2003 Dodge Caravan 9 to 10 miles city - 15 to 16 miles high

Tiny
LYLY
  • MEMBER
  • 2003 DODGE CARAVAN
  • 6 CYL
  • AWD
  • AUTOMATIC
  • 103,000 MILES
Dodge Grand Caravan 2003 ES model 3.8L engine - All wheel drive, current mileage 103,000.
I bought this van in June-09, everything was fine with it, the gas mileage was 15-16 mile per galon city, 21-22 mile per galon highway.
This calculation is with a known distance, not with the speed odometer, or the overhead display.
6 weeks ago I found out the mileage per galon suddenly dropped down 9 to 10 miles per galon city, 15 or 16 miles per galon highway.
This calculation is with a known distance, not with the speed odometer, or the overhead display.
I though, may be the Oxygen sensor was dead, then I tried to replace the Oxygen sensor, I removed the heat seal to get litle more room to fit the socket into the Oxygen sensor,
I saw the back exhaust manifold was cracked very very bad (caused by what I don't know), I got so exciting and told myself "problem solved". I odered the exhaust manifold from dealer
and replaced it.
To measure the MPG, I drove the van till the fuel warning light's up and filled up 5 gallons and drove till the fuel warning light's up again, all I got was 48 city miles, I filled up another 5 gallons
and drove 1-1/2 hours on highway till the fuel warning light's up again, all I got was 78 miles.
So replaced the cracked exhaust manifold did not fix the "9 to 10 miles city - 15 to 16 miles highway per gallon".
The van runs near perfect, I could drive as fast as I wanted to, I bet even top mechanics drive this van can not tell this is a problem van.
I scanned with the ScanMaster-ELM5 USB hardware, and ScanMaster-ELM, no trouble codes found.
There's no Check engine light, no roughing idle, what so ever.

I did test the back preesure to see if the CAT plugged, nope the CAT is not plugged.
I checked all around the exhaust manifold area to see if leaking, nope no leaking.
I checked the fuel tank along the hoses to the canister and to the engine area to see if leaking, nope no leaking.

Now I've replaced the following parts:
New exhaust manifold.( Of course) Still about 9 to 10 miles city per galon.
New oil and filter. Still about 9 to 10 miles city per galon.
New air filter. Still about 9 to 10 miles city per galon.
New sparkplugs, sparkplugs wires. Still about 9 to 10 miles city per galon.
New O2 sensors (before and after CAT). Still about 9 to 10 miles city per galon.(Bosh brand, somebody told me these must be genuin, after markets no good.)
New MAP sensor. Still about 9 to 10 miles city per galon.
New Throttle position sensor. Still about 9 to 10 miles city per galon.

Any sugestions to fix this.
Thank you.
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Wednesday, November 4th, 2009 AT 3:00 PM

4 Replies

Tiny
BMRFIXIT
  • EXPERT
What is your operating temperature
thermostat and coolant sensor

Fill tank and do you test
and not on an empty one
also consider switch gas stations
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Wednesday, November 4th, 2009 AT 8:46 PM
Tiny
CH112063
  • MEMBER
I'm interested to understand how you are measuring these known distances. And if, after filling your tank with 93 and retesting let me know what your odometer reads at fill-up, and when you are near empty. Just the odometer. What type of distance sensing are you using now. I'm just curious. The warning lamp is not usually used for mileage testing. But how does it run, with 100,000 miles it is pretty good running. Have you ever replaced the fuel pump yet. They don't last too long. Everything was Mopar. New champions also? I liked the 4 wheel drive models. Not too good on gas even new, sorry. OK sir. I'm thinking of getting one, it has no engine but the rest is in good shape. I'm not keen on the 4WD though. You are alone, driving? Thanks.
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Wednesday, November 4th, 2009 AT 11:06 PM
Tiny
LYLY
  • MEMBER
The coolant temperature sensor and the themostat is new.
This case is not low fuel consumption, but Incorrect fuel consumption.(Caused by ?????)
Next step:
Replace the O2 before CAT with the genuin O2 from dealer part.

This route I drive every day for 10+ year, unless the Google map is wrong, the Yahoo map is wrong, the Bing map is wrong, the satellite system is wrong.


http://www.2carpros.com/forum/automotive_pictures/430785_5_MILES_1.jpg

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Thursday, November 5th, 2009 AT 4:06 PM
Tiny
BMRFIXIT
  • EXPERT
I am sure that CH12063 didn't mean to indicate that you are wrong but The method that we are used to use to determine mileage per gallon is that fill the tank mark down the mileage and drive the vehicle until need gas, fill tank
check how many mile did you drive and divide it by how many gallons did it take
that would be the average mile per gallon the you are doing
the method that you explained not a very accurate method

now all that is said I dont think changing O2 sensors is going to help
but feel free to do so its not going to hurt for sure
the PCM is in control of the air fuel ratio and if for a sec that was different it will set a check engine light on and a code

if all was done try and switch fuel or fuel station
fill it up and check you average mileage
dont forget that weather is a big factor too

good luck
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Thursday, November 5th, 2009 AT 5:40 PM

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