Auto Service Professional

APR 2018

Magazine for the auto service professional

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22 | ASP April 2018 Technical combustion chamber, so you must replace the seal. A special tool is needed to install a new injector compression seal. ere are some common problems on these GDI systems that have started to surface. Number one is carbon buildup on the tip of the injector causing a reduced and distorted injector spray pattern resulting in a lean density misfire. e number two problem is carbon deposit buildup in the combustion chamber which can raise the compression ratio and can glow red hot causing spark knock. Most modern GDI systems will retard spark timing per cyl- inder in the event that detonation is detected from individual cylinders. On GM systems you will have scan data for this problem from each individual cylinder. e third most common problem involves carbon buildup on the back of the intake valves. Remember, we no longer have the solvent effect from fuel pulsed to the back side of the intake valves. is problem is caused by crankcase fumes from vaporized oil molecules sucked through the PCV system. Synthetic or semi synthetic oils reduce this possibility. Of course, we all have customers who neglect the recommended oil change intervals and the recommended specific type of oil. e fourth problem becomes more serious, with carbon deposit buildup in the top com- pression ring land of the piston. is prevents the top compression ring from expanding, resulting in blow-by and loss of compression. In my opinion, these problems can be adequately addressed by an extended chemical soaking. e idea here is to allow an extended soaking period, as in overnight, to allow the chemical to break the molecular bonding of the carbon. Obviously, this will not remove all deposits, but by giving it an extended soaking period it will produce an improvement. For more info on this you may want to visit BGs website at e BG people sell a three-can kit where one can is used to clean the injectors through the rail. e chemical known as 44K is sprayed through the intake to address the carbon buildup on the back of the valves. In extreme cases it will be neces- sary to remove the intake manifold's upper plenum. Half of the intake valves will be closed. A few ounces of 44K are applied to the back of these intake valves. A minimum 15 minutes of soak time is needed. e kit comes with large wooden toothpicks to punch at the carbon and break it up. In addition, a wire brush is also supplied to scrub the back of the intake valves. All of this can be viewed on BG's website. With the number of these vehicles increas- ing every year, these systems are going to come into your shop with some of these common problems. As it goes in our industry, "Show me a problem and I will show you an opportunity." ■ Figure 5: Example of a GDI application. Notice the injector exposed to the combustion chamber between the two intake valves. Bill Fulton is the author of Mitch- ell's Advanced Engine Performance Diagnostics and Advanced Engine Diagnos t ics manuals. He is also the author of several lab scope and drivability manuals. He is a certified Master Technician with over 30 years of training and R&D experience. He currently owns and operates Ohio Automotive Technology, which is an automotive repair and research development center.

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