Just bought a 95 Blazer with a 4.3 that had a terrible rattling sound. Drove it home ok and pulled it into the shop. It sounded like it was the exhaust, so I cut the exhaust off just after the flange in back of the converter and no more rattle. The only problem is, now it won't idle, just wants to die. After I run the thottle up it smoothes out. It has a slight miss but does smooth out. When I let off the gas it just wants to die. Also the SES light came on. Could this be because there is no back pressure in the exhaust system, because before I cut the exhaust off, it would idle.

Thanks Mike

 

I'd say cutting off the exauhst did it.

 

Why would that do that? Just curious. If you put on a high flow exhaust on, would the ECM have to be recalibrated?

 

Not sure about the 95 but my 99 has an O2 sensor after the cat. Hopefully you didn't cut that off. A high flow exauhst still has some back pressure. Are you setting any codes?

Does it idle ok when cold(I.E. in closed loop operation). When it warms up to open loop its reading the O2 sensors etc.. vs using default values.

Just a guess but if the O2 sensor is right there at the end of the open pipe it may be out of range.

If it only has the one sensor in front of the cat it may just be a coincidense.

Do you have a way to put the pipe back on just as a "drive way" install?
I.E. cluge the pipes together with a couple soup cans or something.
Not to drive it around.

 

I put a new muffler and tailpipe on and it at least will idle now,but still runs kinda rough. All the O2 sensors were left on. I'm going to pull the plenum top off, look in there and while I have access, I will clean the EGR valve.

 

Got ahold of a scanner and code P1406 came up. According to what I've read, that indicates EGR valve problem.

 

clean your egr valve with carb cleaner and clean your iac valve too that what makes the truck idle

 

I already had cleaned IAC and just went ahead and put a new EGR in. Man, what a difference. Runs great now.

Thanks Mike

 

glad to hear good luck !