Greetings all. 2004 GC 3.3 104K miles bought used w/92k bout a year ago. 1300 mile road trip a few weeks back consistently got 22.5-23.1 mpg. I was unimpressed. Was hoping to get 25+ (a 98 caravan 2.4l 3 speed loaded in a similar fashion and same 65-75 mph driving years ago on the same trip gave 26+). OEM spark plugs and air filter were installed months ago, trans fluid and filter replaced summer 2015, suburban driving never gets more than 21mpg. I noticed since aquiring this van that sometimes when I let go of the gas pedal to coast, I don't feel any engine braking. In fact, on the highway during this road trip, several times it almost felt like I was using cruise control when I was off the gas at 70 mph. I dismissed it as just a normal loaded van characteristic. Now, I recently got an ultragauge and have been using it during my drives. It is a cool gadget to have and I have it set up to show o2 sensors 1 and 2. It also on the same screen shows open/closed loop operation. On a stick shift vehicle I have, when coasting, it immediately goes to open loop and the o2 sensors read 0.004volts or very lean shortly afterwards. This is expected as fuel cutoff is taking place and the o2 sensors read high oxygen exhaust content. If coasting and I get below 1200rpms, this car starts adding fuel and I go to closed loop again, or immediately after touching the gas. Now in my GC, I don't get the same results. I found that after a good 5 seconds of coasting in OD or 3rd gear in this caravan, I am still in closed loop, and getting ordinary o2 sensor voltage fluctuations, which tells me the engine is still getting fuel when it should not be. Sometimes and I mean like once every 10 attempts, it will go open loop, but only after several seconds of coasting. I also saw the threshold for fuel cutoff is right around 1300 rpms by the way. I have tried coasting in OD and 3rd above 2000 rpm and cannot get into open loop as described. Was thinking this might just be the reason for the lackluster mpgs I've been getting. Was also thinking a throttle position sensor might think I'm touching the gas. What do you guys/gals think?

 

https://www.fueleconomy.gov/feg/Find...20126&id=14635


its only rated at 24mpg hwy and that's not at 65to 75mph in the winter.

lack of fuel cut off during hard decell would not even make a 1% difference in mileage.

is this van drive by wire or throttle cable.

 

Yes, I've seen variable sticker mpgs from different sites, but it was supposed to be 26 for 3.3 when I almost bought a new one 10+ years ago. I remember because my 98 2.4 liter was 26mpg on the sticker and I was impressed that a 3.3 got the same a few years later. Anyhow, trip was to Miami, all straight highway, very warm, few ounces of lucas oil in every tank. It's also a bit of a safety concern as it tends to keep the speed longer than expected when letting go of the gas on the highway. No drive by wire on mine. Did find out today with my ultragauge that throttle position with foot off the pedal stopped in park, vehicle on position, engine off is 14.3%. Floored gets 78%. Will investigate that soon to see if that is the norm. Thanks.