Marine Power 6L Problems

[IDBoating]

Anything that magically happens and is repeatable at a very specific RPM strongly suggests the ECU is making an intentional decision. It might be the WRONG decision, based on bad sensor data or similar, but the fact that it happens at the same predictable value means something intelligent is in the loop. That doesn't give you an answer per se, but keeping that in mind may help with diagnosis.

[GUY_RPM]

Any chance it could be the throttle position sensor?

[chpthril]

Any chance it could be the throttle position sensor?

Yes. but the data stream would likely show it.

[Smcqueen]

There is no way the cam position is actually changing 50 degrees even with variable timing. So I would suspect sensors. As mentioned check smooth curve on TPS as it will drive the variable cam timing. MAP sensors and throttle position sensors are really not very expensive and typically very easy to change out so you might have a look at those.

[IDBoating]

MAP sensors and throttle position sensors are really not very expensive...

Hoo boy, I hope that's true in this case. The TPS on my previous Mercury V6 engine was over two hundred dollars from the factory! For what is really just a potentiometer! Arrrgh!

[cpropes2005]

Yeah I was thinking TPS too but the log doesn’t show any variation in that sensor when the issue happens. I actually replaced the pedal position sensor a while back before I got the scanner and was just throwing parts at it but obviously that wasn’t it. The MAP sensor does spike but I think that is a real reading based on the fact that cam angle changes at the same time which would cause the increase in pressure.

I agree that it really acts like something to do with the logic of the system based on how it is so consistent at 2000 rpm. Like you said either a sensor is giving it bad information and it is making the wrong decision or the actual logic built into the ECM is bad. That is the main reason I didn’t pull the trigger last year when the dealership wanted to charge me $1200 to $1500 to replace the CAM phaser solenoid valve. It just doesn’t act like a mechanical issue. The only counter-argument I could think of to support the dealerships position was if the ECM is triggering movement of the CAM at 2000 rpm and the solenoid valve is semi functional then maybe it sticks and jumps around instead of operating smoothly.

Bob at OBD took a look at my logs and his opinion is that the sensors all appear to be functioning so he thinks it is something funky with the programming on the ECM. My plan now is to take the ECM off and send it to him. If he can break the password he is going to dig around through the programming and see if he can tell what is causing the issue. If he can’t break the password I will have to make a decision because the only option would be to completely wipe the ECM and flash it with a tune for an Indmar LY6 that he has and knows is good. I am hoping he can break the code because there is no going back if he has to wipe it and there is always a possibility that there is something slightly unique about the Marine Power LY6 where the Indmar tune wouldn’t work so I am not sure if I will be willing to risk it.

Actually, as I am typing this I think I will see how expensive the MAP sensor is. I don’t think that’s what it is but if it isn’t too expensive I might just replace it and see what happens before I go to the trouble of removing the ECM and shipping it out.

[cpropes2005]

So I went through the log frame by frame and the best I can tell this is the sequence of events. This all happens over about 1 second.

1. Throttle position sticks at 31.6% and desired throttle position continues up to 32.4% for a 0.8% gap. Previous largest gap between these two on normal acceleration was 0.4%.
2. Next frame shows first RPM drop from 2012 rpm to 2004 rpm with no change in throttle position. No change in MAP or cam position in this frame.
3. Subsequent frames show cam angle, MAP and injector pulse width increase as RPM continues to fall.

I did notice 1 other thing I thought was strange. The rev limit threshold is at 3000 rpm for most of the run but shortly after the hesitation it changes to 5100 rpm which seems like a more realistic number. It bounces back to 3000 and then back to 5100 one more time later in the run. I am not sure exactly what is going on but it seems like the scanner is sampling this value at a much lower rate so it may just be a default value vs what it is actually reading. In the log I took where I had no hesitation it stayed at 3000 rpm the whole time. Is it normal for this value to change?

[cpropes2005]

Last "normal" reading:
2.jpg

TPS and desired TPS start to get out of whack:
3.jpg

Max RPM reached:
4.jpg

RPM drops from 2012 to 2004 with no change in throttle position:
5.jpg

MAP, Cam angle and injector pulse width respond as RPM continues to fall
6.jpg

[IDBoating]

1. Throttle position sticks at 31.6% and desired throttle position continues up to 32.4% for a 0.8% gap. Previous largest gap between these two on normal acceleration was 0.4%.
3. Subsequent frames show cam angle, MAP and injector pulse width increase as RPM continues to fall.

Perhaps sticky throttle actuator? My thinking is that if the ECU is trying to increase the throttle due to perceived load (the "increase in desired throttle position"), but the actual throttle position isn't changing ("throttle position sticks"), then maybe the throttle actuator can't respond for some mechanical reason. The subsequent changes in injector pulse widths are consistent with the ECU trying to get more power out of the engine (by putting more fuel into the cylinders) but if you can't get more air (stuck throttle) you'll go too rich.

[cpropes2005]

That makes a lot of sense. This is probably a stupid question but does the throttle body remain completely closed until the IAC reaches 100% open?

I did notice that the IAC gets to 100% approximately at 2000 rpm where the issues is happening so it would make a lot of sense that the throttle body just hangs up a little as it tries to open initially if that is how it works.

[Smcqueen]

I must admit, I am not familiar with the way Marine Powerprograms their ECU, but I have never heard of anyone using a variable rev limit. Could rev limit number bounce around and be cutting spark? It depends how their rev limit feature is set up. Some will cut spark, some will cut fuel flow, some will cut timing. Your data does not show any of this happening. Your MAP and fuel flow seem to be doing what you would expect. As rpm drop off, TPS constant, manifold pressure will begin to increase which will call for more fuel flow. This is what you are showing. Why is rpm dropping? Increased engine load?doubtful. Loss of fuel flow? Data does not show this. Actual loss of manifold pressure? Manifold air leak would cause this. Could their be an air control valve popping open? You would see a lean condition on your O2 sensors. Cam timing could be driving the change in manifold vacuum. Since cam timing is showing 548degrees I would have to assume that is measure by crank degrees rather than cam degrees since the crank makes two revolutions for every cam revolution. So your valve timing is kicking in at 2000 rpm with a 44 degree shift at crank angle or 22 degree actually on the cam. Need to research if these values are normal. I don't know off the top of my head.
Also don't know why actual throttle position hangs up. Is this drive by wire? Throttle moved by electric motor?

Will have to do some research.

[Smcqueen]

Looking back earlier in your thread, what they are telling you may be accurate. The cam angle should be a variable and responding as rpm changes when it appears that you are seeing a step change in timing. That would seem to upset the ECU fuel delivery and power output.

[cpropes2005]

Yeah I am thinking that the rev limit changing may just be a function of how the scanner works.

I agree that the cam angle should change gradually. Looking at the log where I dont have the hesitation it really doesnt change much at all and hovers around 506 to 508 degrees but this is with no load and only revved to about 2200 rpm so I would imagine under load and going to higher rpms it would move a little more but still be a smooth transition. Maybe it has some logic built in where if it sees a certain set of conditions it jumps to another table for all of the values? Could that criteria be a greater than 0.4% difference in throttle position vs desired throttle position? That could explain the sudden step change.

Of all the logs I have done so far the throttle position never gets above that 31.6% value even on the ones where I didnt have the hesitation. I am going to run a few more test and push the rpm's up a little higher to see if the throttle position will go higher than that or if it always sticks there.

And to answer my own stupid question, the tps tells you how much your throttle is open, duh.

[Smcqueen]

A pretty good article on GM's system. http://www.hotrod.com/how-to/engine/...-valve-timing/

You mentioned the engine was rebuilt? Any chance the builder put the wrong cam in the engine?

My BMW has a similar problem with the VANOS solenoid getting gummed up. Only takes 10 minutes to change out on the BMW. Looks like a real pain on the 6.0.

[cpropes2005]

Thanks for the article. I have done a fair amount of research but that looks like some really good info.

From what I understand the engine was a new crate motor and not a rebuild. Unfortunately it was put in before I bought the boat and I don't have any documentation for it so I am not sure on all of the details on other than the dealer telling me for some reason the previous owner put in a whole new motor instead of rebuilding the old one.

I think it is actually pretty straight forward to change the solenoid on the 6.0 too but the problem is that it is basically impossible to get to on a v drive. Dealer said they would have to at least partially pull the motor to be able to get to it.


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