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Discussion Starter #1
I bought a stock (used) Exige S with 1100 miles on the clock. I drove it for 400 miles without issue. One day I got caught out in bad weather and drove through a large puddle of water on the road - the MIL immediately came on. I bought a reader and it indicated a P0420. I thought this was a one-off and cleared it. A few days later the MIL came on again; my reader indicated 2 codes - P0420 and P0171. Could these be related? I have searched to see if anyone has experienced the same with stock exhaust. I put 91 octane in the Exige initially but have since been putting 93 into the tank (Shell) hoping this would clear the P0171 - no luck as yet.
I'm wondering if the water I drove through could have shorted something or worse; caused something to cool/crack.
The nearest certified mechanic is in Dublin, OH and I haven't read very glowing reviews about them :(
Any advice would be great.
 

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I bought a stock (used) Exige S with 1100 miles on the clock. I drove it for 400 miles without issue. One day I got caught out in bad weather and drove through a large puddle of water on the road - the MIL immediately came on. I bought a reader and it indicated a P0420. I thought this was a one-off and cleared it. A few days later the MIL came on again; my reader indicated 2 codes - P0420 and P0171. Could these be related? I have searched to see if anyone has experienced the same with stock exhaust. I put 91 octane in the Exige initially but have since been putting 93 into the tank (Shell) hoping this would clear the P0171 - no luck as yet.
I'm wondering if the water I drove through could have shorted something or worse; caused something to cool/crack.
The nearest certified mechanic is in Dublin, OH and I haven't read very glowing reviews about them :(
Any advice would be great.
In my case, the P0171 did seem to be fuel related, it only occurred on one particular tank of fuel, as has not reoccurred.

How deep was the puddle of water? Was it enough to submerge or soak the catalytic converter? Otherwise I'd suspect a wiring/sensor problem. If you can hook up your car to an OBD-II reader that shows real-time data, you should be able to see both O2 sensors... they should be switching back and forth from about 0.1V (lean) to 0.9V (rich), with the post-cat O2 sensor switching back and forth more slowly than the pre-cat O2 sensor.
 

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Discussion Starter #5
In my case, the P0171 did seem to be fuel related, it only occurred on one particular tank of fuel, as has not reoccurred.

How deep was the puddle of water? Was it enough to submerge or soak the catalytic converter? Otherwise I'd suspect a wiring/sensor problem. If you can hook up your car to an OBD-II reader that shows real-time data, you should be able to see both O2 sensors... they should be switching back and forth from about 0.1V (lean) to 0.9V (rich), with the post-cat O2 sensor switching back and forth more slowly than the pre-cat O2 sensor.
I got caught in a sudden cloud burst and pulled into a gas station to get off of the road. The puddle was deeper than expected and it gave the engine bay a good soaking.

Thanks for the advice, I will go the O2 sensor route for the P0420. Hopefully the higher octane fuel will take care of the P0171.
 

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Its either bad fuel (running a tank would fix it) , exhaust leaks, vacuum leak or bad MAF or O2 sensor.

if it repeats after a few tanks, then i'd check for exahust and vacuum leaks, they're the most common in my experience, followed by maf and o2.

since you have a stage 2, i'd check that the exhaust clamps were replaced and not reused and that its all snug, as well as checking the cat for any leaks while you're in there.
 

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Discussion Starter #9
Its either bad fuel (running a tank would fix it) , exhaust leaks, vacuum leak or bad MAF or O2 sensor.

if it repeats after a few tanks, then i'd check for exahust and vacuum leaks, they're the most common in my experience, followed by maf and o2.

since you have a stage 2, i'd check that the exhaust clamps were replaced and not reused and that its all snug, as well as checking the cat for any leaks while you're in there.
Thank you sir ... a fantastic help.
 

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Discussion Starter #10
Faulty O2 Sensor

I'm under the impression that the second O2 sensor (yellow) should nearly match the first O2 sensor (blue) but be slightly out of synch. I drove for 15+ minutes under various conditions and there were several (lengthy) instances where there was > 0.5v difference. Any thoughts?
 

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Hi RM of interest what scanner did you get I need to purchase one that would work on the lotus and Honda any suggestions?
 

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Hi RM of interest what scanner did you get I need to purchase one that would work on the lotus and Honda any suggestions?
Tommy,
I ordered it from palmerperformance.com
1 x PCMSCAN + OBD-II Hardware Interface (USB) (PPE-ELM5-USB) = $209.95

The software works with a number of scanners but I ordered a bundled product. Plugs into the USB port on your notebook. Highly configurable software.


Rick
 

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Here's a plot of a data log I took a few days ago. The second O2 sensor switches less frequently than the first, not just out of phase. According to the manual, if the second O2 sensor switches at greater than 0.6 times the rate of the first O2 sensor, the cat is not working properly. (i.e. if the second is switching at the same rate as the first, a ratio of 1.0, the cat is probably completely inactive).

In my plot, the second O2 sensor is switching much less rapidly than the first.

It's a bit hard to tell on your graph, but in the second line of plots, it looks like the second O2 sensor is switching at the same frequency as the first... if you can expand it a bit, count the number of times each one switches in a fixed interval, and divide the number of times the second sensor switches by the number of times the first does...
 

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Discussion Starter #14
O2 Sensor Plot

apk919 thank you for the input.
I dumped the data into Excel and did a plot over two minutes. Unless I'm misreading this, it looks like I nearly have a 1:1 ratio between the two O2 sensors.
 

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Here's what the manual says:

The ECU compares the waveform of the oxygen sensors located before and after the catalyst to determine
whether or not the catalyst has deteriorated. If the catalyst is functioning normally the front oxygen sensor will
be switching between rich and lean whilst the rear oxygen sensor should also be switching between rich and
lean but more slowly. When both the oxygen sensor waveforms change at the same rate, it indicates that the
catalyst performance has deteriorated. The ECU counts the number of pre and post catalyst oxygen sensor
switches and divides one by the other to determine a ratio number. If the ratio number is greater than 0.6 ('06
M.Y.; 0.165) the code is set.
And...

Malfunction Criteria
• Closed loop fuel control enabled
• Coolant temperature > 60 °C (140 °F)
• Baro > 756 mbar
• Vehicle speed < 130 km/h (81 mph)
• MAF < 40 g/sec
• Air inlet temp > -10°C (14°F)
Looking over my plots, there are times when the second sensor is switching as fast as the first, but that's when the engine is outside the malfunction criteria (i.e. MAF > 40 g/sec).

If you're inside the criteria, and your second sensor is switching at the same rate as your first... that's going to throw a code. I can't tell from your latest graph whether you're in or out of the criteria... if that's happening at idle, I'd say you have a problem.
 

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Discussion Starter #16
apk919 thank you for the valuable input.
I've plotted values for when I am in the malfunction threshold - pulling into my driveway/idle. To quote you, I "... have a problem."
BTW, I have a pending P0420.
 

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