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Carbon-izedPosted 4/14/2004By Criag Zuidema
"Who needs a dishwasher when you have kids?" was one of my mom's adages. As the youngest able-bodied kid, I was often beset with cleaning the pots and pans. One night while scrubbing, one of my elder siblings scolded me, "You shouldn't be complaining so much because that burned-on black is only carbon." "How would you know what carbon is?" I sneered. "Carbon is the same element as in pencils - pencil lead is soft." "Hmmph, it's about as soft as diamonds," I muttered into a Brillo pad. "Diamonds are carbon," she stated. "No way! They're the hardest thing ever!" "Diamond is an allotrope of carbon," she resounded. "Girls are so dumb! An allotrope has four legs and antlers and grazes on the prairie!" "No, that would be an antelope ..." And then she patiently explained as much inorganic chemistry as my sprout-like brain stem could absorb. Many years later I thought I had become quite a skilled auto technician. As a recertified ASE master tech, I worked at a dealership for rudely expensive European cars. One day a Maserati 228 came in as if on a mission to prove I wasn't using my knowledge of chemistry effectively. It had a misfire at light load, sometimes under boost, and just a general lack of power. The Marelli ignition and fuel injection systems were thoroughly grilled, using brand-new factory test equipment. A compression test revealed a weak right bank of the bi-turbo V-6 engine. Valve timing and clearance were of course verified, and no intake or exhaust restriction could be found. The decision was made to pull the cylinder heads, exposing not burned valves or scored cylinders, but a powder-thick coating of brownish-black soot covering everything in the combustion passage. After cleaning everything thoroughly and soaking the cylinders with a solvent-type cleaner to loosen the carbon-bound rings, the motor was reassembled and reset. The result was a smooth and snappy, responsive engine that idled like a watch and happily smoked the tires when the turbos hit maximum boost at WOT. But when I realized that three days of work could have been avoided by a decarbonization, an oil change, and a 20-mile drive on the freeway, the satisfaction of the repair was lost. Carbon can bind piston rings in their grooves, preventing an effective cylinder seal, which in turn can cause a loss of intake vacuum, compression and power. It can accumulate on valve stems and seats, causing them to stick and not seal. It can bind throttle plates and set false codes, illuminating the MIL. It can accumulate so heavily in the combustion chamber as to cause preignition and set false knock sensor codes, retarding the timing. It can also restrict intake manifold passages - causing a loss of airflow and power, as the following demonstrates. A caller was battling a loss of power on a Volkswagen TDI diesel. The engine had been scanned; no codes were stored. After replacing the filters, fuel volume checked OK. The glow system was functioning normally, and the mass airflow sensor and the powertrain control module had been swapped from a matching, good-running vehicle. The turbo was checked for excessive play, and a boost test was acceptable with maximum pressure achieved within specs. After replacing a stuck-open thermostat and cleaning a plugged intake screen under the air filter, the technician thought he had a fix, but the VW was still gutless. A VW-compatible scanner was used to verify the injection pump timing. Finally, the tech used a smoke machine to check for leaks in the intake system and found smoke leaking from a flange on the EGR cooler pipe. When he inspected the EGR valve, he found it was completely blocked with carbon and soot. The intake manifold was removed and cleaned, and the intake ports were cleaned with the head installed. The reassembly was simple. Now the TDI had the fuel economy for which it is renowned and the power was respectable. Automobile engines are developed and tested under excruciating conditions of abuse. All of the maintenance you are able to do sometimes can't recover them from the misuse done by neglectful, indifferent car owners; so different maintenance procedures are needed. Throttle body cleaning should be on your tuneup list even if not specifically called for in a maintenance list. A maintenance procedure on an engine with 90,000 miles or more should include a decarbonizing flush or combustion chamber cleaning. Engines running on an extended oil change interval should use synthetic oil only, with the best quality filters available. Any vehicle driven in the USA requires a "severe" service program. If you need a better understanding of the importance of those maintenance procedures, just imagine the cylinder walls and valve stems being ground away by diamonds. Using additional "clean engine" procedures in your maintenance procedures can add to the repair time so you may have to charge a little more. The payoff is that it should help your customers' vehicles last longer and prevent worrisome problems.
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Copyright (c) 1996-2009. Automotive Service Association®. All rights reserved.
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