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Old 13-08-2009, 18:53   #1
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Diesel Engine Backfires?

Every once a couple minute or so it seems my engine pops or backfires. Never heard a diesel backfire or make that noise before. It only seems to happen above 1600 RPMs not at low idle. It is a newish (70 hours) Volvo MD20. My Air filter is off, could that be the source? - no abnormal temps or pressures.
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Old 13-08-2009, 19:08   #2
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Do you have a waterlift muffler?

Does the water in the exhaust run out at a constant rate or does it build up and then shoot out?
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Old 13-08-2009, 19:15   #3
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NO not likly.. your injector pump timing could be off a hair...or you have a faulty nozzle.

Do the RPMs oscillate at high revs?
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Old 13-08-2009, 19:38   #4
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Didn't notice a rpm change/flux if it does it is very small. Its not the exhaust at least it doesn't seem like it. It is a very sharp pop or backfire but not a cough - can you tell we have reached the plateau of my diesel knowledge? it has been 10 years since I worked on one so I have forgotten so much! I have rebuilt VWs and tinkered with many a diesels cause I was the only one small enough to fit in the bilge so I know it will come back to me - please pardon the lack of knowledge. Saturday I will run it harder and see if he (engine is a he ) pops more or at the same rate.
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Old 13-08-2009, 21:18   #5
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Hi Erica..

Pump timing is best left to your mechanic as you have to synchronize the opining and closing of valves and its lash position to the timing marks..
Running it harder is not going to clear it up IMHO...it is not a carbon build up and some hot spot pre-igniting the fuel. It is a fuel delivery issue.

Does it happen less under load... then it does unloaded? My guess is it does.
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Old 13-08-2009, 21:27   #6
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Will I hurt the engine if I run it? I am moving OG to a new marina (better hurricane protection) this Saturday. It is less than a mile and all in protected waters so I can baby the engine.
Thanks David and stillraining for the help,
Erika
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Old 13-08-2009, 21:33   #7
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Hi Erica:

There are better qualified people than me togive you advice but after looking at the Caulder Bible for a couple of minutes it sounds like some type of fuel problem. Could be an injector starved for fuel or as some one else said a fuel pump timing problem. A way to track down the problem suggested by caulder is to loosen the injectors one at a time and see if the misfire continues or goes away. Good luck with it I am sure Cheif Engineer or someone else real clever will give you good advice. Let us know what you find out.
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Old 13-08-2009, 21:50   #8
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Hmmmmmmmmm....gotta put my thinking cap (OSHA APPROVED) on for this one
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Old 13-08-2009, 21:52   #9
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Quote:
Originally Posted by Chief Engineer View Post
Hmmmmmmmmm....gotta put my thinking cap (OSHA APPROVED) on for this one
This may not be for the weak of heart.
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Old 13-08-2009, 22:00   #10
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Its a sharp pop and seems to only happen above 14-1600 RPMs it never pops at idle.
Thanks you guys! Love this site
Erika
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Old 13-08-2009, 22:11   #11
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Well it isnt doing it a lot of good as it hammers the rod and main bearing on the wrong impulse but you should be ok your not crossing the Atlantic ..keep it below the RPM's you stated like you said to keep it at a minimum and get it checked out after your trip for sure...Im sure its one of the two causes I mentioned.

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Old 14-08-2009, 01:40   #12
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Have you checked that your rocker clearances are OK and you do not have a valve sticking intermittently? Regards, Richard
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Old 14-08-2009, 07:25   #13
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No, I haven't checked that but will...when I figure out how
Erika
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Old 14-08-2009, 09:16   #14
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sounds like a sticky valve or valve adjustment out
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Old 14-08-2009, 09:59   #15
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have you posted your issue on the Cape Dory board?? Lots of CD30 owners over there...

Best of luck
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