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Jack Smith: Creating the Road Runner

1957: two steps forward...

1967! (A half century later)

Fixing Low Mileage / Power Loss

A 1985 Daytona with a turbocharged 2.2 liter engine and 140,000 km on the odometer had excessive gas consumption and lacked power. Cylinder compression was fine, and the engine had just been tuned. The computer showed no problems and the exhaust was analyzed with acceptable results.

These would be my troubleshooting steps:

1). Put a scan tool onto the computer and monitor the coolant temperature sensor's output.  You may find that it's changing abnormally slowly and indicating a lower than normal temperature.  On fuel injected cars, the coolant temperature sensor is the #1 sensor in importance (MAP sensor is #2).

On EEKs, the computer will switch a lot of things at exactly 180F.  If it takes an abnormally long time to reach this temperature (from the computer's perspective) you will not set a fault code but you will have reduced fuel efficiency.  In my LeBaron, the fuel efficiency went up about 5% after replacing the CTS ($15 for a Tomco aftermarket one) and harness ($5).  A scan tool showed that the temperature in my car did reach  180F -- after 30 minutes! In reality, it reached 180F after about 10 minutes.

The #1 cause of problems in this area is corroded electrical connections.  You may consider spraying the connector and CTS's pins with television tuner cleaner (Radio Shack stuff is adequate) and seeing whether you have an improvement.

If you don't have access to a scan tool, but are handy with a high impedance multimeter, [you may be able to find] a table giving CTS voltage vs. temperature vs. year of car/engine.  The voltage change is "interesting" because Chrysler computers use a varying reference voltage to minimize quantization error in the analog-to-digital converter.  It would be best if you knew which wires on the computer (in the passenger compartment) are used for the CTS.

3). Measure fuel system pressure at idle and with the throttle changing.  Your pressure better vary with throttle changes (this is true for ported fuel injection -- like you have -- for TBI there better be NO change).  If your pressure's too high you may have some of the symptoms.  I'd also be curious to see how the pressure changes with the engine off and the fuel system pressurized (i.e., leaks anywhere?)

Note: Matthew Hayden found that the poor gas mileage, bucking, and (eventually) black smoke on his turbo 2.2 was caused by a dirty intake sensor, which caused the Charge Air Temp Sensor to in turn get dirty. He cleaned one and replaced the other, which solved the problem; it seems to be a common issue.

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