Volvo D6 370's, Starboard will stay sync'd but then drops RPM's

[jspin101]

I have twin 2006 Volvo D6 370's w 635hrs
They both stay sync'd up to about 2800 RPM's. When I bring them both beyond that the Starboard will drop a few hundred RPM's then bounce back up, then drop down, then up, etc... It seems to drop back to around 2800. I got them both @ WOT doing almost 26 kn. Up to 2800 RPM's doing 15kn they both run fine.
A friend of mine said he had the same issue and his turned out to be the Turbo Charger.
Anyone know a way to test/prove it is the Turbo?
Anyone have a better/cheaper remedy than changing (about $4500/engine) out the Turbo?
Thanks,

[jspin101]

P.S. I have changed out the primary & secondary filters. They didn't look bad.
I bought vacuum gauges for the Racor's but haven't put them in yet.
Wondering it it was lack of fuel flow at higher RPM's

[Tireless]

I had the same issue with my Starboard engine last year, I have the same engines and year with the electronic shifters. Do you also find that when you put your Starboard shifter into position one (idle forward) that the shift hesitates and you need to give it a little push forward for it to engage.

This is what was happening to me. I though it was a bad shifter at first. This spring I went under the dash, removed the wires from the back of the shifter and sprayed the wire connection with an electronic contact cleaner. I worked the connection a bit by plugging and unplugging it, making sure the connection was clean.

I just returned from a 2 week trip to the north channel after the fix and I had no issues. Ran on plane and operated at idle speed with no issue. I had no shift issues and no rpm drop at all.

I am not saying this is what your issue is, but this worked for me.

I am still interested in the result of you question about your turbo's and how to check them.

This may be something else to look at before you start replacing turbo's.

Greg

[jspin101]

Thanks for the reply Greg.
I'd like your solution to the issue.Much less $$$$.
I don't seem to have the issue you were having shifting into fwd idle but I'll double check it
I'll have to take a look this weekend.
I'll keep you posted.

[Hugo]

To check turbos you will need to find a port on top of the intake manifold and hook it up to a hose with a boost gauge. Find your boost specs for your engine. I have the previous TAMD63ps, mine are mechanical diesels and max boost pressure on mine is 34psi. I see 26-30psi at cruise depending on load. You'd be looking for a difference, drop in pressure between two engines. I used ISSPRO gauges and also installed EGT gauges in my exhaust. I felt these were necessary to monitor health of engines.

Earlier this year I had the turbo air hose split open, lost power and right away the gauges showed a drop in boost and increase in EGT. Make sure you're making at least 2850 rpm WOT fully loaded (water, fuel, all) and if not take pitch out of props or motors won't survive long.

[Midnightsun]

My 370 Volvos have the EVC gauge option so I can read turbo boost digitally on the multi function gauges. If he has this then most problems will show up on the gauge or refer him to see a certified mechanic.

D6 370 Volvos should max out at 3500 rpm with a max cruise at 3200.

[Tireless]

My D6 370’s max rpm is 3600 and I run them at 90% as per manual, 3240 RPM on plane.

Jspin101, were you able to try cleaning the shifter connections to see if it helps your situation.

Greg

[Hugo]

Sorry guys, I was thinking of my 63ps when I said 2850, I see the D6 are higher rpm motors.

Run it like you stole it. What's the worst that happens, blows up and buy a new one.

[jspin101]

Greg, I finally got to test the starboard out after cleaning the connection right in the back of the shifter ( it didn't look bad but I put Di-electric grease on it anyway. It ran up to 2800 RPM fine, when I went to 3000 it ran fine. 3100 and it dropped about 200 rpm and came up. Up and down a few times. I took it to 3500 and it dropped down about the same. I was gettng 26kts @ 3500 WOT in low chop. So it seemed a little better, not as much drop in RPM as before. I'll have to trace the shifter cable and see if there are any other connector/s are. I'll keep you posted.
Unfortunately I don't have the EVC displays. I have the "B" version and they don't support the EVC display. I have been looking for a 3rd party display but haven't found anything yet.

Thanks Hugo for the gauge suggestion, I'll have to look into that.
I'll update as I find things out.

Thanks all.

[Viper]

Before you start throwing a bunch of time and parts into this, you may want to have a tech hook up Volvo diagnostics and look at some numbers while she's running as well as checking whether a software update is advisable. It does sound like a fuel delivery or an induction issue though, but could be as simple as a faulty sensor.

Anti siphon valves are always suspect but if you have electric fuel valves at the tanks, you should ensure the connections are sound. If fuel selector valves are applicable, make sure they are in the full open position. If you do have selector valves, try switching the tank for that engine and see if that makes a difference. You also want to ensure the starb tank is venting properly.

You should check the pins in all the plugs on the engine also. I've come across more than once where a pin was pushed out likely from someone not being careful when re-inserting a plug. Chances are they won't be corroded though you should look for that. You'll also want to ensure any unused ports have dust covers on them.