loss of engine power

[jgale74]

Hello all I am trying to figure out why my truck is running rough the problem I am having is when you push the gas peddle more than a 1/4 of an inch it shudders and has no get up and go and also if say I'm doing 40 MPH and hit the gas you can hear the engine rev up but I will lose all power and actually lose speed I thought maybe the cats were bad and I changed the plugs for good measure but I can't seem to figure it out also I had the fuel pressure checked and its pulling pressure is great so yeah any ideas would be greatly appreciated

[j cAT]

Originally Posted by jgale74

Hello all I am trying to figure out why my truck is running rough the problem I am having is when you push the gas peddle more than a 1/4 of an inch it shudders and has no get up and go and also if say I'm doing 40 MPH and hit the gas you can hear the engine rev up but I will lose all power and actually lose speed I thought maybe the cats were bad and I changed the plugs for good measure but I can't seem to figure it out also I had the fuel pressure checked and its pulling pressure is great so yeah any ideas would be greatly appreciated

helps to know what model year/engine is with your problem.

sounds like a restricted exhaust system. remove the upstream O2 sensors and see if the power returns with the O2 exhaust holes open.

then the intake manifold vacuum leaks can also do it. doing the fuel pressure test procedure will reveal any fuel delivery component failures.

[jgale74]

I'm sorry my truck is a 98 Chevy silverado with a vortec v8 5.7 liter

[j cAT]

Originally Posted by jgale74

I'm sorry my truck is a 98 Chevy silverado with a vortec v8 5.7 liter

being this age do the testing as mentioned. post back whats up.

[J-Ri]

I agree it sounds like plugged cats. These O2 sensors like to get rusted in, so if they don't come out easily, you can check with a vacuum gauge. Connect the gauge to manifold vacuum, it should be 17-21" Hg idling. Drive the truck. Vacuum should drop a little bit as you open the throttle. At half throttle, you should still have some vacuum. If vacuum drops to zero before about half throttle, you have a restriction in the exhaust. In extreme cases, as yours sounds like, you can tell just by putting your hand by the exhaust. On these trucks especially, you should be able to feel distinct pulses in the exhaust each time there's an exhaust stroke. If it's a steady stream of exhaust, you've got a big restriction.

It could also be fuel pressure. Did you power brake the truck or drive it with the gauge connected? Idle pressure can be good, but with load on the engine it can drop off.

[nolan.meininger]

I have a '99 Silverado 1500 4.8L with a very similar problem. I typically have no power coming out of a stop as well as poor acceleration while already moving. I also occasionally have what seems to be a backfire, but I think it's somewhere internal. Not exactly sure what it is.

I recently had to go in to do an Emissions test and failed the test with the code P0101. This led me to the MAF, which I pulled out, cleaned, and re-installed.

While I was driving around today, my check engine light came on again. I assumed it was the same code and that cleaning the MAF didn't do the trick. Figured I would just replace the sensor.
HOWEVER:
I pulled the codes off the most recent check engine light and received P0137 & P0157. These codes are for the o2 sensors that are downstream of the CAT.

I have a few questions:
-Why didn't the o2 sensor codes show up on the emissions test?
-How long should I have to wait before the engine will go through enough cycles to tell if the MAF sensor is bad.? I'm concerned that cleaning it didn't do the trick.
-What should I do from here? I want to pass emissions first, and then get my truck running properly.

[j cAT]

these codes are the heater circuits for the down stream O2 sensors. check the wiring at these for improper routing melting on the exhaust chaffing or some one hacked up the wiring by installing a generic O2 sensor that caused a wiring failure. the fuses must be checked should be called O2 B 15 A.... I say the wiring because if the fuse is blown this is usually why. if the sensor wiring on these is messed up buy new @ amazon denso O2 sensors these are the OEM and are about 50 USD...