94 Blazer v6 vortec..Just got through changing out the map sensor. tested per the mnual and it tested bad, blew 50 bucks on a new one and it didn't do S&*$. Still runs like crap. getting a code 45 now. where the heck are the o2 sensors and how can I bypass them to check to see if it helps. [:@][:@][:@]
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Thanks

 

Mine was just past the Y pipe facing upward. Mine's a 94 too, so it should be the same.

 

Thanks, I'll take a look. From what I understand from the manual I thought it had three. One of the codes I got said left bank sensor lean. I can't seem to find any other so I'll have that one checked.

 

it should have three or four. One on the left Y, one on the right Y, one after the Y, and sometimes one after the cat.

 

Thats what I thought too. Mine has 1. I even dropped the Y pipe when I changed my head gaskets, and only saw one. And it is a vortec cfi 4.3.

 

Just disconnect the 02 sensor to test it. If your engine runs properly, replace the sensor. If it still runs like crap its something else. When the sensor is disconnected the PCM goes into a preset defualt mode. Your gas mileage will suffer big time, so don't think unplugging it will solve your problems. It is only for diagnosing a fualty 02 sensor.

Have you cleaned your EGR yet?????
I would start there.

 

I have cleaned the EGR valve. I have a feeling that this is probably vacuum related. Yesterday I was looking for possible vaccum leaks etc.. I pulled the vacuum line on the back of the intake manifold off while the engine was running and the rough idle smoothed out, I put it back on and it idled rough again. Any ideas? In order to disconnect the O2 sensor do I need to disconnect the wire from the PCM or is there someplace in the engine compartment I can do it. I also thought this had 2 or 3 sensors, what I thought was an O2 sensor turned out to be a knock sensor. So far I can only find one O2 sensor and that is just past the Y before the cat. Sure do appreciate the help.

 

The only place the 02 sensor will be is in the exhaust pipes. Should be a short pigtail (12" long or so) on the sensor before you get to a connector.

 

Okay, thats great I'll check it out. Now then, can someone explain this one for me. I was messing around the other day and I pulled the vacuum hose off the back of the intake manifold and noticed that the engine smothed out. So, just for kicks I went out today and pulled it off again and took it for a drive. The thing ran just fine, it idled a bit rough initially then smoothed out and ran just fine and the service engine light went out. Whats up with that? The code 45 I was getting, the manual says its a rich mixture. Is it possible that by pulling that hose I am allowing enough extra air into the intake to counter that. If so, were then would my problem be?

Thanks

 

What is the other end of the hose connected to?
PCV valve? Is it stuck?