Aww Shucks! Wierd runaway diesel problem

[Reefmagnet]

Just looking for clues on what would cause a runaway diesel issue. The boat's been out of the water for almost 4 years now, and I do try to start the engine every 6 months or so. It developed a bit of an odd issue about a month or so before she came out of the water in that on first start after being left for a week or two, the engine would immediately over rev and I'd have to turn the ignition to stop, and then restart the engine and all would be fine.


Today I restarted the engine, and it over revved - but activating the stop button didn't do a darn'd thing. Fortunately, I was johnny on the spot and had immediate access to the air intake and managed to shove a bit of wood over it. It slowed it enough and eventually the motor conked out. A few starts and stops (via the blocking of the air cleaner) the problem isn't going away. To cut a long story short, I'm pretty much of the opinion that the injector pump has some kind of fault based on the earlier symptom which I think is related to this problem. This engine is an eight years old Mitsubishi S3L2 3 cylinder engine of about 30 hp and has 180 hours in total on it, probably about an hour or two which has been added in the last (just under) 4 years.


It's difficult to find information on runaway diesels that don't relate to turbo or sump oil issues, so the question is, does this sound like the correct diagnosis? I'm guessing if not we could have gummed up rings or something like that?


Boats sure are fun!

[jimbunyard]

http://www.cruisersforum.com/forums/...rt-213299.html

[Reefmagnet]

Done a little more research this afternoon and it seems most likely the issue is a seized pump caused by basically lack of use and old fuel. They just need to be cleaned after some minor disassembly, it would seem, so hopefully I can hunt down someone who'll do that and not want to totally rebuild it.

[jimbunyard]

With patience you can do it yourself, these minipumps are very simple. Could be that the rack is sticking, but probably more likely the P&Bs are. Take pictures at each step in disassembly, as with some of these pumps you can get parts aligned improperly and the pump will seem to work, i.e. everything will move as it should, but the relationships between the parts within the pump will be wrong and the fuel delivery will be off or nonexistent.

[Reefmagnet]

Cheers. I'm having a read through the factory workshop manual for the engine now. Had multiple diesel vehicles over the years, even installed one on the last boat from scratch but never had to take a serious spanner to one. And I usually have to do everything twice because I screw it up the first time so I still might see if I can find someone to do it a reasonable price first. If not, I'll order the bits and have a crack!

[a64pilot]

Your on the right track.
Right or wrong, but I have always viewed diesel injection as critical pieces of equipment, while you may can do a DIY clean job on pumps and injectors, I don’t think you can properly test them and ensure they are working correctly and if they need adjusting like an injection shop can, you just don’t have the equipment.

[DougR]

Maybe it's being mis-diagnosed .....

Is it a "runaway" or is it just that you just can't control the RPM? That is, does the rpm race out of control, well over the normal high idle, or is the engine running at a fixed rpm but you can't control it.

The fact that it has happened in the past, and one start up seemed to free up the system and then it was OK indicates that something is sticking and then breaks free.

I think it's unlikely that something in the fuel side of the injection pump is gummed up and sticking. Normally when pump plungers or barrels get gummy and stick, the plunger(s) gets pushed up by the camshaft and they then stay stuck at the top of their travel, and that means that they don't inject any fuel and the engine won't run at all. The fact that it runs, and runs plenty fast, indicates to me that the plungers are free to move up and down and so I wouldn't dive into the pump just yet. It is possible however, that the rack which controls the plungers is getting stuck and can't be moved by the governor and then you have no control. If you can FREELY move the rack back and forth then it's unlikely that the pump has a problem.

Are the governor linkage parts and governor weights moving freely? A little rust or corrosion on something here could cause loss of control of the injection pump and a seeming runaway, which might not be a runaway but rather uncontrolled steady state high rpm.

Another thing I have see is an over fuel runaway caused by blocked fuel return lines. Simply opening a closed return line valve solves the problem......but that doesn't sound like your problem.

DougR

[zeehag]

KA LUNK was runaway due to governor on fuel pump.
stopped the issue by cracking all 4 injectors. mechanic choice. luckily didnot throw rod or blow piston out the block. details in thread named KA LUNK
interior of engine was a destructoderby first prize.

[boat driver]

Runaway may also be a stuck/cracked ring worn hard permitting the engine to utilize crankcase lube. Compression check while injectors are out. easy and cheap- before pulling pump. Air shut off is on a diesel engine for this reason. Fuel shutoff either failed to work (stuck because old fuel) or is broken- Not many hours for an 8 year old engine which might suggest a piston wearing from a stuck ring prior to layup.

[Reefmagnet]

Pretty sure it's gunk in the injector pump. Majority of the hours were put on over 18 month period, so the engine has spent a lot of time unused, even when first installed. And it has been soaking in what is now over 4 year old fuel. I test ran it a number of times yesterday specifically to determine if it was a stuck ring or pump issue and everything points to a pump issue at this stage.



After hearing what Jim had to say, and having a read of the manual, removal of the pump and governor assemblies are very easy on this engine, and it will provide access to the rack that has a published inspection test for checking binding, so I'm going to give that a shot later in the week. Then I'll call in the experts if I have no luck (and keep that bit of plywood handy near the air intake!)

[Iaangus]

Originally Posted by jimbunyard

With patience you can do it yourself, these minipumps are very simple. Could be that the rack is sticking, but probably more likely the P&Bs are. Take pictures at each step in disassembly, as with some of these pumps you can get parts aligned improperly and the pump will seem to work, i.e. everything will move as it should, but the relationships between the parts within the pump will be wrong and the fuel delivery will be off or nonexistent.

I had a throttle rack sticking intermittently on a large diesel engine, I was skeptical but before removing pump and sending to shop (would have cost $1000) I added a can of Sea Foam to the engine oil, (engine oil lubricates the fuel rack in the pump) It quit sticking and has worked fine for years since. It’s worth a try.

[TeddyDiver]

Originally Posted by boat driver

Runaway may also be a stuck/cracked ring worn hard permitting the engine to utilize crankcase lube. Compression check while injectors are out. easy and cheap- before pulling pump. Air shut off is on a diesel engine for this reason. Fuel shutoff either failed to work (stuck because old fuel) or is broken- Not many hours for an 8 year old engine which might suggest a piston wearing from a stuck ring prior to layup.

This! There's also possibilty of leaking valve seals causing engine oil fueled ignition but in that case the runaway lasts most likely only a short moment.

[drcot3]

Hello Check your oil level in engine if its increased sign of oil/diesel combining cause a runaway condition only hope before destruction is to stop air getting into engine causing the engine to stop,otherwise a Governor fault. kind regards David

[Compass790]

Let us know how you get on. I'm with jimbunyard, most likely something sticking. I'm not afraid of diesel injection pumps anymore after rebuilding ours but it took me 2 attempts ( my time is cheap & diesel shop I had no confidence in after they lost a part of it when I got them to test it). Cant comment on yr particular unit but ours had a stamped rack mark & paint on it to align the rack. Wouldn't attempt fixing it if you are not mechanically inclined. Takes a bit of nutting out. If you have compression & air there is only one thing left. Check to see if injectors are squirting. Seen a few diesels start up alright after being left for a long time but not if they have water or gunk in fuel

[Reefmagnet]

Originally Posted by Compass790

Let us know how you get on. I'm with jimbunyard, most likely something sticking. I'm not afraid of diesel injection pumps anymore after rebuilding ours but it took me 2 attempts ( my time is cheap & diesel shop I had no confidence in after they lost a part of it when I got them to test it). Cant comment on yr particular unit but ours had a stamped rack mark & paint on it to align the rack. Wouldn't attempt fixing it if you are not mechanically inclined. Takes a bit of nutting out. If you have compression & air there is only one thing left. Check to see if injectors are squirting. Seen a few diesels start up alright after being left for a long time but not if they have water or gunk in fuel

Will do. I came to the boat today to sort it out, but found out there's a diesel mechanic running around here somewhere, so I might get him to have a look if I can hunt him down. I'm confident it is just gunked, and that I could get it going, but I got a lot of other projects on at the moment and I'm keen to get this tub splashed!