fuel and oil parts, etc, and she started first turn.

Checked all connections for fuel, oil, and water leaks; all clear.

Tested under load but doesn't sound good. Rough running and missing a lot. Also won't hit 4000 anymore, lucky to get 3500. There is no water in 4, so that's good. I pulled apart the vapor separator and found the tiny screen in the return line, mostly clean, float valve and all ports clear, reassembled.

I rechecked all wiring connections from take down pictures and manual. I highly recommend taking lots of pictures. Came in handy after many weeks. All good.

I decided to pull the four injectors and send out for a proper clean, not sure if it's throwing money away, but much less than four new ones.

Not sure there is anything left to check. I did recheck compression, #4 is about 5psi less than the other three now, but not enough to worry about.

My back up plan is a new Suzuki. One might think after reading all of this I should be tempted to go back to Mercury, but, I have to give a lot of credit to an engine that keeps running on three out of four cylinders (and gets up on plane), when any other brand may have left us calling for a tow miles offshore.

I'll let you know what happens when the injectors come back this week.

[Solarman]

While I know you have run the motor, but anytime you remove the head, or have water in cylinder you should run with a minimal premix 100:1, until your sure the oil system is functioning/ pulling oil from tank, just to be safe, plus the added oil helps to clear out any of the moisture in bearings, crank, rings, etc

Thanks for the updates.

Good luck. Post back when able.

[Mlkurtz]

Fuel injectors back and clean. New o rings.

Runs smoother, back to 4400 WOT though.

Seem to be back where I started this exercise, except no water in cylindr and charging properly now.

Any suggestions?

[Solarman]

From all you have done, i'm thinking your TVS may be failing at WOT? Unless the motor is surging at WOT, this would indicate a shortage of fuel. If surging at WOT, I would check the back side of the float needle valve, possible small piece of trash restricting fuel flow?

If not surging, but running steady and just maxing at the 4400RPMs, with more throttle left, but no change in RPMs, then test TVs by book, if reading seems good at lower throttle, what happens at/ around the area where throttle would go from 4400 to WOT? Does throttle open the butterfly more? If not opening butterfly more, why? If it is opening more, does TVs reading continue to change, or remain the same?

Good luck, post back what you find, when able.

[Mlkurtz]

TVS Fail Safe

Question.

From the manual, "Fail Safe Operation":

When the CDI is in Normal Mode, if the TVS fails, the engine defaults automatically to the gear counter coil to solely determine engine speed.

From the same section, if the gear count coil has failed (or pulse rate coil), the engine won't start at all because the CDI will not pulse the fuel injectors.

If the TVS is to blame at the upper limit then in theory I should get more RPMs without it.

Could I not simply disconnect the TVS and retest?