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Author Topic: Help! 6V71 suddenly producing more smoke and less power.  (Read 1721 times)
Craig R
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« on: September 09, 2006, 10:08:19 PM »

My MC5c with a 6V71, up-sized injectors, Jake brake and Alison automatic began misbehaving recently. When the wife and I set out for a few days exploring over hill and dale the rig blew an embarrassing amount of black smoke if asked to climb even the gentlest grade or to accelerate even modestly and it had noticeably less power than I had remembered. When last driven any significant distance a few months ago we had neither of these problems. Since arriving home I have coincidently removed the lower housings from each of my three air cleaners and have found something peculiar (which may or may not be related); there was a large collection of water in the bottom of one while the other two were bone dry.
A diesel mechanic I found in the yellow pages (on Labor Day) declared the 6V71 a very simple beast and stated that he could think of no reason for such a precipitous change (after offering, “sounds like it’s just getting old).
How important is it to seek out a “bus mechanic” for engine work when you can instead of a “diesel mechanic” -- or even a “marine diesel mechanic” when in an isolated coastal community? I am within 100 miles of Southern Oregon Diesel but the passes between the Rogue River Valley and the Umpqua Valley seem daunting with such a misbehaving engine.
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TomC
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« Reply #1 on: September 09, 2006, 10:17:00 PM »

Craig- what size injectors are you running? I have an 8V-71N with N65 brown tag injectors that will make the engine smoke at anything much above sea level.  If you have 70 or larger injectors in a non turbo engine, it'll smoke almost all the time with full throttle.  Get above 4,000ft and you'll be really smoking.  This is why I am having a turbo installed and just increasing the injectors to 7G70's.  If you can effieciently burn all the fuel you're injecting (translated no smoke) then you'll have the most power along with the best fuel economy possible.  As far as your smoking, try running for a short distance on a clean road (no dust) with the air cleaner off and see if it still smokes.  That'll get your answer.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Happycampersrus
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« Reply #2 on: September 10, 2006, 04:41:21 AM »

If your air filters are the paper element type and they got wet, that is most likely the cause of your troubles. Wink

After the element gets wet it causes an air restriction condition that will cause the black smoke you are seeeing. Cool


Dale


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Beatenbo
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« Reply #3 on: September 10, 2006, 08:12:59 PM »

If you have ANY water getting into air filter find imediatellyl.  I had just rebuilt an 8V71 in a 4106 years ago and in about 5,000 it went to puffing smoke.. Pulling the bottom head we found the 2 center pistons gualded. There was water seeping the the back panel that had replaced rear window and a few drops of water was findind the easist point beeing the 2 lower middle. A small amount of water will compress along with the firing and cause excess compression on that cylinder creating stress. Detroit 2 cycle cannot deal with water. Hope your engines not broke. Blessings
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Craig R
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« Reply #4 on: September 12, 2006, 07:14:21 AM »

Although I don't know the size of my injectors, TomC, the fact that I have not had this problem until now suggests that's not the problem. Right?

Other than track down how the water got into the air cleaner (any ideas, guys/gals?) how should I proceed, Beatenbo; are there things I should avoid or precautions I should take to prevent damage in the immediate future?

Craig R
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Beatenbo
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« Reply #5 on: September 12, 2006, 10:40:05 AM »

Don't know if you have dry or oil bath. Just make sure water doesn't pass into blower on to cylinders.
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Dallas
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« Reply #6 on: September 12, 2006, 12:26:17 PM »

My MC5c with a 6V71, up-sized injectors, Jake brake and Alison automatic began misbehaving recently. When the wife and I set out for a few days exploring over hill and dale the rig blew an embarrassing amount of black smoke if asked to climb even the gentlest grade or to accelerate even modestly and it had noticeably less power than I had remembered. When last driven any significant distance a few months ago we had neither of these problems. Since arriving home I have coincidently removed the lower housings from each of my three air cleaners and have found something peculiar (which may or may not be related); there was a large collection of water in the bottom of one while the other two were bone dry.
A diesel mechanic I found in the yellow pages (on Labor Day) declared the 6V71 a very simple beast and stated that he could think of no reason for such a precipitous change (after offering, “sounds like it’s just getting old).
How important is it to seek out a “bus mechanic” for engine work when you can instead of a “diesel mechanic” -- or even a “marine diesel mechanic” when in an isolated coastal community? I am within 100 miles of Southern Oregon Diesel but the passes between the Rogue River Valley and the Umpqua Valley seem daunting with such a misbehaving engine.

Craig,
Just to stick my pair of pennies worth in here, it sounds as if you've lost an injector tip, or you hav an injector that has frozen.

Pull the rocker cover and manually pull the rack to the full open position, checking to see if any of the injectors are hanging. I would also check to see if there is a broken injector actuator somewhere along the line.
If that isn't the problem, check to make sure you have air going through the engine... remove the air cleaner to blower tube and see if the smoke clears up. If it does, I'd look for a plugged intake, not just a single air cleaner that is plugged. It's amazing how the squirrels and rats can make homes in the weirdest places.

If none of the above finds the problem, you may need to pull the injectors one by one. It is very possible you have lost a tip from an injector, which is just throwing raw fuel into the cylinder. A possibly asy way to find the problem is to loosen the exhaust manifolds and find which port is wet. If you find one, thast is a bad injector or operating parts.
If you have more than one it could be the same thing.
If all of the ports are wet, Check the intake again and start looking for other reasons.

IHTH

Dallas
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akroyaleagle
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« Reply #7 on: September 12, 2006, 01:47:11 PM »

My first action would be to change the fuel filters. One of them may be collapsing under power.

Happened to me once. Went through the whole diagnostic process with more than one shop until a mechanic friend in Florida changed the filters. You could hear something in one filter when shaking it. Cut it open an voila!

Let us know how this turns out.
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Joe Laird
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Huron, South Dakota
Craig R
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« Reply #8 on: September 13, 2006, 07:16:30 AM »

Regarding injector malfunction, Dallas, if one were to monitor the temperature of each exhaust port by laying hands on appropriate places on the manifolds directly after fire-up (before heat is conducted throughout the manifold) might they get the same information as from loosening the manifolds and examining the ports. I seem to recall that a "cold jug" could be detected on my old VW by this method way back when.

Loss of power makes sense with a collapsed fuel filter, Joe, but did you also experience the increase in exhaust smoke?

Beatenbo, my air filters are dry -- when they're not saturated with water.

Thanks for all the insight, guys.

Craig R
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Dallas
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« Reply #9 on: September 13, 2006, 07:34:52 AM »

Craig, yes you can use the touch it method, but it also may be firing intermittantly, which will heat the manifold quickly.

I also wasn't sure how accesible your manifolds are to be putting your hands in while the engine is running. I'm not conversant with the MC5 setup. (Although I probably will be by the time NCbob leaves after the rally)!!

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Busted Knuckle
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« Reply #10 on: September 13, 2006, 07:41:07 AM »

Craig, yes you can use the touch it method, but it also may be firing intermittantly, which will heat the manifold quickly.
I also wasn't sure how accesible your manifolds are to be putting your hands in while the engine is running. I'm not conversant with the MC5 setup. (Although I probably will be by the time NCbob leaves after the rally)!!

Dallas you might be, but if my memorie serves me correctly Bob's is a "HOT ROD" with an 8V71 and jakes! Might not be quite the sme animule anymore! FWIW BK  Grin
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Busted Knuckle aka Bryce Gaston
KY Lakeside Travel's Busted Knuckle Garage
Huntingdon, TN 12 minutes N of I-40 @ exit 108
www.kylakesidetravel.net

Grin Keep SMILING it makes people wonder what yer up to! Grin (at least thats what momma always told me! Grin)
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