Sudden loss of fuel mileage

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easys4.2gq

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Sep 28, 2010
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Hi Everyone I have a 2008 LMM Duramax and Allison fitted to my Nissan Patrol. The engine had 35,000 miles on the clock when I fitted it and I have done about 28,000 miles since.
I was getting about 18miles/gal and it has suddenly dropped to about 11miles/gal Truck seems to go as well as normal - every now and then it throws a B2AAA code which puts the truck into limp - fine once cleared I have put new fuel and air filters in changed oil/filter
I have logged the injectors balance rates and attached the results. Does anyone have anything else I should be looking into? Thanks Elliot
 

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easys4.2gq

New member
Sep 28, 2010
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Since the change in economy I have done no changes.

The engine has no egr, I have re routed the pcv, has dsp5 with standard tunes through to 450hp but run on standard. Truck has 3.9 diffs and 285 75 16 tyres. I have a cat in the exhaust so next thing is to check if it is blocked.
 
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easys4.2gq

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Sep 28, 2010
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When I first turned the vats off I checked dpf and it looked like all settings were switched off. I will check again to make sure all is off
 
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easys4.2gq

New member
Sep 28, 2010
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Since plugging in efi live and removing my scan gauge 2 I haven't been able to get a code or the truck into limp.
Fuel economy is still crap

When comparing injector balance rates are you comparing what they are running at live or comparing min to max or average?

Thanks
 
Rancelot211

Rancelot211

Boyd
Jan 28, 2015
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Ohio
Balance rates don't mean an injector is good. Return rates can be bad. What rail pressure are you seeing and have you changed ur fuel filter?
 
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easys4.2gq

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Sep 28, 2010
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Yes put a new filter on.
At idle fuel pressure says 30mpa and in neutral and rev it up it goes up to 136mpa
Went for a drive and it went up to 184mpa the actual and desired matched as far as I could see
 
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RPM Motorsports

RPM Motorsports

smokinum
May 13, 2008
3,271
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Central Valley Ca.
Drop the exhaust and see if your fuel Milage comes back. Not knowing the quality of your diesel there, it might be dirty enough to plug a cat on a stock tune. Still making the same boost and egt's as before?
 
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easys4.2gq

New member
Sep 28, 2010
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I pulled the cat and fitted a straight pipe - the cat did look pretty dirty but now gone through 2 tanks of diesel and no change to economy still around the 11.

The truck hasn't thrown any codes for ages so still waiting with the laptop and EFI live to scan it when/if it happens

Can the Allison cause poor economy? torque converter? 90% of the time the engine is run on a stock tune the other tunes are towing and up to 450hp
 
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