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“Twas the night before Christmas and all through the shop, not an engine was smoking except that damn diesel.”

Sunday, December 1, 2013

This month’s article will cover basic troubleshooting methods for diagnosing any smoking diesel. First we should consider the difference between the mechanical workings of an LPG engine compared to diesel. The LPG engine revolves around air, fuel, compression and spark where the diesel requires only air, fuel and compression. The diesel’s higher compression creates the heat needed to ignite the diesel fuel. This explains why some diesels may smoke upon cold startup. The heat from the compression is absorbed into the cold engine block and does not completely ignite the fuel. Compression is critical to the operation of a diesel engine and should usually be around 300 to 450 psi. Refer to the engine’s service manual for exact specifications. The LPG engine has spark plugs, a distributor and an LP fuel system. The diesel has a more complex fuel system that revolves around an injection pump. Just as rotating the distributor advances or retards the timing, so does the twisting and turning of the injection pump. However for safety reasons, this should never be done while the engine is running. Alright, enough. Let’s troubleshoot that smoking diesel for the holidays.

Santa’s Smoking Diesel Checklist:
White Smoke – this is caused by the burning of coolant. You will actually be able to smell the coolant burning.
Causes
• Blown cylinder head gasket
• Warped cylinder head or engine block deck surface
• Cracked cylinder head or engine block

Black Smoke – this is caused by a rich fuel mixture (Either too much fuel or not enough air)
Causes
• Clogged air filter
• Injection pump out of adjustment (check the max fuel stop screw)
• Improper or contaminated fuel
• Faulty injector

Bluish White Smoke – incomplete combustion
Causes
• Low operating temperature (Check the thermostat)
• Faulty/Stuck open injector
• Low compression
• Early (advanced) fuel injection pump timing
• Injector lines crossed

Blue Smoke – burning oil
Causes
• Worn valve guides
• Worn piston rings or glazed cylinder walls

Quick diagnosis methods are pop testing the injectors to check for proper fuel spray. Both wet and dry compression tests to show any loss of compression and direct you towards either the valves or piston rings. If you believe the problem is in the fuel system you can check each cylinder by breaking loose the fuel lines one at a time and observe any change in the engines performance. The line that does not change performance is the cylinder with the problem. These simple tests will help direct you towards the cause of the problem and you can kickoff the New Year minus the smoke.

Maintenance is critical with a diesel engine. Diesels are traditionally operated in outdoor, dusty, and harsh environments. Your standard oil and filter change, fuel filter, and re-adjustment of the valves are all of the important components of routine maintenance. Be sure to address any over fueling problems immediately as it can wash the oil off of the cylinder walls and cause the cylinders to become glazed. It is also good practice to routinely inspect the air filtration system for punctures, cracks, and/or loose hoses. It is commonplace in the reman business to see dusted rings or dirt ingested diesel failures. A well designed diesel engine is one that has an efficient air filtration system. Word of caution, do not assume that an air filter is correct just because it came out of the engine last. Always check to ensure proper seal and fit of the air filter to avoid needing another reman engine this Easter. Like always, inexpensive maintenance can save thousands of dollars in the long run.

So although it’s a brief overview, this checklist may be all you need to help figure out why that damn diesel smokes. For any additional Tech Advice, feel free to give us a call at (877) 303-LIFT.

Thank you for your attention to TechTalk in 2013. Happy Holiday’s and Happy New Year! Talk to you next year!

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