its a 98 and the o2 sensor was in the cat

 

1998 was the year they changed it IIRC, some 1998s have the older style, some have the newer style. So you got one of the older style exhausts. Not a big deal.

You need to put a hole in your pipe some place shortly after the manifolds and thread in an O2 sensor that can plug into the connector that went to the original "in cat" O2 sensor. Or have a exhaust shop do it for you.

 

i dont know if that will work or not though...because the o2 sensors that are in the cat take readings from both exhaust pipes...not just one. idk if it would make a difference though. i was curious about it myself.

 

The 2nd (downstream) sensor provides data that the PCM uses to determine that the cat is working properly. This is the one that would get replaced with a simulator if you started seeing CEL's. The upstream sensor is what tells the PCM how to feed gas to the engine.

 

idk, my truck doesnt even have a downstream sensor...doesnt have a simulator either, to my knowledge. no codes or anything. weird...but regardless, he's having trouble with the truck running, so i would imagine that would be his upstream sensor...and if he has a cat like i do, the sensor pulls readings from both pipes at the same time right before the cat. if he just goes and puts it in a random spot on ONE pipe, then won't it screw the readings up?

 

Some trucks don't throw a code even after gutting the cat so it's a random thing. In order for the computer to get an accurate picture of what's going on, the sensor has to sample all cylinders.

 

so im bringing it to the shop tomorrow to have a cat welded in.. i talked to the guy and hes doesnt think its the cat he said he thinks it could be something with the fuel system or compression..

any thoughts?

 

it could be something with the fuel system...bad fuel pump maybe...but unless your compression is EXTREMELY low, like at 80-90...it wouldn't be compression. so i dont think you have to worry about that. just get a compression test and ask to see the results and post them here...dont let him jack you around. i've had it done to me and i didnt have it. i fixed it myself lol.

 

If you don't have an upstream O2 sensor, I can guarantee its part of your problem, at the least. Might not be the whole problem, but at the very least its part of it. The computer needs that sensor to adjust the fuel/air ratio properly. If a cat and O2 sensor are welded in (or at least just an O2 sensor), that should at least fix some of your problems.

 

sooo 800 dollars later...

it just ended up being water in the fuel!