It is sure that the problem is Temperature Related.
And there is no code(s).
When an intermittent starting or driveability problem only occurs when the engine is hot, only when the engine reaches normal operating temperature, or only when the ambient temperature is high, the temperature is affecting something. The question is what?
Changes in operating temperature could affect the way the PCM controls spark timing, the fuel mixture and other emissions functions. If an intermittent problem only occurs after the vehicle has been driven several miles, it may be occurring when the PCM goes into closed loop. The underlying cause might be a bad oxygen sensor signal, airflow sensor signal or MAP sensor signal that is upsetting the air/fuel mixture.
If a problem seems to occur only when the engine is running in closed loop, that would tell you it's probably a sensor or PCM-related issue. The strategy here would be to look at some of the key sensor inputs with your scan tool to see if readings are within normal limits. Some problems may occur too quickly for the normal data stream to detect a fault, so you may have to hook up a digital storage oscilloscope to detect a momentary glitch.
Temperature also can cause mechanical things to stick as a result of thermal expansion when a part gets hot. Valves and lifters can stick if an engine overheats. EGR valves can stick from heat or a buildup of accumulated carbon deposits. Relay contacts may be affected by changes in temperature, too
if the problem is not temperature related, then it could be motion related.
Motion-related intermittent problems also can occur when harmonic vibrations in the exhaust system, driveline or suspension feedback through the powertrain or chassis. This may affect the operation of certain parts or make you think your engine is running rough.
Moisture is especially damaging to PCMs and electronic circuit boards. Moisture can cause corrosion that shorts out circuits and causes all kinds of weird electronic problems. That's why flood-damaged vehicles are so unreliable. Sooner or later, they usually need to have the PCM and/or other electronic modules replaced. Check your vehicle history.
Sunday, November 1st, 2009 AT 5:27 AM