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jimnmad 07-08-2008 16:25

Perkins Diesel Fuel Injection Question
This will be kind of an indefinite question, but , here goes. My brother in law just bought a boat with a perkins 4 cylinder diesel in it. On it's on, at idle it will begin to run faster and faster. I think that cutting off the airflow will stop it. Where would be the best place,or, places to start troubleshooting? we are going to take a look at it on Saturday and would appreciate any help.

btrayfors 07-08-2008 16:35

Changes in engine speed can be due to several things. You said it goes "faster and faster". I assume you don't mean it assumes a "runaway condition" wherein it will just keep accelerating at very high rpms. That could be due to a malfunctioning governor and/or other problems.

Assuming you mean it runs faster, then slows down, then faster....i.e., appears to "hunt", I'd consider the fuel system first. Could be due to poor or contaminated fuel, clogged fuel filters, air getting into the fuel lines, etc. Sometimes these problems are simple to fix; sometimes they're the very devil.

Years ago I had a problem on my Perkins 4-108 which was driving me crazy. Finally tracked it down to a pinhole in the bottom of a copper fuel line running in the bilge -- out of sight. Found it only by sound (hissing when the manual fuel lever was pumped) and by touch.

Recently, after many years of no such troubles, I had another "hunting" problem with my Perkins. Every two to three minutes when at 2300rpm cruising speed, the engine would speed up a few hundred rpm, then drop back within a few seconds. Tracked that one down to loose connections on the on-engine fuel filter. Easy fix :-)

Good luck,


jimnmad 07-08-2008 18:09

I'm speaking secondhandedly, but I think that it will runaway ie goes faster and faster. I'm building a troubleshooting list so what else besides the governor could I explore. Thanks

PS We have a good engine manual as well.

btrayfors 07-08-2008 18:38

I'm no diesel expert...just a guy who's learned to keep his diesel running most of the time :-)

But, there's plenty of good info out there on runaway diesels, including causes and fixes.

Here's a start: Run away diesel, why does it happen? - ShopForum

For more, just Google "runaway diesel engine"


jimnmad 07-08-2008 19:20

Thank You. I'll give it a google.

Chief Engineer 07-08-2008 20:48

First look at your throttle linkage.

I have seen many vessels particulary those with pedestal mounted throttles have a creep to them some times they speed up.....others cannot hold in a advanced throttle position and creep back (these are the boats you see with a bungee cord on the pedestal somewhere).

Next I would make sure that the linkage at the injection pump is not loosey-goosey.

From there, I would go witha previous posters advice of looking at the fuel delivery system......check for system integrity.

Has the engine sped up to a point that you were alarmed?

Could you not shut it off via the shutdown cable or solenoid?

I have seen a few "runaway" Detroit Diesels over the years...they are two cycles
71 Series.

I have never witnessed a 4 cycle runaway

Chief Engineer 07-08-2008 20:52

Sorry....brain flatulence.....I did have a Universal Diesel do that to me.

Startup short idle then to WOT......The cause was the owner "monkeyed" with the injector lines at the injection pump and in attempting to remove them twisted the "barrels" causing the "rack" to bind in a WOT sure gets yer attention

I did have a small board handy to cut off air supply.

Alan Wheeler 08-08-2008 01:20

I can think of a dozen different directions. We really need more detail on what you mean by "run faster and faster". Just as Chief asked, does it reach an alarming speed? or is a slight increase in RPM as it warms up? or....

jimnmad 08-08-2008 13:06

Thanks for the responses. We'll be working on it this week-end. I think we should have enough possible avenues to explore. I'm pretty sure we can get it sorted out. If we do, I'll let you know what it was......if not, I'll be asking for more help.

Thanks Again,


easterly 08-08-2008 16:49

The only way a diesel can run faster and faster is with more and more fuel. It is a fuel problem.

GordMay 09-08-2008 04:29


Originally Posted by easterly (Post 191370)
The only way a diesel can run faster and faster is with more and more fuel. It is a fuel problem.

It's a "fuel" problem, but not necessarily a primary diesel fuel problem - it could be lubricating oil "blow-by".
Hydrocarbon vapors (oil blow by) in the intake air will sustain a runaway, even with the primary fuel source shut off.

Chief Engineer 09-08-2008 19:41

Doest that occur in four stroke diesels?
Just curious


Originally Posted by GordMay (Post 191474)
It's a "fuel" problem, but not necessarily a primary diesel fuel problem - it could be lubricating oil "blow-by".
Hydrocarbon vapors (oil blow by) in the intake air will sustain a runaway, even with the primary fuel source shut off.

Alan Wheeler 15-08-2008 02:05


Doest that occur in four stroke diesels?
Just curious
Yes absolutely. But I am not sure this is the problem in our above situation. Running on lube oil leaves one important little tell tale. The entire marina would have just disapeared in a smoke screen and the engine sounds like it has a bag of jack hammers inside it.

tartanss 18-06-2010 21:57

perkins 4108 injector pump leak
cant help with the speeding up
Can anyone advise me on fixing a diesel leak coming from the throttle linkage on the injector.
cheers Rob

CFR 27-06-2010 23:36

hi all need also advice in the same field: i changed my throttle cable on a 2 zylinder Sabb with 2 mechanical Bosch injection pump. engine was running until yesterday without problem, after touching the governor handle and attaching the new throttle cable the trouble starts. engine did not hold rpm, going down from 1000 to 500 by himself. going up tp 1000 again. later i used it without the cable and the egine runs at 1500 , after going back with the handle to idleing the engine keeps running at 1500 for 2 min and i could finally stop it. i chekce the flywheel, the intrenal link of the 2 pumps etc everything looks fine but ofcourse i can not check the pump internally. any idea. in total i was trying running stopping for more then 30 min and i assume that air is not the problem. fuel is perfect clean, all 3 filters are clean, no water

please help

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