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Auto Doctor: No easy fix for foul exhaust odors

Exhaust odor, such as that experienced by an

Exhaust odor, such as that experienced by an owner of the 2011 Toyota Highlander pictured above, often stems from the catalytic converter that cleans the exhaust. In some cases, there is no remedy for this issue. Credit: Toyota

Dear Doctor: I own a 2011 Toyota Highlander with 12,000 miles on it. From time to time I notice a foul odor inside and outside the vehicle. The serviceman recommended only using branded gasoline, such as Mobil, BP, etc., but unfortunately, this didn't fix the problem. Any suggestions? -- Nick

Dear Nick: The most common odor is from a warm exhaust caused from the catalytic converter cleaning the exhaust. Changing the gas brand and octane can sometimes help reduce the odor. In some cases there is no remedy and you will have to live with the occasional odor.

Dear Doctor: I'm in the market for either a Suburban or Yukon XL. A friend told me you had an article indicating a couple of things you recommend for these vehicles. He said they include a performance chip, a thermostat change, a free flow exhaust, and a cold air intake. Why are these upgrades needed, especially the thermostat change? -- Jim

Dear Jim: There are a lot of bolt-on performance items that do make a noticeable difference in all around drivability. Installing a lower temperature will still allow the computer to operate and the lower engine temperature helps eliminate engine ping/knock under load. The low restriction exhaust and air filter allow more air in and more exhaust out. The performance computer chip, or programmer, allows personal performance settings for both engine and transmission settings.

Dear Doctor: I own a 1998 Subaru Legacy with the 2.2-liter engine, which I think has a blown head gasket. At times the temperature gauge goes close to the "H" and I have to turn on the AC to get the temperature back to normal. Sometimes the engine sounds like a diesel engine, but eventually smoothes out. Could these problems be related to a blown head gasket? -- Ed

Dear Ed: It's not unusual to find an older Subaru with a bad head gasket or cracked cylinder head. A check of hydrocarbons (exhaust gases) in the cooling system needs to be done. At our shop with engines that have a head or head gasket problem, we remove the thermostat center, allowing more coolant flow to prevent overheating. Poor heat can also be a hint of a leaking head or head gasket, preventing coolant flow through the heater core.

Dear Doctor: I have a 2002 Chevy Blazer with 123,000 miles and the 4.3-liter V-6. There is no power going to the fuel pump. I checked the power at the pump and the relay. I replaced the fuel pump with a Delphi brand. Is there an inline fuse or connector that runs along the rail that I can check? -- Larry

Dear Larry: I see many older vehicles with wiring problems leading to the in-tank electric fuel pump. On more than one occasion, I have found poor wire connections in the harness, and on a few older GM SUVs corrosion in and under the fuse box. Subscribe to and download the wiring diagram of the fuel pump circuit complete with the wire color. Just because you have power at the relay does not mean the power is leaving the relay.

Dear Doctor: I own a 1987 Mitsubishi Montero 4x4 with a 5-speed manual transmission. It's powered by a family 2.6 T2FFC3 engine. Sometimes after driving 100 miles the engine starts missing, as if turning the ignition off and on very quickly. Most often I have to limp back home by getting spurts of acceleration along with skipping. Some technicians say the bushings are worn out in the distributor's shaft housing and some other technicians say it may be a carburetion problem. Can you help? -- Tony

Dear Tony: These older vehicles have limited computer access for drivability issues. Test equipment needs to be connected and the vehicle driven. The sporadic skip you mention seems more like ignition than fuel. Even a partly open EGR valve causes drivability problems. A spark tester is a simple way of seeing if the engine losses spark when the problem occurs. Distributors were a big problem with these engines. -- Junior Damato, Motor Matters

Junior Damato is an ASE-certified Master Technician. Email questions to Mail questions to: Auto Doctor, 3 Court Circle, Lakeville, MA 02347

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