Blue smoke from exhaust on startup of 751

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bobbie-g

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Mar 15, 2004
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When my 751 (Peugeot deisel engine) is cold (first start of the day, perhaps 55 or 60 degrees F) it does not want to start immediately, but coughs and spits out blue smoke from the exhaust. Catches in 2 to 3 seconds and begins to run, then continues with blue smoke for a couple of minutes until it seems to warm up a bit. Then occasionally it misses and puts out a puff of blue smoke, until completely warmed up in about 5 to 10 minutes. Later starts during the day seem normal (starts up immediately with no blue smoke). No misses under load, and seems to run fine when warmed up. I believe the problem just started after the fuel injector pump replacement. Is it possible it has been set up to run too rich? I don't really care all that much about the smoke, except I'm not sure what action to take if it one day fails to start. Tnx --- Bob
 

StuZ

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Nov 22, 2003
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Did they test and adjust the injectors when the changed the pump ? Sometimes you will get a nozzle that won't seat good, and over a few hours drops of fuel will leak down into the cylinders, causing both smoke until it is burnt out, and a slight miss till the pump replaces the fuel that has leaked into the clyinder. Case 2 would be the valve seals. Over night the oil will leak down through the valve guide and into the cylinder, causing smoke until it burns out. I would have to look to see if the Peugeot even has valve seals or not. If that is the case, the valve guides would have to be replaced.
 

Tazza

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Did they test and adjust the injectors when the changed the pump ? Sometimes you will get a nozzle that won't seat good, and over a few hours drops of fuel will leak down into the cylinders, causing both smoke until it is burnt out, and a slight miss till the pump replaces the fuel that has leaked into the clyinder. Case 2 would be the valve seals. Over night the oil will leak down through the valve guide and into the cylinder, causing smoke until it burns out. I would have to look to see if the Peugeot even has valve seals or not. If that is the case, the valve guides would have to be replaced.
I too would suspect valve stem seals, blue smoke indicates burning engine oil. If it was diesel fuel it would burn black if it was rich. Over fueling will puff black smoke (or blocked air filter), un-burnt fuel blows white smoke, burning engine oil will puff blue smoke.

As StuZ says, worn or hard valve stem seals will leak engine oil down into the cylinder over night causing excessive smoke at start up that will continue until it has all been burnt out.

It shouldn't cause the engine to miss while warm, as the amount of oil leaking down shouldn't do anything but blow a small amount of blue smoke.
 

bobbie-g

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Mar 15, 2004
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576
I too would suspect valve stem seals, blue smoke indicates burning engine oil. If it was diesel fuel it would burn black if it was rich. Over fueling will puff black smoke (or blocked air filter), un-burnt fuel blows white smoke, burning engine oil will puff blue smoke.

As StuZ says, worn or hard valve stem seals will leak engine oil down into the cylinder over night causing excessive smoke at start up that will continue until it has all been burnt out.

It shouldn't cause the engine to miss while warm, as the amount of oil leaking down shouldn't do anything but blow a small amount of blue smoke.
Thanks, StuZ and Tazza. It still seems this problem started just when the fuel pump was replaced, but perhaps it is not actually related. The dealer told me today it was probably just running a bit rich at the higher altitude (8000 ft now vs the 5000 ft where the work was done), but that seems like it would produce black sooty smoke. His advice was to just use the block heater so it would not get too cold. We shall see how this turns out. I do have what are probably leaky valve seals on my gasoline pickup (140K miles) and I get blue smoke for about 2 to 3 seconds on startup. The Bobcat puts out blue smoke for 2 or 3 minutes when cold, seems a bit too long for leaky valve seals. Another Bobcat person said it was perhaps worn pistons/rings, and after a few minutes the pistons warmed up, expanded, and helped seal to the cylinders better. Seems plausible. As long as it starts OK and runs well, I'm not inclined to do much to it. Tnx again for the advice and info. ---Bob
 
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