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  #11  
Old 04-10-2012
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Re: Why does my diesel not rev when in gear?

One item nobody has mentioned is the exhaust elbow. If a diesel will rev without load but not with load a clogged exhaust elbow is one of the most common causes. It is also the least expensive fix. Diesels need clean fuel, compression, and air - both in and out. A clogged elbow will restrict the revs as much as a clogged air intake and over a few years it is a common place for build up crud to cause a problem.

A barnacle covered prop will do the same.

As far as starting the batteries probably contribute to the problem, and may along with too small wiring and a bit of corrosion on connections be the bulk of the problem. I re-wired my Yanmar YSE-8 with new larger cables - 1/0 vs the original 4 awg - and my starting time went from about 15 seconds or more to about 5 seconds.
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Old 04-10-2012
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Re: Why does my diesel not rev when in gear?

I forgot to mention one other thing that sometimes contributes to not reving - plugged exhaust. I've not experienced it, but a friend suffered it last summer. It would restrict air flow effectively causing a super rich condition, which would be accompanied by black smoke or at least a very distinct diesel odor.
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Re: Why does my diesel not rev when in gear?

Check the tappet adjustment. Comments on blocked exhaust are relevant.

Also small engines idling for most of their life cause rings fouling.

If you have a clear exhaust and tappets adjusted, run the engine flatout tied to a dock for 8 hours to burn the rubbish out of the cylinder piston and rings. Cheapest service ever is to run flatout for a day and burn the rubbish out of the engine.

After the hot run give it an oil change.

If it won't run flatout for 8 hours tied to the dock then its not seaworthy.

Try to do it when the marina is empty, not on a Sunday afternoon.

Last edited by INMA; 04-10-2012 at 06:09 PM.
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Old 04-10-2012
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Re: Why does my diesel not rev when in gear?

Quote:
Originally Posted by INMA View Post

If it won't run flatout for 8 hours tied to the dock then its not seaworthy.

Sorry, gonna have to disagree with that statement, my sailboat has an AUXILIARY engine on it.

It might be more accurate to say that a Captain that can't sail his boat (without using the engine) in and out of a harbor/slip/mooring isn't seaworthy. Though I'd disagree with that statement as well.

Maybe you wanted to say the engine wouldn't be reliable, IDK.
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Re: Why does my diesel not rev when in gear?

Thanks for all the good input...following is additional info per various above suggestions:

I'll checkout the injectors (though not sure what they're supposed to look like dirty or clean)...
Yes, new batteries are in order although I'm not sure this has anything to do with the lack of reving in gear (and check the wire gauge/connections)...
I've checked for air leaks but not detected any (maybe they're too elusive for me)...
I'm on lake Texoma (in Texas) so no engine preheat...
Had the same engine/propr setup for the 6 yrs I've owned it so don't think that would be the problem...
I'll have to get the marina to do the compression check but it's probably worth doing...
I'll recheck the linkage...
It is am MD7B as stamped on the engine (maybe I'm wrong about the 13hp?)...
I've long suspected the tank could stand to be emptied/cleaned and filled with fresh fuel but not quite sure just how to do all that...
I'm in the process of changing filters and will check all that out...
I believe the exhaust to be black (never really understood the visual blue to look for) and I'll clean the filter (it's reusable type)...
The engines worked fine in past years but got progressively worse last summer and now has my attention...
When I say along time to start I'm talking 10-15-20 minutes (not seconds), when it does start it starts catching as I continue to crank until eventually it "catches up" and I can stop cranking, usually dies 2-3 times but restarts fairly quickly (10-20seconds)...after it gets up to temp it restarts for the remainder of the day as it should (but doesn't always rev in gear)...
Is it true you can't flood a diesel?
I'll check the governor (didn't know I had one)...
Replaced the exhaust elbow/water muffler last summer so do think that's clogged...

Thanks...
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Old 04-11-2012
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Re: Why does my diesel not rev when in gear?

"but got progressively worse last summer" "Replaced the exhaust elbow/water muffler last summer"

Check the exhaust since issues started when you put the new exhaust bits on. Did the exhaust installer check the back pressure after installation? Blocked exhaust causes excess soot which fouls the exhaust more.

If it has a glow plug check its working.
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Old 04-11-2012
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Re: Why does my diesel not rev when in gear?

Hello,

Considering how many possibilities there are, and your lack of experience, my suggestion is to find a mechanic.

Barry
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Re: Why does my diesel not rev when in gear?

That is an unbelievable amount of cranking.

Since you are not jumping at the idea of hiring a mechanic, I assume that you are cost sensitive. If this is the case, start with the stuff that you can easily do yourself for very little in parts costs. Check the throttle linkage and shutdown linkage again. Change your fuel filter and cut the old one open. Check your air filter. Check your exhaust hose visually by simply taking it off. I would also recommend cracking your fuel bleeder while cranking and seeing whether you get solid fuel or air and fuel.

Once you get through all of the visual checks, you want to make sure to start by doing tests that will tell you the most about the most likely culprits. Since you are not seeing blue smoke, a compression test would not be the first thing that I tried. The first thing that I would do is to check your fuel pressure. You can do this easily yourself with a gauge or you can get a mechanic to do it. If your fuel pressure is low (meaning <15psig), then you need to fix it before you do anything else. Low fuel pressure will cause many of the symptoms that you describe because the injectors fail to pop off. Next, I would check compression, again you either need a gauge or a mechanic. After that, I would think about pulling the injectors and testing them.
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Re: Why does my diesel not rev when in gear?

Perhaps your tank vent is plugged. Try it with the fuel filler cap removed. Probably too easy of a fix, but easy to do.

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Old 04-12-2012
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Re: Why does my diesel not rev when in gear?

This has to be a fuel system / throttle control problem.

When you said that you can put it in neutral and get it to rev up a little and then put it back in gear and it stays revved up whereas you can't put it in gear first and and then rev it up is the biggest piece of evidence that suggests there is some throttle / governor problem.

There's no need to check compression or starter speed or anything. It's not getting fuel! When starting it is taking a very long time to build up enough fuel at cranking speeds to do anything.

I think the governor may be built in with the injector pump, which is probably where all the problems are.

Last edited by steel; 04-12-2012 at 11:56 PM.
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