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96' Cummins 12v 5.9L - under 8 mpg! Please Help

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Old 10-09-2014, 10:08 AM
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Question 96' Cummins 12v 5.9L - under 8 mpg! Please Help

Hey there Diesel Bombers - I have already found this site quite useful in my band's quest for a Cummins powered bus.


My main question is : Is there any chance that this is due to simply needing the basics (new fuel and pre fuel filter, new air filter, etc) or does this sound like something more serious?

Details :


Despite the terrible fuel economy we had during our first drive, we still feel we got a great deal on a very unique bus with a great engine that needs some proper attention. We are a hard-working group of musicians, not afraid to get our hands dirty and are very excited to have such a unique and roomy vehicle to travel in.


We got the bus for a great deal - it is a 1996 OshKosh by Goshen with a 5.9L Cummins with the Bosch P7100 sitting on a Frieghtliner MT-55 Chassis (the same chassis found on step vans and smaller fire trucks) I have heard such great things about. We got it knowing it was going to need some TLC both mechanically and visually. We started off needing Leaf Spring Packs in the front, a new tire rod assembly, new alternator, new turbo boot clamp and some other minor repairs. We had them taken care of before even picking up the bus and picked up the bus from a mechanic who had good reviews online at least.

We purchased the bus in Maryland and drove it home to Savannah, GA last night - After calculating the approximate MPG at our second fill up - I realized something was up, as we only were getting around 7 MPG. Next fill up I realized this wasn't just a fluke or miscalculation and since it was the middle of the night we just drove it home despite the poor fuel economy. It is running nicely, shifting smooth, just using a lot of diesel.

Some Specs on the vehicle -
1996 OshKosh by Goshen on a Freightliner MT-55 Chassis
Model : MB19FD
19,000 GVWR
2nd Gen - Cummins 5.9L 12v with Bosch P7100
Possibly Governed to 65 MPH (a hospital owned this bus as a shuttle)


So - I have looked into the typical causes through out this forum and just some of the common sense things to address right away.

-Pre Fuel and Fuel Filter
-New Air Filter
-using fuel additive to Ultra Low Sulfur fill ups
- should Low Sulfur be avoided with the 5.9?
-training the rest of the band to optimal driving habits
-Adjusting the governor and idle
-replacing fuel lines (hopefully not)
-tire pressure

Some things I have come across, but just have little or no experience with :

-Valve Adjustments
-removing 'silencer ring' on turbo
-straight pipe exhaust (some say 4" - and even direct from turbo)
-removing / replacing catalytic convertor (legality?)


Anyway, any suggestions / links would be surely appreciated - if you need any more info - please let me know. From the research I had done on the engine and people running RV's with Cummins 5.9s (since Fleetwood RV's also make Goshen - both under Allied), I was expecting and hoping for 13-19 MPG. I mean is there any chance this is just a case of needed some of the basics (fuel filters, air filters, etc) or does this sound like it could be more serious.

Thank you!
Tyler

A link to eBay where Purchased it from (many pictures) : OshKosh Goshen by Freightliner Cummins Diesel 23PASS AC Low Milesno Reserve | eBay
 
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Old 10-09-2014, 12:56 PM
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Default Also, any suggestions to upgrades would be appreciated

As we replace parts - if anyone has any upgrades that we might as well look into - that would be very appreciated.
 
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Old 10-17-2014, 09:19 PM
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Small engine, large vehicle, don't expect 20 out of her! I do not know about many busses getting better than 8-9...
 
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Old 10-20-2014, 09:36 AM
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The bus we have is basically a Fleetwood RV with shuttle bus windows under the name Goshen made by Allied. On RV forums some guys with the cummins 5.9s are getting 11 mpg towing and 14 - 17 mpg. Would love to be in that range
 
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Old 10-20-2014, 12:20 PM
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Another thing to look at is ur gearing on ur axle if it has 4.11 or even 4.55 u can't expect good fuel mileage or even hight interstate speeds without being wrapped out.
 
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Old 10-20-2014, 12:25 PM
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Yea currently weighing options - the lowest I can go with the Dana 70 hd is 3.54 - I am hoping there is a higher ratio in now and 65 mph will be closer to 2000 rpm - but I am considering getting another transmission as the allison 545 is only a four speed Hear good things about the allison 2000. Someone also recommend an auxiliary overdrive transmission - but I haven't found anyone who has done that with an allison 545
 
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