I have a 1997 gmc suburban with a 454 vortex 7.4 ltr engine, it is sputtering and losing power as you push down on the gas pedal. We have changed 2 out of 4 of the o2 sensors and replaced the fuel filter. But, it still does the same thing. It won't go past 15 mph consistently. it does have a check engine soon light on. We checked the codes and it comes up 131, 151 & 171 codes. It idles real rough. I also checked the plugs, wires, coil and timing but not the fuel pressure. Can you help me before I pay an arm and leg to a mechanic and it still not get fixed?

 

you didn't mention if you checked/changed plugs, wires, coil,timing, fuel pressure? check all the simple stuff first and post back.

 

Do you have a check engine light? If so what are the codes?
How does in run at idle? Any issues starting?

 

Anything you might want to add about the history of the vehicle, and maybe some recent problems and/or servicing?

Does it bog and /or run erratic even if revved up in the driveway, so one can rule out something like a stuck parking brake (or a kid depressed it when you weren't looking - albeit a light probably would come on if it were) or other brake issue?

Other issues that can this are restricted exhaust and swelling of pistons if motor is hot. Doubt the latter, otherwise you probably would have said more, but this is an example of how it helps to say all you can. For example, what if you had a blown head gasket where you have been adding coolant and you could have a hydrolock situation going on in a cylinder. That is why one can never say TOO much about their car and what might be relevant.

If you do not have a gauge and have individual injection, I guess you can get some idea of your fuel pressure by depressing the schrader valve to see if gas comes out under a lot of pressure.

 

I would check the fuel pressure.
Top of my head guess would be fuel pump.
One area you said you did not check. Fuel pressure. Common problem.