Q: I have a ’90 GMC Safari van with a 4.3-liter V-6 engine. The problem is that my van’s engine hesitates, runs poorly, and stalls, especially when it’s cold outside. I’ve been told it’s the fuel pump but that doesn’t make sense to me because it runs better on warmer days. I’ve also been told it’s the ECM system. I’m at a loss and don’t know what to do. Please help. -- S.C.

A: S.C., if your van still has its original fuel pump, it likely needs replacement. To understand why it could be the fuel pump, an engine’s demand for fuel goes down with warmer temperatures. An engine needs much more fuel at colder temperatures. That’s because at cold temperatures fuel doesn’t atomize (break up into tiny droplets) as well. The cold cylinder walls in the engine cause the fuel to condense and more fuel must be added for combustion.

Knowing that, I wouldn’t change the fuel pump, though, unless a fuel pressure and volume test confirm that it’s bad. If the fuel pump isn’t faulty, it’s possible your van has a bad coolant temperature sensor. A coolant temperature sensor that is out of range could cause the Engine Control Module (ECM) to inject less fuel than the engine actually needs. So that no unnecessary components get replaced, take your van to a technician that is at least ASE-certified in the A8 (Engine Performance) category.

Q: When I turn a corner, mainly left turns, my ’93 Ford Escort wagon seems to hesitate and jerk. I was told it might be the engine. What do you think? -- P.B., Steger

A: P.B., I doubt something’s wrong with the engine. I haven’t heard this complaint in a long time, not since carburetors were replaced with fuel injection systems. With a carburetor, a low fuel level in the carburetor’s float bowl could cause a stumble or hesitation when the fuel would slosh around during a turn. Thanks to fuel injection systems, that’s no longer a concern.

A technician will need to test drive your fuel-injected Escort to determine if the hesitation during turns is engine performance related or driveline related. An engine performance related hesitation could be caused by something wrong with the fuel, ignition, or engine control system. A driveline hesitation could be caused by excessive wear in driveline components like the CV-joints.

Q: I own a 2001 Buick Regal. It only has 20,000 miles on it and the front brakes need to be replaced for the first time. The brake pedal pulsates when stopping, too. The technician measured the brake rotors and said that they’d be too thin after machining so I had to buy new ones. How can this be possible with such low mileage? -- D.O., Glenview

A: D.O., when new, the front brake rotors on your Regal measured 1.270-inches. Your front rotors can be machined to as thin as 1.224-inches. That doesn’t provide much room for wear and machining. That’s commonplace on newer vehicles as manufacturers look for ways to shave weight off the car. Years ago, brake rotors had lots of extra material on them and you could go a couple of brake jobs before needing replacement.

AutoAdviser: Ira Siegel is an Automotive Instructor and ASE Certified Master Auto Technician. If you have auto-related questions for Ira Siegel you can call and leave your questions at the Auto Adviser Hotline at 708-633-6839 or e-mail a question to Autoadvisr@aol.com.