[tcasoccer13]

My buddy has an 04 Gt and i have an off road H-pipe because i put on on off road X pipe on mine, he is going to order the eliminators for it this week but wants to go ahead and put the H pipe on. i told him he wont get the full gain with out the eliminators because the check engine light will come on. i just wanted to know how much the check engine light will rob him and see if it is worth it to go ahead and put it on and put the eliminators on when they come in the mail.

[DanTheMan]

I think it'd just make the engine run richer..

[MustangMatt96GT]

Originally Posted by DanTheMan I think it just make the engine run richer..

Meaning you will lose power. When ever running rich, you are lossing power, running lean, means you are making power.

[DanTheMan]

i'd personally just wait to get the eliminators.. like matt said rich=power loss

[Trick Tuners]

It wont do anything. The rear O2s are only used to monitor the Cat efficiency and are not considered in the fuel calculations. The rear O2s are commonly turned off in most SCT tunes.

[cliffyk]

Originally Posted by Jgorm It wont do anything. The rear O2s are only used to monitor the Cat efficiency and are not considered in the fuel calculations. The rear O2s are commonly turned off in most SCT tunes.

+1, all it will do is throw a code once the PCM figures out the rear O2 sensors are saying the cats aren't working (this can take 30 to 200 miles)--the rear sensors have NO effect upon the operation of the engine...

[DanTheMan]

well i've learned something today

[marcd]

so if you have long tubes should i run mil eliminators on both sets of o2s?

[cliffyk]

Originally Posted by marcd so if you have long tubes should i run mil eliminators on both sets of o2s?

No, the front O2 sensors are essential to the engine's operation, it will run pig rich and throw a bunch of codes if they are missing, disconnected, or have the signal altered by MIL eliminators (this is what MIL eliminators do...).

from the '03 shop manual:

The front sensors (HO2S11/HO2S21) before the catalyst will be used for primary fuel control while the ones after the catalyst (HO2S12/HO2S22) will be utilized to monitor catalyst efficiency.

[Trick Tuners]

Right, the upstream O2s are used for all part throttle fuel calculations. Sometimes there are a few tuning tricks to get them to work better with the LTs.

[Mustang RacR94]

not running eliminators will effect performance, if your rear 02 sensor reads no change from the front one it will tell your car that your cat isnt working, your car can go into a limp mode, it will effect your performance, ive went thru this before, any 96 and up stang will need this if you run no cats or even some very high flow ones, tell your friend to get those eliminators if he's gonna be driving the car

[MATT02GT]

I sure there is some kind of "safe mode" the car goes into when the check engine light comes on. It cant be helping performance, I'll say that much.

[Trick Tuners]

Originally Posted by Mustang RacR94 not running eliminators will effect performance, if your rear 02 sensor reads no change from the front one it will tell your car that your cat isnt working, your car can go into a limp mode, it will effect your performance, ive went thru this before, any 96 and up stang will need this if you run no cats or even some very high flow ones, tell your friend to get those eliminators if he's gonna be driving the car

I dont believe this. What were the symptoms you had that you determined to be limp mode?

[johnr2001]

sometimes it throws the cars computer into a safe mode sensing something is wrong and you will lose hp until its corrected with the eliminators or another way.

[marcd]

so i only need to run them on the rear?

[Blk01ponyGT]

yep. only on the rears

[marcd]

how much of a gain will there be i did my lt and mid pipe a few months ago but just orderd the mil eliminators a few days ago.

[Geoff]

I don't know a whole lot about this but I know that right now on my car one of the rear o2 sensor's isn't working, there for throwing a check engine code...... the car is working fine!

[cliffyk]

The engine's operation on a EEC-V PCM is not impacted by failed rear O2 sensors.

It will throw a code, and you will fail inspection i8f you are unfortunate enough to live in a place that wants a squeaky clean OBD-II readout--however it does not and cannot affect engine performance, the rear O2 sensors exist solely for monitoring the performance of the cats...

[Doc8224]

I don't have mil's or turned off rears yet. I am sure it is not in limp mode because It runs just fine under WOT but is has been rich as hell and it seems like it is always searching for the AFR, this may have nothing to do with them but just thought I would throw that out there.