We had been underway for about two hours when the RPM on our 2QM15 slowly started to decrease. When we dropped into neutral the RPM went back to normal. After a minute we went back in forward and motored for another 15 minutes to our destination without any problem. Two days later on our way home we had been running for about 2 hours and the same thing happened. The RPM dropped, came back up when in neutral. However, this time when we went back in forward the RPM dropped after about 5 minutes of running. I tried reverse and the same RPM drop happened after about 30 seconds. We were able to get home (1.5 hours) by running at a lower RPM..about 75% of our normal cruising RPM. There was no trouble when running at the lower RPM. The first time I thought we might have picked up something on the prop or shaft but would it run OK for two hours and then have the RPM drop if it were a prop problem? Doesn't sound like a fuel problem since the RPM comes back up in neutral and runs OK at a lower RPM. The engine sounds great during this. Gears shifting is smooth, sounds good. Thanks for your ideas..
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Slipping shift lever
Is your shifter slipping? You may just need to tighten up some linkage(s). This happens to me all of the time. Andy
Is your shifter slipping? You may just need to tighten up some linkage(s). This happens to me all of the time. Andy
I'd bet your governer is having problems
Diesel engines don't have a throttle like gas engines. When you "set the throttle" on a diesel engine you are really telling the governer that you want to operate at xxx RPM. So when you shift out of gear the motor does not rev up like on a gas engine. The governer controls the flow of fuel to the engine to make it run at a constant speed. If you unload the engine without changing the throttle the governer just supplies less fuel and the engine maintaines a steady RPM. Sooooo, since you get an RPM drop without changing the throttle position I would suspect the fuel flow is being restricted to/from (there is a return line on diesels) the governer or the governer is malfunctioning. Since you say the RPM came back up after shifting into neutral (you unloaded the engine and the governer correctly gave you the RPM you set it at) I'd suspect the fuel flow is restricted. This is also supported by the fact that you can't reproduce the problem on demand. A governer will usually break and stay broken, a fuel restriction (filter or kinked line is my guess) will mess with your head as the filter randomly restricts the flow rate at random times. Also since you get this at full power or near it would also suggest that the filter is partally clogged but not enough to effect the flow at lower power and lower fuel flows. I'd replace the filters and check all the fuel lines to and from the engine and make sure it is not bad fuel before I started looking at tearing down the engine. Good luck
Diesel engines don't have a throttle like gas engines. When you "set the throttle" on a diesel engine you are really telling the governer that you want to operate at xxx RPM. So when you shift out of gear the motor does not rev up like on a gas engine. The governer controls the flow of fuel to the engine to make it run at a constant speed. If you unload the engine without changing the throttle the governer just supplies less fuel and the engine maintaines a steady RPM. Sooooo, since you get an RPM drop without changing the throttle position I would suspect the fuel flow is being restricted to/from (there is a return line on diesels) the governer or the governer is malfunctioning. Since you say the RPM came back up after shifting into neutral (you unloaded the engine and the governer correctly gave you the RPM you set it at) I'd suspect the fuel flow is restricted. This is also supported by the fact that you can't reproduce the problem on demand. A governer will usually break and stay broken, a fuel restriction (filter or kinked line is my guess) will mess with your head as the filter randomly restricts the flow rate at random times. Also since you get this at full power or near it would also suggest that the filter is partally clogged but not enough to effect the flow at lower power and lower fuel flows. I'd replace the filters and check all the fuel lines to and from the engine and make sure it is not bad fuel before I started looking at tearing down the engine. Good luck
check the vent for your fuel tank
open your fuel filler when this happens and see if your pulling a vacuum on the tank. You may have a blocked or restricted tank vent. Also change filters and seperators and check all your fuel lines for collapsing or kinking to eliminate the usual suspects.
open your fuel filler when this happens and see if your pulling a vacuum on the tank. You may have a blocked or restricted tank vent. Also change filters and seperators and check all your fuel lines for collapsing or kinking to eliminate the usual suspects.
try tightening the throttle lever
tighten the tension bolt in the pedestal for the throttle linkage.
tighten the tension bolt in the pedestal for the throttle linkage.
sounds like filters to me
When the engine is under load it burns more fuel. the engine runs fine for a while and then gradually starts to run a little short on fuel. You problem is more than likely dirty fuel filters. let us know what you find.
When the engine is under load it burns more fuel. the engine runs fine for a while and then gradually starts to run a little short on fuel. You problem is more than likely dirty fuel filters. let us know what you find.
Gas engine
Bill how would you respond to the question if it was a gas engine? I have an atomic 4, and I'm having the same problems.... a couple of times the engine just stops and want start back up until its cooled down... You would save me lots of $$$$ if you could answer my question.... Thanks, Katie
Bill how would you respond to the question if it was a gas engine? I have an atomic 4, and I'm having the same problems.... a couple of times the engine just stops and want start back up until its cooled down... You would save me lots of $$$$ if you could answer my question.... Thanks, Katie
Water in fuel
I had similar problem with my 1GM. Drained water from seperator solved problem. Change filter too!
I had similar problem with my 1GM. Drained water from seperator solved problem. Change filter too!
Prop shaft heat
Its probably something real simple so check those first (cable isn't slipping is it) But is there a chance??that you don't have enough water dripping through the stuffing box, its getting hot, and seizing up so as to smother the engine? Next time it happens, feel the shaft 'tween the tranny and stuffing box. Is it too hot to hold?
Its probably something real simple so check those first (cable isn't slipping is it) But is there a chance??that you don't have enough water dripping through the stuffing box, its getting hot, and seizing up so as to smother the engine? Next time it happens, feel the shaft 'tween the tranny and stuffing box. Is it too hot to hold?
Great suggestions..
Thanks to all of you for your suggestions. Looks like I'll start by taking a close look at the fuel system this weekend and hopefully see something that confirms the problem. Andy's comment about the stuffing box crossed my mind too. While the problem was occurring I did glance at the box and noted that it wasn't dripping; however that's not unprecedented but it hasn't been a problem before. I didn't take the next step of feeling it since it was in gear (duh). It's on the list for a weekend adjustment. Thanks again!
Thanks to all of you for your suggestions. Looks like I'll start by taking a close look at the fuel system this weekend and hopefully see something that confirms the problem. Andy's comment about the stuffing box crossed my mind too. While the problem was occurring I did glance at the box and noted that it wasn't dripping; however that's not unprecedented but it hasn't been a problem before. I didn't take the next step of feeling it since it was in gear (duh). It's on the list for a weekend adjustment. Thanks again!
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