SUV occasionally loses output when put in gear
Question: I have a 2004 GMC Envoy SUV, V-6 with 125,000 kilometres. For about the past six to nine months it seems to lose power about every 20 starts. It starts, no problem, but when it’s time to get in gear and move, it makes a sound that is hard to describe and seems not to want to move forward or backward. This lasts for a bit, and then the sound disappears and it drives just fine until the next time it happens. The sound is similar to cold engine idle in the winter.
Turning off the engine and restarting makes it disappear. My mechanic has test-driven it to labour the transmission and has checked the engine codes as well. Nothing. Any ideas? I dread the dealer taking it for hours at $160 per. Other than this seemingly stupid problem, this truck is a dream. It’s in the last two months of an aftermarket warranty, so I am pretty desperate to find an answer so it doesn’t cost an arm and a leg later to fix it.
A.O. Answer: This is a tough one to understand and figure out. In a follow-up communication, A.O. confirmed the tachometer reading was rather high as the fault occurred. She had also seen an article/reference about “reduced engine power” and wondered if this might be her concern.
Based on A.O.’s description I’m wondering if the transmission might be slipping, possibly due to low fluid level or another fault. Using a mobile phone to take a narrated movie of sounds, conditions and the instrument panel display as the fleeting fault occurs may be the best bet to demonstrate the symptoms to the service tech. Since it happens in forward or reverse, it doesn’t appear to be a fails-to-upshift issue. The “reduced engine power” reference was likely speaking to a possible electronic throttle-control symptom. Should a fault in this system occur, engine power will be reduced, either about half or almost completely, depending on fault severity, for safety reasons, along with an illuminated check engine light and stored diagnostic code. If this should occur, there would be little/less engine noise/RPM, not more.
Q: You mentioned once in your column that modern ultra-lowemission vehicles have catalytic converters that activate faster than traditional cats, so the exhaust is clean almost from startup. How do they achieve this? Using a different catalyst? Exhaust heaters?
B.W. A: Cold-start emissions are the holy grail of emission control efforts. Modern engines run so well they can tolerate a leaner/cleaner air-fuel mixture at start-up, and efforts to achieve rapid light-off of the catalytic converter are strong. Moving the converter closer to the engine, adding a small/low-mass preconverter, and adding an electric heating element are current strategies, along with new catalysts that can begin functioning at less than the typical 800 degrees F.
Q: With the engine idling, how long does it take to consume a litre of gasoline? I’m asking because I wonder if shutting off the engine at stoplights actually saves anything or if it is simply hype.
G.E. A: Based on work developed by Argonne National Laboratory, the idle fuel consumption rate with no load (no use of accessories such as air conditioners, fans, etc.) varies widely. Compact cars with 2.0-litre engines consume about 0.6 litres per hour. A large sedan with a 4.6-litre engine consumes just over twice as much fuel at idle That might not sound like much, but carmakers are seeking ways to save every extra drop of fuel to meet federal corporate average fuel economy standards.
Q: As a teenager in the 1960s, I learned to drive in a car with a column-mounted three-speed manual gearshift. What year was the last American car with a “three on the tree?” Are the modern transmissions cheaper to produce, provide better economy or are they safer? Or is the customer just too lazy to be bothered by the physical effort needed to change gears?
B.P. A: Wikipedia reports that the column-mounted manual shifter disappeared in North America by the mid-1980s, last appearing in a 1987 Chevy pickup, if you can trust Wikipedia. Sadly, most North Americans prefer automatic transmissions. Perhaps it is because shiftless kids never learned to use a manual shifter or, as you suggest, they are simply too lazy.
Q: I have a 2009 Lincoln MKZ with almost 160,000 kilometres. When I put it in reverse, a beep warning alarm goes off if it is about to make contact with some object. When I backed the car out of the driveway a few days ago a dashboard light came on saying to check the “parking aid assist.” I took it to a dealer who said it might need a computer module that would cost $2,500 and that it would cost $100 to run the test to determine what the problem actually was. Spending up to $2,600 to fix a backup alarm buzzer sounds ridiculous to me. Any suggestions for a less expensive solution?
R.S. A: One simple solution is to install an aftermarket backup camera. Many of them simply mount to the licence plate frame and are wired into the backup lights to power them in reverse. Recently, however, there has been an explosion of self-powered (battery) backup cameras that use a smartphone to display the image to the driver. No wires attached! Not only is this less expensive than repairing your warning system, it updates to the current backup technology.
Q: During the course of a 20-minute highway drive it is not unusual for me to see four cars with a single headlight ... and I’m being careful not to count motorcycles. It does make for a good game of Padiddle though!
C.T. A: I’ve heard that Padiddle started out as a kissing game, but morphed into being the first to touch the car’s ceiling (or punching your brother) when spotting an oncoming car with only one headlight. We are not sure what is causing the phenomenon you report, but we would like to remind our readers that when one light goes out, you should replace both. After all, they are the same age and the second might soon fail.