Letters: Heat could cause Jeep to stall

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Q: I have been having problems with my 1998 Jeep Wrangler (six-cylinder). At first it would run only for five minutes. Then it wouldn’t start back up until it sat for five to 10 minutes. I have fixed multiple parts including the spark plugs, spark plug wires, battery, throttle position sensor, crankshaft position sensor and ignition charge. What else could possibly be wrong? — Mike, email

A: It sounds like the problem might be heat related. Sometimes a faulty electrical component or poor electrical connection acts up with changes in temperature. See if the electrical connections at the powertrain control module are secure.

You also can wiggle these connectors with the engine running. If the engine stalls when any of the PCM’s three electrical connectors are wiggled, suspect poor connections or a faulty PCM. If that’s not the problem, suspect the replacement crankshaft position sensor.

Was the replacement crankshaft position sensor purchased at the dealer? If not, you might consider getting a replacement unit from the dealer. Sometimes aftermarket sensors purchased at the local auto parts store aren’t of the same quality as original replacement sensors, and this can often make a technician doubt his original diagnosis.

You’ll want to determine if the engine is losing spark and/or fuel injector pulses when the engine stalls and won’t start. Since the ignition coil and fuel injectors are powered up by the auto shutdown relay, it should be checked for possibly being the cause.

Q: The check engine light keeps coming on in my 2002 Toyota Sienna. A P0420 code shows catalyst efficiency. I have replaced the catalytic converter and the oxygen sensors, and the problem is still there. What else could it be? — Charles, Chicago

A: Your Sienna has multiple catalytic converters. One or more of them could be causing the problem. Also, if the replacement converter is not an original Toyota converter, it could be the source of the problem. Same goes for the oxygen sensors. Make sure they are Toyota sensors.

Another possible cause could be an exhaust leak. Have your exhaust system thoroughly inspected for leaks. The best way to do this is with a smoke-tester. With a smoke-tester, smoke is forced into the exhaust system through the tailpipe. Exhaust leaks then can be easily identified visually.

Q: The brake pedal in my 1997 Ford Explorer is very hard to depress. I replaced the master cylinder but this didn’t make the pedal any better. The guy at the auto parts store said it might be the vacuum brake booster. It’s pretty expensive, and I wanted to get your opinion before I replace it. What do you think? — Jerry, Oak Park

A: I agree with the guy at the auto parts store. But since the vacuum brake booster needs engine vacuum to work properly, check to make sure the vacuum hose between the engine and the booster isn’t restricted or leaking. With the vacuum hose disconnected from the booster, there should be strong engine vacuum present with the engine idling. If there isn’t, fix the hose or hose connection. If there is strong vacuum present at the hose, replace the booster.

Questions for Ira Siegel? Call the Auto Advisor Hotline at (708) 633-6839 or e-mail ira.siegel.is@gmail.com. Siegel is an automotive instructor and an automotive service excellence-certified master auto technician.