Expert: Roland Finston - 1/16/2012

Question
QUESTION: Car starts just fine in the morning but drive the car for 10 to 15 minutes stop and get back in the vehicle to start and vehicle just cranks and cranks with know start.  Have been in this same situation before with a 96 dodge intrepid and was the crank shaft sensor.  On the LHS same motor (3.5L) have change crank and cam position sensors, checked battery voltage at start and while vehicle is running both ok.  Have also checked fuel pressure.  I am confused been working on chrysler products all my life and this one has got me floored.  Now what about the coolant temp sensor could that be giving the computer some bad feedback or what would you suggest being the next place to go with this car besides the junkyard.  LOL

ANSWER: Hi Brad,
There are on-board diagnotic capabilities that should be taken advantage of before doing anything else. Try the ignition key approach:"on-off-on-off-on and leave on" doing that in 5 seconds or less elapsed time. Then watch the odometer window to see if the mileage reading changes to show 4-digit numbers preceded by a P. Let me know and we'll go from there. If that doesn't work, then go to a nationwide autoparts store such as Autozone where you can often get a free fault code readout using a plug in code reader. Or an independent garage will do it for $40 or less, typically.
I would believe that something specific will come from that effort. There are a number of tests one can do, of course, but the engine computer is doing those all the time and may already have identified what the problem is.
Roland

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QUESTION: The car has no codes stored in computer have checked with scanner many times.  Any idea where to go with this next.

Answer
About the only item that isn't well monitored is the exhaust gas recirculation valve. If that doesn't close fully when you slow down to idle and turn the engine off then when you come back and try to start it the mixture will be too lean. So I would start by checking out that valve to be sure it isn't cruddy and preventing the spring from closing the valve.
You can also check the signals from the cam and crank sensors when it won't start. Measure between the gray/black and the black/light blue at the crank sensor and between the tan/yellow and the black/light blue at the cam sensor while you turn the crank over by hand using a socket on the crank pulley bolt. The voltages should oscillate between 5 and 0.3v if the sensors are good. Do this when it won't start, of course.
Roland