Code 17 means the engine is running cold too long. Most likely you can ignore that one. Every Chrysler product has that code in winter because during prolonged idling after starting, the engine doesn't reach normal temperature within six minutes. That code will not turn on the Check Engine light.
If the thermostat is opening too soon, the engine won't reach proper temperature. That in itself will result in more fuel being used. The computer will not go into "closed loop" where it modifies fuel metering based on the oxygen sensor's readings. That results in too much fuel entering the engine too. If the computer sees the engine is still cold, it will command more fuel. The temperature gauge on the dash will give an approximate reading, but viewing live sensor data with a scanner is much more accurate. Also, the gauge and computer use different temperature sensors.
Code 27 is "injector control circuit does not respond to control signal". I've never run into that one before.
As far as "changing parts", that's not the best way to solve a problem. It's actually the most expensive and least effective way to approach it. The amount of fuel entering the engine is controlled by how long the Engine Computer commands the injectors to remain open during each pulse based on information sent from the MAP sensor, ambient air temperature sensor, (sometimes called the intake air temperature sensor or the battery temperature sensor), and the coolant temperature sensor. The MAP sensor has the biggest say in how much fuel is needed but if it reports an incorrect value, you'll usually have a stumbling, hesitation, or stalling problem, or black smoke from the tail pipe. As long as the values it reports are within the acceptable limits, no fault code will be set even though those values could be wrong.
Fuel pressure also affects how much fuel enters the engine. The computer calculates the injector on-time from a number of variables and one of them is the designed fuel pressure. If that pressure goes up, more fuel will be forced through the injectors. A cracked or missing vacuum hose to the fuel pressure regulator will cause two related problems. That will mimic hard acceleration, (low intake manifold vacuum) which tells the fuel pressure regulator to increase pressure. Air sneaking in from the detached vacuum hose will show up in the exhaust system where the oxygen sensor will report that as a too-lean condition. The computer will try to correct that by commanding more fuel. No matter how much more fuel it commands, there will still always be that unburned oxygen in the exhaust. Oxygen sensors don't measure unburned fuel, only unburned oxygen, so the computer has no way of knowing it's commanding too much fuel. All it knows is it needs "more". Actual fuel pressure is not monitored so the computer can only assume the fuel supply system is working correctly.
The best place to start is by connecting a scanner that can display live data and view the short and long-term fuel trim numbers. If they are high positive, the computer is adding a lot of fuel beyond what it was programmed for in an attempt to correct a problem. If the numbers are high negative, the computer knows too much fuel is going in and is trying to correct that, without success.
I just dug my '95 Grand Caravan out of mothballs an hour ago after sitting for over four years. It fired right up but that vacuum hose I mentioned was rotted off, and within a few minutes I had a huge gas leak from three of the four hose clamps rusted off the fuel filter along the right frame rail. New hose and hose clamps and it's running fine on four-year-old gas!
Wednesday, November 9th, 2011 AT 2:08 AM