AARON-SS-TC

iTrader: (3)

Got these 2 codes again today for the second time.
Reduced power mode and misfire, followed by a solid engine ligh
My car has been misfiring(machine gun sound) under full throttle between shifts (1-2)(2-3) for a while now, so i just have not been full throttle in a while, but obviously its a major issue now.

I am thinking its the HPFP(high pressure fuel pump), because I doubt my injectors or seals are bad using 93 octane and 51k miles.
I have replaced the purge solenoid on the gas tank and on the intake manifold. I have also replaced the cam sensors recently.
My car has a slight idle issue, and the vacuum seems a bit off as well.

Let me know what you guys think.

09CobaltSS1

Do you have any access to software or a scan tool to monitor and/or log rail pressure? It sort of sounds like you could be getting injector misfire due to low fuel rail pressure but it's kind of odd to have it only on cylinder 3 and not a general engine misfire across all cylinders (p0300).

AARON-SS-TC

iTrader: (3)

nope, no access to log it.
everytime i have ever had a misfire, it would be on cylinder 3.
reduced power mode was new though and that came while i was going from 60-80 on the interstate.

09CobaltSS1

I mean it's possibly a bad hpfp, bad #3 coil, bad #3 plug/plug gap, bad fuel pressure sensor, bad injector and even possibly a couple other bigger issues (which isn't likely but still possible), but's it's sort of tough to give a definitive diagnosis without seeing some feedback from the engine or the sensors. Do you know anyone with even a scan tool you can borrow?

AARON-SS-TC

iTrader: (3)

my brother works for a chevy dealer in town, but i dont ever see him much...the local chevy dealer refuses to work on my car though, so i would have to figure it out myself, or just go to a random place that would troubleshoot just like me.
but obviously, it could be 2 seperate issues like a bad #3 coil and a bad hpfp like you said and i was thinking...

AARON-SS-TC

iTrader: (3)

well, i am buying coils and a hpfp today, so hopefully that helps

09CobaltSS1

All four coils? I'd do some more digging into the issue before assuming the coil(s) are definitely the issue. The easiest thing you can do is swap the hole with the issue (#3) with another coil. So for example, swap #3 and #4 coil and wait to see if the issue follows the coil. If now you're consistantly getting a p0304 instead of a p0303 then you nailed down the issue. However, if you STILL get a p0303 then you know the coild was never the issue to start with and you need to further troubleshoot. Personally man, I would nail down the issue a little better before assuming what the issue might be without correctly diagnosing it. You may just have a bad fuel pressure sensor on the rail stuck in a full closed position telling the ecm to cut back fuel pressure to the hpfp which is in return is now actually causing a low fuel pressure situation which as a result of all that could cause a bad injector misfire. So now you just spent money on 4 coils and a hpfp that was never bad to begin with. I'm not saying that is definitely what happened, but I hope you get my point. Don't just get frustrated and throw parts at it hoping to fix the issue without knowing the full story.

kdub1492

iTrader: (8)

Agree 100%

AARON-SS-TC

iTrader: (3)

oh I know guys. And thanks again for your input. The parts off of mongo were so cheap, i had to get them just in case, plus they are things that will eventually go out soon enough anyways on these cars. That sensor is my concern right now and i need to find out which one it is so I can possibly pick that up as well.
Unfortunately, I am always at work or busy with my kids, and my local dealer sucks doodoo, so I will try a few of these cheap parts myself to hopefully fix the issue, and pray it works, if not, I will have to try and find a good mechanic to drop it off too and rent a car....

What sucks is that the car drives fine at slow normal speeds and acceleration, its only at 10psi+ it starts to act up, other than the Vacuum being a little off lately.
I am sure with my luck, its like 3-4 things at 1 time that is wrong...hahaha

Powell Race Parts

iTrader: (3)

coked inlet valves?

Omiotek

iTrader: (2)

Mileage on the car? When was the last time the plugs were changed? What plugs? Who's tune is in the car terms?

AARON-SS-TC

iTrader: (3)

2008
51,500 MILES.
15K MILES with Terms tune and the tune was perfect.
i think it was 16.5* timing, .82 lamda, perfect air/fuel...somewhere around there.
As far as my plugs, i use the stockers at stock .32 gap and change them evEry other oil change(6k miles)