CD 31 diesel engine problems

[len]

my universal M25 diesel has the following symptoms, ? thoughts re diagnosis, further tests, and treatment:

1. when cold it never starts on the first try
2. it always starts after a few tries
3. when warm it starts on the first try
4. when cold, on the first few tries, although it doesn't start, it makes a few revolutions, and it does disengage the starter
5. when cold, on the first few tries, it runs very rough for the short time it goes on its own, and then it dies
6. once running, it is completely smooth within 30 seconds and runs perfectly, idling at less than 1000 RPM - (boat is still on hard so i don't know how it does with a load yet)

thanks in advance

len



md.frel@nwh.org

[Tom]

my universal M25 diesel has the following symptoms, ? thoughts re diagnosis, further tests, and treatment:

1. when cold it never starts on the first try
2. it always starts after a few tries
3. when warm it starts on the first try
4. when cold, on the first few tries, although it doesn't start, it makes a few revolutions, and it does disengage the starter
5. when cold, on the first few tries, it runs very rough for the short time it goes on its own, and then it dies
6. once running, it is completely smooth within 30 seconds and runs perfectly, idling at less than 1000 RPM - (boat is still on hard so i don't know how it does with a load yet)

thanks in advance

len

Len,

I'm guessing from a long way away, but my first inclination is to say bad glow plugs or the system that feeds them. Look at it this way - what would be ths symptoms if you didn't use the glow plugs? First of all, it would be hard to start. As you turn the engine over the pistons compressing the air in the cylinder would heat it up a little bit but not like having a real pre-warming via glow plugs. A partially heated cylinder would finally fire but it would run crappy for a little while until it warmed up a little bit, then it would run fine. Once the engine was already hot from running, you wouldn't need the glow plugs for pre-warming and thus it would start fine after being warm. Once it warmed up it would continue to run fine because glow plugs are only for starting. These certainly sound like the symptoms you describe.

Glow plugs do wear out, just like sparkplugs. And of course you can have a break in the wire between the glow plug button and the glow plug also. Or you could have corrosion on the wires at the glow plugs that don't let full current through. Or you could have dirty battery cables that don't let full voltage get to the plugs. (Although if that were the case it probably wouldn't crank right either.) Or you could have a bad glow plug switch. This switch is carrying a lot of current and tends to carbon up and not make good contact.

You can eliminate the switch by putting a jumper cable around it. As I recall it just has two lugs on the backside inside the starboard cockpit locker. Make up a little wire with alligator clips on both ends and clip onto both lugs (the classic "hot wire" of car thieves). Here again I doubt this is it because if it were, I don't think it would crank right either since the cranking current has to go through this switch also.

More likely it is bad glow plugs. As I recall these are wired in series so that if the first one shorts out it kills the juice to the following two. I'd take a voltmeter and check the voltage to the first glow plug, with somone holding the button for you or with a jumper cable attached. I'm 100 miles from my boat, but as I recall the forward plug is the first in line. Then check the second in line and see if the current is getting through to #2 etc. Voltage won't tell you everything, what you'd really like to know is amperage, but you're not likely to have the meter to measure that. If there is no voltage on numbers two and three though that will certainly tell you something.

If all the connections are bright and all the glow plugs are working then you might have a bad head gasket that is letting water into a cylinder. The water puts out the explosion in the cylinder and makes it run rough until it builds up enough pressure to hold back the water and it gets hot enough to turn the water into steam. Or you might have a cracked head which creates the same situation. If you get white smoke out the exhaust after it starts but before it smooths out that's a bad sign because it could be water being turned into steam. At that point it's time to call in the pros.

I am not a mechanic. I'm just giving you some possibilities to consider which I've learned in the school of hard knocks. These engines are not hard to start when they are right and normally kick off immediately. Any real mechanic with the equipment can check the glow plugs for you in very short order so it shouldn't cost much to eliminate them as a possibility.

Just my input but remember I am not a mechanic so none of this should be chiseled in stone. Good luck and let us know what you find. That's what this board is so great at doing.



TomCambria@mindspring.com