My '04 has been a pretty good little van. I try to keep up on all the maintenance, changing fluids, plugs, wires, EGR, etc... No codes and runs respectively good for the amount of miles on it.

Generally it will maintain an average of about 22 mpg which is somewhat acceptable given that its always been this way and it currently has 192,000 miles on it. But recently within the past couple months or so the average mileage has started to drop to around 18 mpg.

Another strange thing is that when I'd drive down the freeway and reset the average mileage overhead display, the mileage would jump way high up in the 30's and then slowly tick down to about 25 mpg, as long as I was cruising along on the freeway that is. But now within those past couple months, when I do the same thing the overhead doesn't jump up to 30(ish) but resets to only around 21-22 and then quickly drops to about 18-19 mpg. Somethings obviously wrong.....

Could a weak fuel pump cause this? Looking for any advice you guys know of. Thank you.

 

What engine you got?
Could it be your board computer expects much better mpg but measures lower mpg so adjusts accordingly?
I would also calculate MPG by filling tank and set day trip counter to 0 and calculate manually when refilling tank to exclude board computer error

for reference: my 2002 2.5 crd does 33mpg (1L:14Km) in current weather conditions..

 

22mpg sometimes 18mpg...Cough Cough...wait till I faint....Oh god...Must be Petrol and in US of A...

 

22mpgUS on highway/motorway for a vehicle this heavy (2.4tonsUS) doesn't sound bad to me... Oops, think I've a cough too.
Being serious, if you have that gut feeling it's not right, and the engine doesn't seem partic. down on power, see to the injectors. Petrol injectors CAN be cleaned with cleaner, unlike diesel (since they can get gummed up) but you may have to pour it in the fuel filter. Use the same as mechanics use, e.g. Forte is very popular among british mechanics. Otherwise it's injectors out and have them ultrasonically cleaned. See they go back in the same holes.
Also check your ercos for any fuelling fault.
BTW, hope your motor isn't so old it has carburetors...

Leedsman.

 

The engine is the 3.3, fuel injected. No codes. 25 mpg averaged just driving on the hwy is the best this van would ever accomplish too, so if thats just a US thing then it is what it is..... 22 mpg average around town and hwy is the norm. Even the newest Mopar minivan models are still very close to that in fuel mileage. Only vans like the Honda or Kia will achieve better mileage.

But that said, power sometimes seems a little lower but again, with 200k miles on this van, I'm not expecting it to charge the streets with authority. I do remember reading somewhere that if the fuel pressure drops then it will affect fuel mileage and power but I cant seem to find anything indicating this again. Over the past year and a half I've run a few bottles of injector cleaner but there's no great change in power or mileage. The main thing I did seem to notice after using injector cleaner is the fuel pump got real quiet.

 

There are a lot of helpful and knowledgeable members on this forum and although many drive petrol engines the most used engine here is CRD (Diesel) type of van.
I would post you problem on "the other" forum too, best try 2 sources of knowledge in cases like this
4th. Generation Chrysler Minivans: 2001-2007

 

Really, considering your partic. circumstances, high miles on the clock, old vehicle not worth much, the best you can do here is keep up with sensible maintenance.
1) Keep tyres blown up well, 42PSI. front, 35PSI rear. Check there is no feathering of tread due to wheel misalignment by gently running fingers across tread. Check if one tyre is warmer than the rest after a journey. This area can be a major waste of fuel.
2) Get rid of the junk inside.
3) Remember cold weather is always heavier on fuel. So short journeys will always be heavier on fuel than long ones.
4) Remove any brake-bind. This is common with the handbrake/parkbrake on GVs.
5) Drive like a hypermiler; if you don't know what one of them is, Google it. This method of driving involves big anticipation of near-future traffic, traffic lights etc. so you don't waste fuel DRIVING your vehicle into a stop situation, but rather coast into it in neutral. Your autobox will prob. do this for you, mine does.
6) Both spark plugs and high-voltage spark should be good. Long ago it was established that there can be a slight misfire undetectable to the driver which will ruin your mpg figs. Most modern motors have coil packs, i.e. one coil for each plug (thereby elininating the spark-voltage distributor) each coil's primary being driven by a microprocessor based system. If you lift off each coil from its spark plug carefully with engine idling (and keeping your fingers away from the high-voltage) you should be able to hear a noticeable "cracking" noise as the power jumps the gap between coil tip and sparkplug tip. If one is different i.e. a lot quieter, there is a problem there. Some systems have the coils directly on top of the plugs (like my XJ6) and some have a short connector wire for each high-voltage connexion. This will be special supressor wire to reduce electromagnetic interference being radiated. This special high-voltage supressor wire can be faulty, it is only graphited string inside instead of actual copper wire. This is not for the faint-hearted.
And so on and so on.

Leedsman.

 

Thanks for the input guys. I certainly appreciate it. I guess I didnt realize I'd be talking with so many people from other parts of the world who dont have the same exact thing as I do, nor the same road ways or fuel. Hard to compare under those variable differences.

But that said, just to be perfectly clear, driving habits and conditions are all the same as they have been. Vehicle maintenance is kept up too. But if a vehicle used to achieve 25 mpg on a flat freeway at 65-75 mph and within two months that same vehicle under the same conditions is now achieving only 18-19 mpg.....something significant is definitely not right.

 

A "lazy" upstream O2 sensor can cause a drop in mileage without setting a code.

 

Thats worth checking into.