Those of us who maintain our own vehicles know that a task like changing spark plugs can sometimes be complicated. In the July 2014 issue of Design News, an article by Bradley Miller describes the effort he put into changing the plugs of a 4.0-liter V-6 engine in a 2002 Ford Explorer. Design News readers have commented about having to lift engines or make holes in the car body to change spark plugs.
This article describes a particularly frustrating spark plug issue with the 2004-2008 Ford 4.6-liter, 5.4-liter, and 6.8-liter 3-valve “modular” engines.
Ford modular engines have come in many different varieties: 4.6-liter, 5.0-liter, 5.2-liter, 5.4-liter, and 5.8-liter (V-8) and 6.8-liter (V-10) displacements, cast iron or aluminum block, and 2-, 3-, and 4-valve versions. The engines have been produced since 1991 and have been marketed under the Triton, InTech, Coyote, Voodoo, and Trinity names. The term “modular” refers to modular manufacturing cells, not that the engines are composed of modules. Some engines are referred to as “Romeo” engines, but the Romeo, Mich. engine plant is not the only location where these engines have been assembled.
MORE FROM DESIGN NEWS: Unsafe Stove Has Owner Seeing Red
The Ford modular engines have had their share of spark plug issues. One of the issues was stripped or missing threads in the spark plug holes of 4.6-liter, 5.4-liter, and 6.8-liter 2-valve engines. Another issue is what Ford refers to as “difficulty with spark plug removal” from 4.6-liter, 5.4-liter, and 6.8-liter 3-valve engines.
My 2006 Ford Explorer, which is equipped with a 4.6-liter 3-valve engine, was misfiring and had more than 90,000 miles on the original spark plugs, so I decided to change the plugs. I was aware of the spark plug removal issue, and had read Ford’s removal procedure in Technical Service Bulletin (TSB) 08-7-6.
Because this engine is an overhead-cam one, and each spark plug is centered between the three valves, the spark plugs are installed in deep holes and have a long reach. The spark plugs were made with two-piece shells: the upper piece has the wrench hex and threads, and the bottom piece is a smooth tube that extends the reach of the plug down to the combustion chamber. After the spark plugs have been in the engine for a while, carbon deposits form around the spark plug tube, between the spark plug and the cylinder head. The carbon causes the lower half of the spark-plug shell to stick in the head and separate from the upper shell when the spark plug is turned for removal.
MORE FROM DESIGN NEWS: Tricky Spark Plugs Take Hours to Replace
The recommended procedure is to first let the engine cool, because removing plugs from a hot engine increases the likelihood of thread damage. This is because the strength of the aluminum is lower at elevated temperatures, making it more susceptible to galling. The next step is to loosen the spark plugs slightly, then add carburetor cleaner to the spark plug holes so that it soaks in and loosens the carbon deposits. After soaking, the spark plugs are alternately tightened and loosened as they are unscrewed from the cylinder head.
Despite following the Ford procedure, I still broke three out of eight spark plugs while removing them. Ford expects that some of the plugs will break during removal, even when their procedure is followed, so they provide instructions in the TSB for removal of the broken plugs. The plugs can break in one of three modes:
- The lower portion (tube) of the shell remains in the head, and the rest of the plug comes out.
- The entire porcelain insulator and lower portion of the shell remain in the head.
- The upper section of the porcelain breaks off, leaving part of the porcelain in the head with the lower portion of the shell.
MORE FROM DESIGN NEWS: Microwave Has a Bad Connection
Special tools are available for removing the spark plug fragments from the head. The Ford procedure for removing the porcelain involves bonding a pin into the porcelain using Loctite 638 Retaining Compound, and then pulling the porcelain out with the pin. The empty shell is removed by threading its ID, then using a threaded rod to pull it out.
Because I did not have the special tools for removing the mode-3 broken plugs, and I had to return the vehicle to service the next day, I had it towed to a Ford dealer. I reasoned that the mechanics at the Ford dealer have undoubtedly had considerable experience removing broken spark plugs from 3-valve modular engines. The towing was $110.50, the eight new spark plugs cost $104.72, and the Ford dealer charged $323.68 for broken-plug removal labor. The grand total was $538.90, a high price to pay for a spark plug change.
MORE FROM DESIGN NEWS: Writers Are Getting 3D Printing Wrong
Warranty coverage? No. The warranty expired at 36,000 miles, and the spark plugs are not normally replaced until 100,000 miles. If there had been a specific reason (other than customer request) to change plugs while the vehicle was under warranty, then removal of broken plugs would have been covered.
Some readers may remember the infamous Ford Thick Film Ignition (TFI) module failures. Some 22 million vehicles, made from 1983 through 1995, had TFI ignition modules mounted on the distributor, one of the hottest places on the engine, to save money. The TFI modules were susceptible to failure when they got too hot, causing the engine to suddenly run roughly or stall. It took a class action lawsuit to convince Ford to extend warranty coverage on the ignition modules to 100,000 miles.
Tell us your experiences with monkey-designed products. Send stories to Jennifer Campbell for Made by Monkeys.