A Stumble When Accelerating Indicates a Misfire in Engine

November 21, 2009/Steve Tackett

MOTOR MATTERS ASK THE AUTO DOCTOR BY JUNIOR DAMATO

Dear Doctor: I own a 2000 Acura TL with under 80,000 miles. The problem is a slight stumble under light acceleration, 25 to 40 mph with the engine at operating temperature. What could it be? Richard
Dear Richard: Any kind of stumble under light acceleration is usually a misfire. Weak ignition spark, a lean fuel mixture, or even a lazy ERG valve can cause a misfire. These can cause your problem without setting a “check engine” light. It is possible the computer could have a pending code in memory. The engine should have a performance test before replacing any parts.
Dear Doctor: I own a 1997 Lincoln Mark and the left headlight burned out. The replacement cost for this High-Intensity Discharge light is $1,600. My mechanic has had no luck in finding a cheaper solution. Any suggestions? Sue
Dear Sue: Your choices are to buy an aftermarket HID replacement, a used headlight assembly, or convert both headlights over to a conventional light system.
Dear Doctor: My 2005 Jeep Grand Cherokee V-6 has 39,000 miles on it. The dealer just installed the fourth starter under my extended warranty. I am tried of getting stuck with a no start condition. Is there an aftermarket company that makes a reliable starter for this engine? Bill
Dear Bill: I have not had any common trend with faulty starter motors on these vehicles. Common starter failures are mainly caused from low voltage at the starter and poor ground connections. I suggest having an independent ASE-certified technician check the connections, both positive and negative, as well the voltage at the starter motor. A battery voltage test should also be done.
Dear Doctor: The wipers on my 1997 Chevrolet Cavalier don’t go down. They work properly, but when I turn the wipers off they come back up on the window and stop there. How can I get them back down to the cowl of the windshield? Betty
Dear Betty: Wiper motors have a park position. Some GM vehicles have a park bracket that gets bent slightly and causes the wipers to stop at the top of the windshield. You will need to have this repaired by a qualified technician.
Dear Doctor: I own a 2006 Dodge Grand Caravan. When I start the minivan I hear a slight whining from the engine. When I’m driving on the highway for a period of time the whine gets louder at high speed. When I slow down to get off the highway the whining becomes worse. When I step on the gas the sound increases. What should I do?

1997 Chevrolet Cavalier

Dear Ro: Without actually hearing the noise it is hard to advise. We use a stethoscope when searching for a noise source. You can also start with disconnecting the serpentine belt then start the engine. If the noise is gone, then with the engine off turn each pulley and feel and listen for any noise. If the noise is still present with the belt off, look for the noise at the transmission pump.
Dear Doctor: I have a 2004 Nissan Murano with 94,000 miles on it. When the “check engine” light came on we took it to the dealer the next day and they said it had multiple engine misfires. It cost $560 to do a compression check to see what was wrong. They found out that cylinder #5 had zero compression and that cylinder #3 had only 100 psi. They did a wet/dry test with no difference. They advised to replace engine at a cost of $10,084. I still owe $10,000 on the car and it’s out of warranty. What do you recommend? Help! Ted
Dear Ted: I suggest to get in touch with Nissan customer assistance center. If this is a dead end, then I would get a second price check on a used engine from an independent shop verses buying a new engine.
Dear Doctor: I own a 1969 Ford big block V-8 classic with the code “U” C-6 transmission connected to the code “6” 3.00 standard rear axle. I learned I do not have a posi-rear. Is there a way to make my axle posi-traction, without having to change the whole rear? Jim
Dear James: I use a company called Randy’s Ring and Pinion (1-866-631-0196) for all my rear-end posi units. They ship the same day and have the knowledge of the driveline that is needed. You simply remove the open rear-end case and swap the ring gear onto the new posi case. — by Junior Damato, Motor Matters

Junior Damato is an ASE-certified Master Technician.

E-mail questions to info@motormatters.biz

Mail questions to: Auto Doctor, 3 Court Circle, Lakeville, MA 02347

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Copyright, Motor Matters, 2009