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Discussion Starter #1
Ok so vehicle info, 2009 g8 gt has ARH exhaust system cat delete( 1 7/8 headers 3" x pipe to pypes violater axle backs) spectre cai, and rcr tune, rest is stock. I have had the car for five years and mods been on for 2 1/2 years including rcr tune with no problems, great car. Car has 112,000 miles no had the tranny fluid change, radiator flushed, and rear end fluid over a year ago. I'm located in leavenworth, kansas and the temp has dropped here dramatically starting early
December. It was below 0 degrees started the car to let warm up and cel came on shortly after, my scanner read p0171 and p0174. Car seemed fined driving after warmed up, but then noticed it revved up and rough idled when I came to stop signs and lights. My thought 02 sensors so next day replaced both upstream 02 sensors as the rear o2 is tuned out. Deleted the cel and it seemed ok after I drove it about 10 miles so parked it, note it was about 48 degrees out. Well next morning about 25 degrees started it up and let warm up, well went to drive it and cel came on same codes p0171, p0174 and now 2 more codes on top of that p0132, p0152. It was rough idling puttering out while giving gas even backfired once, once it got going it smoothed out kinda normal but idles rough when stopped. So did research on this forum looked up some possibilities, already replaced 02 sensors upstream, pulled the air filter and mass air flow and cleaned both of them. Checked the cai couplings and auto clamps readjusted and vacum line from valve cover to cai while vehicle running, the tube no cracks or leaks had strong suction after plugging with thumb. Checked the tube from passenger side tb to driver rear valve cover seems no leak, so pulled it off the rear valve cover and it started idling way worse so put it back on. I'm basically down to checking fuel rail pressure and hope it's not the fuel injectors or worse the fuel pump. Does anyone have any advice of what else I can check or do?
 

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Show us some LTFTs and STFTs from driving cycles.

O2 Sensor voltage oscillates from .1 - .9V and high voltage means it is a rich mixture. The other codes are showing a lean system.

Its possibly a false lean reading. There are lots of guesses, but those fuel trims are important to get a look at.
 

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Discussion Starter #3
Show us some LTFTs and STFTs from driving cycles.

O2 Sensor voltage oscillates from .1 - .9V and high voltage means it is a rich mixture. The other codes are showing a lean system.

Its possibly a false lean reading. There are lots of guesses, but those fuel trims are important to get a look at.
Ok tomorrow I will drive it and log the left and soft and post am update, thank you for the response.
 

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Discussion Starter #4
Show us some LTFTs and STFTs from driving cycles.

O2 Sensor voltage oscillates from .1 - .9V and high voltage means it is a rich mixture. The other codes are showing a lean system.

Its possibly a false lean reading. There are lots of guesses, but those fuel trims are important to get a look at.
LTFT* and STFT*
 

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Yes, but I was indicating for both banks. :)
 

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Before we go further, what did you do at 4:19 into the 2nd video (the one from the parking lot). Your values reset.
 

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That's very strange, because I've never really seen that happen. What is the peak coolant temp while driving and while idle?

If you unplug the MAF does the idle smooth out? Replacing the sensor blade is a bit cheaper than the whole sensor housing (they do come out) if necessary. A significant under report would indeed give you this condition. And since we witnessed a mystery reset, it could indicate your MAF sensor is giving sporadic readings possibly due to a failed connection. It might be as simple as cleaning the plug.

What is your idle vacuum when compared to atmospheric pressure?

I have other ideas, but I don't want to get too confusing by chasing them all at once. :D
 

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Discussion Starter #11
That's very strange, because I've never really seen that happen. What is the peak coolant temp while driving and while idle?

If you unplug the MAF does the idle smooth out? Replacing the sensor blade is a bit cheaper than the whole sensor housing (they do come out) if necessary. A significant under report would indeed give you this condition. And since we witnessed a mystery reset, it could indicate your MAF sensor is giving sporadic readings possibly due to a failed connection. It might be as simple as cleaning the plug.

What is your idle vacuum when compared to atmospheric pressure?

I have other ideas, but I don't want to get too confusing by chasing them all at once.

So I went back out after reading your reply and did some more recording, got the coolant temp idle and and driving. I also pulled the maf plug while running and recorded that for you also. 3 Links below for recordings.
https://youtu.be/CkHM2h4lNkw
https://youtu.be/MnmUMD2zo-0
https://youtu.be/Lq_rQT7HYoo
 

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Check your ground connections. The reason I mention that is because your system seems to reset itself inexplicably while driving. A faulty ground causes a power drain and that can create or mimic all sorts of issues from faulty injectors, to a bad pump.

Check battery connections and associated grounds as well.

Test your alternator to be sure it is putting out good power, and that its grounding bar is also secure.

If you had a vacuum leak, your fuel trims should drop as you throttle up. A small leak relative to an open throttle blade is insignificant next to the same small leak with a closed blade. You can test this in your driveway by testing trims at idle, revving up to 1,500 and holding for 15-20 seconds while watching trims, then up to 2,500 while doing the same. If trims don't change, it doesn't usually indicate a vacuum leak.

That said, check your Brake Booster hose. Disconnect it at the booster, plug it, and then turn the car on and observe trims. If nothing changes, turn the car off.

Reconnect the booster, and then disconnect the evap solenoid line to the intake manifold and plug THAT up with a rubber cap if you have one (so it can't get sucked in). Start the car and observe. If nothing changes, remove the plug from the port and reconnect the evap solenoid tube.

If either of those show changes, then you've located a defective part to replace. If not....

Of course, I assume you've checked your manifold bolts. Those are usually threaded with blue loctite, so they won't back out unless YOU back them out (the first time).

Be sure that your valve cover bolts are tight. Torque is 106 in/lbs.

Test your fuel pressure. Low pressure can indicate a bad ground connection. (I always suspect voltage drain before suspecting a pump failure.)

I don't think it has anything to do with injectors, unless your fuel in Kansas is god awful. You can do the "in car" cleaning, but that may not have any effect, and you would have then wasted your money. :(

That's the most I can think of without being there to look around myself. I'm most convinced that it is a sensor problem or electrical problem because of the way your trims behave, especially given the reset. That appears to be a KAM reset mid-drive....
 

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Check your ground connections. The reason I mention that is because your system seems to reset itself inexplicably while driving. A faulty ground causes a power drain and that can create or mimic all sorts of issues from faulty injectors, to a bad pump.

Check battery connections and associated grounds as well.

Test your alternator to be sure it is putting out good power, and that its grounding bar is also secure.

If you had a vacuum leak, your fuel trims should drop as you throttle up. A small leak relative to an open throttle blade is insignificant next to the same small leak with a closed blade. You can test this in your driveway by testing trims at idle, revving up to 1,500 and holding for 15-20 seconds while watching trims, then up to 2,500 while doing the same. If trims don't change, it doesn't usually indicate a vacuum leak.

That said, check your Brake Booster hose. Disconnect it at the booster, plug it, and then turn the car on and observe trims. If nothing changes, turn the car off.

Reconnect the booster, and then disconnect the evap solenoid line to the intake manifold and plug THAT up with a rubber cap if you have one (so it can't get sucked in). Start the car and observe. If nothing changes, remove the plug from the port and reconnect the evap solenoid tube.

If either of those show changes, then you've located a defective part to replace. If not....

Of course, I assume you've checked your manifold bolts. Those are usually threaded with blue loctite, so they won't back out unless YOU back them out (the first time).

Be sure that your valve cover bolts are tight. Torque is 106 in/lbs.

Test your fuel pressure. Low pressure can indicate a bad ground connection. (I always suspect voltage drain before suspecting a pump failure.)

I don't think it has anything to do with injectors, unless your fuel in Kansas is god awful. You can do the "in car" cleaning, but that may not have any effect, and you would have then wasted your money.


That's the most I can think of without being there to look around myself. I'm most convinced that it is a sensor problem or electrical problem because of the way your trims behave, especially given the reset. That appears to be a KAM reset mid-drive....
"Update" so I disconnected the battery cleaned off terminals and post, then checked ground on alternator and block, cleaned that and reconnected. Reconnected battery started it up ran got warmed up then got choppy and cel came on again, had the alternator tested at shop around corner said everything looked fine. Went home ordered new maf, Installed Monday afternoon reset cel. After car warmed up cel back on, went to drive it to Wal-Mart around the corner( note: snowed day before been below 25 degrees since) car was really bad! Back firing miss choppy cutting out stalled at stop light twice! So I immediately said forget this and drove straight to chevrolet dealership barely making it. Dropped it off last night, and it's been there all day. Called them about 20 mins ago around 5pm my time and they told me they have been working on finding the problem all day he's down to thinking it maybe be some injectors going bad, they tested the fuel pressure and said the fuel pump is good, I already told them all the stuff I replaced such as, plug wires, plugs, o2, maf etc. So far no luck on what's going on, but it got alot worse then it has been last month and last week when i recorded the ltft and stft. Like so bad i couldnt event drive it.
 

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It appears that your MAF indeed was bad. In fact, a lot of times cleaning or replacing only makes the problem escalate. So, you can rest easy if you think the MAF was a waste of cash at least.

Essentially, the injectors were able to keep up enough to make things feel ok when the motor "thought" less air was coming in, but now that more air is being reported they really can't keep up.

I didn't want to go there until you (we) were sure. I usually don't expect injectors to be clogged enough to be that serious at even 150K. Mine weren't really all that bad and I had 152K on the motor when I had them cleaned.

Sometimes you gotta cave and take it to the shop. You did the right thing there. :)

Curious, do you go to the same gas station on most fill-ups?
 

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Discussion Starter #15
It appears that your MAF indeed was bad. In fact, a lot of times cleaning or replacing only makes the problem escalate. So, you can rest easy if you think the MAF was a waste of cash at least.

Essentially, the injectors were able to keep up enough to make things feel ok when the motor "thought" less air was coming in, but now that more air is being reported they really can't keep up.

I didn't want to go there until you (we) were sure. I usually don't expect injectors to be clogged enough to be that serious at even 150K. Mine weren't really all that bad and I had 152K on the motor when I had them cleaned.

Sometimes you gotta cave and take it to the shop. You did the right thing there.


Curious, do you go to the same gas station on most fill-ups?
Yeah I think your right as soon as I put a new maf on and then started it the next day and let warm up it got worse which made no sense to me. I went to drive it and literally got even worse after I put it in to gear and then started driving it. It was cutting out smelt really bad and stalled when I came to a stop light 2 times and had to restart it. Called my wife after I pulled over to follow me to the dealership in her car. She said she can hear it running rough and cutting out and she said she could smelt the gas from The exhaust. So if that was the issue then what do i do to get it to start running normal again?
 

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Wait... I can't believe I didn't think of it before. When you said you smelt gas, I had a EUREKA moment. The part about the MAF still makes sense, but now I realize why you have High Voltage codes (rich = high volts) and lean codes at the same time.

O2s obviously only detect O2, and a leaky injector or two has caused your motor to misfire. A seriously rich mixture may fail to combust completely (or at least partially), and thus it dumps unburned oxygen into the exhaust and fools the sensors into thinking it is running lean. They dump more fuel and make he problem worse.

When you installed the new MAF it complicated the issue by reporting more air and thus injecting MORE fuel.... Your ECU just kept saying "MORE! MORE! MORE!"

Yes, I feel pretty strongly that they're gong to confirm that you have some bad injectors.

You might consider paying them to fix it unless their cost is outrageous. I can't see it being that bad considering what it would cost you to send it home on a rollback (safe bet), pay their diagnostic fee, and then do the repair yourself. $100 for the rollback, maybe even double that for diagnostics. Another $50 per injector.... O-ring kit..

If their cost is ridiculous next to even a full set of 8 DIYed plus their fee.... well you can figure that out... :D I just don't see that happening.

Driving is at your own risk. I don't like driving with a motor that's acting like a popcorn popper.
 

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Wait... I can't believe I didn't think of it before. When you said you smelt gas, I had a EUREKA moment. The part about the MAF still makes sense, but now I realize why you have High Voltage codes (rich = high volts) and lean codes at the same time.

O2s obviously only detect O2, and a leaky injector or two has caused your motor to misfire. A seriously rich mixture may fail to combust completely (or at least partially), and thus it dumps unburned oxygen into the exhaust and fools the sensors into thinking it is running lean. They dump more fuel and make he problem worse.

When you installed the new MAF it complicated the issue by reporting more air and thus injecting MORE fuel.... Your ECU just kept saying "MORE! MORE! MORE!"

Yes, I feel pretty strongly that they're gong to confirm that you have some bad injectors.

You might consider paying them to fix it unless their cost is outrageous. I can't see it being that bad considering what it would cost you to send it home on a rollback (safe bet), pay their diagnostic fee, and then do the repair yourself. $100 for the rollback, maybe even double that for diagnostics. Another $50 per injector.... O-ring kit..

If their cost is ridiculous next to even a full set of 8 DIYed plus their fee.... well you can figure that out...
I just don't see that happening.

Driving is at your own risk. I don't like driving with a motor that's acting like a popcorn popper.
New update! So um dealer called me and said they ran test on the injectors and fuels pump everything checked out normal. So the ran test on the spark plugs and wires and they were good, then checked the new maf and it was also good. So he tested the o2 sensors and said bank 1 sensor 1 is bad. I just bought new ones but there cheap sensor from autozone. I'm just having them replace the the 2 o2 sensors I replaced, with GM ones, and crossing my fingers that this was the problem. I will respond back with new update once I pick up the car.
 

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That's good news. Glad I was wrong about the injectors. :)
 

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That's good news. Glad I was wrong about the injectors.
Well no one's really wrong any one of those possibilities could have been the problem, and I'm not making the judgement call till I pick up the car and drive it lol. Keep you all updated.
 

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Fingers are crossed.

I just wonder why both banks would show up lean if it was just one O2 sensor. I guess you'll know soon.
 
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