Hi summerfan. Welcome to the forum. If the coolant temperature sensor was off by 11 percent, the Engine Computer would have known it and would have learned the proper value. It knows that it must agree with the ambient air temperature sensor, (aka battery temperature sensor), after the engine has been off long enough to be cold. Even when you trick the computer into thinking it's colder than it really is, there should not be so much extra fuel out of the tail pipe that you would smell it. I installed "bugs" in cars for my students to troubleshoot. In one of them, the coolant temperature sensor always read 50 degrees. The engine always started and ran fine if the temperature was over about 40 degrees, had no fuel smell, but did run rich after it was warmed up. You still had better not be smelling exhaust inside the vehicle or you have worse problems. Once completely warmed up, readings from the oxygen sensor in the exhaust system are used to fine tune the fuel mixture. Even if the coolant temperature sensor was inaccurate, the O2 sensor has the final say in fuel metering.
Ford has had a ton of trouble with coolant temperature sensors. Failure on Chrysler products is almost unheard of. It is more likely the engine wasn't completely cooled down when your mechanic tested the sensor. I have no way of knowing how he tested it. He could have just read the value on his hand-held computer, called a scanner, and figured it read differently than the temperature in the shop, or he could have noticed it read differently than the ambient air temperature sensor. That would not be an accurate test unless the engine had cooled down for at least six hours.
Do you smell the fuel before starting the engine? If so, that eliminates anything sensor, engine, or exhaust-related. The smell has to be coming from the fuel supply system. Before starting the engine, look around the injectors to see if there are signs of leakage past the o-rings that seal them to the fuel rail. If you don't smell fuel by the engine, look next inside the frame rail ahead of the right rear wheel. The fuel filter is there with two hoses that have quick-disconnect fittings. Those fittings can corrode and the rubber hoses can deteriorate and leak where the metal fittings are crimped on. If you live in a state where a pound of road salt is used to melt an ounce of snow, suspect pinhole leaks in the metal fuel lines due to rust. Leaks from the filter or fuel lines will show up as stains on the ground or as a film floating on standing water. If you don't see that, it is possible for leakage to occur around the seal where the pump assembly is set into the tank. A clue the seal is leaking is the smell will be worse after adding fuel and letting the car sit in the hot sun, and when filling the tank and the gas pump shuts off automatically, you will be able to add another 1/4 to 1/2 gallon after waiting a few seconds. There is a large air space in the tank to allow it to collapse in a crash. If the pump seal is leaking, air will slowly escape, (along with the strong fuel smell), and make room for more fuel. If you do this long enough, you will be able to add an extra five or six gallons beyond "full", and eventually fuel will spill onto the ground. I suspect the tank seal is not the problem because this car has a leak detection system and will turn on the Check Engine light if that type of leak exists.
Thursday, May 20th, 2010 AT 2:52 PM