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Discussion Starter · #1 ·
I need some help. I have an 02 LB7 3500 4x4. it has 4" exhaust, and FIPK from K&N. 3.73 gears, Allison, stock tires, 70MPH is like 2100RPM

I have a 35ft tag (not a 5th wheel) open car trailer that sees use with two cars on it regularly. I tow about 12000 lbs loaded 1/3 of truck life, 4000lbs unloaded 1/3 of truck life, and drive locally the other 1/3.

I am getting around 13.5 unloaded, and 11 loaded on the highway.

I need more than anything fuel mileage. Power I am not too worried about, but is always nice to fill some punk kids car with black smoke at a stoplight.

Any suggestions? where is the sweet spot that you are running down the highway for fuel mileage?

I was thinking of putting in an edge with outlook, or something similar that i can adjust on the fly. no flash programming the ECM.
 

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The edge juice will bump up the mileage for sure. But they recommend to tow in a low setting. I would suggest the attiude or the a2 monitor also just kinda nice to be able to see what is goin on with the truck. Im kinda new to these trucks but have an edge on mine and it gets way better mileage when i use it. I got 15 to 16 towing with it last weekend. thats my .02
 

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Something sounds funny here. I tow close to 14,000 lbs and average 12.5/13 mpg. And that is a 39' 7" 5th wheel that stands 13'3" in the air. Empty on the highway I average 21/22 mpg and in town 17/18 mpg. My truck is 100% stock. If you are averaging 13.5 mpg unloaded, I would first start by looking into why? Before adding any more parts. I am on my 2nd LB7 Duramax and my previous one got close to the same fuel mileage. I also have over 71,000 miles on this truck.
 

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there is something way wrong with that mileage on a 2002 with 75,000 miles. Has it always sucked fuel like that? I get better towing a 4500lb boat at 70 than you do empty. Empty after it's warmed up at 65, 20+ is routine. 60 MPH even better.

wait till it warms up and check the mileage for a long highway run at 65, it can't be as bad as you are saying unless there's a basic problem - and if so fix that instead of buying a tuner. Tuner won't get you close to what you should from where you are starting.
 

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These engines rely on sensors telling the ecm what to do. Bad sensors or poor values can kill fuel economy. Hook up to a scan tool and check the data stream.
 

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D.Camilleri;1627068; said:
These engines rely on sensors telling the ecm what to do. Bad sensors or poor values can kill fuel economy. Hook up to a scan tool and check the data stream.

Thats all the advice you needed.

Also, My dad uses the Quad at 90hp (not towing) and he added2-3+mpg in town and the 60hp when towing and added about the same. Stock tranny '02 LB7 3500 CC 4X4..

-Colin
 

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new2DmAxnAlli;1627264; said:
Thats all the advice you needed.

Also, My dad uses the Quad at 90hp (not towing) and he added2-3+mpg in town and the 60hp when towing and added about the same. Stock tranny '02 LB7 3500 CC 4X4..

-Colin
Is that hand calculated?
 

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Discussion Starter · #8 ·
I just bought this truck a month ago. I took my truck on a long run from toledo to cincinnatti and back, got 10.5 with the cruise set at 70 the whole way. 2 cars on the 35ft trailer. I have changed the injectors since then, but am still getting the same mileage. I can not get my scanner into my truck, cause it only goes to '01.
 

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My 03 dually gets 13 unloaded and 8-9 pulling 40ft. enclosed race trailer with 65 hp tune. The mileage is accurate when hand calculated. The predater tuner does not let it calculate correctly. It says 22 when it is really 13.
 

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D.Camilleri;1627068; said:
These engines rely on sensors telling the ecm what to do. Bad sensors or poor values can kill fuel economy. Hook up to a scan tool and check the data stream.
Out of curiosity, what would one look for in the data stream?
 

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For starters, towing a 35' trailer with 2 cars on it and getting 10.5 mpg is very acceptable. Trailer towing is more about wind resistance than weight. I just got rid of a 26.5' Jayco travel trailer that only weighed about 7500 loaded and yet I could never get over 10 mpg towing it (3 different trucks and engines, Duramax, Cummins and 300hp 6.5) and that was running 65-70 mph. Mileage would go up to almost 12 at 55 and down to 8 at 75 plus.

My new 5th wheel yields almost 12 mpg at 65 (better aerodynamics)

As far as the data stream, you need to look at the main players as far as sensors go, MAF, MAP, coolant temp, intake temp etc. Look for values that are way out of range. Example would be fully warmed up engine, dash guage shows around 190f but engine coolant sensor only shows 135 on the scan tool=problem. The ecm derives all of its input from the engine sensors, not your dash guages.;)
 

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what kind of scanner?

spuds89chevy;1628155; said:
I just bought this truck a month ago. I took my truck on a long run from toledo to cincinnatti and back, got 10.5 with the cruise set at 70 the whole way. 2 cars on the 35ft trailer. I have changed the injectors since then, but am still getting the same mileage. I can not get my scanner into my truck, cause it only goes to '01.

What kind of scanner are you using? I have a Snap-On MT2500 and my cartridge only goes to 01, however the snap on guy told me to try and fool the scanner by playing with the vin number on intial setup. It worked for me. If you have this scanner and cannot get this to work, let me know, I will give you my "fake" vin so you can try it out. I think once your in the computer, you will use K-9 key.
 

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what kind of scanner would one look for when trying to find out this information? i get 14-15 mpg driving 1/2 highway and 1/2 back road. i noticed this shortly after getting my new tires, and i didnt have the edge yet. what would the varying temps mean as far as from actual to what the guage reads? cause my coolant guage reads 185, but the edge reads 170.
 

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spuds89chevy;1628155; said:
I just bought this truck a month ago. I took my truck on a long run from toledo to cincinnatti and back, got 10.5 with the cruise set at 70 the whole way. 2 cars on the 35ft trailer. I have changed the injectors since then, but am still getting the same mileage. I can not get my scanner into my truck, cause it only goes to '01.
Do you hand calculate your mileage or just look at the DIC?
 

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check your rpm also, i turn about 1900rpm at 70mph, might not be locking torque converter or going into 5th.
 

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Discussion Starter · #17 ·
I do not have the fuel computer in the truck. I hand calculate it all the time.

As far as the scanner goes, I have a Snap-On Mt2500. I tried changing the year in my vin to a 1 instaed of a 2, but the data stream is way off of what it should be-it is the scanner- had it checked by a tech 2 last week.

My torque converter is locking up, everything is working as it should
 
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