Intermittent bog while revving
Thread Starter
Burning Brakes
Joined: Apr 2023
Posts: 1,087
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From: Florida
2025 C6 of the Year Finalist - Unmodified
Intermittent bog while revving
2007 LS2 A6 runs awesome but I’ve noticed ever since getting the car if you try to rev it up from an idle or close to, sometimes it seems like it “loads up” or bogs. If it does that and you give it a second rev etc it’s fine and revs normally. I’m aware of the 4500rpm limiter on auto’s so it’s not that… Is this normal with A6’s? As mentioned the car runs really strong, no funny idle or anything. Would being catless with a current o2 sensor code cause this?
Moderator, Tech Contributor
Joined: Sep 2013
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From: Cape Coral, Florida
I don't see a P0070 for a 2007...if you don't have cats there is no downstream O2 sensor so you will get the P0060 and P0420...maybe those DTC's were not "turned off" with tuning software...I'd look at your MAP which should read 101 kPa engine off/ ignition ON and MAF at unloaded hot idle should read no LESS than 6 grams/second...this car has been probably tuned so maybe visit a tuner...I don't touch tuned cars.
Thread Starter
Burning Brakes
Joined: Apr 2023
Posts: 1,087
Likes: 392
From: Florida
2025 C6 of the Year Finalist - Unmodified
I don't see a P0070 for a 2007...if you don't have cats there is no downstream O2 sensor so you will get the P0060 and P0420...maybe those DTC's were not "turned off" with tuning software...I'd look at your MAP which should read 101 kPa engine off/ ignition ON and MAF at unloaded hot idle should read no LESS than 6 grams/second...this car has been probably tuned so maybe visit a tuner...I don't touch tuned cars.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,508
Likes: 4,000
From: Cape Coral, Florida
Those DTC's would not cause a rich condition...If the car were not tuned or DTC's turned off I would expect to see a P0054 for B2S2 heater resistance and a P0430 for bank 2 cat efficiency...the downstream O2's (S2's) only monitor the cats and are not involved in fuel scheduling...to check cat efficiency the ECM looks at the downstream O2's....the downstream O2's remain fairly constant around 700Mv's and the up streams "switch" between 200-800Mv's...if your scan tool can graph the upstream O2's watch them as you roll into a WOT...the up streams should go RICH nearing 900Mv's to 1 volt...if not you have a fuel delivery or a possible bad MAF...you need to look at your fuel trims too...watch the 2 part video made by a friend of mine...learning this stuff is not difficult....look at those 2 data PIDS I mentioned and unfortunately I can't diagnose this for you over the Internet.
Thread Starter
Burning Brakes
Joined: Apr 2023
Posts: 1,087
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From: Florida
2025 C6 of the Year Finalist - Unmodified
Thank you, the previous owner said he replaced the fuel pump. Unknown what pump he used but the fuel level sensor doesn’t function properly 90% of the time either. I’ll clean the maf and double check all the connections. The car has been doing this since I got it but runs great other than that. I’ll have to check the fuel trims and watch that video. Thanks again for all your help.
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Thread Starter
Burning Brakes
Joined: Apr 2023
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From: Florida
2025 C6 of the Year Finalist - Unmodified
The weird thing is only does it when in park or neutral… Was thinking possibly the auto’s wouldn’t let it rev as freely to prevent transmission damage ie. the 4500 rpm limiter but doubt it. The car definitely pulls hard for being mostly stock and never misses or anything like that. Was trying to figure out why it only does it in neutral/park.
Melting Slicks
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Drifting
Joined: May 2007
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From: Huntersville, NC
Normal in park or neutral. The PCM is pulling fuel and timing to save the engine from what you are doing (high revving in P or N). Quit revving in P or N while you still can.
These engines are "interference" engines. which means the timing of the exhaust valve is really late in the exhaust stroke. Over revving with no load, could cause the piston to tap the exhaust valve if you inadvertently rev to valve float RPMs. That first tap is OK, the next exhaust stroke usually sends a con rod out the side of the block.
If it never hesitates with load going down the road then all is cool. If it does, might be a fuel rail pressure issue, or a knock sensor causing timing to be pulled.
On another note, the P.O. gutting the cats would concern me. Why? if they get plugged up, then fuel trims are off or the car is burning oil. Might want to do a little diag like looking at such things as fuel trims, the PCV system, Borescoping the piston tops for signs of oil burning. I would wonder what problem was to be solved by gutting the CATS.
These engines are "interference" engines. which means the timing of the exhaust valve is really late in the exhaust stroke. Over revving with no load, could cause the piston to tap the exhaust valve if you inadvertently rev to valve float RPMs. That first tap is OK, the next exhaust stroke usually sends a con rod out the side of the block.
If it never hesitates with load going down the road then all is cool. If it does, might be a fuel rail pressure issue, or a knock sensor causing timing to be pulled.
On another note, the P.O. gutting the cats would concern me. Why? if they get plugged up, then fuel trims are off or the car is burning oil. Might want to do a little diag like looking at such things as fuel trims, the PCV system, Borescoping the piston tops for signs of oil burning. I would wonder what problem was to be solved by gutting the CATS.
Thread Starter
Burning Brakes
Joined: Apr 2023
Posts: 1,087
Likes: 392
From: Florida
2025 C6 of the Year Finalist - Unmodified
Normal in park or neutral. The PCM is pulling fuel and timing to save the engine from what you are doing (high revving in P or N). Quit revving in P or N while you still can.
These engines are "interference" engines. which means the timing of the exhaust valve is really late in the exhaust stroke. Over revving with no load, could cause the piston to tap the exhaust valve if you inadvertently rev to valve float RPMs. That first tap is OK, the next exhaust stroke usually sends a con rod out the side of the block.
If it never hesitates with load going down the road then all is cool. If it does, might be a fuel rail pressure issue, or a knock sensor causing timing to be pulled.
On another note, the P.O. gutting the cats would concern me. Why? if they get plugged up, then fuel trims are off or the car is burning oil. Might want to do a little diag like looking at such things as fuel trims, the PCV system, Borescoping the piston tops for signs of oil burning. I would wonder what problem was to be solved by gutting the CATS.
These engines are "interference" engines. which means the timing of the exhaust valve is really late in the exhaust stroke. Over revving with no load, could cause the piston to tap the exhaust valve if you inadvertently rev to valve float RPMs. That first tap is OK, the next exhaust stroke usually sends a con rod out the side of the block.
If it never hesitates with load going down the road then all is cool. If it does, might be a fuel rail pressure issue, or a knock sensor causing timing to be pulled.
On another note, the P.O. gutting the cats would concern me. Why? if they get plugged up, then fuel trims are off or the car is burning oil. Might want to do a little diag like looking at such things as fuel trims, the PCV system, Borescoping the piston tops for signs of oil burning. I would wonder what problem was to be solved by gutting the CATS.
Race Director
Joined: Dec 2013
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What air filter system in play (if after market), and when was the last time you Maff spray cleaned the MAF sensor.
Some after market air filter system case clean air flow problems across the Maff, and oiled air filters that have been over oiled, can cause oil fouling to the Maff sensor.
Short of that, monitor the Pre O2 sensor, to make sure you don't have one going lazy.
Some after market air filter system case clean air flow problems across the Maff, and oiled air filters that have been over oiled, can cause oil fouling to the Maff sensor.
Short of that, monitor the Pre O2 sensor, to make sure you don't have one going lazy.
Thread Starter
Burning Brakes
Joined: Apr 2023
Posts: 1,087
Likes: 392
From: Florida
2025 C6 of the Year Finalist - Unmodified
What air filter system in play (if after market), and when was the last time you Maff spray cleaned the MAF sensor.
Some after market air filter system case clean air flow problems across the Maff, and oiled air filters that have been over oiled, can cause oil fouling to the Maff sensor.
Short of that, monitor the Pre O2 sensor, to make sure you don't have one going lazy.
Some after market air filter system case clean air flow problems across the Maff, and oiled air filters that have been over oiled, can cause oil fouling to the Maff sensor.
Short of that, monitor the Pre O2 sensor, to make sure you don't have one going lazy.
Drifting
Joined: May 2007
Posts: 1,547
Likes: 210
From: Huntersville, NC
It is normal for thePCM to limit fuel and spark advance to over-ride gas pedal inputs in neutral or park. As I said these engines are interference engines which mean the travel path of the exhaust valve goes below the top deck of the block. So there is a potential interference between the valve and the piston (the top of the piston comes to the block deck each TDC). Now this is not a problem, with intake valves unless you bust a timing chain. They are interference too, but close much earlier in the compression stroke.
The PTV (piston-to-valve) clearance for the exhaust valve on a stock cam is less than 3/16 inch. If you put an aggressive cam in, this can go to lass than 1/8 inch, and be much later in the sequence in order to complete scavenging the combustion chamber.
There have been many many LS3 and LS7 engines where failure begins with piston contact with the exh valve. The LS1 and LS6’s not as common.
I’m sure I don’t have the full story, so my suggestion would be to enjoy the car as it is, and do what you can to correct the mistakes of the P.O. He got above his pay grade messing with things best left alone.
The PTV (piston-to-valve) clearance for the exhaust valve on a stock cam is less than 3/16 inch. If you put an aggressive cam in, this can go to lass than 1/8 inch, and be much later in the sequence in order to complete scavenging the combustion chamber.
There have been many many LS3 and LS7 engines where failure begins with piston contact with the exh valve. The LS1 and LS6’s not as common.
I’m sure I don’t have the full story, so my suggestion would be to enjoy the car as it is, and do what you can to correct the mistakes of the P.O. He got above his pay grade messing with things best left alone.
Thread Starter
Burning Brakes
Joined: Apr 2023
Posts: 1,087
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From: Florida
2025 C6 of the Year Finalist - Unmodified
Good info, thanks! I’m replacing the stock manifolds and gutted cats with speed engineering headers & catless x pipe. No emissions here and I want the car loud. Currently the car is “straight piped” and it’s still not as loud as other cars I hear, some with mufflers even. That part I don’t understand… Not sure why a 392 scat pack or 5.0 coyote is louder than a free flow exhaust LS.