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Recently purchased 2008 solstice gxp with under 50k miles. Totally neglected maintenance wise driven with check engine lights on for year. Only maintenance done was oil, runs but rough and rich. When I diagnostic checked seemed to just need abunch of sensors and solenoids. Car Was only few grand spent hundred dollars in sensors. camshaft (intake and exhaust) crankshaft sensor some kind of vacume solonoid put them in my self car ran great for 2months/2k miles....until recently p02178 rich at idle. Car sputters when I start it up acts out of breath then drives fine and throw rich exhaust codes aswell po420 (I think). However when I clear codes car runs PERFECT again for few drives? I'm thinking it's MAF (cleaned it) or 02 sensor maybe ?
Everytime clear codes runs perfect. something is adjusting fuel to air incorrectly.
 

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Well....p2178 could possibly be your HPFP (been there, done that). Its not hard, nor is it too expensive to replace. However, make sure it's needed before you throw parts at it. Do you have T-clamps on your IC piping and throttle body? If not, do that first... Smell your oil...is it really strong with raw fuel smell? Does your HPFP have a rhythmatic tick or is it erratic with no rhythum? It should be tick tick tick tick...not tick........tickticktick..................tick.........tick. Your p0420 is either your cat is shot, your downstream O2 sensor is shot, both or you have an aftermarket cat and they never put the O2 bung on it....
 

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One other thing....a slightly weak battery can cause all sorts of different codes and weird issues with these cars. I've seen batteries by as weak as just 0.1V do some wacky stuff. Also, there are several major ground wires that corrode and cause issues. Take them off, clean them and put them back on. One is driver's side front of engine, other is behind turbo.
 

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Had issues with battery connections in begining. I went thru cleaned+tightened best I could (though tbh design's not great).Battery's good. I don't understand why erasing codes makes car run perfectly (for afew drives). There's lil smell of gas in oil. hpfp does have some residue around it, but seems to tick rythmicaly. When I run ac car seems to run lil rougher (more vibration). have diagnostic reader but maybe one that allows me to see all info while driving would help me pinpoint issue? Idk
 

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I will put some tclamps on see if that helps.when it does act up it sounds like it's trying hard to suck air.
 

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Thanks. I'll try to clean ground wires as well that's good idea.It just seems strange it runs perfect with no codes sometimes. Ill update after thanks again hadn't thought of that.
 

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If you can follow your LTFT and your STFT, those will tell you if you have a HPFP issue. Generally what happens is the bladders fail and push fuel into the crankcase. This builds up and gives a p2178. Mine only happened every 20 minutes in a drive.
 

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the original poster never stated the age of the battery. Just because the battery reads 'good' does not mean it is a good battery when the age is greater than 5 years. As others have said, if the battery is questionable, you will get ALL SORTS of weird codes. If the battery is older than 5 years, do yourself a favor and change the battery.
 
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Congrats on the new car.

At my old Buick club, my title was "Buick newbie...since 1989"
 

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the original poster never stated the age of the battery. Just because the battery reads 'good' does not mean it is a good battery when the age is greater than 5 years. As others have said, if the battery is questionable, you will get ALL SORTS of weird codes. If the battery is older than 5 years, do yourself a favor and change the battery.
Battery is 3 years old voltage was 12.7 engine off and 14.1 I think engine on (tbh it was month ago I tested it, I'll test again). So batteries not new or old but it does look cheap it could be issue or the ground but im thinking the hpfp seal is probably going as I do smell gas in oil. Honestly car was so neglected could be all of the above but i don't want to throw fixes at it. For the moment I erase codes (even if there are no codes) when I get in and drive with ac off and car seems to run perfectly... I have another sports car a toyota 86 (tbh solstrice is faster with WAY more torque it also gets more compliments). My original plan was to flip solstice but now Ive gotten attatched to it. I want it running well so I can throw trifecta tune on it by thanksgiving (hopefully they will have black friday sale). When I get some time this weekend ill check out ground and order live diagnostic for ltft and stft. Hopefully I can get car sorted.
 

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Congrats on the new car.

At my old Buick club, my title was "Buick newbie...since 1989"
thx. ya ive been lurking the forum afew months. Forum has helped me immensly with half a dozen codes car initially had but Im finally stumped it could be multiple things.....
 

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P0420 is a catalyst fault that could be a failed converter or a bad oxygen sensor (or wiring). It could also be a leaking or obstructed exhaust system. The cat can be damaged by:
  • misfire
  • high oil consumption
  • retarded timing
  • weak spark
  • lean mixture
  • rich mixture
  • damaged O2 sensor or harness
  • high sulphur fuel
  • physical damage
P2178 is an out of range fuel trim and should only be addressed after all other DTCs have been solved.
 

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Discussion Starter #13
P0420 is a catalyst fault that could be a failed converter or a bad oxygen sensor (or wiring). It could also be a leaking or obstructed exhaust system. The cat can be damaged by:
  • misfire
  • high oil consumption
  • retarded timing
  • weak spark
  • lean mixture
  • rich mixture
  • damaged O2 sensor or harness
  • high sulphur fuel
  • physical damage
P2178 is an out of range fuel trim and should only be addressed after all other DTCs have been solved.
When I purchased vehicle previous owner said o2 sensor possibly needed replacement (he never got around to it and wasnt sure that was the issue). Car ran rich for so long I hope it didnt burn out cat. Is there way to test o2 sensor? Theres two 02 sensors one in front of cat and one behind? I have an idea of what the issues could be I just would prefer way to pinpoint them rather then throw fixes at it. I live in oahu mechanics here are insanely expensive and not very skilled, plus its uncommon car.
 

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Discussion Starter #14
So looked up online how to check o2 sensor ill give it go this weekend. Hopefully I don't end up chasing repair after repair...however I knew this was possibility when purchased car it was way too cheap and you get what you pay for. Previous owner was very honest about completly neglecting car for years hence low price. TPS light and airbag light is also on although that's least of my worries.
 
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