2004 Grand Caravan poor fuel economy


#1

I have a 2004 Grand Caravan 3.8l FWD with 148K miles. I mostly use it now for just traveling but it recently had a significant drop in fuel economy. It was parked one time for about 5 months and that’s when the problem started. At first I was getting a light for emmisions. I tracked that down to a broken vacuum line by the accumulator. That fixed the light but then noticed the drop in mileage. The van runs great except for an occasional hicup at around 40 mph and there is no engine light so no codes pop up. I’ve replaced plugs, fuel/air filter and wires. I removed the injector rack and cleaned/checked the injectors and they seen fine. This is really driving me crazy because there is no performance incicator. Can anyone point me in a direction to solve this problem.


#2

A stuck open thermostat or bad coolant temp sensor can be a culprit.

Check for dragging brakes - especially given that 5 mos of sitting.

I assume that the tire pressures have been checked with a decent gauge?

Some manufacturers have - for whatever idiotic reasons I don’t know - programmed the PCMs such that manufacturer specific codes (those over P0999) don’t trigger the engine light even when there are codes present. I don’t know whether Dodge is one of these. It may be worth it to pay someone with a professional quality diagnostic equipment to scan it. Someone with a good scantool can also tell you all about things like coolant temp, O2 sensor behavior & fuel trims.


#3

I had a 92 Voyager and my mileage dropped significantly 2 months before the check engine light came on . It was the oxygen sensor, and when I changed it, the mileage came back up.