Higher RPM - Dropping/Hesitation OptiMax 250 M2

[MKITGO2]

Okay so I thought I was through my 'newbie' challenges this weekend after sorting a few minor things out with this new to me '04 Utopia with Merc 250 Opti M2... but no.

Installed my VesselView Mobile this weekend, which helped me gain some data in a couple situations I am experiencing hesitation and/or a drop in RPMs:

Scenario 1.) 6 passengers and overnight gear. From Idle to Full throttle to get on plane. At approx 4K RPM it hesitates and holds, RPMS stop climbing, engine feels a bit rough and feels like its being held back/struggling. Then....
a.) It clears out, jumps up 200-300 RPM and continues to accelerate. (the drop off last 3-5 seconds or so)
b.) after 5ish seconds, I reduce throttle momentarily, then get back into it, jumps up 200-300 RPM and continues to accelerate as normal.

Scenario 2.) Tubing the kids (3 @ 60 lbs each, + 3 adults @ 175-200lbs onboard) Running at 4K to 4.5K RPM steady.. not under acceleration, without any throttle input from me, the RPMs Drop approx 500 -700 rpm, engine feels a bit rough and feels like its being held back. Then after a few seconds it clears out, jumps up 500-700 RPM and back to normal and smooth.

Start up and Idle are all good. I don't have any excessive or lack of smoke. I can hear the fuel pump before start up.

I am thinking TPI (TPS) sensor may be the culprit, but not entirely knowing its role on this engine I am unsure. With my suspicion is that if the TPI is off/worn in a spot and feeding the ECM bad data I am either over or under fueling or sparking the engine as a result... but the TPI is not 'bad' enough to throw a complete code or warning light... Does that make any sense? Is TPI a hard one to replace?

If it was a bad Coil, I would expect more rough running at a variety of RPMs and rougher running.

If it is a bad injector or 2 I might expect similar level of rough running... but would expect it to be more consistent, not intermittent at specific RPM... but this may not be a fair assumption of behaviour.

MK

 

[Dr Honda]

It could be an injector that's sticking. And, since you say messing with the throttle helps... I'm leaning toward that. It can never hurt to send the injectors out for a proper cleaning.

With that said... your general description really sounds like an ignition issue. I would be pointing at a controller over a single coil. It will drop out 2 coils together, and that will cause the +500 rpm loss.

As far as the TPS... I would say... probably not that. The opti needs the TPS, and when they go bad... it will throw a warning, and even go into limp mode.

As always... before doing anything... check your air and fuel pressure.

 

[MKITGO2]

Thanks again Dr. H for the insights.

Ill add injectors to the list of things to look over. I know I can check the coils for ohm's... any thoughts on tests or methods to test the controllers?

I wonder if I can pull injectors and give them a 'basic' cleaning on my own,as sending them out would have to wait.

I'll have to learn about checking fuel and air pressures. I get the idea, just not something I've done before. May have to wait until fall too. The boat is in the water (3 hours north) so I am doing all this dockside at the cottage which can be a bit limiting.

MK

 

[Dr Honda]

Well... checking the coils and controllers using a meter may not be the best way since they seem to be intermittent. You may need to grab a couple in-line spark testers, and go for a ride, and have a helper watch for spark. not the easiest thing to do... but it's the best way. If you see good spark when the problem comes up... then you know it's fuel

Normally... I say someone brave can open injectors at home, and do a basic cleaning, and rubber parts replacement. But I've never cracked open an Opti injector... so I don't know what's inside. SO... if you decide to tackle that... please post pics.

 

[MKITGO2]

Yeah.. don't think I'll be cracking the injectors open. Looked up a few pieces of info on cleaning injectors in general, seem pretty straight forward using some tubing and a can of carb clean, then pulsing the injector open ... then I looked up the style of injector we have, more the SPI style with injector intake on the side of the body and not through the top like most... it would be tricky to rig up a feed line to say the least.

Gonna start by checking the ohms on each.. thats easy enough, and same with TPS while I'm at it. Then will check the air and fuel pressure hopefully, and may see about an on engine injector cleaning system if I can get it on a loan tool program or something.

Doing anything while running will be tough with the Utopia design needing the rear lid needing to be up to access the engine I am pretty sure it would end in a bad YouTube video of my rear sun pad ripping off the boat as the wind catches it and iwth the problems occuring at higher RPMs.

We'll start with what we can and see what we get.

Cheers,
MK

 

[75sausage]

I had this issue on my 250 DFI and it was caused by the coil driver misfiring top 2 cylinders.

 

[MKITGO2]

How were you able to identify that it was the coil driver?

 

[Dr Honda]

he had a simple volt meter on the wire. But hooking up an oscilloscope would give a better picture.