Foreign Service

Motor, Dec 2004 by Marinucci, Dan

The diesel engine's reputation for reliability may cause owners to neglect maintenance work. Dan explains what to do when VW diesel performance takes a nosedive.

Last month I stressed that throttle housing service is as important on foreign vehicles as it is on domestics. This time I'll delve into a contamination issue that literally goes deeper than the throttle blade and afflicts a specific family of foreign cars. Both dealer technicians and independent Volkswagen specialists report that thick, carbonlike deposits are occurring inside the intake manifolds of turbocharged 1.9L diesel engines in the Jetta and Beetle. Although the condition has occurred in 1998-2003 em's, it seems to be most prevalent in the '99 to '01 models.

Common symptoms are sluggish acceleration and an overall lack of power. Performance is so poor that many people assume the turhocharger has failed. Sometimes the manifold is so restricted the engine will harely run. Sources attribute the deposits to the EGR system, crankcase ventilation system, inadequate maintenance and poor-quality fuel. Plus, short-trip driving aggravates the condition.

The accompanying photos, which illustrate a typical restricted manifold on a 1.9L diesel, come courtesy of Steve Poole at Tom Dwyer Automotive Service in Portland, Oregon. Photo 1 at right shows the overall layout of the intake manifold, EGR valve, EGR cooler and EGR supply tube. If you know diesel fundamentals, you realize that a diesel engine doesn't have a throttle blade. Here, the EGR valve assembly is located where the throttle housing would be on a traditional gasoline engine. Therefore, all the air entering this VW diesel flows through the EGR valve assembly.

Diagnosing a restricted intake system on this VW diesel requires nothing more than removing the air duct from the EGR assembly and shining a bright light into it. Photo 2 shows what you're likely to see. At this point, you'll wonder how die engine ran as well as it did. Unfortunately, that's just the beginning because the intake manifold itself will also be loaded with that black crud (photo 3 below). Last but not least, the accordion-shaped EGR supply tube is usually severely contaminated, too. The bottom line is that you may have several hours of cleaning time ahead of you.

At European Autowerks Inc. in Kissimmee, Florida, VW ace Angelo Campana has serviced his share of these 1.9L diesels. The first thing Campana emphasi/es is that these carbon deposits can be very stubborn. For instance, dipping the enlire inlake manifold in carburetor cleaner, decarbonizer or solvent is usually worthwhile. However, a successful soak job could range from 90 minutes to overnight, depending upon the chemical you're using.

Secondly, Campana warns that soaking may not dissolve all the deposits. You may end up chiseling out the remainder of the carbon or attacking it with a bead blaster. Bead blasting is extremely effective and relatively fast. But you must thoroughly scrub and flush out the manifold afterward to be sure there's no blasting media left inside it. Third, cleaning the EGR supply tube on these engines usually requires the same measures as cleaning the intake manifold.

Fourth, as I have already shown you, the EGR valve assembly is usually carboned up pretty badly. But because its vacuum diaphragm isn't removable, you can't dunk the entire thing in cleaning solution. However, you still have to clean the throat of the assembly as well as the EGR piston that's shown in photo 4. Campana explains that this is another area where sensible bead blasting is the fastest, most effective way to clean. While you're at it, remember to retract the EGR piston by applying vacuum Io the EGR diaphragm with a hand-held vacuum pump. Then carefully wash off the head-blasted areas of the EGR assembly with throttle-housing spray cleaner and a small brush.

Fifth, Gampana reassembles everything, warms up the engine and gives it two chemical treatments followed by a vigorous road test. By the time this car has reached his shop, you see, it's usually due for some serious maintenance work. So he cleans the injectors by running the engine on a reservoir containing several cans' worth of LUBROMOLY LM2005 Diesel Purge (www.olyonline.com/Lubro moly.asp). Then he uses a refillable, air-powered sprayer to "mist" or "log" a can of BG Induction System Cleaner (No. 21.1. decarbonizer) directly into the engine. This step may remind some techs of the old days when they slowly led a can of Delcos X66 right down the throat of the carburetor. The engine may smoke and belch at first, but it'll run so much better when you're finished!

Alter these treatments, Campana puts that diesel through some full-throttle sprints before returning it to the customer. Unfortunately, many of these Jetta or Beetle diesels aren't exercised on the open road nearly as often as they should be, he says.

Last but not least, Campana recommends running a can of BG's 211 or an equivalent decarbonizer straight through the intake manifold as described earlier, and doing it at least every 30,000 miles. Also, urge your diesel-driving customers to buy fuel from a reputable, high-volume fuel station and to insist on fuel with a cetane rating no less than 45.