2006 2500HD horrible mpg

[jt metal]

I finally got her started. Got her up to highway speed and the orange engine light started flashing. Drove the truck appx 130miles. And took almost half the tank. 34gal tank. Truck ran & drove perfect

 

Where should I start?

[markwilks]

I just had the flashing light on my 03.  Low fuel pressure was found and needed a new fuel pump and they cleaned a screen or something that is in the fuel system.  The also cleaned the MAF.  I haven’t had a problem since.  I would be running 70 and all was fine.  As soon as I have it gas and hit about 74 the check engine light would start flashing at me. 

Edited August 26, 2018 by markwilks

[Supreme Pizza]

10 minutes ago, jt metal said:

Where should I start?

 

 

   Go to your local auto parts store and say this: 

 

   "Please scan my car for OBD2 codes" (free service)

 

  Write down those codes, and post them in this thread. 

 

   That would be a great starting point. 

[jt metal]

Will do & thank you......

[jt metal]

14 hours ago, starman8tdc said:

 

 

   Go to your local auto parts store and say this: 

 

   "Please scan my car for OBD2 codes" (free service)

 

  Write down those codes, and post them in this thread. 

 

   That would be a great starting point. 

P0300 random misfire detected. they suggest to repair cylinder head ground wire?

[Supreme Pizza]

20 minutes ago, jt metal said:

P0300 random misfire detected.

 

   So the problem is not specific to one cylinder, which means you don't have a single bad injector, or a single bad spark plug. It would need to be a problem that is common to all the cylinders, such as a fuel pressure issue or clogged air filter. Could even be a problem with the fuel quality or something else simple. 

 

    If you run it too long with that problem, the extra fuel in the exhaust can damage your catalytic converters. 

 

   As for the ground wire, just grab any old piece of wire, and attach it to a bolt on the head, and attach the other end of the wire to a bolt on the body. Then disconnect the battery for 5 minutes, and then hook it back up. (that will clear the code, and turn the dash light off) . If the code comes back after driving it a few times, then the ground wire was not the issue. 

[jt metal]

Ground wire appears to be in good shape. Honestly, truck idles & drives good. Converter damage would seem to be inevitable. Need to fix......

Just killing me at the pump. 

I know if I disconnect the battery to reset, code will reapear.........at this point. 

[Supreme Pizza]

Just gotta start going through the possible issues one by one. 

 

Vacuum leaks

Dirty mass airflow sensor

Bad spark plugs / plug wires

Dirty throttle boday

Front end allignment

Tire pressure

"auto" rather than 2x4 mode

PCV or other emissions issue 

Defective engine fan clutch 

A/C clutch stuck on 

uh....... 

 

 

Any other MPG ideas guys? 

 

[rusty503]

Do not assume that the ground cable is good just by looking at it. A lot of problems are actually caused by corrosion inside the terminals and in the cable itself where you cannot see it. It may look like a dream on the outside but hell inside. I have read numerous instances where someone removed the terminals, cleaned them up, put it back together with no improvement of the issue. They would then change the cable and problem solved. I am not saying that that is your issue but looks can be deceiving.

[jt metal]

While i agree with responses. Especially the funny ones. The possibilities of a code P0300 are endless. I'll update when the tech let's me know. 

[newdude]

Intake manifold gasket leaking is a somewhat common P0300 cause on the Gen III LS/Vortec small blocks. 

[txab]

^^ +1

[carkhz316]

Can you plug it into a scan tool to view live data and/ or post the freeze frame data? I'd hate to have you throw parts at it and find it was nothing big. I saw your other thread that mentioned the batteries were dead for an indefinite amount of time. I'm going to guess that even with the engine light flashing at 70mph+ the engine continues to run smoothly? Before you do anything else (besides the aforementioned) perform a crank angle relearn, especially since you said it runs fine otherwise.

[jt metal]

Here we go.....

 

Tune up $225. Did not solve the problem

 

Clean up crank sensor.....$210. did solve the problem

 

Thanks guys! Hopefully this can help someone else. 

 

 

Edited September 4, 2018 by jt metal

[jt metal]

False alarm......lite back on. Bring it back to guy this week.