2004 Sierra 2500 6.0L No power at 1/2 throttle or more.

[maintenance]

Hello again,

We have a 2004 gmc Sierra 2500 with a 6.0L engine, auto trans. Trans is not an Allison.

It starts good, and at less than 1/2 throttle it seems to run fine. But when you go past 1/2 throttle its power just drops off. Engine will rev, but it acts like it has no power. If you lift off the throttle it will start pulling again. You can drive it up to 60-65 mph but if you need to pass someone and go past the 1/2 way point in the throttle it will start to lose power, If you go w.o.t. it will lose so much power it will start to slow down! I'm stumped.

 

[Molson02536]

Hello again,

We have a 2004 gmc Sierra 2500 with a 6.0L engine, auto trans. Trans is not an Allison.

It starts good, and at less than 1/2 throttle it seems to run fine. But when you go past 1/2 throttle its power just drops off. Engine will rev, but it acts like it has no power. If you lift off the throttle it will start pulling again. You can drive it up to 60-65 mph but if you need to pass someone and go past the 1/2 way point in the throttle it will start to lose power, If you go w.o.t. it will lose so much power it will start to slow down! I'm stumped.

Have your Catalytic converter inspected to make sure it's not causing a restriction of your exhaust flow. Sounds like a Cat that has gone bad and is restricting the air flow causing your engine to drop off ay higher RPM's.

Start with this and post back to us, good luck and hope it's this simple fix.

Molson02536

 

[maintenance]

Thanks for the reply! We had the exhaust flow tested and it tested fine. We have also changed the plugs, wires, air filter, and cleaned the Mass Air Flow Sensor. It almost seems like the transmission is slipping during kick down but it shifts fine when just driving around town. As of right now I'm stumped.....

 

[Molson02536]

Thanks for the reply! We had the exhaust flow tested and it tested fine. We have also changed the plugs, wires, air filter, and cleaned the Mass Air Flow Sensor. It almost seems like the transmission is slipping during kick down but it shifts fine when just driving around town. As of right now I'm stumped.....

Have you inspected your TPS, a faulty TPS (Throttle position sensor) will give you the issues that your have described. Have your TPS checked and have you had your Sierra scanned for any DTC codes???

Post back and lets see about getting your ride running 100% again soon.

Molson02536

 

[maintenance]

No, we have not checked the TPS. Honestly not sure where its located. Had 2 codes for lean cylinder banks left and right. We cleared them and they have not returned.

 

[Molson02536]

No, we have not checked the TPS. Honestly not sure where its located. Had 2 codes for lean cylinder banks left and right. We cleared them and they have not returned.

Ok back to basic, have the fuel filter been replaced on the Sierra??? The TPS is located on the side of the throttle body where the throttle body blade pin runs through the throttle body.

Have that checked with a tech II scanner and replace your fuel filter if it has not been done yet unless you have the non serviceable fuel filter. The 2004 was the mix years where most are non serviceable and the fuel filter is built in with the sending unit.

Keep up the great work and post back how your making out with your Sierra.

Molson02536

 

[maintenance]

Ok, here is an update.... Went to the local G.M. service dept. we were told that our truck does not have a fuel filter and the motor has been replaced at one time and is 2009 or newer.

 

[maintenance]

Ok, here is an update.... Went to the local G.M. service dept. we were told that our truck does not have a fuel filter and the motor has been replaced at one time and is 2009 or newer.