'97 Yukon Misfire - Need to take the kids to school!

[Burntwoods]

Hello. '97 GMC Yukon 5.7 350 K1500. Some months ago I filled up the gas in town and 10 miles down the road got sudden loss of acceleration, misfire (not backfiring), rough engine. Service engine light flashing. No prior issues. I borrowed a code reader and got:

P0300 engine misfire

P0151 P0151 GMC - HO2S Circuit Low Voltage Bank 2 Sensor 1

P0157 HO2S Circuit Low Voltage Bank 2 Sensor 2

P0158 GMC - HO2S Circuit High Voltage Bank 2 Sensor 2

P0160 GMC - O2 Sensor Circuit No Activity Detected Bank 2 Sensor 2

P0161 GMC - HO2S Heater Performance Bank 2 Sensor 2

At this point I have replaced:
- Bank 2 sensor 1 O2S
- Cap and rotor
- Spark plugs and wires
- Fuel filter
And I dumped a can of seafoam in the gas tank.
Nothing helped. I am sure hoping someone here can and very much appreciate any advice!!

[Blue Bowtie]

Seafoam is not likely to help. It rarely does, except for a few rare instances of carbureted engines, and usually 2-strokes.

Instead of adding oily water with naptha for $8 a can or so (Seafoam) add some fresh, LOW octane gasoline. Lower octane contains fewer additives and is more volatile (thus the lower octane rating) and that volatility can help undo the damage from the water in Seafoam and stale fuel (more than 60days old) in the tank.


Check the heater circuit for O² 2/2. The heater element may be open, and a post-cat sensor usually needs the supplemental heat to generate a meaningful signal until the cat gets really hot.

[Burntwoods]

Bowtie, thanks. Appreciate very much the gas tips - will do. And I'm super sorry... I checked everything I'd done and found I'd switched two wires. Runs great.

[Blue Bowtie]

5 and 7? It's a very common pair to switch.