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Discussion Starter · #1 ·
Wanted to get some thoughts on where else to look. I’m running a 3l with MSDS headers, high-flow cat and 24# injectors. It’s fully tuned.

I’ve replaced the O2 sensors and installed MIL’s and each time it came back after a short period of driving. I haven’t changed the coolant sensor at the back yet just because I wanted to hit the accessible stuff first. The car does feel like it stumbles slightly while cruising, but I’m also dealing with a failing SPEC stage 2 clutch and unsure if it‘s that.

I presumed during the tuning process it would’ve gone away as it ran better, and when I asked the tuner said it’s not something he’d touch. And when I got my final tune back he said everything looks good. I’ve recalibrated my wideband just to see if that’s reading odd, but so far it seems within margins. The fact I’m still getting it with MILs surprises me.
 

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Maybe the MIL's you bought are junk.
Here's some pages form the PCM manual...Most of it seems to be trying to prove bad catalyst so there might be limited value here;

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Here's another thought...I dont remember the specifics of the issue, but I do remember having a surprisingly hard time deciding which O2 sensor went where when we assembled Foundracer. Something about the wiring manual made it seem like they went one way when in fact they should have been reversed.
Might be worth at least double checking that the uppers and lowers are in the right places... The easy way to do that might be to just move the MIL's to the uppers.
 

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I'm not saying this IS the problem I ran into because I don't remember clearly enough, and I cant go check it, but I THINK it was this:
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I KNOW #21 is the top sensor on bank #2, the bank at the front of the car.
I THINK #22 is the lower sensor for bank #2, and #11 and 12 are the top and bottom for bank #1.
This can be confusing because the book refers to them as front and rear instead of top and bottom. But if you accept that the front of the engine is the timing cover, and think about it from that perspective, than it makes sense.
We screwed up initially on our install by thinking of "front" as bank #2 and "rear" as bank #1
So you can check that the right connectors are on the right sensors by checking the wire colors leading to each.
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P0420 and P0430 are for the downstream oxygen sensors. Their purpose is to tell you the cats are bad. If it was the case of the sensors were plugged in wrong, shouldnt you also get codes for the top sensors as well?


Just a thought. Are you actually required to do an emissions test with the car for anything? If not, why not just have your tuner turn off the downstream sensors?
 

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P0420 and P0430 are for the downstream oxygen sensors. Their purpose is to tell you the cats are bad. If it was the case of the sensors were plugged in wrong, shouldnt you also get codes for the top sensors as well?
The PCM wouldnt recognize any problems with the sensors it assumes are upstream. The MIL's might make the PCM think the car is running rich and cut fuel a bit, but its probably well within the PCM's tolerances, or the tuner just compensated for it without even realizing there was an issue.
The real issue is the sensors that are supposed to be downstream of the cats would be reading hotter than the ones that are supposed to be upstream. That's not any kind of normal operating condition so the car would throw the code to tell you somethings wrong.
 

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Discussion Starter · #9 ·
The car is except from emissions (15 years in MA). I could ask the tuner again, but being based in CA it sounded like he doesn't touch emissions stuff. I wasn't running MIL's during the tuning process (previous tuner must've turned the code off), but he was aware I had headers & a high flow main cat. The MILs are brand new, just installed this week so it would be surprising to be bad with not even 10 miles on it before the light came on (did a reset after install), but I have an extra set to try.

3 of the 4 O2 sensors are new with the Bank 2 upper being the older.
 

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If he's in CA he may not be able to. I think SCT actually makes you sign a waiver now saying you wont delete emissions stuff.

Are you using the electronic MIL eliminators?

I had those at one point they were always an issue for me.

I found if you find the sparkplug non fouler things at autozone can be turned into and actual mechanical style MIL eliminator and then bypass having to splice into any wiring for the electronic ones.
 

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O2 sensor tomfoolery/emissions cheating has become an entire cottage industry. Check out these things, with a jam nut and a selection of restrictors:


Household hardware Auto part Technology Audio equipment Metal
 

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Discussion Starter · #15 ·
My biggest concern is if the new MIL's aren't doing the job, and the O2's are also new, what else is going on? I have an extra set of MILs I can try because I doubt the foulers will do much (I'll try them).
 
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