I have a 2001 2dr @wd Blazer with about 132,000 miles.

About 2 weeks ago i got the code P0155 that is the Bank 2 Sensor 1. i replaced that 02 sensor and the light went off until today. Also at the same time I got the code P0420 and i found out that my gas cap was bad the seal was cracked and was not making a good seal, I replaced the gas cap. No light for the past two weeks which brings us to today.

The SES light came on and i want and had it checked and the code P0420 came up. i am not sure which wrote I need to take to fix the error. I can replace the other 2 o2 sensors or replace the CAT. I am not having a misfire that i know of. I have never had a vehicle that has ever misfired so if someone can tell me what to look for in a misfire I would appreciate it.

i am not having high oil or coolant consumption.

I am looking at opinion on which way i should go.
Any help will be appreciated.

Thanks,
Dan

 

You need to get the problem diagnosed. The thread linked to below will help you by giving you the steps that you need to run through to determine the source of the problem:
P0420 - Catalyst System Efficiency Below Threshold (Bank 1)

P0420 doesn't point at your gas cap or anything in the EVAP system that would be triggered by a leaking gas cap seal. I suspect you had a P0440 code earlier.

 

What would be the main cause for the P0420. I will try to diagnosis the problem. I was see if anybody else had the same code on an 01 blazer that can tell me what their problem was.

 

A good place to start is with the trouble code sheet linked to above. To see what others have done with this code is only a search away. "P0420" should get you started in that respect.

 

How can I tell him I have a misfire?

 

Do you have any P030x (where x=0,1,2,3,4,5,6)? That's a telltale that there is a misfire problem within your engine. You can also monitor the knock sensor active count and/or misfire indicators using a compatible scan tool capable of such monitoring.

 

I don't have any other codes Do I need to start the engine while the scan tool is hooked up to get the code. I noticed oday that I has hard start like it make a thump when it starts and it took a second to start like all the cylnders were not firing at the same time.

 

You only have to have the key on to be able to read the codes from the PCM. If it was there, a scan would have revealed it.

 

I just went out to look at my spark plugs. I have attached a couple of pics of what my spark plugs look like. The are Autolite brand plugs. The hex head where the sockets goes is rusted. I am not sure if this is a good brand not only that they were gapped at .065 or bigger. I
regapped them at .060 and it starts better and the idle went down to around 500 RPMs.

There is not a hard start . Hopefully that will help m fuel economy.

 

They don't look all that bad. Gap was a bit large for sure.

If they have been in there for awhile and you don't know the last time that the wires, cap, & rotor were replaced, you may want to do a full tune up on it.