diesel_fan

After reading many a post about the whole "my check engine light comes on after I installed a header" situation, I decided to do a little digging on the subject of eliminating the CEL when installing an RMR or RPW header. If you're already done your homework, please disregard, for those that haven't, maybe this will help.

First a little background about emissions control under closed loop conditions. The 1st and 2nd O2 sensors feed a varying voltage signal to the ECU corresponding to the O2 content in the exhaust stream. On a OBD-II equipped vehicle (like ours), the ECU computes a ratio between the values to see if the pre catalytic converter(s) are operating at a certain efficiency level. For our car, we have a single pre cat integrated into the stock exhaust manifold and another catalytic converter downstream. Mitsubishi refers to the first cat as the warm up catalyst. O2 sensor #1 is installed in the stock exhaust manifold and O2 sensor #2 is installed after the warm up cat, but before the 2nd catalytic converter.

If you install an aftermarket header, you eliminate the first cat. Since there's no longer a warm up catalyst cleaning up the exhaust gasses, the voltages from O2 sensors #1 & #2 sent to the ECU are nearly identical. This makes the ECU think that the warm up catalyst has failed. However, the CEL does not illuminate immediately after you install the header because the ECU uses specific fault detection logic with several criteria (see a shop manual) before it will flag this condition as a valid DTC. If you keep resetting the ECU by pulling the relay or disconnecting the battery for a few minutes, you'll clear all DTC's and turn off the CEL. However, after a few trips, the CEL will illuminate again.

So after a little internet digging, it turns out that this affliction is far from unique, as most OBD-II vehicles out there have one or two "pre-cats." They're in the same boat as we are when they put an aftermarket header on. I found a link to an electronics company that sells what is called an O2 simulator. In essence it's a little gizmo with capacitors, resistors, and a few other electronic items that changes the voltage produced by the #2 O2 sensor before it is sent to the ECU. Once installed in series at the sensor, it should trick the ECU into thinking that the first cat is still installed and working, eliminating the CEL.

I'd be interested if any of those who purchased RPW headers would give this a go to see if it can solve the CEL w/aftermarket header issue. The gizmo is $49 before shipping, so it's not a major investment considering you spent about $350 on a header.

Anyway, just thought I'd put this out there for all of you that bought or are thinking of buying an aftermarket header.

Casper Electronics / O2 Sensor Simulator for Import Vehicles

SWIFT1

iTrader: (1)

thanks for the info . . . when i purchase my header . . . i'll try it . . .

Smoktout

iTrader: (1)

I believe IPT performance (a registered EVOLUTIONM.NET vendor) is selling this same product for a fraction of that price. IPT's kit, however, needs wiring and is not "plug n play". I have it right now, but i installed it wrong so it's not working as of yet. hopefully one day soon i'll get under there to see what is wrong. maybe next weekend.

diesel_fan

Smoktout, thanks for info about a forum registered vendor.

Mitsiman

With vehicles with teh duel cat setup what we recomend doing with our RPW header system is relocating the 2nd O2 sensor after the cat converter and place the first O2 sensor in the O2 sensor bung provided on the flex pipe.

Since then both O2 sensors woudl be reading the correct voltage levels etc there should be no problem with a CEL light.

David THomas
www.rpw.com.au

WADADLIG_OZ

iTrader: (9)

How would you suggest we go about this relocation of the 2nd O2 sensor? What kinds of tools would be needed? I want to have everything prepared to put these headers in.

WADAD

Severous

replacing the second 02 sensor to the rear of the cat will also eliminate this problem. it will also keep you on the ups with problems in your system. relocating the sensor allows you to keep the computer operational and not in a tricked mode. in the tricked mode, if you had a cat failure or clog, you wouldnt know about it until the cat started smelling like rotten egg. the simulator is an excelent idea if you have a cutout or are going to be removing the legal stuff. the simulator will remove the check engine and will make things better, but when something goes wrong you wont know.

cyrax5709

I had an idea the other night. What about taking the #2 cat off and turning it around? That way the second o2 sensor would have a voltage reading like the #1 cat was working...? Just an idea, Im probably going to try that cause I dont feel like messing with wires or screwing up my O2 sensor