Fixing Low Mileage / Power Loss |
The problem:
A 1985 Daytona turbo with 140,000 km uses a lot of gas and lacks power. Cylinder compression is OK, and the engine was tuned. The computer shows no problems and the exhaust was analyzed and is OK.
Bohdan replied:
I recommend the following:
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 EFI cars, the coolant temperature sensor is THE #1 SENSOR in terms of importance (MAP sensor is #2).
On K-cars, 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 and you will have reduced fuel efficiency. In my Le Baron, 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 of highway driving whereas, in reality, it reached 180F after about 10 minutes of city driving. 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?)
Cordially,
Bohdan Bodnar
Another Possible Solution
Matthew Hayden found that the poor gas mileage, bucking, and (eventually) black smoke on his turbo 2.2 (whose computer registered a bad oxygen sensor) 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. His instructor told him it was common.
