Engine/Transmission (1994 - 1998) Good highway milage (22), POOR city (10) -????

[tp0d]

Hopefully someone has some speculation on my problem here... Ok, here goes...



Bought a 96 CTD a few months back, great shape, great price... As far as I can tell its completely stock, no afc or plate mods. All filters have less than 2k on them. On the highway, I get aprox 20-22mpg at 60-70mph @ 1900rpm (3. 54), but... in the city, which is about 40-50% of my driving, depending, I get aprox 8-12mpg. Truck runs great, no misses, no smoke (at ALL, which is kinda strange... Ive -never- seen it even puff), stock exhaust (I have a new 4" turbo back on order). The only thing I can think of is its possibly my transmission, which is the original, but has been removed at least once for some type of work. It shifts ok, and I have done a stall test on the converter to see if its slipping, and as far as I can tell it isnt. Might be my valves need adjusted? I have no service records for this truck, I think I`m going to call dodge and see if they can reference records via my vin, to see when and what was done last...



Any suggestions would be appreciated...



-j

 

[DBentley]

mabey a timing adjustment would help. I have same truck and I get 12 city winter, 14 city at best in summer and 16-17 highway at best with summer or winter mix fuel. How do i do a stall test to ck the converter?

 

[tp0d]

Dbentley:



My 96 service manual sez to warm up transmission to normal temps by driving it regular for a few miles. Then apply front brakes and parking brake. With truck in drive, mash pedal for a max of 7-9 seconds to find top RPM. If above 2100-2300, your converter is slipping. *note* This procedure causes a spike in transmission temps, do NOT go over 10secs in this procedure, and when done, shift to neutral for at least 30secs to cool oil...



In my opinion this really doesnt do too much, as it will only give accurate results with a bone stock engine, and even then it doesnt tell too much... I`m thinkin about a new transmission... sigh. . there goes the bank account. . heh



-j

 

[JohnE]

Stock slip converter.

I have an after market converter that is much tighter than stock and I average around 20 combined town & highway driving.



I say town as I puposely drive to hit all four traffic lights on my way to work.



I don't understand slip in an un locked converter. Stall is based on fixed impeller & turbine fin geometry. How do they slip?

 

[bmoeller]

A torque convertor doesn't really slip itself. Just a fluid coupling. The only only thing that can actually slip, is the lock-up clutch.



They are trying to check the stall speed of the convertor.

 

[JohnE]

Originally posted by bmoeller

A torque convertor doesn't really slip itself. Just a fluid coupling. The only only thing that can actually slip, is the lock-up clutch.



They are trying to check the stall speed of the convertor.

Exactly my point.



The factory converter is pretty renowned for poor fluid coupling and high (for a diesel) stall rpm.



Fluid coupling is based on impellor & turbine fin geometry and factory stator (forgot about that in first post). If it falls out side the rpm window does that point to a factory defect in fluid supply or TC build?



I burned the factory lock-up clutch which prompted my after market replacement. (If I slip this after market converter than something is really wrong!). The tighter fluid coupling is sometimes a pain but rewards with better fuel economy.

 

[tp0d]

So slack in the valves couldnt have any affect on mileage? I dont hear any excessive noise in the engine, at least when I compare it to my dad's overvalved '99... heh. . guess I gota start saving my pennies for a better transmission... sigh





-j

 

[I-6DZL]

tighter fluid coupling a pain ?????

Originally posted by JohnE

Exactly my point.



I burned the factory lock-up clutch which prompted my after market replacement. (If I slip this after market converter than something is really wrong!). The tighter fluid coupling is sometimes a pain but rewards with better fuel economy.

John how is tighter fluid coupling a pain??? Examples?

 

[JohnE]

Re: tighter fluid coupling a pain ?????

Originally posted by I-6DZL

John how is tighter fluid coupling a pain??? Examples?

Much harder to adjust the idle.



Winter I have to drop it way down to keep from powering the rear tires at snowy stops.



Summer I have to up the idle to keep from stalling when running A/C and standing in gear at a stop.



Higher idle means the trany slams when shifting into gear.



Low stall also means it takes a bit longer to spool the turbo when looking for the fast get away.



I'll live with the nuisance stuff. It beats the slop (stock) converter hands down.



edit

Most of my examples are higher torque multiplication coupled with lower stall.

 

[McCRam]

When I got my truck the mileage was very disapointing. 14 - 16. The tank after I replaced the fuel filter gave me 19. It ran a lot better to.