Cruise control problem may be faulty switch

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This article was published 01/09/2006 (7015 days ago), so information in it may no longer be current.

QUESTION — I would like your opinion on a situation that happened to me while I had the cruise control on during a recent drive on Interstate 29 in North Dakota. The speed limit was 65 mph and I set the cruise at 110 km/h. My car is a 2000 Acura 3.2 TL, with automatic transmission. Everything was working fine until I drove over some rough spots — some dips and bumps. At first, I didn’t notice until I glanced at my tach, and saw the revs falling, then realized that my cruise control disengaged by itself.

I thought that I had accidentally touched the brake pedal when I came up to the rough section, until it happened again. When the cruise went off the first time, I set it again, and all was well until the next rough section came up. This time I was more alert to the cruise control, and it disengaged again by itself. I set the cruise again, and again it went off by itself when I came to another rough section. The rough sections of the highway are not real seat belt tightening wrenches but are more gentle bounces making the coffee in your travel mug ripple. After this, the cruise worked fine, even on the return trip, but then, the highway is divided and perhaps only going south has the rough sections. What do you think?

ANSWER — From your description, it does sound like the cruise control cutout is a little sensitive. Two main inputs are used to disengage the cruise operation. When the brake pedal is pressed, cruise cuts out. When the transmission is shifted out of drive, cruise cuts out. Switches are used to send the signals to the cruise unit and perhaps one of the switches in slightly out of adjustment or worn so that the rough road surfaces cause it to signal the cruise to cut out. I would check these first.

Next, I would inspect all electrical connections at the cruise module, the engine computer and the steering column switches. A loose or slightly corroded connection could cause the problem. You may not see anything, but simply disconnecting and reconnecting the connectors may “fix” the problem.

Finally, I would check operation of the cruise control switches. Wiring in the tilt steering column may have been pinched or broken, causing intermittent operation. The cruise module itself may be faulty, but I suspect a misadjusted switch or loose electrical connection is the likely culprit.

QUESTION — I have a 2000 Chev Silverado 1/2 ton extended cab short box, with a 4.8L V8 engine. My question is concerning a pinging sound coming from the motor while travelling down the road (what it sounds like is that the timing is off — like on the older vehicles when you are going up a hill). I have had a recent tune up, changed the valve cover gaskets, changed the fuel filter, and had a new download on the computer. None of these seemed to help.

When I am travelling down the highway in drive, I shift from drive to overdrive at about 70 km/h. This is when it starts to ping. At 100 km/h, if I go from overdrive to drive the motor will still ping but not as often. The garages are baffled. Have you heard of this problem before?

ANSWER — When you shift into overdrive at around 70 km/h you are placing maximum load on the engine. Lean cruise fuel mixtures and high loads at low rpm can make the engine ping. It can still ping at higher speeds but usually not as much.

Pinging is the sound of the vibration caused by fuel igniting before it is supposed to because of high heat and pressures in the combustion chambers. If an engine pings under high loads, it is usually incorrect ignition timing or bad fuel. However, pinging under light loads such as your truck is usually caused by incorrect Exhaust Gas Recirculation (EGR) operation. The EGR should occur during cruise and stop during high engine loads such as fast acceleration.

When EGR takes place, the burned gases take up some of the room in the combustion chamber. This decreases room for fuel and air, so less heat and pressure are generated. Because maximum power isn’t needed during cruise, the EGR operation has no impact on performance.

The EGR valve may be defective, the passages plugged with carbon or the control system may have problems, but it should be easy to diagnose. The EGR system can be operated with a handheld scanner and engine smoothness should change at an idle if the system is allowing exhaust gases through. That is where I would start before replacing any parts.

Jim Kerr is an experienced mechanic, instructor of automotive technology and member of the Automobile Journalists’ Association of Canada. You can e-mail questions to Jim at the address below.

kerr.jim@sasktel.net