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Old 09-03-2017, 07:52 AM   #1
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Fuel mileage improvement

Since the ISB fuel pump was replaced a year ago, my fuel mileage has improved from 7.5 mpg to close to 10 mpg. This is based on 11,455 miles traveled on all kinds of road conditions in the lower 48 states.

Cummins diesel, ISB 24 valve with 66,xxx total miles and an Allison 6 speed transmission. Typically drive 62 - 66 mph on the interstate, which accounts for 90% of the miles. 28,000 pounds total weight, INCLUDING the 4,000 toad. Diesel gen set runs about 200 hours this past year, total hours close to 5,000.

I know, at times when fueling, there is foam or air which causes the pump to shut off before it's actually full, but over time, this should equal out.

Has anyone else experienced this same increase in mileage after replacing the fuel pump or does it have more to do with the diesel engine finely breaking in?
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Old 09-03-2017, 08:43 AM   #2
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Quote:
Originally Posted by tizzyfit View Post
Since the ISB fuel pump was replaced a year ago, my fuel mileage has improved from 7.5 mpg to close to 10 mpg. This is based on 11,455 miles traveled on all kinds of road conditions in the lower 48 states.

Cummins diesel, ISB 24 valve with 66,xxx total miles and an Allison 6 speed transmission. Typically drive 62 - 66 mph on the interstate, which accounts for 90% of the miles. 28,000 pounds total weight, INCLUDING the 4,000 toad. Diesel gen set runs about 200 hours this past year, total hours close to 5,000.

I know, at times when fueling, there is foam or air which causes the pump to shut off before it's actually full, but over time, this should equal out.

Has anyone else experienced this same increase in mileage after replacing the fuel pump or does it have more to do with the diesel engine finely breaking in?
I can only think of two possible causes for such an event. The first being the break-in theory. However it seems a bit steep in such a short time frequency.

The second, and I have experienced this once, is a transmission program change. This would require that the service people, for some reason, disconnected the chassis batteries briefly. When this occurs, the transmission configuration remaps the operations of shift patterns and timing. Still, your change seems pretty drastic. Mine was a whopping 10% or so, no where near your numbers.

Anyway, that's all I can come up with.

Peter
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Old 09-03-2017, 10:46 AM   #3
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I can only think of two possible causes for such an event. The first being the break-in theory. However it seems a bit steep in such a short time frequency.

The second, and I have experienced this once, is a transmission program change. This would require that the service people, for some reason, disconnected the chassis batteries briefly. When this occurs, the transmission configuration remaps the operations of shift patterns and timing. Still, your change seems pretty drastic. Mine was a whopping 10% or so, no where near your numbers.

Anyway, that's all I can come up with.

Peter
Hi Peter, Interesting comment about the Allison transmission. Rocky Mt Cummins in Billings, MT replaced the fuel pump. I was heading ESE to Rapid City, SD. The following morning, on the way to Sioux Falls, SD, the transmission WOULD NOT upshift, so my maximum speed was 45 mph on the interstate where the speed limit was 80 mph. Not fun listening to the emergency flashers blink/buzz constantly for 7 or 8 hours. I spoke with the Allison repair facility in Sioux Falls and they suggested I take it to Cummins next door and have them run the diagnostic, which they did and it showed NOTHING. The mechanic played with it for 7 hours and took a flyer on replacing a solenoid on the top of the transmission. He said, in 20 years, he'd seen a few fail and they didn't show up on the diagnostic. So, for a $75 part, it seemed like a good bet. Sure enough, that was the problem. Getting back to your comment, I'm not sure if they reprogrammed the Allison transmission or not, but it's something that could have happened and might account for the improved MPG. The only other thing I can think of, Rocky Mountain Cummins made the decision, WITHOUT asking me, to disconnect the Banks program from the engine. The only difference I noticed from that was neither the boost gage and the turbo temp gage moved off of zero from the moment I left Billings, MT.
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Old 09-03-2017, 05:02 PM   #4
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I can't help you with why your mileage suddenly changed. I can confirm though, that your 10 mpg is very consistent with what our ISB has given us in our 2013 Ventana LE 3434 since we got it, so I think you can count on it remaining at that level.

Years ago we had several 5.9 liter Cummins engines, and they were always very fuel efficient. Our last motorhome had a 9 liter CAT engine that averaged about 7.2 mpg, so I was thrilled to learn that our current motorhome with the ISB engine was back up in the area of 10 mpg.

Good luck with your motorhome, and I hope the fuel economy stays where it is!!!

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Old 09-03-2017, 06:56 PM   #5
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When I replaced the factory fuel pump with an after market in our ISC I gained about 1.5 mpg.

Don
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