So I have an 04 duramax lb7 and I had it plugged in today for the second time, first time was just to check balance rates and today was to check what possibly could be causing my **** poor fuel mileage. Last Sunday made a trip 3 hours and only average about 14 and then 13 on the way back towing a 16ft flat bed trailer unloaded. Well my Fuel Pressure Regulator was running at 35% at Idle! the mechanic said it should only be around 10% and he said he could fix it for 400 bucks which i thought was fair. My only issue is I would like some opinions if that is the correct operating percentage of the Fuel Pressure Regulator and if you think it could make my fuel mileage worse? Common sense says yes because if its dumping 35% fuel at idle thats 25% more than normal and would explain the low mileage and rough idle. Please just looking for some input and enough of you guys have been around these trucks and would love to hear your input. Thanks, Corey Also my #1 injector is running at 3.0 and a month ago when it was plugged in the damn thing was at 2.0-2.5 so may have to battle with the dealer as these were done in November!

 

lots of factors go in to your prob. last time you changed your fuel filter? last time you ran injector cleaner thru your truck? How much does your truck smoke? when you say 35% does that mean it is producing more pressure than normal, if so then you may have a clog. the higher the pressure means you are getting less flow, vs low pressure, you are getting high flow. so in lue of that, if you are running rich, your truck is going to smoke more and get less MPG, vs if there is very little to no smoke you are running lean and you could possibly be starving your tuck for fuel. course you are running an LB7 and they are known for thier fuel probs (mostly injectors)

I like i said, sounds like your fuel sys is clogged or in desprate need of a cleaning.

 

So I should have posted this after it I went and had my truck plugged in again, I never got the Fuel Pressure Regulator changed because I took my truck to a different mechanic who proved that the FPR was operating normally because he had another duramax and started it and the FPR was the same as mine but also my injector balance rates keep jumping around on different injectors. The first time my number 1 and 6 were high then the time after just my number 1 and last time it was just my number 7 and my number 1 was reading low at 0.5mm and before that like a week or so it was up at 3.0mm so im at quite a loss of what would cause my injectors to be fluctuating so wildly and different ones each time. Someone has been telling me the CP3 and I ran half a bottle of standyne through my tank and it jumped up to around 16 mpg in town but when I went on the highway it didnt go above 15 ? I know I have a fuel issue somewhere but so far its not the FPR and my desired and actual PSI for fuel was dead on the mechanic said when we went for a test drive so if anyone has any insight please let me know! Corey