02 avalanche codes and low power

[redline customs]

Traded my envoy for an 02 avalanche 5.3. Had a noticable miss when I got it but wasn't too bad and wasn't consistent so im figuring basic tune up. I checked codes and has codes for all 4 O2 sensors and heater circuits, as well as knock sensor code and random multiple. Well today I pulled out and was trying to climb a smallish hill and just wouldn't not go. Then the check engine light started flashing and it started back firing. I got up finally and didnt have much issue but it does have extremely low power. I was able to check one of my 02 sensors and wiring last night and will try to check the rest tomorrow. The heater circuit wiring tested at 11.97v with key on(ac and headlights on, plus battery is 3 years old) and the heater in the sensor tested at 5.4 ohms. This was the bank one sensor 2. But I had O2 code for the sensor not switching as well as eater circuit. I don't have a torch I can test the switching with, can that be done with a scan tool? Thanks!

 

[Mooseman]

As a side note, the engine wouldn't miss with a bad O2 sensor. In fact, it can run with them disconnected and run on pre-programmed tables using other sensor data like the MAP and MAF. However you should still fix that problem.

 

[redline customs]

Any ideas on the bad miss and the backfiring? Would bad cats cause those?

 

[Mooseman]

You would have to do the usual troubleshooting for misfires. If you have a scan tool capable of live data, check which cylinders are missing. It always comes down to the basics. Air, fuel, compression and spark.

 

[mrrsm]

As this is on a similar Chevrolet Year, Model and exact Engine Platform bearing very similar problem symptoms, here is an excerpt from:

Hesitation an backfire under acceleration

www.silveradosierra.com

"Check cam position and / or crank position sensor. Classic symptoms..."

 

[gmcman]

So it appears they have had issues with the crank and cam position sensors? If that's the case it warrants a look there.

If I had to try to figure this out, I would cover a few bases first. A knock sensor code makes me want to know if there's a lot of carbon built up, and or quality of fuel and ignition circuit health.

What is the vacuum reading at idle? Is the gauge fluctuating rapidly or steady with a slight deviation as it changes load? This would point to intake valves being gunked up if it rapidly fluctuates.

Place an envelope at the tailpipe when the engine is running and see if it constantly gets pushed away from the exhaust flow or does it occasionally get sucked back into the tailpipe? This would check for exhaust valve seating.

Being it's worse under load, take a look at one or 2 of the spark plugs. Are they clean, dirty, worn?

Any recent work performed? Plugs, coils, fuel pump? Fuel pressure?

Does the fuel have an oily residue? Maybe someone accidentally put diesel or E85 but I don't know what woukd happen with E85 so can't help there.

It's a stretch but you could try an analog multimeter or a DMM with a bar graph on the crank sensor while cranking and observe the pattern, look for any irregularities.

Please report your findings so we can help you more.

 

[budwich]

Any ideas on the bad miss and the backfiring? Would bad cats cause those?

it is more likely that the misses caused bad cats which can cause a lack of power because of the plugged exhaust flow.

 

[gmcman]

it is more likely that the misses caused bad cats which can cause a lack of power because of the plugged exhaust flow.

Forgot there was a mention of very low power, I agree an exhaust backpressure test would also be a good idea.