Engine/Transmission (1994 - 1998) Poor Performance/Mileage

[PSInt]

I bought this truck a couple of years ago, paid a premium price over a gas engine, because I wanted the great performance and fuel mileage of the Cummins Diesel that I've heard so much about. To date I've had neither..... best mileage has been 15 but usually between 12. 5-13. 5. NOT GOOD ! The power leaves some to be desired too, but I've been living with it. Recently the front clutch hub in the automatic transmission let go and I decided while the trans was out, I'd do an upgrade. Bought a converter, valve body and HD overhaul kit from Sun Coast Converters in Ft. Walton Beach, Fl and installed them. The transmission works and shifts GREAT ! and the instant spooling to 2000 rpm is no longer there (hated that !), but now it's REALLY a DOG until I reach 15 mph or so. Haven't set the timing or valves yet (on my list). Tried to find a place in Jacksonville, Fl that could set the timing but not even the Cummins shop wasn't interested. They sent me to a couple of independents that knew less than I do. Are there any clubs or just maybe a support group in the Jacksonville, Fl area ?

 

[Heetseeker_1]

bump the timing up

If you bump the timing up you will probably notice a difference in the low end torque and mileage. The problem with the tighter torque converters is that when they hook up sooner (at lower rpms) the turbo doesn't spool up as fast. This causes an increase in smoke and a doggy feeling starting from a dead stop. Put a 6k trailer behind it and start off up a hill from a dead stop and you will have people running towards you with fire extingishers! If you find a way to get around this, let me know.



Steve.

 

[PSInt]

Wouldn't mind a little smoke if the darn thing would just move ! Put my 7000 lb boat behind it now and It'll be cold outside before I get it to the water ! Maybe I'll just replace the plate and see what happens. Costs about the same as the tool to set the timing... .

 

[Heetseeker_1]

more fuel

Well, that couldn't hurt for sure. It will give you more fuel to throw at the situation and that ain't bad! You could try turning the star wheel on the AFC housing towards the engine a few clicks at a time and see if more fuel at low boost will help some. I know it will give more smoke!



I have a #6 tst plate 250hp/635 tq and I could always use more power. What plate are you running now?



I see you have the 3:54 gearing. How many miles on the beast and at what rpm and speed do you usually drive?



Steve.

 

[PSInt]

I haven't done a thing to the engine yet. Still stock as far as I know. Most of my driving is back and forth to work (10 Mi). All the roads here are pretty much flat. Occasionally I tow a 7000 lb boat but not often. Bought the truck with 86,000 mi and now it has 104,000. The transmission was gone through in 1998 and just overhauled again last week. Hope it's a forever transmission now. I can't help but think the timing is way retarded just because it's such a pig and uses so much fuel. going to get into it soon. I'm torn between getting a cam plate first or ordering the tool to set the pump timing. Hoping for some input from here to help me make up my mind.

 

[Heetseeker_1]

questions/questions...

If it were me, I would do the timing first. If you put a plate in now with the timing supposedly off, your mileage will really dump. You will be using the new found power that the plate will bring and there might be a slight drop in mileage as a product of you dropping the hammer and racing around.



One of the hardest things to to when bombing, I have found, is assign priorities to each mod and follow through with them. ... Yea, guages look cool, but how can you pass up power mods first?... .



The GAF method...



G guages

A air mods (intake, exaust)

F fuel mods (cam plate, afc adjustments)



Be carful not to attempt these in reverse! That method might raise a few eyebrows...



Steve

 

[JSmith]

I would put in gauges,have the valves adjusted,then a # 6 TST plate,and have it timed.

 

['956Wheel]

Time it to 15 or 15. 5 BTDC and you will be able to pull water skiers up! NO BOAT needed, just a road by the water... . and a good skier!:--)



Mike

 

[Bseg]

Everyone talks about timing on these, how do you time one? What's the max you can go up to?

 

[Dennis Garrett]

You can pick up a Haynes manual at most any auto parts store, they have a pretty good chapter on how to replace the pump, &/or set the timing. Have a few timing charts for different CPL's too.

 

[jimk]

timing

Set the timing to 15. 5 and slid the stock fuel plate all the way forward along with the afc housing.

Next buy some gauges and later on install a tst plate and a governor kit. Check the rocker like Piers suggest when you install the fuel plate. I would use a 4k spring kit next time as it is suppose to make more power than the 3k kit.

The timing is the only thing that I have done that increased mileage, from 15 to 19. 5 but never 20. What a dog the 95 was.

No wonder the guy sold the truck. I bought a snap on tool timing set and some dilivery valve washers. I would say the difference is like from going from 2 degrees btdc to 12btdc on a small block chev. lol Jimk

 

[redramnc]

Something is definitely amiss with your combo if you are not getting over 15 on the road. My 96 2WD pre-bomb got 21. 3 at 75-80 mph with the AC on. With just a 4" headpipe back (no cat) I went up to over 23 mpg on long runs. My truck has 116K with a stock rebuild (lousy stock replacement TC) on the trans and 3. 54 and is getting these numbers. I would suspect that you may be right about your timing, especially now that you have a tighter trans.



Good luck sorting it out.

 

[Bud Fox]

I had the same problem as you and tried to chase it down to no avail.





The short trips are killing your truck. I get 11-13 in the city and have the timing done, plate, GSK etc etc etc and my mileage still sucks. The guys who drive 30 miles to go food shopping and to Home Depot are the ones who get the better mileage not short trip guys like us





You can do the timing etc if you want to. Yor truck will be alot more fun to drive but your mileage will not increase with these mods.





You need to move to Montana to get good fuel mileage



7000lb trucks dont get good fuel mileage in stop and go driving

 

[PSInt]

I've done several road trips with the truck and even then it only gets around 15 or so. I think I might have broken 16 once, and that was on a flat, straight road in Florida. Most tell me they get around 19-22... ... I'm not even close ! Valves are set now, but it didn't make any difference..... Didn't really think it would. Guess I'll just have to keep on trying..... After spending almost $2000. on the transmission repair I'm kinda' buried in it.

 

[Bud Fox]

19-22 with a 2wd maybe





I'd bet no one gets 19-22 with 4x4 auto in Jacksonville

 

[sfelts]

I get 15-19 depending on how I drive. usaly around 16. 5. My tryck is stock including the trany. I drive 50 to 100 miles one way to work. the short drives will kill mileg espacily in a dodge.

 

[Gary - K7GLD]

SIGHHhhh!



The guys with the 4x4's NEVER get it!



"Something is definitely amiss with your combo if you are not getting over 15 on the road. My 96 2WD pre-bomb got 21. 3 at 75-80 mph with the AC on. "



YUP - easily done on a 2x4 - but a 4x4?



FORGET IT! On average, it just doesn't happen...



You go out and pay LOTS of $$$ extra for those extra fancy gear boxes and transfer cases (that you probably RARELY use!) - guess what it takes to keep them turning!



FUEL FUEL FUEL... . and $$$



Welcome to the real world of physics and mechanical advantage...

 

[PSInt]

:{ I expect to lose maybe 2 mpg for the 4X4, but the front axle doesn't even turn in 2X4. Yes, the left front is always connected but that will just spin the spiders in the front axle. That and the gearbox shouldn't make THAT much difference. By the way, I'd like to take this opportunity to thank the engineers at Chrysler for designing yet another front diff that will not accept locking hubs. Automatic 4X4 is great for the preppy, people that are not mechanically inclined enough, or are too lazy to operate manual hubs but for durability and economy you can't beat lock outs. They could have at LEAST made the front axle so it could have been converted.

 

[redramnc]

I'm with PSInt - give me a mechanical locking mechanism for the hubs or make it full-time like my 78 Powerwagon I have several Scouts and we are going to put a Scout driveline under a 1960 Dodge Town and Country. The locking hubs used on the Scout are as good a design as can be found and I have never had any problems with them. Also, you know when they are engaged - no electro-vacuum-mechanical crap to go through - they either is or they isn't and you get to decide.

 

[sfelts]

Originally posted by Gary - KJ6Q



The guys with the 4x4's NEVER get it!



"Something is definitely amiss with your combo if you are not getting over 15 on the road. My 96 2WD pre-bomb got 21. 3 at 75-80 mph with the AC on. "



Ok now I totaly understud that the 4X4 would not get the miledg that a 2X4 would plus I have 4:10 gears that dont help. For me to be doing 75-85 mph I am running at max RPM. and by puting bigger tires on and having the longest dam truck I could buy at the time. Makes for low miledge. But as I said if I maintain 65 MPH I will get 18 mpg. So it is not so much the 4x4 that makes the low miles it is a combo of things.