I just got a 96 blazer ls with the 4.3 engine and automatic tranny.When i got it the check engine light was on so i asked the guy what that was all about and he said the o2 sensor was bad.What the blazer does is once it hits like 180degrees it seems to lurch like it loses power and comes back.If i step on the gas or let up it stops.Today i was coming down the highway at about 60 and it started to do it and i think it was at normal operating temp by then.So i was wondering if anyone had any experience with this type of problem? I have not had any scans run on it yet.When i first got it it didnt seem to do it that often but it seems to be doing it more often, i also found out there are 4 o2 sensors which im sure anyone that has had this problem knows that.I have no other problems with the blazer but that,everything else seems to work fine. please help

 

You need to find out what the code(s) are. You may have more than one code and it should also let you know which O2 sensor is the problem.
Once you have the codes you can look them up on this forum. Use the search feature or click here: https://blazerforum.com/forum/showthread.php?t=45945

 

well might be a cat starting to clog up. since it does have a o2 sensor code could be a clogged cat giving it a bad reading.. have to find out if there are any other codes and what sensor is bad

 

ok i got a code reader and this is what came up, po147,171 174. so i read the description from the codes but im still not sure which o2 sensor is bad.can anyone help?

 

The first code has nothing to do with the sensors which are used to control fuel.
P0147 - HO2S Heater Circuit Bank 1 Sensor 3
This is the sensor located behind the catalytic converter. I would swap this sensor with the one directly ahead of the catalytic converter (B1S2) and see if the code changes to P0141. If it does, then the heater circuit in that sensor is bad and the sensor needs to be changed.

These two codes in unison indicate that there is something that is causing a lean condition. They do not necessarily mean that there is a problem with the upstream (B1S1 & B2S1) sensors. There may be a leak (either vacuum leak or a leak in the intake duct work) that is allowing air that is not sensed by the MAF sensor into the engine. Since both sides are affected, I would bet on a leak that is allowing air into the engine that the MAF sensor is not seeing. If it were localized to one bank, an exhaust leak could cause the condition.

Here are the diagnostic pages for the lean codes:
P0171 - Fuel Trim System Lean Bank 1
P0174 - Fuel Trim System Lean Bank 2

 

when you say a leak in the intake duct work, what exactly is that? Is that a bad gasket or something? or just some hole in the hose with the air filter attached to it? There is a plastic ball attached to the underside of the hood that doesnt have a vacum line attached to it anymore and im not sure if that may be the vacum leak or even where the vacum line comes from to hook into it.

 

The intake duct would be the hose between the MAF sensor and the throttle body which also includes the fresh air make up line that runs from the back of the intake duct at the throttle body over to the passenger side valve cover.

If the vacuum reservoir is not connected, that could explain your situation. The source comes from the same fitting that the PCV line connects to on the driver side of the upper intake plenum. From there, it runs through a check valve that splits off to two lines. One line will run into another 'T' if you have 4wd. Now there are 3 ports, one runs to the vacuum reservoir, one runs into the firewall for the hvac, and the third runs down to the transfer case (again, if 4wd).

 

Ok thanks for your help, i guess i need to find that vacum line or get a new one on there.Im not sure where some of this stuff is located on the engine,most of the vehicles ive owned have been mid 80's so i never had to deal with alot of this so this will be a learning process for me.If i read you right the plastic ball attached to the under side of the hood is a vacum reservoir?

 

I found the hoses and the t and it looks like everything is pluged in.I cant seem to be able to find out what connects to that ball on the underside of the hood.I also took the air filter hose off to the intake and on the flat plastic piece over the intake on the back of it i found i piece coming off of it that doesnt have anything connected to it and it is a prety good size ,and there isnt anything connected to it either,any idea what goes there? Thought maybe it was just something that had a plug on it and wasnt used because i cant find anything for that either.

 

I found out where everything went , went to the pull and pay and i have everything hooked up,thank goodness.