Hesitation and no power

[1998_K1500_Sub]

I don't understand the fuel trim numbers yet but will read up on that next.

"Fuel trim" is discussed in the FSM, that's not bad place to start reading if you want to know more.

If you don't mind, if the fuel trim readings are off, is there a primary culprit?

I'm not strong in that area, let's see what others say.

Replacing all the O2 sensors might have been the better approach, since you were already at work on them. O2 sensors can be considered a service item, and a weak / bad O2 could push the fuel trims out of line.

But IIRC, odd fuel trim values can be caused by a number of factors, e.g., a failed injector, a vacuum leak affecting only one cylinder or bank of cylinders, a leak b/t the exhaust manifold and the head,...

 

[1998_K1500_Sub]

While you’re rummaging around under the hood, check the ground straps.

Probably not related to the problem, but…

The ground straps are something you should check on a vehicle this old. The last thing you need now is an electrical gremlin.

There are two are up front, just behind the passenger's side exhaust manifold.

One strap runs from the back of the engine head to a stud on the body, and the other from the same body stud to the frame. Those form the ground return path for the fuel pump, tail lights, and other circuits.

Too, there also a ground wire that runs from the passenger's side fender to the negative terminal on the battery.

 

[1998_K1500_Sub]

…. When pressing the gas there is a hesitation with a heavier, thumpier sound, most notable at low rpm and takes slightly longer than normal to reach higher rpm.

This “thump” sound… could it be a misfiring cylinder(s)?

Any new codes from the ECU?

Are the ECU’s misfire counts showing any oddities?

 

[Schurkey]

Bank 1 fuel trims are much different from Bank 2. There can be several reasons for this--O2 sensor problems, injector problems, misfire problems...but given the age and engine, I'm wondering about vacuum leaks due to intake gasket failure.

This “thump” sound… could it be a misfiring cylinder(s)?

Any new codes from the ECU?

Are the ECU’s misfire counts showing any oddities?

Yup. I'd be looking at all sorts of scan-tool data, but cylinder-by-cylinder misfire counts would be high on my list of priorities.

 

[1998_K1500_Sub]

Any update?