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Discussion Starter · #1 ·
i was thinking a oxygen sensor at first, now im not certian, seems to run o.k., has both a po 430 & po174 codes, lean bank2. looking through the scan readings it was idling at 1,100 rpm (engine was cold) fuel pressure 38psi. also said "mil active 687 miles" i assume thats how long the check engine light has been on. its a regular 3.0 in a 2003 merc sable. i did put a cam sensor in this car about 4 months ago, car was recently in a minor colission, im sure its not related to these codes, but i thought id mention it on the outside possibility it could be.
 

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The problem is NOT the upstream O2 sensor on bank 2. If you dont have a pending P0171, I would suspect a vac leak that only effects bank 2, such as leaking intake gaskets. BTW, do you have the long term fuel trims for each bank? If so, post them. The P0430 is bank 2 cat efficiency. If you are lucky, fixing the 174 MIGHT clear up the 430, but if it has been running lean on bank 2 for a long time (600+ miles since the CEL set with the 174) , the bank 2 cat may have been overheated and is now toast. 430 is VERY likely NOT due to the downstream O2 being faulty.
 

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Discussion Starter · #3 ·
long term fuel trim(1) 4.6-7.0 ____long term fuel trim (2) 7.0-9.3 sorry it took me awhile to get back to this. i had hooked up the scanner to the wife's blazer so i could write everything down for later reference in case i needed to refer to it, of course it cleared the data i got earlier. this '03 merc is a neighbors im working on. i did reset the check engine light earlier in the day (probly about noon) and when i was able to collect data again at 8:00 the light had not returned. i wrote everything down this time while it was running, fully warmed up. i really dont understand the "fuel trim " data. engine was idleing at 700-718 @ 212 temp while writing down data. showed a throttle postion of 17% which i thought was strange, i know when i was recording data from the blazer it had a throttle postion of 0% which makes sence since it was idleing in park. might be a difference between ford/gm, i dont know, but it did get my attention. didnt find any vaccum leaks under the hood, but they aint always easy to find.
 

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p0430 is cat converter for bank 2 below efficiency, right? As Jeff K said, bad downstream O2 sensor cannot trigger p0430. Bad upstream O2 sensor may.

I hope fixing the lean code for bank 2 (vac leak possibly) clears p0430 though.
 

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Those fuel trims are way to high, and the high fuel trims are affecting both banks. You are only getting a code for one bank because the lean condition is not affecting both banks equally, and the bank#1 trim is within what the computer can handle, but the value indicates how bad the situation really is. This pretty well rules out that a bad O2 sensor is causing your problem, though the condition may be damaging your sensors.

As the other posters here stated, those values are very indicative of a vacuum leak or intake gaskets leak. To be honest, if it were my car, I would resolve all those possibilities in on fell swoop. I would get myself a new set of spark plugs, upper and lower intake gaskets, and some vacuum hose. I'm pretty sure you would need valve cover gaskets as well, not sure if the valve cover overlaps the lower intake on your engine. This replacement will take a good Saturday. Take special note of the condition of the old spark plugs. Their color and condition can give you clues to what went wrong, and where.
 

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Discussion Starter · #7 ·
well, i just put plugs in it about a month or 2 ago, so anything showing up with the plugs will be recent. im laid off from work right now, so as long as its not raining, ive got plenty of time to tear down the top end. i just hope i find something. it seems strange that i dont have a high idle with a vac leak, but there is that 17% throttle opened at idle witch doesnt make sence either. guess i find the autozone website and start hunting down gasket sets.
 

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Closed throttle TPS at 17% is typical of a correctly operating TPS.
 
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