I just purchased a 40' trawler boat with a pair of Nanni MB diesels turbo 5 cyl-300's (OM617.9).

BOTH engines are doing the same thing? Which is... under no-load they will rev up to 1400 rpm and hold any setting just fine, but if you bump it another 50 rpm they will take off on their own (with no linkage movement) and go to red line. The place where you lose control is that exact and equally matched in both engines. When in gear, both engines perform perfectly and will stay at what ever rpm I choose.

I contacted the previous owner and he admitted to being aware of the engines being "frisky" as he put it. i can think of lots of reasons for an isolated engine to do this, but both? It's gotta be something in how these engines were marineized. There is no inspection plates with parts numbers on either the turbo's or fuel injection pump - only casting numbers. This one's got me stumped!

Thanks,

Sounds like your vertical throttle stop (also misnamed as the idle adjustment screw by many) is adjusted too far in CW.
https://docs.google.com/document/d/1QkAv-HFaLqpK_5wKCln6DODkfw_DkjBHVYZXm0nUtEw/edit?hl=en_US&authkey=CJXuhs0I&pli=1

Try adjusting it out CCW 2-4 turns (on each IP) to regain your return to idle function. (# 2 on the thumbnail on the forum link below);
http://www.peachparts.com/shopforum/3094984-post27.html

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

I think in neutral this is normal behaviour... I seem to remember reading that the IP's on these are ungoverned above idle and will do this when not under load.

__________________
2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

I believe I have noticed this in my 617's. Above a certain rpm, in neutral, they'll just keep running faster.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

The idle governor function gets overridden around about 1200 RPM I think, so if your engines are idling 1400 (twice what it should be!) the idle governors aren't doing anything at all.

In a car, if you set the idle knob once started on a cold morning, the engine will "run away" once the engine warms up and the fuel gets burnt properly as the idle governor has been overtaken by the "throttle" input.

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1978 300D, 373,000km 617.912, 711.113 5 speed, 7.5mm superpump, HX30W turbo...many, many years in the making....
1977 280> 300D - 500,000km+ (to be sold...)
1984 240TD>300TD 121,000 miles, *gone*
1977 250 parts car
1988 Toyota Corona 2.0D *gone*
1975 FJ45>HJ45
1981 200>240D (to be sold...)
1999 Hyundai Lantra 1.6 *gone*
1980s Lansing Bagnall FOER 5.2 Forklift (the Mk2 engine hoist)
2001 Holden Rodeo 4JB1T 2WD

i trust 1400 rpm is not your idle speed... that's fast.

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'77 240D, 504H, OM617.952, etc.

I've noticed a similar thing with my '83 300d turbo. (Basically the same engine.) mostly an issue if I'm reving the engine to jump start something. (Last time it was a 454 chevy) I think it's the turbo building boost and increasing output from better combustion with the same amount of fuel, but maybe someone with some marine experience can confirm. Pushing the linkage, I have been able to steady it by letting off of the throttle as it tries to climb. For you, the fact that both do it so equally makes it sound like your engines are very well balanced to each other!
Cool power plants for your boat!

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'83 300D turbo diesel (334k daily commuter)
SOLD '80 240D 4 speed manual, #2 piston pitted from crushing a 10mm nut. Running it 'till it burns through.
'78 F-150 300cid 4spd od (with my great unkle's original sales receipt)
SOLD '66 Ford P-350 delivery truck (almost driveable)
'49 Dodge B1D (1 ton Pilothouse era truck) not running but all there, candidate for om617 and 4x4 conversion when money permits.

LOL... no, 1400 is not the idle rpm. They idle about 800 to 900 I never take them above 1100 when docking as it's too hard on the tranny to shift much more than 1000.

Actually 1450 seems to be the magic number. Below 1450 and the rpm will hold in neutral, anything above it and the rpm's just start climbing headed for the redline?

Have you checked your oil level? A high level, usually from fuel leaking into the sump will cause run away. But to have both engines do that is highly unusual.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Woops, I misread there.

I doubt the engine is running away from anything other than the IP throttle input. I would disconnect the throttle linkage right on the injection pumps and see if the engines still do it, that rules out a binding throttle cable etc perhaps.

__________________
1978 300D, 373,000km 617.912, 711.113 5 speed, 7.5mm superpump, HX30W turbo...many, many years in the making....
1977 280> 300D - 500,000km+ (to be sold...)
1984 240TD>300TD 121,000 miles, *gone*
1977 250 parts car
1988 Toyota Corona 2.0D *gone*
1975 FJ45>HJ45
1981 200>240D (to be sold...)
1999 Hyundai Lantra 1.6 *gone*
1980s Lansing Bagnall FOER 5.2 Forklift (the Mk2 engine hoist)
2001 Holden Rodeo 4JB1T 2WD

Don't rev the engines over 1400 rpm with no load. Problem solved.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.