Q. The catalytic converter on my 1987 Chevrolet 3/4 -ton pickup is damaged. The auto parts store will sell me a "test pipe" for $35 to replace the $300 converter. No shop will install this pipe, but I was told I could install it myself. What do you suggest?
A. That information is emphatically untrue. You could be fined $2,500 if you -- or your designee -- remove the converter and install the pipe. A shop that removes the catalytic converter could be fined $10,000. The California Air Resources Board members should petition the EPA to levy penalties against the real culprit, the test pipe manufacturer.
Q. The tires on my 1990 Chevrolet go "thump, thump" on the road. The right front is cupped in one spot. Do I have a tire problem or is it something else?
A. It sounds like a tire problem. Ask your Chevy dealer to direct you to the nearest tire dealer.
Q. My 1990 Dodge Caravan has a light tap for a few seconds after cold start. What is it? Is it harmful?
A. It is probably a valve tappet noise or a lifter. It is not a major problem. It is covered by the seven-year, 70,000-mile warranty.
Q. I bought a 1978 Grand Prix with 42,000 miles. The oil pressure is 35 to 40 pounds at cruising speed. At idle it reads below 3 to 5 pounds. Do I need a high-pressure pump?
A. Probably not. Check your engine idle speed and make sure it is set within factory specifications. Next, check with a local Pontiac mechanic to see how many pounds is considered normal at idle. If the pressure is still low with the idle set to factory specs, you may need a high volume pump, and possibly new rod bearings, main bearings or both.
Q. I am sending you an article about "secret warranties." My car was repaired twice at no cost under a secret warranty. Is this fair?
A. These are policy adjustments, not hidden but often forgotten by auto owners and repairers. Note that the article cites only American manufacturers. All manufacturers use the same methods. Many repairs are so secret the owners never hear about them. They occur when a car is brought in for routine servicing.
Q. Why do you recommend that owners of fuel-injected engines occasionally use super-unleaded fuel?
A. A tank of high-detergent, super-unleaded 92-93 octane once every five or six fill-ups will clean sticking injectors. A side benefit are cleaner combustion chambers, valve and spark plugs and a cleaner catalytic converter.
Q. My 1988 Chevy Spectrum overheats and the brakes do not last. I think they should be recalled. What do you think?
A. I hate to disagree, but I think that if you have the brake calipers and pistons freed up, both problems will disappear. Your gas mileage also should improve. Your brakes are dragging.
Q. My 1973 Buick has 130,000 miles, but lately it emits black, sooty smoke after morning start-up. What causes this condition?
A. It is caused by a rich fuel-to-air mixture. I'd say the choke is stuck closed, the carburetor is leaking or plugged, or there is a high float bowl level due to a sinking float.
Q. Why do you advise readers to adjust cold idle speed on electronic fuel injection engines? It is not adjustable.
A. I recommended showing my article to the repairing technician. The technician responsible for the repair would consult the appropriate manufacturer's manual in order to determine the manufacturer's specifications. To refresh your memory, I'm sure you are aware that idle air speed, idle speed control or throttle position sensors are all fundamental inputs to the computer. Coolant temperature sensors, barometric sensors or manifold absolute pressure sensors are important input also. A mere voltage variation of .2 to .5 from the TPS will create performance malfunction over all speed ranges.
Q. My 1989 Chevrolet Corsica has stalled and refused to start several times. Each time the dealer replaced parts but it has done this four more times. Can I trust this car now that it is fixed?
A. I hope so. Ask the dealer to check your computer for trouble codes. If it is clear of codes, I'd bet the car will be dependable. However, your symptoms are those of someone who overfills the tank by removing the nozzle part way and pumping more fuel in. That habit could cause a plugged up charcoal canister. The replacement cost is $100 to $250.
Q. My 1985 Ford has developed a ping and a rattle in the engine. High-test fuel hasn't helped. Can you?
A. Have the timing checked while the engine is under load. Change the timing belt if your vehicle has more than 50,000 miles or if it is out of specifications on timing advance. Also, clean or replace the EGR (exhaust gas recirculation) valve. One or all will fix it.
Q. Why does the steering wheel on my 1990 Honda rattle and jerk?
A. The reader writes that the steering wheel on his 1990 Honda rattles so badly that it's impossible to talk and drive at the same time. The rattling stops when the wheel is turned. The dealer won't help. Take the car to another Honda dealer. Unless you have logged unusually high mileage, it still should be under warranty. It sounds as if you could have a CV joint problem. Perhaps a mast jacket bearing at the top is loose or missing. If the other dealer doesn't help, call the Honda distributor, (213) 783-2000.
Q. My 1991 Mitsubishi has a dreadful rotten egg smell. The dealer claims that is normal. Is that true?
A. There are several possible causes for the smell: over-rich mixture, wrong timing or failed catalytic converter. The California Air Resources Board may be able to help you. In some new cars, that smell diminishes after break-in. It is probably coming from the catalytic converter. Try a different brand of gas before filing a complaint.