2003 4.6L - can I get a definitive answer on downstream O2 sensors?

[MyExplorer03v8Lim]

I'm looking at making my '03 4.6L "off-road only" after realizing the nightmare that is the aftermarket catalytic converter market.

It seems the only viable option for good replacements are the oem from ford for $2k+. Everyone says that high flow and aftermarket cats are all varying degrees of garbage, and I don't want to get into the game of new cats every six months. So I might turn the old girl into an off-road only machine and get rid of the cats.

I know that it's possible to use spacers to fool the rear O2 sensors. But my concern is that my computer might be using the downstream sensors to adjust fuel trims.

CAN ANYONE TELL ME WITH CERTAINTY
Do the downstream O2 sensors affect fuel trim? Or do the honestly only report catalytic efficiency?

What's the preferred method to handle this situation?

 

[87350gta]

Downstream oxygen sensors are only converter monitors. They in no way affect fuel trim. They weren't even required on cars until obd2 came out in '96. I am a ford senior master tech, I have worked as a tech since '99, I have made tunes for my own explorer.

 

[MyExplorer03v8Lim]

Downstream oxygen sensors are only converter monitors. They in no way affect fuel trim. They weren't even required on cars until obd2 came out in '96. I am a ford senior master tech, I have worked as a tech since '99, I have made tunes for my own explorer.

Ok awesome thanks for your response. Do you think in my case a custom tune is required?

I've read about "custom tune" all over the web in regards to this topic, but I wouldn't even know where to begin.

Is this something that can be done with forscan? Do I need a special device?

Or should I just put in some straight pipes and a spacer on the downstreams and call it a day?

For the record, I want it to run correctly, it's not a beater even though it'll be "for off road use only".

Anything you can tell me about custom tunes would be much appreciated. For the record I realize youve got a lifetime of knowledge behind this, and you can't possibly educate me to do it on my own. Just a little info on where to start would be great.

 

[87350gta]

I think a custom tune would be overkill, if you planned on doing some other mods that would require a tune, then that might justify a tuner. You wouldn't need to go custom though, an off the shelf SCT tuner or similar should be able to shut off catalyst monitors. In my experience, the aftermarket converters are not as good as the oem ones. And I know they are expensive. If you aren't worried about emissions and don't have state inspections, you could just slap some pipes in there. There are a couple ways to defeat cat monitors. You can just hang them in open air, this isn't the preferred method, but it works. You can get a couple resistors and a diode and make an o2 simulator. Or if you are lucky enough to find someone selling them, you can go that route.

 

[87350gta]

Hey have some extension things that look like they might work also. Do a google search for ford oxygen sensor emulators or simulators.

 

[boominXplorer]

Throw some generic fit MagnaFlow cats in it and call it a day. They are cheap and usually will keep the light off. I'd be concerned about that cat with the bad reading failing to the point of blocking the exhaust up.

All SCT tuners x3 and above will shut rear o2s off if they have the most recent update.

 

[MyExplorer03v8Lim]

All SCT tuners x3 and above will shut rear o2s off if they have the most recent update.

I had read that those devices don't work on the 3rd gens 2002 & 2003 because they still have the cable for throttle rather than electronic throttle. Maybe this is bad info. I know litterally nothing about tuners/ where to get or borrow one/ how to use them at all. Not trying to say your wrong. Just passing what I've read elsewhere.

 

[boominXplorer]

Hmm I can't say yes or no. I have a 04 3rd gen I know it will do it on there but can't vouch for 02 and 03. Also sct put out a ton of updates for the x3 tuners and if it's not updated it might not have it. The used x3 I put on my 01 ranger (97 v8 pcm) had to be updated to gain the rear o2 sensor delete option I know for a fact.

 

[87350gta]

I have an sct tuner on my 02, works just fine.