2004 LB7 Low Fiel Mileage High EGTs

[NJChevrolet]

Hey I’m new to the forum. In desperate need of help! So I have come to summons the gods. My truck is a 2004 CCSB lb7 FED with 250k. Cold air intake 3” turbo mouth piece. Batmo wheel on the ihi turbo. Boost increase valve and off the shelf edge tuner. I’m lifted on 35 nitto mud terrains. So the story goes I use to get 18-19 flat highway unloaded. I have for about 2 years. 20-21 with AT tires. 17-18 hilly/mountain highway and 14-16 towning dependomg on load. For the past few months my mileage has been steadily decreasing and my egts have been increasing. I now get 13.53mpg hand calculated per tank on flat highway unloaded. Freeway is 800-1000 egt amd 1200+ towing. Engine use to burn super clean no smoke but now I have a small black cloud or brown haze under hard acceleration. I’ve checked all the basics. Intercooler boots all looks good. No obvious tears or holes. Boost still hits 22psi easily. Pressure test kit on order. My injectors balance rates are all +\- 1.5 on the worst injector most are around +\- .01-.03. Idle is smooth no surging. I’ve cleaned the MAF but honestly have no idea what to look for on the tech 2 for the maf. My actual rail pressure is spot on with desired pressure. I’m not seeing any real blow by from the engine. I gotta dona compression test still. But With with the “oil cap blowby test” the oil cap doesn’t puff up at all. I was told by a shop my cp3 is failing and that’s why I’m getting low fuel and high egt. That the pump can’t keep up with the tuner requirements. But don’t see how that’s possible if my actual amd desired rail pressure are spot on.im calling bs on the shop diagnosis trying to get me on the hook for $8k. I’m totally lost. Any ideas or help would be greatly appreciated!!!

 

[2004LB7]

my first guess is a plugged cat but you say it's federal emissions no no cat

high EGT is from too much fuel for the amount of air you have. boost psi isn't necessarily mean high air flow. one could have a restriction or dirty intercooler and that will raise boost psi but limit the actual air the engine sees. I would make sure the turbo is good, check the shaft and compressor wheel. check air filter, check for a plugged or dirty intercooler, even a plugged muffler. anything that will reduce the airflow through the engine. don't forget the up pipes. leaking up pipes can reduce boost too but you will not likely see any difference except at higher boost loads and not just light cruising

on the fuel, the balance rates are only part of the picture. we need the main rate too to be able to make since of the balance rates. good idea to just post up all the numbers

MAF normally sits close to 40 grams sec. 38-42 or so is normal during idle

one last comment, with 35s, I seriously doubt you are getting the MPG you state. odometer is likely off or you are calculating something wrong. but as long as you are comparing the same setup from before to now the ultimate number is not important, only the difference from before to now

 

[NJChevrolet]

my first guess is a plugged cat but you say it's federal emissions no no cat

high EGT is from too much fuel for the amount of air you have. boost psi isn't necessarily mean high air flow. one could have a restriction or dirty intercooler and that will raise boost psi but limit the actual air the engine sees. I would make sure the turbo is good, check the shaft and compressor wheel. check air filter, check for a plugged or dirty intercooler, even a plugged muffler. anything that will reduce the airflow through the engine. don't forget the up pipes. leaking up pipes can reduce boost too but you will not likely see any difference except at higher boost loads and not just light cruising

on the fuel, the balance rates are only part of the picture. we need the main rate too to be able to make since of the balance rates. good idea to just post up all the numbers

MAF normally sits close to 40 grams sec. 38-42 or so is normal during idle

one last comment, with 35s, I seriously doubt you are getting the MPG you state. odometer is likely off or you are calculating something wrong. but as long as you are comparing the same setup from before to now the ultimate number is not important, only the difference from before to now

Ok I’ll check the MAF readings and see what shows.
The tires I’ve had on for 2 years so nothing has changed on that aspect except for them get slightly smaller with time as they wear. My speedo I set with 2 different gps readers so I’m 99% sure it’s correct. With the truck bone stock I was getting 23 when I first bought it. The aftermarket compressor wheel boosted my mileage intially 4mpg.
I forgot to mention I am straight piped with 3” PPE down pipe as well.
As far as the balance rates what is the main rate? I’d say I’m pretty mechanically inclined just not sure what the main rate is?
When I get the leak test I’ll inspect the intercooler or possibly have it hot tanked while it’s out if it holds pressure. Thank you for your help! Anyone else have any ideas?