Custom exhaust system...throwing check engine light

[sreilly77]

this explanation is going to be a little long but i need all the help i can get...

i have a 1996 dodge dakota with the 3.9L V6 and recently i gutted the exhaust system from the headers back (i replaced the cat, muffler, and tailpipe). there was a flowmaster on it and i upgraded to a thrush glasspack (it sounds SOOO nice haha). but anyway when i was in the middle of gutting the system i broke one of the O2 sensors and it threw the check engine light which i expected it to do. but i did put a nut in the hole where the sensor would be. other than that the truck runs great.

so today i put in the new O2 sensor and cleared the computer of the check engine light. after a short time the truck began to sputter pretty bad and the check engine light came on again. turned out that it was the new O2 sensor because i took it out and put the nut back in and the truck is running great now. my question has to do with that check engine light. is there any way to by-pass the computer so the light goes out even though one of the O2 sensors (the one after the cat) is missing? this is for inspection reasons because in PA you have to inspect your car once a year and the mechanics will not pass it unless that light is out. so any suggestions would be greatly appreciated.

[2001jettavr6]

it might be causing that because the sensor monitors the gasses coming out. and with a glass pack free flow and and if its a high flow cat it might not filter it right. the engine light comes on when there is an emission problem also linked to the o2 sensor. and it it set to monitor a certain level and it might be thrown off with the new exhaust system. if you have the old cat i would try and put that back on and the o2 and see if it works.

[sreilly77]

Originally Posted by 2001jettavr6

it might be causing that because the sensor monitors the gasses coming out. and with a glass pack free flow and and if its a high flow cat it might not filter it right. the engine light comes on when there is an emission problem also linked to the o2 sensor. and it it set to monitor a certain level and it might be thrown off with the new exhaust system. if you have the old cat i would try and put that back on and the o2 and see if it works.

yea i tried that and the light is still on. is there like any high performance O2 sensors that are sold? i mean like do they make sensors that put up with a high flow exhaust like that?

[rhandwor]

Did you buy a quality sensor with the wires hooked up so it plugs up correctly.
This should have 3 wires you could ask if they will exchange it. These require power to heat up the sensor until the engine is warm. Use a logic probe or DVOM and check the unit gets power to heat up.
Go to advance or auto zone and ask for a free computer code check which will help you narrow it down.

[Andydg]

You could look for an O2 simulator which will make the computer think everything is fine and dandy.

[sreilly77]

Originally Posted by Andydg

You could look for an O2 simulator which will make the computer think everything is fine and dandy.

that is what i ended up doing. however it still threw the check engine light and the computer is telling me that its the O2 sensor but now it is the other one that is before the cat. so at least i got one problem figured out. i'm away for 2 weeks so when i get home i'm going to replace the other one and see what happens. i'll use another simulator because it obviously did the trick with the sensor after the cat.

[Andydg]

Glad it worked...let us know if using a sim on the front one helps too.

[xj31]

The sims don't work on the frt o2s.The reason it works on the downstream is because that sensor is just there to monitor catalyst efficiency.The voltage that the pcm sees should remain fairly steady,and the sim sends it a signal that keeps it happy.The upstream o2 is for fuel control.The voltage varies quite a bit and if the pcm saw a constant voltage,like a sim,it would put a check engine light.The sims are for fooling the pcm into thinking a catalytic converter that has been removed is still there.