Auto Doc: Mustang exhaust 'popping'

2002 Mustang GT.

2002 Mustang GT. (Credit: Wikimedia Commons)

Dear Doctor: I have a 2002 Ford Mustang GT. The car has a lot of "mods" made to it. Under normal driving conditions the car performs perfectly. I only have the above issue in that rpm range. I have checked for codes and nothing comes up. Can you help? -- Paul

Dear Paul: The popping sound from the exhaust is an indication of a lean or over-advanced timing problem. At this rpm and light engine load, the engine is in a lean condition and with modifications it is even leaner. Many times Ford vehicles will not register a misfire code under a condition like this using a small code reader. The use of a professional scan tool in mode 6 operation will usually show what is actually happening in live time, as will using a scan tool in the graphing mode. For testing purposes, first unplug the vacuum line going to the fuel pressure regulator and then road-test the car. Next unplug the EGR valve for testing purposes. I have seen Ford engines that have similar problems after modifications when reprogramming of the computer has not taken place. Computer programming is a very important part of modifications. -- Doctor

Dear Doctor: I have a 2010 Mercedes-Benz ML320 BlueTEC with 69,000 miles, I change my own oil, using Mobil 1 just for that car. It takes 9 quarts to fill. I drain the oil from the plug when I refill it. The oil is already black on the dipstick, before I even start the engine. Is this normal? -- Gary


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Dear Gary: Yes, the black or dark color is normal. Diesel engines rely on heat from the high compression to ignite the fuel and there is always some unburned fuel that mixes with the engine oil that causes the dark oil color. The high grade synthetic oil has detergent that also cleans as it lubricates, which also adds to the dark color. When you pour the oil into the engine it cleans the area and parts as it flows down to the oil pan -- that's why it is discolored before you even start the engine. You can change the oil sooner than the factory recommendation to help remove some of the dark color. -- Doctor

Dear Doctor: I have a 2000 Ford Ranger 4x4 with an intermittent problem when starting the truck. When I go to start nothing happens; no clicking or any other sound, yet all lights on dashboard work. If I fool around with the shifter or put it in neutral and push the vehicle a few feet then it starts. Does this sound like it could be a bad neutral safety switch? The problem has been happening more and more frequently, but I always do get the truck to start. I have also replaced the starter motor. -- Steve

Dear Steve: The neutral safety switch is a common problem on these older Fords. Any time I see a condition like this I connect a test light -- usually a small bulb aka "marker light" -- to the starter solenoid switch terminal and run the wire and bulb up to the lower windshield area so it can be seen by the driver. This will tell if there is power getting to the starter. -- Doctor

Dear Doctor: I have a 2001 Lexus RX 300. My "check engine/Trac Off and VSC" lights are on. My mechanic has put it on the computer three times and even run a smoke test. Everything comes back okay. What else should we look at? -- A.J.

Dear A.J.: Your older vehicle might have rust on a lot of under body lines, fittings, connections and solenoids, and you mention even having a smoke test. It could take a few hours to locate the fault and there could be more than one problem. I can tell you that faulty charcoal canisters and related valves and solenoids are a common fault. Have your technician get in touch with Identifix and Alldata, where he will have access to check the wiring and correct voltage at the solenoids. -- Doctor

Dear Doctor: I'm thinking of getting a Scion FR-S. Do you know what's it's like behind the wheel? -- Jordan

Dear Jordan: I recently drove the 2014 Scion FR-S -- a rear-wheel-drive small car, powered in partnership with Subaru's 200-horsepower four-cylinder boxer engine with the six-speed automatic with paddle shifters. The FR-S rides hard and there is considerable engine, exhaust and road noise. This is not a sports coupe for owners who just want to "ride" in the car. This is for drivers looking for all the road feedback feeling and more. The handling is like a go cart; all you do is turn the wheel and the car responds. This car reminds me of the older Mazda RX7, but has a lot better ride than the Mazda had. -- Doctor

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