Expert: Roland Finston - 10/23/2011

Question
HELLO ROLAND I'VE ASKED U QUESTIONS ABOUT MY CHRYSLER IN THE PAST ITS A 98 CHRYSLER SEBRING LXI V6. AND THE LAST THING THAT I HAD AN ISSUE WITH WAS THE EGR VALVE WHICH HAS BEEN REPLACED AND FIXED THE ISSUE I WAS HAVING WITH IT DYING WHEN COMING TO A STOP AND WHEN MAKING A SLOW TURN SINCE I'VE RELACED THAT PART I ALSO NEEDED A NEW ALTERNATOR AND REPLCED THAT AND A WEEK SINCE THAT THE CAR WAS RUNNING LIKE NEW BUT NOW THE OTHER DAY I WAS IN A DRIVE THRU AND IT STARTED TO SHOW ON THE GAUGE IT WAS OVERHEATING WHEN I WAS IN ONE PLACE FOR 10 MIN BUT WHEN I DROVE IT, IT WAS FINE THEN A COUPLE MILES DOWN THE ROAD THE CAR STARTED TO HESITATE WHEN I WOULD PUSH ON THE GAS AND THE ENGINE WAS SHAKING REALLY BAD. ITHOUGHT AT FIRST KNOWING I HAVE A FAULTY OIL PAN GASKET THAT I RAN OUT OF OIL BUT CHECKED IT AND IT WAS FINE. SO WHEN I PULLED IN MY DRIVE WAY I PUT IT IN PARK AND IT TURNED OFF BY ITSELF THEN THE OIL LIGHT CAME ON THE OIL LIGHT HAS NOT COME ON SINCE THEN AND THE CAR STILL TURNS OVER BUT I DONT KNOW IF THE CODES THAT CAME UP ON THE COMPUTER AT ADVANCE AUTO IS TO BLAME FOR THIS PROBLEM. THE CODES WERE P 172 AND P175. WHAT OTHER POSSIBLITIES COULD IT BE?

Answer
Hi Kayla,
Those codes say that the fuel mixture sensors on both banks of cylinders of the engine (which are called the O2 sensors) are saying "too rich", which certainly could cause the miss/shake. There are however a number of causes such as: a plugged catalytic converter (which can be tested at an honest exhaust system shop), a faulty MAP sensor, the fuel pressure regulator being "off the pressure setting value", and as long shots a faulty computer, a faulty upstream O2 sensor (but that would require both sides sensor's to have failed, which is unlikely), a wiring flaw that affected both banks of cylinders. I am not sure which of these several possibilities could be the cause. It could also be one of the temperature sensors is off value (such as the intake air temp sensor or the engine coolant temp sensor (which also operates the temp gauge) but not so badly as to set a separate code for one or the other. It is even possible that there is a leak in one of the exhaust pipes.  I wonder whether the temporary overheating could have been involved in causing this, but I am not sure why.
My best suggestion would be to ask around to find an independent engine tune up shop that know the engine that you have there,  and let them have a copy of this and tell them the story and let them try to diagnose it. If they are smart with their test instruments they should be able to identify which of all those possibilities is the correct one, fairly quickly, and if so only replace one or so parts that are responsible. In the hands of an incompetent it could be a mess. So be sure that the problem is showing when you get to the recommended shop or wait until it does to go in.
Roland