LLY: fuel usage

[jrJones44*]

2004.5 GMC just purchased used. I am the 3rd owner.
First trip out got almost 10 MPG. Discovered the Turbo unison ring was locked up due to rust. Replaced the turbo now it squeezes almost 11mpg.
Disired and actual fuel pressure match. Injector balance within + - 2 at
idle in park +- 4 in drive. Is this all I can expect from this rig?
Sierra short bed 2500HD. What else should I look at?

 

[Burn Down]

What other mods are done?

 

[2004LB7]

Clogged cat? High back pressure?

 

[jrJones44*]

To the best of my knowledge no other mods have been preformed.
However I suspect that it may have had a tune put on it as the mil will not come on.
A friend with a scan tool with Bi/Di commanded the MIL to come on and there was no response. How can I tell if it has had a tune installed?

 

[DAVe3283]

Does the MIL come on when you first turn on the key but before it starts? If not, there could be a wiring problem.

You can use the scan tool to pull the OS calibration numbers, then look up the checksum on GM's site and see if it matches what is in the ECU. That will tell you if it is tuned.

Sent from my Cat S60 using Tapatalk

 

[jrJones44*]

Is approx 11 MPG all I should expect from this rig??/
I have "heard' that it should be doing 15 to 16 MPG.
I have also seen a post that claims 11 is pretty much normal for these rigs??
Any input from you will be helpful.
Thanks in advance.

 

[oscyjack]

Did you check all the basics? Tire pressure, Filters air and fuel, fluid levels, maf map sensors, intercooler boots, brakes?

What size are the tires?

 

[torqued2dmax]

With that light of a truck you should be starting with 15 and going toward 20 with the right mods found on this site ! Good luck finding the problem or problems ! Change one thing at a time and check your progress , its alot of fun !

 

[joshd472]

My lly ecsb got 16-19 depending on speed with 33x12.5 tires. I also got 13-14 towing a 4k lb boat. Hope this helps.

 

[jrJones44*]

Thank you Joshd472. Now I have a base line or perhaps a goal.
ECM had a u1016(code ( not logging into the network) sent it off for a rebuild to A-1 Cardone on Jan 19th LSS (long story short) They dropped the ball and I just put in a brand new ECM which cleared up the code (U1016) and eliminated the P0636 code ( glow plug on Cyl # 6) plus HVAC works proper now. That is why I have not been in the forums for the past 6 weeks.
The theory behind why I replaced the ECM in hopes of better fuel economy goes like this. ECT is reported directly to the ECM but if it does not share that info with the other modules ( such as the FICM and BCM) then default should be rich from the FICM.
I have not run a full tank through the vehicle as of yet so don't know if my theory will prove out. There are no Mods on the truck. I just want it to get reasonable fuel economy and be dependable to operate.
If after I run this tank of fuel through it and it does not get at least 14MPG I will be back in here looking for expected parameters to be displayed on my EDGE monitor in order to identify any other possible problems.
Thank you for your reply.
jrJones44

 

[2004LB7]

The FCIM and BCM dont determine fuelling. The tables are all in the ECM. You are correct in if the coolant temp is reporting wrong it could be fuelling different thus lower milage but this is not something a "U" code will cause

 

[jrJones44*]

Replaced the ECM for the U1016 code .. now getting a solid 14 MPG. better than 11 but I really expected a bit better from this rig. My theory being that the FICM did not know the correct engine temp.I also noticed that the EGT temps are now approx 200F lower. Seems that the dual zone HVAC responds faster that before.

 

[torqued2dmax]

Replaced the ECM for the U1016 code .. now getting a solid 14 MPG. better than 11 but I really expected a bit better from this rig. My theory being that the FICM did not know the correct engine temp.I also noticed that the EGT temps are now approx 200F lower. Seems that the dual zone HVAC responds faster that before.

A good turbo mouth piece , 4 in exhaust , lift pump and mild tune you will see 3 to 4 more !

 

[2004LB7]

Replaced the ECM for the U1016 code .. now getting a solid 14 MPG. better than 11 but I really expected a bit better from this rig. My theory being that the FICM did not know the correct engine temp.I also noticed that the EGT temps are now approx 200F lower. Seems that the dual zone HVAC responds faster that before.

Once again these are not the same as a Ford FICM. It does not have anything to do with engine temp. The ECM does all of the calculations and tells the FICM what to inject.

 

[Bmax]

Remember-Winter fuel=less MPG