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Discussion Starter #1
Well, I can't seem to shake the dreaded P420 code. It started at about 40K miles - no problems before that. The reader/resetter I have that works with the Lotus won't give me any other info so I can't tell the precise problemTADTS.

I believe the root problem is one of three things: upstream OX Sensor, downstream (post cat) OX Sensor, or the Cat, a Forcedfed hi-flow that came with my street header. I'm planning to start with replacing one or both of the sensors.

Does anyone know a reasonably priced :rolleyes: source?

Generic, splice-in is OK with me, as long as they work the same. Used sensors would be fine as well...as long at they work.

Thanks.
 

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Maybe you considered the following already, but I'll just throw it out here.

Given that your exhaust header and cat were replaced, could you have an exhaust leak that is causing incorrect oxygen sensor readings? The oxygen sensors were removed to put in the ForcedFed cat. Could they have not been retorqued properly? Could a washer be missing on a sensor, thus causing the oxygen sensor to not be properly positioned in the exhaust stream?
 

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Discussion Starter #4
Thanks ChrisH. Those were my thoughts as well. I've checked and confirmed that both the sensors and cat are properly mounted and there are no leaks. Also, the header and high-flow cat have been on for roughly 30K miles without problem before now.
 

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ed,
how many miles on the car total? is the cat original to the car? does your state require emissions testing, if so, has it been done lately (ie. since the appearance of the P0420 MIL code) and how were the results?

i have little faith the in the cats on these cars, so unless you're able to rule that out as the cause, i'd run that one to ground.

good luck.
 

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Discussion Starter #6
42K miles on the car. The Forcedfed high-flow cat and headers have been on roughly 30K of those. The original cat (and "header") are in the garage. I've had no problems before now. Emissions testing in CA doesn't start until the car is 5 years old, so another 2.5 years for me. I'm starting with the OX sensors because they're under $50 (generic) and I'm afarid the cat is at least double.
 

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42K miles on the car. The Forcedfed high-flow cat and headers have been on roughly 30K of those. The original cat (and "header") are in the garage. I've had no problems before now. Emissions testing in CA doesn't start until the car is 5 years old, so another 2.5 years for me. I'm starting with the OX sensors because they're under $50 (generic) and I'm afarid the cat is at least double.
ah, i missed the part about the FF cat. so you've got quite a few miles on an aftermarket cat. i wonder what the life expantancy is on it and if there have been any reported failures? it's not unreasonable to think that the FF header was marginal (by design) and that over time it's performance has degraded to below threshold. i dunno. just throwing gum at the wall.

IIRC the stock cat pipe doesn't match up with the FF header, so there's no easy way to swap and check.

i guess it's your call on the sensors. hacking them in would be shame, especially if they're not the cause.

how about the OE sensors, do they come with the harness attached (plug and play)? price point looks to be ~~$80 per. maybe buy them locally from the dealer and just eat the restock fee (if allowed) if they prove to be not the cause?
 

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The post O2 sensor usually has to be working for it to throw the P0420, I guess its possible for it to fail in such a way to throw the code, but when its all working, the trace is close to a flatish line, when the cat isn't working it starts to show a sin wave, which in turn throws the code.

I was think the same as ace, might be the cat has worn out.

A quick check with a scope on the post o2 will tell you right away, but its a bit more expensive than a replacement sensor.
 
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No problem... I bought this one as it listed the 2zzge sensor. I varified the output with my OBDII connector and engine monitoring software and there have been no issues.

Q
 

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Discussion Starter #13
OK, I have the $25 Denso sensor now and am ready to replace the pre-cat sensor in the Elise. Old sensor wires are white, white, grey and black. New sensor wires are black, black, blue, white. Does anyone know the "translation"?
 

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Discussion Starter #14
Well, I found some addition info on the WWW. The following notes the colors of the old sensor as being the same as my new one and their new one is the same as my old - confusing? Anyway, assuming that switch doesn't impact the mapping, it seems the old white wires should go to the new blacks, the old black wire goes to the net blue and the old grey wire goes to the new white. Can anyone confirm? :shrug:

"The factory O2 sensor has 4 wires: blue, white and 2 black wires. The two black wires are for positive and negative battery connections for the heater in the O2 sensor. (doesn't matter positive or negative for a heater element). The Blue and white wires are for the O2 reading to the computer. Blue is positive and white is Negative. (Don't argue, I'm right. Even though white is usually a positive voltage color it's not with O2 sensors. Go check if you don't believe me)

The NTK sensor has 4 wires: Black, Grey, and 2 white wires. The two white wires are for the heater element. The black and grey wires are for the O2 readings, black is positive and grey is negative. (Don't argue with me, I'm right again)"
 

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Discussion Starter #16
The sensor went in fine with the mapping I found on the internet. Unfortunately, the P420 came back @ 100 miles - just like with the original sensor. The problem must be the Forcedfed cat. I called them and it's out of warranty. The replacement is not cheap (from FF). I'll be shopping for new high flow from another source next week.
 

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The sensor went in fine with the mapping I found on the internet. Unfortunately, the P420 came back @ 100 miles - just like with the original sensor. The problem must be the Forcedfed cat. I called them and it's out of warranty. The replacement is not cheap (from FF). I'll be shopping for new high flow from another source next week.
congrats on getting the 02 cut in.
i think these cars are tough on cats. OE due to the engine movement and hi-flows due to design.
$800 every couple of years isn't very attractive.
good shopping!
 

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The sensor went in fine with the mapping I found on the internet. Unfortunately, the P420 came back @ 100 miles - just like with the original sensor. The problem must be the Forcedfed cat. I called them and it's out of warranty. The replacement is not cheap (from FF). I'll be shopping for new high flow from another source next week.
I noticed that the high flow cats PPE includes in their kits cost in the range of $250 to $400 depending on the application. You might enquire with them if they could configure one for your setup.
 
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Still no problems with mine.

yes, the wiring is different. Just google and match the colors.
 
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