Expert: Roland Finston - 9/28/2011

Question
Hi, I have a 99 sebring convertible jxi with a 2.5 in it, It has spark and fuel but wont start, Its been at the shop for a week and they cant figure it out. Its not throwing any codes though it has in the past and did 4 days before it died.the code it keeps throwin is a small evap leak code. We have replaced all the vac lines the purge cylinder and everything it said it could be it has done this on and off for the 3 yrs ive had the car, It was running fine the night I parked it, the next mornin it would turn over and not start and that is where were still at over a week later. Im at a loss as is the mechanic, please help, this car only has 143,000 miles on it and other than that evep code and a fuel pump and distributer Ive had no issues with it. could it be a sensor?

Answer
Hi Tonya,
Spark/fuel but no start usually means the mixture or fuel/air is off-value.
There is one sensor that can fail but not so badly as to set a code. That is the manifold absolute pressure sensor which can misread the local pressure and cause the computer to believe that you are say at a high altitude though you may be close to sea level. That would cause a too lean mixture to start and sustain an idle.  So ask the mechanic to check the signal voltage of the MAP sensor with his diagnostic tool and see if that translates into an ambient air pressure that is about what it should be where you are located. At sea level it should read around 4.6 volts between the dark green/red and the black/light blue wires.  
Even before he does that though there is one other part that can also affect the mixture such as to cause a no start, poor idle, die off of the engine when slowing to a stop. That is the exhaust gas recirculation (egr) valve. If that egr valve is stuck slightly ajar that thins out the mixture too much to allow the engine to 'catch' and idle, and also to die when coming to a stop.
The valve is located by first finding the egr solenoid, a round black object with a vacuum hose, just below the oil filler cap. Follow that vacuum hose around to the rear corner of the engine to find the valve, mounted sideways in a small exhaust pipe that comes from the rear exhaust manifold hidden behind the engine.  It too has a round top attached to the other end of the vacuum hose, and then a flange that separates the round top from the body of the valve which is mounted in the small exhaust pipe. In the flange area you will see a rod which is the valve stem and it has a circumferential slot into which you can insert the tip of a screwdriver so as to move the stem back and forth, against spring-action in one direction whose purpose is to close the valve. If that stem gets gummy then the stem may not move to the full closed position. So spray some WD-40 on the stem where it enters the valve body and then work the stem back and forth to be sure it moves freely and that it closes to a dead stop via the spring. Then see if that corrects the 'no start'.
I hope that the egr is the problem because it doesn't have to be replaced, and I wouldn't replace the MAP sensor unless its 'reading' with the ignition turned 'on' but no attempt to crank it over shows that it is misreading the air pressure ambient where you are. To do that without some evidence would just be 'throwing a part' at the problem hoping it fixes things.
Roland