Drive it forever
Q: I took apart my alternator, looking to diagnose an intermittent-charging problem. Now I can't get it back together. Specifically, I can't get the voltage-regulator brushes back in past the lip of the case. They keep hanging on.
A: This is an easy one, and you would have figured it out yourself if you had picked up a new voltage regulator/brush assembly to replace your gnarly old one. And, judging by the pictures you sent me, you need a new one badly.
Worn brushes won't conduct enough current to the slip rings, because the springs behind them can no longer press against the brushes hard enough for good electrical contact. Check the slip rings for pits, burned spots, and out-of-round areas. The new regulator will have a short metal or plastic pin inserted in the brush holder, which keeps the brushes back against the spring, so you can use a small finishing nail, toothpick, or paper clip to reinstall the old regulator.
Replace the regulator, pull the pin, and count to 14, because that's how much voltage your alternator should put out when the battery is fully charged, the engine is at idle, and all of the power-consuming accessories are shut off.
Q: I own a 1998 Dodge Ram 1500 truck with a 318 engine.
I usually set the A/C controls to blow cold air through the ducts on the face of the dashboard. However, under almost any acceleration, the air suddenly redirects itself toward the windshield, as though I have turned on the defrost setting. Then, as soon as I ease up on the accelerator, the air goes back to blowing through the ducts on the face of the dash.
What gives?
A: Your truck, like many vehicles, relies on manifold vacuum, a condition of low atmospheric pressure inside the intake manifold that occurs when the engine is running, to power small actuators located under the dash. These actuators swing doors open and closed inside the A/C plenum to change the direction of the airflow.
Normally there's a check valve in the vacuum line from the intake manifold, as well as a vacuum reservoir to hold a small backup vacuum, to power these doors. When you accelerate or climb a hill, your car's engine pulls harder, so its throttle plates open farther, reducing intake-manifold vacuum.
You've got a leaky check valve or a vacuum leak somewhere in the system, and that's causing the doors to move on their own.
Q: What should have been a routine replacement of a timing belt and tensioner, camshaft seals, crankshaft seal, and water pump on a 1990 Plymouth Voyager 3.0 engine has me, an auto-mechanics teacher and certified auto mechanic, mystified.
After replacing all the parts mentioned, I manually turned the crankshaft two revolutions to make sure that everything turned smoothly and that all the timing marks were in position. This is a noninterference engine. I turned the crankshaft clockwise three-quarters of the way around, using the crankshaft bolt and a ratchet, when the No. 3 and No. 6 pistons near top dead center came to a dead stop. I tried to turn the crankshaft counterclockwise, and it stopped very close to the same position.
I have done a number of tests, including rotating the camshafts individually, a visual test of all valve springs and valves, and a pressure test of all cylinders to check for leaky valves. I found only one intake valve at the No. 6 cylinder that was leaking. So I brought No. 6 piston up near TDC, pulled the spark plug, and probed the cylinder with a magnet and then with a vacuum attachment, trying to locate something, but came up empty-handed.
Assuming now that the cylinders are clear, is it possible that the oil-pump rotors or something in the torque converter or transmission somehow got jammed? Everything was working fine before the job started.
Do you have any suggestions on what to check next before pulling the heads?
A: I'm guessing that the camshaft is out of time.
Mike Allen is a senior editor for Popular Mechanics magazine. Questions should be sent via e-mail to driveit@nytimes.com.
