Auto Q&A: Stalling, hesitating has no clear cause in Forester

"There doesn't seem to be any rhyme or reason to when the stalling or hesitating happens."

It's difficult to say if the hesitation/power loss symptom and the stalling are caused by one issue, but it's possible.
It's difficult to say if the hesitation/power loss symptom and the stalling are caused by one issue, but it's possible. –Dreamstime/TNS

Q. Over the past year, my 2010 Subaru Forester intermittently stalls and hesitates while I’m driving. By hesitating, I mean the car loses power and the check-engine light comes on and flashes. I can limp the car along until it “kicks” in and lurches ahead at which point the check-engine light goes off and the car returns to normal.

At other times, the car will stall when I’m stopped. There doesn’t seem to be any rhyme or reason to when the stalling or hesitating happens, but these episodes are becoming more frequent.

I have taken the car into several different mechanics (including the Subaru dealership) to have the car scanned, but no one has been able to diagnose or fix the problem. Of course, when I take the car in, it runs normally. A recent scan indicated the catalytic converter needs replacing (but the problem existed well before this), and other scans indicate misfires.

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Mechanics have cleaned the fuel injection system, changed the wiring to the O2 sensor, changed the EGR valve, changed spark plugs … all to no avail. I’m at a loss. Any ideas what could be causing this? Any suggestions would be greatly appreciated.

–Linda

A. In a follow-up message Linda indicated there was mention during two repair attempts of diagnostic trouble codes pointing to cylinder 1 and 2 misfires, but it seems the repairs were largely focused in other areas. This would be consistent with the flashing check engine light, which indicates a catalyst threatening misfire is occurring (continued driving is highly discouraged).

It’s difficult to say if the hesitation/power loss symptom and the stalling are caused by one issue, but it’s possible. I’m thinking there may be a problem with either the ignition coil or one of the spark plug wires. On this 2.5 L non-turbo engine Subaru employs a waste spark ignition system, meaning one ignition coil fires two cylinder’s spark plugs in a loop configuration. Both coils and the ignition control module are combined into a single unit. Looking at the cylinder groupings, cylinders 1 and 2 share one coil, and 3 and 4 share the other. This is just too large of a clue to not run with!

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When it’s time for either cylinder 1 or 2 to receive spark, the coil is fired and spark travels the loop, firing both spark plugs, one in the forward direction, one in reverse, even though only one of the cylinders needed it. That’s where the term “waste spark” comes in; one of the sparks is unneeded at that time. It’s a slick system, not as cool as individual coils, but it’s vulnerable to spark leakage, which can take out both cylinders. I wonder if that’s what’s happening, as spark leakage is as fickle as can be, depending on conditions.

Perhaps the ignition coil has a tiny insulation fault, or one of the spark plug wires has a crack or split, or is chaffing against sharp or hot metal. Under certain operating conditions the desired spark path is more favorable, and during others, perhaps hot/under moderate engine load, the leakage path is momentarily preferred — causing two cylinders to misfire.

I’d try wrapping aluminum foil tightly around the ignition coil (also touching engine metal), encouraging spark to leak (the insulation fault could also be internal, passing this test). If the symptom worsens, replace the coil. Carefully inspecting/rerouting the spark plug wires may point out a problem there. A head gasket failure between cylinders 1 and 2 is also possible but not likely, as the symptom is intermittent.

Auto Q&A: Don’t worry about tires that have sat in a warehouse

By Bob Weber, Chicago Tribune

Q. The local car dealer was advertising “buy three get one free” tires. While researching the information on the tires, one listed brand and model had a recall notice posted on their website and another said the model has been discontinued over a year ago. The dealer told me that they wouldn’t be selling a recalled tire. The dealer was offering road hazard service in the package. Should I be concerned my free road hazard program would be useless if the model I bought was discontinued? I was told that tires sitting in warehouses for years is not a good thing.

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How about some tips on tire buying? I’m wondering if I bought these tires at Walmart and brought them to dealer for alignment, would they tell me tires I bought are not suitable for my car? Because the cost of tires can add up, who should a consumer trust for tire buying info?

— D.L., West Palm Beach, Florida

A. Most tires come with a road hazard warranty and that includes models that have been retired from their line. Tires sitting in a warehouse do not really age or get stale, and I would have no problem buying tires that are well past their manufacturing date. But high-volume tire sellers seldom have such old stock hanging around. Buy your tires wherever you wish and get your alignment wherever you wish.

You won’t be turned away because of the tires on your car. The most comprehensive website for tire information, which sells almost every brand, is www.tirerack.com. Click on the Research & Advice tab then select “tires” from the menu.

Q. The last few cars I have had use the quick windows, which I think are a pain. Is there a fix to change them to work how you want them to?

— D.H., Barto, Pennsylvania

A. When you say “work how you want them to,” I presume you are referring to the ability to open the window a crack or halfway, instead of full up or full down. I don’t know what kind of car you have, but on most, there is a simple solution. Press the button halfway down (or halfway up) and the window will stop when you release the switch.

Many cars have a slight bump in the switch travel, although it is not always easily felt. With practice, you will gain full control of your windows without resorting to retrofitting your car with hand cranks.

Q. I’ve heard that magnetic oil drain plugs remove abrasive, small metal shavings that the oil filter misses. Do you think that one of these plugs could enhance and prolong a trouble-free engine life?

— L.F., Chicago

A. I like magnetic drain plugs, but not because they trap stuff that the oil filter won’t. The filter will, indeed, trap the stuff. Particles on the drain plug provide a hint to wear: no particles, no excessive wear. Remember though that magnets only attract ferrous (iron) particles, not anything else. On my Harley, there is no transmission filter, so a magnetic drain plug is worthwhile.

Q. I have a 2018 Toyota 4-Runner. The dealer says to change the oil (zero viscosity) every 10,000 miles. However, my mechanic says every 6,000 or even every 5,000. What say you? Also, any thoughts on the 4-Runner in general?

— G.C., Chicago

A. Your 4-Runner is a fine vehicle and you will never go wrong changing your oil more frequently than necessary, but you will waste money. Synthetic oil is not cheap and only synthetic is able to meet the zero weight — the 0W-20 viscosity your vehicle requires.

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