Cars have changed since you were a teen

Dear Mike: I was trying to diagnose an electrical fault on my car with the trusty tach-dwell meter that I’ve had since the 1960s. I was pulling connectors apart and probing with the leads supplied with the meter.

The high-school kid next door told me that I was going to damage my car with this dinosaur, and that I needed to replace the thing with a new meter.

Aren’t volts volts anymore?

— T.S., Seattle

A: The laws of physics remain immutable, but the specific application of them has morphed since you and I learned to fool around with cars in our teens.

I’ve got one of those mailbox-size dwell meters myself, and it’s collected lots of dust recently. First off, no car on the market has points anymore, so the dwell-meter function is useless. Idle speed is self-stabilizing, so you don’t need the tach.

The voltmeter function may be useful, but check that the meter is a high-impedance meter. Older voltmeters are low-impedance and may load a modern, chip-based engine-sensor circuit so much as to produce inaccurate readings. And they could damage the vehicle’s electronics. A good voltmeter should have a rating of at least 10 megohms per volt, and will say so either on the meter face or on the back.

But wait, there’s more. The connectors on modern fuel-injection systems are smaller and less rugged than the ones used on more classic cars, which is why they’re buried inside weathertight seals. Poking the old-fashioned type of probe into one can open the connector and keep it from making good contact when reassembled. And good contact is essential for a sensor circuit that normally carries only millivolts in its normal operating range, instead of the 12 volts we used to meter in most underhood circuits.

To prevent this, always backprobe a connector, even if it’s no longer mated with its other half. Insert the probe into the weather boot from the back side. If the boot is too tight for your probe, use something smaller to fit. Dressmaker’s pins are good, but I’ve also used short pieces of safety wire.

Dear Mike: My 1991 Ford Explorer has almost 2 inches of free play in the steering, which seems like a lot. It pulls to the right most of the time. Also it pulls to the right more after I accelerate hard, which I don’t understand.

I know that an alignment will fix the pulling, but I don’t understand the business of pulling more after acceleration.

— J.McI., via e-mail

A: It’s simple enough: Something in your front suspension is seriously worn — maybe a rubber control-arm bushing, maybe the steering box, probably more than one thing. When you accelerate, the clearances all stack up in some place that makes your front steering pull. Step on the brakes and some of it shifts back.

Eventually it will fail altogether and cause your truck to lose control. You need serious front-end work, and you need it right away — new parts, probably several of them, followed by a new alignment.

Stop looking for simplistic answers and get this car into a shop.

Dear Mike: I have a 1997 Buick with the “check engine” light on. I cleaned the O2 sensors, and now I would like to turn off the “check engine” light.

Can I do this without a code reader?

— J.K., via e-mail

A: If you don’t have access to a code reader or scan tool, how do you know that the problem is an O2 sensor?

If the cause of the trouble code is gone, the light eventually will go out on its own. Or you could pull the fuse to the ECM for 30 seconds, or disconnect the battery ground for 30 seconds. Doing this also will evaporate your radio presets, however, and if the problem hasn’t been resolved the light will come right back on.

Fair warning, though: I’ve never successfully cleaned an O2 sensor. Sometimes it works for a while, but I always wind up having to replace it a week or a month later.

Dear Mike: I own a 1994 Cadillac Seville with the Northstar V-8 engine. I was told that it could run 50 miles without any oil in the crankcase. Will you tell me how this is possible?

— R.H., Miami

A: It’s not. Whoever told you that it was has been watching too many late-night infomercials.

The confusion probably comes from Cadillac’s engineering of the Northstar engine, which can run without coolant for a few miles. This emergency, “limp home” mode preserves the engine by shutting off the fuel to four cylinders at random. This permits an hour of low-speed operation — 50 mph tops — until you get to a repair facility.

But without oil? Never.