I have an 01 Grand Caravan 3.3 with 104k. City driving I get 11-12mpg at best. I have replaced plugs, wires, coils, upstream 02 sensor, map sensor, tried different fuel brands and grades. Still at the same place with 12mpg. When I'm driving, it kind of feels like I'm dragging a boat anchor or a trailer when I give it acceleration. It rolls fine when I let out of the gas or put it in neutral and coast. Transmission seems to always be in the wrong gear when in drive. No check engine light on. I drive it about 3 miles one way to work and 3 miles back home. When I get there, something smells really hot underneath. I am wondering if maybe the catalytic converter is partially or fully clogged up, but again, no CEL on. The exhaust sounds hollow and doesn't seem to move very much out the tailpipe at idle. I am wondering if I should change the transmission control solenoid first and see if it straightens out the driveability issue. I am thinking I have more than one issue going on. Should I have a shop check out the fuel trims?

 

I think that year have problems with melts injector harness. Might want to inspect it.

 

I would check to see if any of the brakes are dragging. Jack it up and try spinning the wheels. It could be a brake hose has collapsed or a caliper isn't releasing.

 

It doesn't have any misfire codes but I will inspect that harness anyways. All the wheels spin easily with the exception that the rears rumble and grind a little bit. Product of drum brakes I think. Nothing sounds or feels too unusual. .

 

I unplugged the 10 wire injection harness connection and peeled back the wrapping. There were 2 wires that were definitely damaged and a couple others that had the insulation sticking together about 3" from the plug. I cut the whole connector off leaving about 1" sticking out of the plug and took about 5-6" of wire out of the harness. I then soldered and heatshrink along with tape 6" of new wire to all 10. I don't think any of the conductor piece of the wires were physically touching each other, but the black with yellow stripe was completely melted through in about a 2" piece. There was also I believe it was green/blue stripe or blue/green stripe that had a portion that the insulation was so thin I could just scrape with my fingernail and get to copper. I put it all back together, zip tied the harness away from the exhaust, and took it for a drive. Everything seemed fine, and I did notice a bit more power and get up. I no sooner than get back and the CEL comes on. Scanned with scanner and it came up something about EGR. I went to the auto parts store and got a new EGR valve and transducer assembly with gaskets. Replaced that and what a difference. Van seems peppy again and doesn't downshift everytime I touch the accelerator. Seems to have more power going up hills as well. Not sure what exactly fixed the issue, but I am going to monitor the fuel mileage and see if it's any better.

 

Fuel mileage is still horrible. When I drive for more than 10 minutes and park, when I get out something smells really really hot. I am thinking maybe the catalytic converter is clogged but I have no check engine light on. Is there any 5 minute way to test it without a thermal imager? I am also thinking about replacing the transmission shift solenoid as it will not shift from 3-4 when it's cold. After I have driven about 2.5-3 miles when it's cold, it finally shifts. Thoughts?

 

Check Trans Fluid level.

Try a Torque Converter Stall test. Apple the brake with your left foot as hard as you can in Drive, and Floor the Gas pedal with ur left foot for 5 second.
(Make sure there is NOTHING in front of your car incase your brake lets loose, do this in empty parking lot)

RPM should NOT go over 2500 RPM, if it goes pass 2800 RPM and you Car is stationary, I think you have a worn out TQ converter.

 

OK I did the stall test. When I hold the brake and floor the pedal, the rpm goes to about 1750rpm and wont go any higher. What is the stall RPM supposed to be?

 

I also read this: There is something like a fifth gear in the torque converter that locks in when the van is on the highway and the computer senses a steady speed over 55 miles per hour. This 5th gear will lock in and prevent any slipping in the torque converter clutches and reduce engine RPM to approx. 1500 RPM's giving you about 2 more miles per gallon on the highway.

Mine never does that. When I cruise on the highway at about 70-75mph, my RPM's are about 2300-2500 and they stay there. When I come to even little hills (no matter if I'm running the pedal or the cruise control is) it downshifts almost like it doesn't know what's going on. It never tries to climb the hill without downshifting.

 

Stall speed is less than 2500 RPM, you are OK.
2300-2500 RPM at 75 MPH sounds normal, and down shift on incline is also normal, part of the traction control system.

kinda hard to tell if you got a clog exhaust unless you stick a back pressure gauge on it. But normally if you floor the gas pedal, and the car goes up to max RPM rapidly, your exhaust should be fine.

maybe your mileage is as good as it gets due to a worn out old engine...