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Discussion Starter #1
I recently purchased a new car and did a PI top end swap. The car has been on non-op for the last year and a half. The previous owner ran it low on oil and seized up the camshafts breaking the guides. So I swapped in a NPI block with PI top end. Car runs great.

Yesterday I took it to get the smog done as Monday I registered it in my name. Drove it all day Tuesday without a single hiccup. Wednesday I drove about 10 miles or so before taking her into smog so she could get warmed up. Long story short she failed smog, specifically the 15 mph test on NOx. Max was 409 and I scored 665. On the way home the MIL came on, checked it at P1131 or bank 1 sensor 1 insufficient switching/lean.

I am curious as to your guys thoughts. It is still untuned, I had planned to get a tune from Don LaSota this week but had to spend the money on a radiator. I know a lean mixture will cause the NOx to go up but what is really causing the problem? Is the o2 unable to supply info to the ECM fast enough causing the bank to lean out? Is it a bad cat? Or is it the fact the car is untuned and the ECM doesn't understand why the engine characteristics have changed?

Any help is appreciated. Oh in case I forgot to mention I live in California.
 

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I had a pi end for a while and never had any codes... start with making sure the injectors work and are pulsing fully. No weird noises and such... check vacuum leak from injector o rings... and intake gaskets... Also would be a good thing to check engine vacuum... this codes sets when there is a lack of fuel or excessive air entering the engine that has not been metered. Also check to see if the sensor itself is switching. .. add in an alternate fuel like propane... propane enrichment can determine a sensor is switching or not... if the sensor is switching rich your problem is elsewhere if not suspect a faulty o2 check for power and grounds before condemning a bad sensor.
 

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Discussion Starter #3
I had a pi end for a while and never had any codes... start with making sure the injectors work and are pulsing fully. No weird noises and such... check vacuum leak from injector o rings... and intake gaskets... Also would be a good thing to check engine vacuum... this codes sets when there is a lack of fuel or excessive air entering the engine that has not been metered. Also check to see if the sensor itself is switching. .. add in an alternate fuel like propane... propane enrichment can determine a sensor is switching or not... if the sensor is switching rich your problem is elsewhere if not suspect a faulty o2 check for power and grounds before condemning a bad sensor.
I already checked the vacuum it's holding at 20inHg. I could introduce propane though and see if it switches on the datalog.
 

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The 02 sensor is bad
 

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Discussion Starter #6

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Swap the two O2s. It could also be a minor exhaust leak upstream (the venturi effect will make it suck air in also).

And if you replace, do both so they stay matched.

(Both banks, that is).

RwP
 

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Discussion Starter #8
Swap the two O2s. It could also be a minor exhaust leak upstream (the venturi effect will make it suck air in also).

And if you replace, do both so they stay matched.

(Both banks, that is).

RwP
Oh yeah definitely do them as a pair.
 

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Discussion Starter #10
I replaced both upstream o2 sensors on the car and cleared the MIL light. So far looks good. Drove it about 50 miles yesterday and no check engine light. I had Don LaSota do the tune on it as well and she runs like a top.
 
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