Vmax 250 cylinder four fouled plugs

[Tenseevols]

Hi,
I have a vz250tlr with new VST pump, crank position sensor, three new injectors,new filters thought out fuel system,tank vent and not stopped up,new water pump, and new coil pulser. Every time I go out and come back the number four plug is solid black and fouled out. The RPM's never get above 5400. Need help figuring out what's next. Compression is 120 on all cylinders and has good spark. I have had it checked. Any help will be greatly appreciated. Thanks

[Sequoiha]

You probably have a ruptured diaphragm in a mechanical fuel pump. Loosen it from the block and squeeze the primer bulb, look for fuel leaking from the pump.

[Tenseevols]

Changed out manual fuel pumps, still same issue. Beginning to hate the engine!

[99yam40]

Hopefully Rodbolt will see your post and reply with some helpful info

[Tenseevols]

Hopefully in the big bass tour on Guntersville and can't get to the weigh in. Could it be one of the drive modules for the one bank? Now the number 2 and 6 look the same.

[boscoe99]

What was the reason for all of the work done on the motor? Was it to solve the plug fouling issue?

What brand of oil is being used?

What brand and model of boat and what brand, model and pitch propeller?

Have you swapped the number four coil with any other coil?

[Tenseevols]

Yes it was to solve the fouling spark plug. Yamalube 2m is use with the ngk spark plug. Boat is a stratos 201 Xl pro. Yes have swapped coils.

[rodbolt17]

I would look at maybe oil line check valves.
maybe intake(puddle) drain check valves.
if it only affects #4 then look at only things that affect #4.
you have 6 little engines that share a common crankshaft.

[99yam40]

Seems #5 post says #2 and #6 look the same now.
I guess he is saying those look like #4 and are fouling also, but I am not sure

[Tenseevols]

The whole bank now is fouling out. Could it be the injector drive modules going out?

[boscoe99]

The whole bank now is fouling out. Could it be the injector drive modules going out?

Doubtful but could be. Easy enough to change injector drivers and see what happens.

[Tenseevols]

Took it to the shop they adjusted the oil metering arm and TPS. Went out and ran for a bit and bam back to fouling the same two spark plugs. I'm confused totally. I have worked on every kind of engines and this one has got me at my wits end. Any suggestions. I have swapped the drivers and you were correct. It wasn't that.

[rodbolt17]

why would you adjust the TPS? sounds kinda stupid if ya ask me.

most folks cannot CORRECTLY adjust the TPS on a Z or VZ motor.

if it was a TPS issue it would affect all 6 cylinders.

myself I would look for something that would only affect the involved cylinders.

does the ECU ever have any stored codes?
if your getting pulser coil or injector codes on a cyl and all the components have been tested.
do a running high speed test on the pulser coil output voltage.

the manual gives minimum voltages.

much above 62V output on the pulser coil and it does funny things to spark and injection.

why? I don't know but that one took me about 2 hrs to figure out.

has the actual ign primary and injector driver voltage output been measured at the failure RPM and load?

remember ya got 6 little motors sharing a common crank.
if it was an intake air,TPS,baro sensor,CTS or other sensors they would affect all 6 cyl.
the pulser coil? that can affect a single cyl,or any cylinders involved.

were the oil line check valves actually tested ?

were the recirc and drain check valves tested ?

ask the tech that and watch his/her eyes glaze over.

[Tenseevols]

Good question. All the mechanic could find wrong with it was those two things. There were no codes and all modules test good on YDS programming. They don't have a clue as to what is causing the issue.

[Tenseevols]

Also there is a lot of oil draining out of the intake into the breather housing. I pulled the oil lines yesterday and cleaned them. I tried to blow through some of the check valves the way the arrow pointed and got nothing. Could it be a bad oil pump stuck wide open?