Exhaust System

[explorer99sport]

I was going to replace the exhaust on my explorer sport OHV and was wondering if I replaced all 4 of the catalyst converters with just 1 high flow catalyst convertor will it mess up the computer and throw codes or will it be ok??

 

[Dan Whitaker]

No you can't run just one convertor. It will mess with the computer as you have 4 oxygen sensors. One before and one after the primary cat on each side.

Legally you can not remove any cats from your exhaust but many have removed the rear (secondary) cats.

 

[ranger7ltr]

Actually the 99 OHV has only 3 o2 sensors...

But removing the catalytic convertors will cause emission issues, PCM drivability problems, and is illegal under any Federal and maybe your State guidelines...

If you need to replace the convertors why not replace them with high flow cats and keep it running right and legal? I have a 99 Sport as well and I replaced all 4 of mine with units from http://performance-curve.com/thunderbolt-spincat.aspx and was never happier...

The units I used up front were under $40 each and the rear units were under $45 each and I decided to go dual exhaust from the flange with the two pipes... I seperated the two series rear convertors into a parallel configuration and used the rear o2 sensor in one of the rear convertors to keep the monitor in place...Plus I get the benefit of dual exhaust with a dual in/dual out muffler and tailpipes...

But even if you keep the original configuration the high flow cats can still be used to keep your emission system happy and the truck legal if you have to past an inspection...

 

[Dan Whitaker]

Actually the 99 OHV has only 3 o2 sensors...

Ah. My 5.0 has four.

 

[explorer99sport]

Why would dropping 1 convertor affect PCM drivability?

 

[KC90]

The way your engine runs is from voltage signals the computer gets from o2/intake sensors. Remove a cat and your changing completely what the o2 sensor reads. Changing the signal will most likely make the engine run like crap from too lean/rich of a fuel mixture.

I personally like carburetors lol...

 

[explorer99sport]

Yea I am a carburetor man myself....So if I remove the last cat converter, the one after the last 02 sensor, it will mess up the balance of the air/fuel mixture?

 

[ranger7ltr]

The rear o2 sensor is behind the last convertor on the 4 liter ohv...

The last sensor is used as a system monitor to determine how well the convertors are working and, depending on who responses, the monitor o2 either has no effect or little effect on the engines' running parameters...

The pipes below are aftermarket units but they show the location of the o2 sensors in question...

 

[Carguy3J]

The rear o2 (after the cats) is, as was said, strictly tor the computer to monitor catalyst efficiency. The readings from this sensor have no effect on the PCM's control of air/fuel ratio. It will, however, turn on the MIL light, and set a code.
Replacing the cats, with properly sized straight pipe, will improve engine performance and fuel economy; provided that you also reprogram/tune the motor for it, as well as turning off the rear o2 in the tune.. Yes, it is also illegal to remove the cats.
Just in case you are tempted, simply gutting the stock cats will almost always REDUCE performance and fuel economy. It creates an expansion chamber, which will reduce exhaust flow.

 

[explorer99sport]

Ok Thank you, I'll probably just buy after market high flow cats and just put a 2.25" pipe to a Flowmaster 44 muffler and then run duel 2.5" pipes.

 

[97explorer sport]

Will cats for a 97 sport be the same as the 99?

 

[explorer99sport]

Yea as far as I know they are. Why?

 

[QuietRiot25]

so my check engine light that came on a bit after i cut my exhaust with a code reading too lean on bank one could just be because i have no exhaust?