Excessive fuel consumption?

My wife and I just purchased a 1999 Windstar with a 3.8 and about 95,000 miles. Our first road trip and we only got about 15 mpg. Since then i've replaced the plugs, air filter, fuel filter, tranny filter and fluid, flush the coolant, and replaced the thermistat. Our latest road trip yielded the same 15 mpg. Does anybody have any other suggestions as to what could be the problem?

I have a 98 Windstar with 105,000 miles. The highway fuel economy had dropped from 22 -> 19 mpg over the last several months, so I replaced the "upstream" oxygen sensors. Just finished the second tank of gas, and see that the fuel economy is back to 22mpg again.

As I understand it, these sensors give a false lean indicator as they wear causing an engine to run rich and waste fuel. Shouldn't take long to recoup my $80 investment.

Regarding replacement: the front sensor was easy. The back (firewall side) sensor was in a tight spot, but not too bad with a long extension, flex-head ratchet, universal/swivel , and ox-sensor socket. Both were accessed from underneath.

My wife and I just purchased a 1999 Windstar with a 3.8 and about 95,000 miles. Our first road trip and we only got about 15 mpg. Since then i've replaced the plugs, air filter, fuel filter, tranny filter and fluid, flush the coolant, and replaced the thermistat. Our latest road trip yielded the same 15 mpg. Does anybody have any other suggestions as to what could be the problem?
you can also try running some injector cleaner through the tank, although not as effective as an actual injector flush it might help. i've found that techron is one of the most effective ones. you can also try cleaning your combustion chambers by running small amounts of water through a vaccum line at full engine operating temp., once again not as effective as running the actual chemicals used to do this but a much cheaper option(some people like to do this but with tranny fluid, never really tried it) and like kelvin said replacing your o2 sensors might also aid, most people are not aware that doing this is considered regular maintance. remember to check your tire air pressure as well.

Low 20mpg range is typical for the 1999+ 3.8's. (22mpg is typical for our 2001) What are the condition of your tires? Keep them aired somewhere between the door jamb specs and sidewall specs. Could be a dirty MAF or failing O2 sensor, but you'd usually get a check engine light if one of those is funky.

Joel

you can also try running some injector cleaner through the tank, although not as effective as an actual injector flush it might help. i've found that techron is one of the most effective ones. you can also try cleaning your combustion chambers by running small amounts of water through a vaccum line at full engine operating temp., once again not as effective as running the actual chemicals used to do this but a much cheaper option(some people like to do this but with tranny fluid, never really tried it) and like kelvin said replacing your o2 sensors might also aid, most people are not aware that doing this is considered regular maintance. remember to check your tire air pressure as well.

Water through the vacuum line to clean the combustion chambers???

Interesting..............I am not sure I would try that one myself.

trying not to hijack the thread, but would it be possible that the o2 sensor could be faulty in our 96 winny? after reading some of the comments here, it seems to be a logical conclusion. our mileage has also dropped a bit from its usual, its also got this little rough idle issue which various sources say could be linked to the o2 sensor causing the engine to run too lean or too rich, the check engine light has been on for as long as I can remember, and the o2 sensor hasnt been replaced since we got the van back in feb. '01 (got it with 70K+ miles and its now somewhere over 100K).

FYI the specs on a '99 are 17 mpg city/ 23 hwy.

dont use water ...

also 02 sensors can be a life saver in instances but if you do not have a engine code for them and replace them anyways and notice no change make sure you hang on to your old ones...


assuming you have checked all your vacuum lines properly..

check into your map sensor...

you can also do a mod on your air filter box too to help increase fuel economy a bit .. but sacrifices some power..

Thanks for all the good advice! The O2 sensors are something I should look into. A mechanic did tell me if the "Check Engine Light" is not, they should be OK. I bought a inexpensiveOBD-II scanner and saw no codes. Before our last trip, I did clean the MAF sensor with some brake cleaner. We also just put new tires on 1 1/2 weeks ago(needed them anyway). Also have run a couple bottles of Fuel Injector cleaner and Premium fuel last couple stops. I may have found something else though. After reading past threads on the IMRC, I found the position on mine were opposite of each other (1 open, 1 closed). Which way is open? Should they be seated against the set screw or intake? I had an assistant rev the engine past 3000 RPM but they didn't move. Shouldn't the PCM light be on if they are deffective? I disconnected them just to see if the PCM light would come on.

Water through the vacuum line to clean the combustion chambers???
Interesting..............I am not sure I would try that one myself.

The 3.8 is notorious for gathering carbon in its cylinders. It's a torque monster and doesn't require high RPM or much throttle to use daily. When you experience serious pinging with almost any throttle setting, the compression is too high from carbon buildup. I treated a 96 Thunderbird with 120,000 that couldn't take 1/2 throttle in 1st gear with premium fuel. I treated a 99 Mustang with 65,000 that would barely accelerate on the highway. In each instance, the pinging went away and the engine became very smooth.
Warm engine, get vacuum hose and attach a basketball inflator nozzle. Attach vac hose near throttle body on vacuum side (top) and run the warm engine at about 2K RPM. Open a can of Berryman's B12 or Seafoam and toss the hose with nozzle attached into it. The nozzle limits the intake so there's no danger of hydro lock. The engine will sputter but the computer will keep it running. As soon as the can is empty (less than 1 minute), kill the engine and let it soak for 15 minutes. Get back in after removing the tube and start it. It will be difficult and there will be enough smoke out the exhaust to obscure the view of everything around you. Once it clears, fill the B12 can with water and do it again. Cheap and effective. The Mustang took two cans to clear up.

I had a similar problem where the engine would run lean, but codes would popup every once in a while and the car would seem to run just fine, but loose gas milage. You may start to see the engine light on in the near future.
I had to clean the EGR ports. It is a very common problem. What happens is oil gets past the PCV valve and gets into the intake and eventually clogs the EGR ports. One of mine was completely blocked. Someone posted a step by step procedure to fix and correct the problem, I'll have to look for the website.
Another problem could be the lower intake gasket. If you have a gas knock all the time, then that would be your problem.

trying not to hijack the thread, but would it be possible that the o2 sensor could be faulty in our 96 winny? after reading some of the comments here, it seems to be a logical conclusion. our mileage has also dropped a bit from its usual, its also got this little rough idle issue which various sources say could be linked to the o2 sensor causing the engine to run too lean or too rich, the check engine light has been on for as long as I can remember, and the o2 sensor hasnt been replaced since we got the van back in feb. '01 (got it with 70K+ miles and its now somewhere over 100K).

It could be numerous items casing the light to turn on.

Step 1. Get the codes read.

simple way to get engine codes for OBD II

http://www.automotiveforums.com/vbulletin/showthread.php?t=518731

My mileage on the freeway with my '96 3.8L is in the lower 20's
During the week, it is really bad...but I drive 10 minutes each way to work, and we have winter formula "Oxygenated" gasoline (with ethanol).
So, there are MANY factors in your fuel economy.
Keeping up on your maintenance, such as fuel system cleaner, air / fuel filters, and tire air pressure are the best things that you can do.