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In Reply to: John Deere 6506 engine problem posted by Eugene on Sunday, July 17, 2011:
Eugene ; just taking this situation at face value and with a few items not disclosed at this time, if the engine was sent in for a head gasket there was some symptoms to cause you to replace the head gasket.
Obviously you feel there was no problem with the horsepower before the head gasket was replaced, and I am sure someone just did not go in and replace the head gasket without other work being done to the head. Therefore your injectors could have been run on a pressure bench test and set for crack pressure and spray pattern but, human error could be involved where one injector could have been damaged upon assembly.
Does the tractor start easily ? Does the tractor idle smoothly at it's normal idle ? If the tractor starts easily and it idles smoothly then throttle it up with no load and see if the black smoke is a consistant air stream or intermittent puffs of black smoke.
Also does the tractor engine reach it's maximum hi idle or at wide open throttle ?
A diesel engine smokes when there is an excessive load on the hydraulic system like running a cylinder to the end and holding the loader control lever. I am curious though on how you have such accurate horsepower readings.
Horsepower is dependant on engine rpm and the dyno's I have used show engine horsepower @ a specific rpm and how they work is to flow fluid through resistance.
One horsepower will pump 1 gallon a minute @ 1500psi backpressure and will pump 1/2 gallon a minute @ 3000psi. So it is important to achieve that optimum rpm which is hi idle on a John Deere.
Anyway there are just a few things that cause your symptoms. One, there is a hydraulic resistance somewhere that has not been evident before causing low horsepower readings at the pto shaft.
Something in the air filter horn restricting the amount of air getting into the air intake system this would cause heavy black smoke also. A turbo not wanting to spin freely. Low delivery pressure at the injector nozzels, or crack pressure not correct on the injectors.
Check out the black smoke as you increase the engine rpm's and see if it's a real consistant smoke trail and watch carefully for the tails of blue or white as it disappears, write back if you need I am sure we can figure this one out.
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