6.0 runs but no power
 

working on a 2006 hummer 6.0.it has only code p0300 random misfire when I push the pedal down it just bogs down and has no power . everything has been changed with no luck .it has new throttle body. pedal .tac .coilpaks plugs and wires still runs smooth at idle .it just has no power when the pedal is pushed down and in gear any help ? [ edit it has the orginal injectors]

Re: 6.0 runs but no power
 

Check fuel pressure. Use a back pressure gauge in the upstream oxygen sensor locations and check for clogged converters.

Re: 6.0 runs but no power
 

I checked the fuel pressure its on 60psi. what is a back pressure gauge ? i will check it maybe the converters i have never had any go bad it can

Re: 6.0 runs but no power
 

Re: 6.0 runs but no power
 

Does your fuel pressure gauge have the bleed port on it?
Hopefully it does, hit the bleeder and see if the engine dies. It shouldnt kill it when you hit the bleeder. P0300 with the description of runability you described id bet $100 that pump has pressure but no volume and it will die instantly when you open the bleeder.

Remove the 1st o2 sensors on each bank(precat 02's) and go drive it, if the power is improved you have clogged cats like mentioned above.

Re: 6.0 runs but no power
 

ok thanks I will try it mine does have the bleeder hose. I did check the pressure with it running but not like you said. also I will check the 02s

Re: 6.0 runs but no power
 

Is it just when it’s in gear? What trans are you using. I had this problem with a 6l80 trans but turned out the trans was in limp mode and stuck in 3rd gear so seemed like no power. Ended up being no power to the trans so it wasn’t throwing a code either. Just something to think about.

Re: 6.0 runs but no power
 

Is it just when it’s in gear? What trans are you using. I had this problem with a 6l80 trans but turned out the trans was in limp mode and stuck in 3rd gear so seemed like no power. Ended up being no power to the trans so it wasn’t throwing a code either. Just something to think about.

Re: 6.0 runs but no power
 

it has a 4l60e

Re: 6.0 runs but no power
 

I give up I am guessing it something to do with the transmission it was running good and smooth and when I went to drive it the transmission would not change and the check engine light came on and wouldn't get over 30mph its in the limp mode .

Re: 6.0 runs but no power
 

You would have more codes than P0300 if it was in limp mode. It would also run good and have decent power at 20 mph+. Limp mode is 2nd and 3rd on the 4L60E/4L65E/4L70E. You have a 4L70E in that hummer btw. It’s essentially a little more heavy duty 4L60E

Re: 6.0 runs but no power
 

it maybe the 4l70e it sits so low I jacked it up and took out the 02 sensors to verify the cats are ok and checked out the injectors .it was running good until I drove it .it would not shift out of gear and the check engine light came on and it wouldn't go over 30mph

Re: 6.0 runs but no power
 

I unplugged the maf sensor and it is running fine with no skip or miss but when I drove it it started to miss and go rite back into reduced power mode . I atleast know there is nothing wrong with the engine .it has to be a sensor or ecm

Re: 6.0 runs but no power update
 

both cats were stopped up they have broke into pieces and they would move around making it bog and run bad this is the first time I have had to ever change a cat .I am just glad that this dang thing is running now

Re: 6.0 runs but no power
 

Good to see you got it worked out.
Jimmy

Re: 6.0 runs but no power
 

That’s why I like to stick the back pressure gauge in there. It doesn’t lie. Glad you got it running.

Re: 6.0 runs but no power
 

me too this hummer has been a tough one I have messed with it everyday for the past 2 months I used a vacuum gauge and that led me to check the cats again. thanks for the help