Port engine intermittent RPM problem at higher RPMs

[jff]

Yesterday I took the boat out, when I went to go up on plane, engines were sync'd, around 1800-2000 rpm the port engine RPMs began to flutter around moving lower than the Starboard. And it felt like we were going about half the actual speed we should be doing, around 12-15mph instead of 20-25mph. I think I could hear a different noise coming from the engine compartment but I'm not sure about that. What I did see then was a system error appear on the Smartcraft, I took a picture of it (attached) along with the two tach guages showing at that moment the port engine running 300-400 rpms lower than the starboard (even though engine sync was on).

Two questions:

- am I correct in looking at the error screen to be an error with the Port engine (I assume so, but just verifying as my local dealer has been focused recently on the Starboard engine)

- what specifically does "IMV Pressure Low" mean?

Two more interesting data points:

- we idled out to a cove after the problem happened and anchored, on the way home later that night I did another test and the boat ran *perfectly* all the way up to full speed. So the problem seems intermittent.

- a week ago I noticed that the Port engine overflow coolant bottle was filled to the very top (should never be), not sure if this is related or not.

Any thoughts/ideas?

Regards,
Jason

 

[fwebster]

"IMV" means inlet metering valve. On your engines it means the pressure in the common rail is lower than spec. The most likely cause is dirty fuel filters........and I'd bet on this since your engine exhibited fluctuating rpms then returned to normal after running at idle or being off for a while.

THe other possible cause is a break in the high pressure line supplying the common rail. THis is a common defect with the QSC since t he high pressure feed line is missing a supporting bracket in the middle. Cummins has refused to issue a recall on the missing bracket but will add the bracket if you have a fuel line rupture........not much help after your engine room is flooded with raw diesel and you turn your $1.0 mil boat into a floating flame thrower.

 

[jff]

Wow, thanks Frank! I asked a local Cummins tech what the IMV meant and he had no idea. Scary.

A few followups based on your response:

- when you say dirty fuel filters, could that include both the Racors and the spin-on fuel filter?

- If there was a break in the high pressure line, wouldn't I see a lot of fuel accumulating below the engine? And I assume that as you said it wouldn't run properly the next time I started it up, once it breaks it's broken ... right?

Thanks again!

Sincerely,
Jason

 

[fwebster]

The high pressure line has 2500+psi of pressure, so you would have a bilge full of diesel fuel and you would smell it because it would be spraying like water out of a pressure washer.

Assuming you are using the recommended 30 micron primary filters and the Cummins secondary filters, the odds are that you will have clogged the Racors first, but that isn't always the case. If it were me, I 'd change the Racors and drain the bowl to see what they look like. If that doesn't do it, change the engine mounted filter and try again. If it isn't one or the other filter, Mr. Cummins is going to have to help you because it will require his computer diagnostics to identify problem.

 

[jff]

Definitely no bilge full of diesel, I looked carefully and don't see even a drop under/near the engine area. I am using the recommended filters. Replaced the spin-on fuel filter April '10 so it's only about 90 days old (probably has 10 hours use on it max). I went ahead and replaced the Racors today, they weren't more than 2-4 months old but no harm in doing it, we'll see if that helps. If not I guess I'm left with calling Cummins ...

Thanks for all the advice Frank.

Sincerely,
Jason