What do you think about this - v6 idles on 3 cyl

[killerpirate]

Earlier i posted with some question about my 200 EFI merc.
I have some idling issues, it also has some troubles getting out of the hole. But once on plane it runs great.
I tested spark by removing the spark plugs one by one with the engine running.

i tested compression - all cylinders have 90psi (i have the cheapest tester)
New switch boxes
Other ECU, same problem

It actually isnt idling that bad at the moment. But when i remove ALL 3 spark plug cables (left bank), nothing changes. It still idles ok for 3cylinders. It definitly has spark. You can hear the arcs jump when removing the cables from the plug. Is it normal for a 200 to do this? I would expect a V6 running on 3 cyl would be a lot worse. As soon as i remove a plug cable from the right bank, it starts to idle bad.

My question: Could it be that an entire bank doesnt get fuel? The 6 injectors fire in pairs, so left and right top cylinders get fuel at the same time, same goes for middle and bottom. How often do the injectors fire per revolution?

https://www.youtube.com/shorts/BCu592rITq0

Any help would be appreciated!

[LakeFever]

Time for a black box delete. That’s my suspicion here. I also had extremely puzzling results when trying the pull a plug wire to verify firing properly test. As in your other thread it seems this test is simply a path to confusion with these efi mercs. As for the injectors, these efi set ups are not port specific so even if one is firing and one isn’t the fuel will get around to both but if you had dead injectors your engine would not last long; at all. My guess is if one or two injectors have failed? The first time you ran it up to 5000 rpm or so it would seize and game over for those pistons. It does not take much or take long for a two stroke to burn itself down in the absence of even small fueling issues.

Considering that motor looks to be in really fine condition I would do the whole recommend procedure of deleting all the black boxes and modules. Delete the oil injection. Have the injectors cleaned and flowed. Clean and service the vst. New water pump. New voltage regulators. Run premix at 40:1 and that thing will likely run well for many many years.

At minimum I would certainly delete the black boxes and oil injection.

[Jim Speros]

It could be a bad stator with a dead bank of cylinders. The stator combines energy from the high and low circuits on each side. The red and blue wires on top side of switch boxes are stator leads. One of the four circuits could be bad leaving not enough to fire plug.
An injected two stroke will adjust itself at idle and run on just a few cylinders.

I would test stator first.

[killerpirate]

Thanks for your replies!

All the black boxes are already removed.

I "tested" the injectors the hack way. Not the best way but it doesnt look like they are failing. https://www.youtube.com/watch?v=4qjfLt0CeFA
I did do compression tests and checked them with a camera after each run, nothing changed and nothing to see.

I also have new voltage regulators
I cleaned the VST (was clean already)
Top speed is the same as before, at same RPM, so there is no lack of power.

I guess stator is next, and check the TPS value with my multimeter

But like @LakeFever said, the injectors fire in pairs. How often do the injectors fire? Do they fire twice every revolution? (1 time for the left bank, and 1 time for the right bank)

[Jim Speros]

If top speed is the same its not likely to be stator. Its hard to tell idling on a hose. Its more telling to idle in gear and see if you hear a change in tone as you pull plugs. The ECU is going to do what it can to hold idle rpm. So you need a good ear LOL.

[LakeFever]

There’s a black box on the side of the motor right in your vid did you delete that since you took the video?

[killerpirate]

Thats correct. I deleted the ones that were keft after this video. Good catch!

[skialot2]

The stator has 4 capacitor charging coils. The 4 capacitor charging coils are composed of 2 high speed and 2low speed coils-1 high speed and1 low speed coil foreach switch box. The low speed coils provide primaryvoltage for the switch boxes from idle to approximately 2500 RPM. The high speed coils provide primary voltage from 2000 RPM to maximum RPM.