Category: Tech-News

Yet, another deteriorated wire harness on this clean one owner 1995 Mercedes 600SL (SL600) V12 with only 49,000 miles. We replaced the upper engine fuel injection harness, The lower engine harness (Starter, alternator, oil level sender, etc.) We re-wired the main body harness (also called body mounted engine harness) with new air mass meter wire harness connected all the way back to both engine computers, and we rebuilt both throttle actuators.

I recently observed a factory Mercedes webinar for the complex problem of diagnosing and repairing Mercedes SCR systems for diesel cars and trucks and Mercedes Sprinter vans. We put this knowledge to use today for repairing a 2010 Sprinter van with an SCR problem.

SCR stands for Selective Catalytic Reduction and the vehicles that have it are usually labeled or badged ”BlueTec” It is the environmentally-friendly diesel technology from Mercedes Benz used to reduce emission levels. BlueTec uses Urea or diesel emissions fluid injection into exhaust gas stream in specially designed chambers in the exhaust to reduce emissions, especially NOx (oxides of Nitrogen).

The factory scan tool can be misleading and it is common for technicians to misdiagnose the system and change expensive parts needlessly. This fairly new technology uses the Mercedes SD connect to connect directly to the high-speed chassis CAN network of the vehicle. This allows monitoring of the raw sensor data and non-calculated information for precise diagnosis. The factory Xentry scanner cannot display and process this information the way this specially designed package can. On this vehicle we discovered a slight difference in the NOx sensor readings between the front and rear sensor and this led to diagnosing a faulty front NOx sensor. These sensors are around $600 at the time of this article but this is still way cheaper than if it was misdiagnosed as an SCR failure (currently $3700).

At Autobahn Performance we can sometimes save money and time for our customers by repairing cracked or cold solder joints. Manufactures seem to use too little solder on some joints with high current/heat. The solder tends to crack over time. Our certified mechanics are experienced at repairing these circuits. Here’s an image of a recent circuit repair.

At Autobahn Performance in Ft. Lauderdale Florida we have done hundreds of timing belt services on Audis. We see some shops replace the belt but neglect to replace the belt tensioner, roller, or water pump. Failure of any of these components can cause the belt to break, causing major internal engine damage. Most Audi engines are interference engines and will break and bend valves if the timing belt breaks. At Autobahn Performance in Oakland Park (north Ft. Lauderdale), we use only high-quality replacement parts and dealer-trained technicians to perform a timing belt service on your vehicle.

Belt replacement intervals change year to year and model to model. The belts are made of rubber and will deteriorate regardless of the miles put on them. It is even worse for a belt to be rarely used than if it were to be used regularly. Timing belts should be replaced every 5 to 8 years, even if the vehicle has low mileage.

We are working on a 2008 Porsche Cayenne V8 Turbo. The vehicle developed a coolant leak behind the engine against the firewall. After painstakingly gaining access, we found that a cheaply made plastic coolant tee connector had become brittle and failed. We obtained a parts schematic from Porsche but nothing in the diagram looks like this. This part is probably a Volkswagen part as the Touareg is built on the same platform.

We could install a brass tee with hose barbs on it in place, but will give the dealer more time to produce the correct part. We may find that the part is available only as a hose assembly. We will add the correct part number and a picture of the new part when we find it.

The VW TDI (Diesel) engine of 2005 is prone to problems with the oil pump assembly. The oil pump that came in the car is chain-driven and the pump also drives the balance shafts that smooths the engine vibrations. VW has updated the balance shaft and oil pump assembly to a gear-driven unit. The chain and chain-tensioner of the original style assembly wears and creates slack, lowering oil pressure. This can eventually break and cause no oil pressure and severe engine damage.

The oil pan needs to be removed to gain access to the assembly. (This also requires lowering of the sub-frame assembly.) The front lower timing cover / crankshaft seal fixture needs to be removed and the factory chain-driven gear pulled off the front snout of the crankshaft with a special puller. Ours came right off with the special puller. We’ve heard of difficulties removing the gear and having it break and needing to be chiseled or cut off. The new crankshaft drive gear needs to be heated to the proper temperature and it will slide right in place. There is no key-way for the drive gear. The balance shaft assembly is timed with a special lock tool. The oil pan and lower timing cover are sealed with sealant only — no gasket. Special VW approved Diesel oil must be used in these engines.

Our good friend Rolf Engelfried had his very clean and original 1981 Volkswagen Rabbit Diesel towed in to the shop with a non working clutch. We had adjusted the clutch cable on a previous visit and thought the clutch may have failed. After inspection it was discovered that the clutch cable had broken its retaining bracket off of the steering column and the cable casing was pushing against the firewall instead of the bracket under the dash.

I remember working on a lot of these cars at my uncle’s repair shop J&R foreign cars of Lowell Massachusetts in the late 80’s and remember seeing this before. Unfortunately the only way to fix this properly is to completely remove the steering column form the vehicle and re-weld the bracket in place. We ground the old weld mostly off and cleaned the area on the column where the new welds needed to go. We welded the bracket on more than just the two ends that were welded from the VW factory. Here are some photos of the process.

It’s been a while since I needed to use this trick and it saved me (and the customer) about 8 hours of labor. This 2010 Mercedes C300 204 chassis vehicle broke the rear axle shaft (1/2 shaft). It sheared clean off where it comes out of the side of the differential. Vehicle was in a minor accident and somehow the axle twisted and broke. We used a miller stick welder and the largest diameter welding rod we had around. We let the rod get a good molten puddle going in the center of the broken axle stub and then pushed the electrode straight into the weld puddle stopping the arc.

We quickly unclamped the rod and shut the welder off. After allowing the rod to cool we used a slide hammer with a vice-grip attached to the pulling end (This is also a neat and useful trick / tool I made). I tightly clamped the vice grip to the end of the welding rod and with one good pull of the slide hammer the broken stub popped out still attached to the electrode. The new axle went in fine and everything worked good without removing and disassembling the differential.

We are working on a very clean and original 1995 SL600 (129 chassis) that has less than 30,000 miles on it. Unfortunately this vehicle was made by Mercedes with faulty wiring insulation that has deteriorated and caused short circuits in many components. The main engine harness (just includes the fuel injector wires and a few others) is in the worst condition. The main body mounted engine harness has some wiring circuits that are bad, Mostly the air mass meter harness. This harness is over$5000 for the part and approximately 60 hours labor to replace. It runs from the headlights to the trunk of the car, behind the dash and under the interior. This job at the Mercedes dealer could legitimately be $14,500. Just for the body mounted harness.

Here at Autobahn Performance Inc. in Ft. Lauderdale Florida we have developed a repair kit and procedure to repair this harness without removal for less than $1800. It will work on V12 engine in the 129 (SL convertible) chassis and the 140 chassis (4-door sedan or 2- door coupe). In rare cases more than the normal wire circuits are affected by the insulation deterioration and the harness is unrepairable. This is usually only in European-delivered vehicles and the sedan 140 chassis. If a wire suffers from insulation deterioration the entire length of wire must be replaced. Trying to splice onto a section of the wire will not work properly and will result in short circuits and possibly a fire. The insulation will start to crumble near where you are trying to repair it and you will probably make your problems worse rather than better.

The throttle actuators (electronic controlled throttle body, TBA Throttle Body actuators): There is one for each side of the engine. (note: the one on the right side of the engine feeds the air into the left side of the engine and vise versa) The actuators have a short wire harness coming out of them, it’s about 14 inches long, that connects to the body-mounted engine harness. These harnesses also have the insulation failure problem. The harnesses are part of the actuators and are not available as a separate piece from Mercedes. The Actuators can be rebuilt and new harnesses soldered into place. Again, do not try to repair these as you will not be able to properly connect new wires to the electrical connector end of the harness. Short circuits in the wiring of the actuators commonly cause damage to the E-GAS actuators (the control units that control the throttle actuators). These also can be rebuilt.

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