Racing engine on MD2B / CD 28

[Queen Elvis]

I fired up the Volvo MD2B diesel engine in my 1975 Cape Dory 28 today. It hadn't been started since around the same time last summer. And the engine started after an appropriate amount of cranking – around 30 seconds. The throttle was set to about halfway.

As expected, she chugged to life, so I opened the throttle a little, expecting to turn it back down again as she gained revs, to settle in at around 1200 rpm. So far, so good.

Then the fun began.

Instead of being able to control the engine revs, it immediately built up to full revs and stayed there! It ran smoothly, but at full tilt. The throttle didn't do anything. And neither did the engine stop.

After a couple of minutes of the engine running like this, I was able to get it to stop by turning off the fuel. There are 3 shutoffs, and I have no idea which one shut down the engine. Or if something else shut her down. There's a shutoff on the fuel tank selector switch (there are 2 tanks). And two on the water separator – one on either side.

After she shut down, I checked the throttle and shutoff cables, and both appeared to be functioning normally.

And I tried to restart, but couldn't get her to catch. The engine does run on engine staring fluid sprayed into the air intakes, so I'm pretty sure the engine itself is fine.

I cracked every fitting and got fuel to flow out – after the fuel pump, after the secondary fuel filter and at the injectors. At first, there was only air at the injectors, but fuel did get there after only a few seconds of cranking.

I'm not convinced that the fuel was under much pressure at the injectors, but I'm not really sure what I should be seeing there. Should the fuel be dripping out? Or squirting under pressure?

It's possible (I'm just not sure) that the engine might not have been started since removing and cleaning fuel tanks last summer. I might have winterized just by cranking and not actually powering her up.

The fuel pump is mechanical – gear driven from the rotation of the engine. Could it have lost its power by having teeth stripped by running at full speed for 2 minutes?

Any thoughts as to what might have caused the full speed on start issue?

And what should I do next to troubleshoot?

[Gary M]

Hi QE,

I was hoping some one would reply.

But until then, I found this interesting.

http://en.wikipedia.org/wiki/Diesel_engine_runaway

[tartansailor]

Check your oil level. It may be over filled.
Hope this helps.
Dick

[bottomscraper]

It hadn't been started since around the same time last summer

Any thoughts as to what might have caused the full speed on start issue?

Did somebody maybe go a bit crazy with fogging oil when it was stored?

[Queen Elvis]

Actually, I didn't use ANY fogging oil, and that might have caused the problem. I certainly will next time I winterize.

One advantage of being a boat hauler is that I've developed a network of mechanically inclined friends that know about diesel engines. One in particular is great because he doesn't succumb to the TABAIACM syndrome. "That's A Boat And I'm A Car Mechanic” in case you couldn't figure it out!

(Have you ever asked a car mechanic about an Atomic 4? I get that answer all the time, even though a Atomic 4 has to be about the simplest gasoline engine out there.)

So the theory I'm working on is that the injectors were stuck OPEN, and this would explain why the throttle or engine shutoff controls didn't do anything. It doesn't explain why she's not re-starting now, unless jiggling the controls post-run have now shut them, and they're stuck shut.

For the education of you all, I'll post what I know and assume. I find this stuff fascinating and know you guys and gals do, to. I just wish I was the student here and not the teacher!

There are two main types of pump system that feed the injectors – a pressure pump that delivers the fuel at the pressure the injectors need, and a lift pump that just gets fuel up there. With a lift pump, the fuel is delivered to the injector at low pressure and the injector has a system in there that pressurizes the diesel and then injects it. It's connected to the cam shaft by a push-rod. So I guess that the injectors have a mini piston in them. Makes sense, right?

I am pretty sure from my recollection of when I installed this engine 3 summers ago, that the Volvo MD2B does indeed have a lift pump and not a pressure pump. I'm going to pull the head off one day soon and look at the cam shaft to see if it is activating a pressurizing device in the injectors.

I'll also pull the injectors and see what I can do to clean them up. I know that these are delicate items, so I might want to send them out to a specialist.

My trucker buddy explained to me that this problem happens a lot with old Detroit diesels. That's a brand of engine not a city, by the way. And the way to stop them when this happens is to shut off the AIR not the fuel. That makes perfect sense because diesels only need air + fuel + compression.

Does anyone have any good marine diesel web forums I can hit up? I used to have some good links, but that was 2 computers ago!

[Steve Laume]

I do not have the greatest understanding of diesel engines. With that said, I do know that the injectors do not create the fuel pressure in the system but merely atomize it while injecting it into the cylinders. You have a lift pump to deliver fuel to the injector pump which then pressurizes it and sends it to the injectors. If you are able to bleed all of the fittings it seems to indicate that the lift pump is working properly and that your primary filter is not clogged. I don't know enough about the pressure pump to really comment on that.

If I was trying to figure this out, I would be looking at compression at this point. Does the engine turn over easily? If the engine sat for a period of time and this was your experience I believe the run away could have been caused by crank case oil getting past the rings. If it ran wide open while cold it could have further damaged the rings to the point that it is not getting enough compression to run on anything other than the starting fluid.

This might not be what you want to hear but it would be worth checking before you start to pull the fuel system apart.

This advise may be worth what you paid for it. It would be interesting to hear what others with more knowledge than I, have to say about this, Steve.

[Steve Laume]

A quick search found this,

http://www.justanswer.com/boat/7tsk8-ya ... eemed.html

I hope this is a minor problem, Steve.

[Queen Elvis]

...I do know that the injectors do not create the fuel pressure in the system but merely atomize it while injecting it into the cylinders. You have a lift pump to deliver fuel to the injector pump which then pressurizes it and sends it to the injectors.

I downloaded the workshop manual today, and you're correct, Steve. (But my comment that the injectors in Detroit diesel engines DO pressurize the fuel stands. I have no reason to believe that a very experienced truck mechanic would be incorrect on that one.)

There is indeed an injector pump, situated just beyond the lift pump and fuel filter, and driven by the camshaft.

If I was trying to figure this out, I would be looking at compression at this point. Does the engine turn over easily? If the engine sat for a period of time and this was your experience I believe the run away could have been caused by crank case oil getting past the rings. If it ran wide open while cold it could have further damaged the rings to the point that it is not getting enough compression to run on anything other than the starting fluid.

This might not be what you want to hear but it would be worth checking before you start to pull the fuel system apart.

Interesting. I know my truck mentor dude mentioned that sometimes runaway engines continue to run even after you shut off the fuel because they start burning the engine oil (yikes!). I don't believe that happened here, but I'll see if I can figure that out.

The engine turns over easily using the starter motor. I haven't tried to turn it manually. There are some manual decompression levers on this baby, and I should check that I didn't throw them in an attempt to stop the engine. I remember reaching for them, but believe I didn't actually activate them. But if I did, that could be my problem right there.

I'll see if I can borrow a diesel compression tester from someone.

[Queen Elvis]

So here's the latest on my engine woes.

Speaking with Trucker Diesel Dude today, he suggested that I look at the smoke, if any, when cranking the engine. For those of you that don't know – no smoke means no fuel is getting into the diesel cylinders. White smoke with a touch of gray indicates fuel is getting injected into the cylinders. And black smoke means a lot of fuel is getting through. Mine was white with grey, and this is the normal color when cranking this engine. As she starts, she emits a lot of black smoke, and quickly turns to no smoke.

So armed with the smoke knowledge, I felt that I was getting fuel.

So we cranked and fired her up using starting fluid. And kept her running for a minute. Maybe even two minutes. But nothing changed – as soon as we stopped the supply of starting fluid, the engine stopped.

Next, we did a quick compression test. The MD2B has compression release levers on top of each cylinder to facilitate hand starting the engine. Releasing the levers made the engine easy to hand-crank, and engaging them made it difficult. So that meant that I was getting at least some compression. Yeah, I know it's not testing for 240 – 300 lbs, or whatever the specs are, so this was only a quick and dirty test.

So I'm getting fuel. I'm getting compression. And there was no reason to suppose I wasn't getting air. The engine should start.

I tried again. No starting fluid. Just cranking with the starting fluid. And wouldn't you know it, she slowly rumbled to life. So perhaps I had air in the fuel lines, and the minute of running with starting fluid sucked the air out and got my fuel flowing properly again.

A word about starting fluid, or ether. If you don't have fuel being injected, prolonged use of starting fluid can damage your engine. I only did this to my engine because I'd done the smoke test first. Even so, I wasn't very comfortable.

Back to the story. The engine slowly starts running. And after a minute, I'm back right where I was – engine racing away. No throttle. No engine stop. This time, I shut her down by putting my hands over the air intakes, one per valve. How I'd stop a 3 or 4-cylinder engine with 2 hands, I have no idea. If you need to do this, I suggest you figure that out before firing up an engine that you know to be a racer!

But she shut down within a few seconds. A lot of sucking pressure on my hands, so be ready for that if you try this.

I happen to have a 2nd MD2B engine in my garage. (Well, who doesn't, after all!) So we started to take her apart to understand the fuel system. It's much easier to work in a garage rather than the cramped engine compartment. The flow is water separator to fuel lift pump to filter to injector pump to high-pressure lines to injectors, and return lines coming back to the filter.

But how was the fuel flow being controlled?

It turns out there's a slide on the injector pump, and this slide is attached to the throttle and engine shutoff cables. And the injector pump has pistons activated by the rotation of the crankshaft. As the crankshaft forces the piston up, the piston pressurizes the fuel and forces it along the brass (?) pressurized lines that go to the injectors. One line per injector.

Inside the injector pump, when you activate the slide, it is connected to the cylinder where the crankshaft piston sits, and a valve at the bottom of the cylinder can be seen to rotate.

My current bet is that either the slide is sticking, which isn't that likely because it's attached via a linkage, and the entire throttle mechanism feels smooth. Or more likely, something is sticking in the fuel-compression cylinders of the injector pump. The injector pump is constantly feeding full fuel, and adjusting the throttle has no effect because the piston just stays in the full-on position instead of moving with the throttle linkage.

I'll post further reports as I have them. And I hope my explanation is clear. And more importantly, that it's useful to someone one day.

I've attached a picture of the injector pump. You see the slider on it – this is what attaches to the throttle linkage. And you can see where the 2 pressurized fuel lines attach, at the top of the 2 crankshaft-driven pistons. At the other end of the pump from where the fuel lines attach is where the pump sits on the crankshaft. (The hex nut on the front of the pump is where the fuel supply line is attached to the pump.)

More later.....

mini-IMG_3817.JPG

[sharkbait]

A red shop rag dipped in gasoline and wrung as dry as possible then placed over the air intake filter is better than starter fluid. Generally will not cause piston slap. Up north in the cold country using a hair dryer to pre-heat the intake air filter will make for easy winter starting.

Be extremely careful about choking down a diesel engine with your hand. This time you got away with it but on a larger engine you could get hurt bad. Never attempt to hand choke a turbocharged engine. I have seen people lose fingers just working around an un-protected air intake.

[Queen Elvis]

Thanks for those tips, Sharkbait. It was indeed pretty scary having my hand over the air intakes. I was foolish enough to try it, but smart enough to know to use the flat of my hand and not my fingers. But even so......

I like the gasoline on a rag idea....

And the hair drier one, too. I don't know about winter starts, but it just might extend the season in November!

[Gary M]

OK QE

I think we've waited long enough.

What the heck is happening!

Gary