thanks to all that have posted in reply! however, i changed out the o2 sensor just before the cat, and now it won't start! I drove it around for a bit to warm it up before taking it out, so it would come out easier. the original one has 4 colored wires. the new bosch one has 2 white 1 black and 1 gray wire! are these the same? i tried putting the old one back in now and cleared the computer and darn thing still won't start.

as for how it ran in idle, great. maybe every few seconds, 10-20, it would have a small hesitate or miss. not really noticeable.

i am lost now that this won't start!~ o2 wouldn't cause a no-start would it?

uhhh!

 

Additionally, the o2 sensor just before the cat is the only one this truck has (i think) as this is the 95 vortec v6 cmfi? (spider)
hope everyone has a great christmas!!

 

The miss every 10-20 seconds was what mine was doing with the bad sensor. I did have my cat replaced too, but that wasn't a fix for a problem, mine was just rotted out (nothing left inside of it) and still had the problem after the cat was replaced. You should have a pre-cat and a post-cat O2, swartlkk please correct me if I am wrong as I am still learning. The post-cat has no affect on performance (as stated earlier). Pretty much it is there to tell you that your cat is bad (which doesn't always work so well as I have found out). The pre-cat sensor if there to tell your ECM to add more fuel, or to back off by determining how much oxygen is coming through, if there is too much, then your ECM adds fuel in response to more oxygen so that it burns more of the oxygen, not enough oxygen (a rich condition) then your ECM will back the fuel off. Are you having any problems such as black smoke coming out of your exhast (unburnt fuel)? This is another of the conditions I had with mine, I have two pre-cat sensors on mine, the drivers side (bank 1 sensor 1) was flat lining, and causing the ECM to add more fuel on that side of the engine, which would cause the misfiring every so often, but under heavy load the engine would chug really hard, being choked with fuel. It was quite a head ache, even for my mechanic, he finally ended up taking a frame by frame screen shot of the output for the vehicle, and notice a slight spike that caused the majority of the problems.

Like swartlkk said, removing the sensor should cause the computer to use a preset fuel curve. Should it cause a no start? I wouldn't think it would, but hey, you never know, I have found these engines to be very tempermental. You may want to check the cat, it may be a problem source, or at least something that is aiding the problem. A clogged cat is not something that is fun to have (my dad had one catch on fire while he was driving the car) and can cause a lot of problems.

 

Hey try unplugging the Mass air flow sensor. Thats what was wrong with mine.

 

well, to make it all the more confusing....
new high-flow cat. clean!
new o2 before cat. don't see any others from either side of the manifolds down.
finally started after clearing computer... no codes.

what it does is..

start great, idles great. revs great.

drive away ok, push gas and stumbles.
from that point it continues to stumble.
then put no load on, it takes off ok, continuous no load is ok.

I have not replaced or cleaned the EGR valve.
I have not replaced the cam-shaft sensor.
Have not replaced the coil.
Have not replaced the ECM.
I am not getting any codes or check engine light coming on.

everything from the fuel pump up is new minus the above.
ready to sell this beast soon

appreciate all the help.

 

ok, tear down of intake ....again, removed EGR, Clean as..well, almost clean, no major deposits..
all sensors AIT, MAF, TPS, CSS,CSPS, all check out.

however, will the module on the coil cause this? spuddering? missfiring?

again, no codes!

merry xmas all!

 

vacuum leak???? thats what im thinkin cause i dont recall you saying you changed the vac hoses yet lol

lemme know if thats the cause or not... im getting a stumble after mine warms up and on light acceleration but if i punch it, its fine till i start cruising at a steady pace ... any ideas on mine? lol

 

just in case-take out and inspect the air cleaner and the complete path of air b4 and after it. I've had one or two of these where some rodents have packed this area full of straw/cigarette butts, etc. Gotta be something weird-good luck. jp

 

im checkin mine now but ive taken the tube off quite a few times so far and never noticed anything but hey i miss alot sometimes lol

 

ok so air filter is dirty , but the housing for it was clear so i removed filter to see if that helps my issue any , but i dont think it will ... update later on after i drive it today.