poor MPGs/High rpms..

[spitfyre]

hi everyone, I'm posting about my girlfriends 99 sport.
its got the 4.0 sohc, and she gets terrible mileage.. about 400-440 kms to roughly 65 litres.. (250-275 miles to 17 gal) so right around 15l/100km or 15mpg, this is mostly highway driving, cruising around 70mph, fairly flat road. I've noticed her rpms around 3300 at that speed. is this normal? it seems to me like the tc isn't locking up, letting it drop those extra couple hundred rpms.
there's no codes showing for the trans, although i know i need to do her intake gaskets before winter. the truck runs fine when its warm out or it warms up in the winter though and only has 140000kms (88000 miles) on it
stock size tires, running 35psi, is this normal mileage for her?

 

[carguy1959]

I have the same problem with my 98 sport. I've been searching to find if there is a lockup solenoid that controls the converter, haven't found one yet. My trans shifts fine, but my rpm's at 70 are almost 3500 and yes my hwy mpg sucks.

 

[deweyville65]

What rear gear you guys running? My 96 4.0 OHV, auto, stock 235-75-15, 3.73 gears, runs an indicated 2200@ 65 MPH, 2500@ 70 MPH. Speeds verified with GPS and time/distance calculation. 20+ MPG.

 

[budwich]

op, sounds high. You should be able to count the shifts / monitor the tack to see how many changes you get. that will tell you a bit.

 

[carguy1959]

The problem is deffinetly a convert lockup issue. I have been searching old threads, most simular threads are on the older trans..