C5 pinging under hard acceleration
Thread Starter
Racer
Joined: May 2021
Posts: 403
Likes: 64
C5 pinging under hard acceleration
I have a pinging problem on my C5. No codes coming out and no modifications. We have since tried running the engine colder with a colder thermostat and lowering the fan temps down to 180. It's still pings under full throttle from mid to high RPMs. 93 octane does not resolve it. Engine has 180k mi
Instructor
Joined: Oct 2020
Posts: 140
Likes: 45
From your descriptionist sounds like the car is missing at high RPM. Very likely if you can feel it, it will be caused by a failing plug. You usually won't see a lot of wear on platinum or iridium plugs. The spark will find somewhere else to go due to resistance and it usually gets worse with load it also won't always do it either. Keep in mind this is an internet diagnostic with not a lot of information. I suggest the plugs because they are easy to pull and very likely you will find tracking or scorch marks down the porcelain or the words Bosch Platinum. It could also be bad wires. MMartinez is right it could be carbon buildup but I've never seen a port fuel injected car develop this issue. I think top engine cleaner is great as well as cleaning the throttle and MAF but I doubt that's your issue. Let us know what you find.
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Drifting
Joined: Sep 2009
Posts: 1,862
Likes: 594
From: Prescott, Arizona
Usually but not always. A lot to learn about knock sensors available on line. If it is truly pinging, something in the knock sensor system is not working:
https://duckduckgo.com/?q=knock+sens...a=privacypromo
https://duckduckgo.com/?q=knock+sens...a=privacypromo
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,500
Likes: 3,999
From: Cape Coral, Florida
I'd replace the plugs with the AC Delco Iridium plugs and as mentioned buy a can of GM Top End Cleaner...if you can get your hands on a borescope you can visually take a look. What do your fuel trims look like under acceleration when the detonation occurs ??...they could be just below the percentage where the MIL will illuminate but being the detonation is under load it would not be a vacuum leak...it would be a fuel delivery issue or MAF sensor issue...I see you are an ASE Tech and shop owner so I'm sure you have a decent scan tool...do you own and use a labscope ??...if so you should get your hammer out and test those knock sensors with your scope...sometimes the PCM won't throw a DTC and so look at your timing under load to see what's happening.
Last edited by C5 Diag; Dec 12, 2022 at 10:40 AM.
Thread Starter
Racer
Joined: May 2021
Posts: 403
Likes: 64
I found the problem and I suspect many others have the same problem and may not know they have it. There's no code from the knock sensors and the short-term fuel trim doesn't fully reflect the problem because the STFT is an average of the full range of use.There's a crimp on clamp in the air tube between the mass air sensor and the throttle body. It doesn't fully secure the tube and since the air filter creates drag there's bypass air escaping inmaking the mixture lean. Change that out for a band clamp with a screw. Take the old one with you to the store. That bypass air also has dirt and is damaging to the engine. This fixed my pinging.You can tell if your clamp is loose Which it almost definitely isby taking a whole air assembly off and you'll notice that the tube can spin at that joint
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,500
Likes: 3,999
From: Cape Coral, Florida
I found the problem and I suspect many others have the same problem and may not know they have it. There's no code from the knock sensors and the short-term fuel trim doesn't fully reflect the problem because the STFT is an average of the full range of use.There's a crimp on clamp in the air tube between the mass air sensor and the throttle body. It doesn't fully secure the tube and since the air filter creates drag there's bypass air escaping inmaking the mixture lean. Change that out for a band clamp with a screw. Take the old one with you to the store. That bypass air also has dirt and is damaging to the engine. This fixed my pinging.You can tell if your clamp is loose Which it almost definitely isby taking a whole air assembly off and you'll notice that the tube can spin at that joint
Thread Starter
Racer
Joined: May 2021
Posts: 403
Likes: 64
This is the clamp design that you should use to replace the crimp on clamp
The crimp on clamp has been removed from its location. On the left you will notice the crimp on clamp laying on the ground. You will notice it beside its position and intake tube. This thing does not seal the system
Safety Car
Joined: Oct 2007
Posts: 4,204
Likes: 1,074
From: South Florida
If the engine was leaking air and running lean you will see it on the wideband sensor.
The real lesson here is every performance oriented vehicle shall use a wideband sensor. Invest the $150 for the most important device you can possibly add to your vehicle.
Performance engines are more susceptible to damage when they run lean than normal engines, it isn't like a corolla you can just let it go lean and expect to engine to survive for a while. You need to know instantly the engine is lean- you MUST have a wideband.
The real lesson here is every performance oriented vehicle shall use a wideband sensor. Invest the $150 for the most important device you can possibly add to your vehicle.
Performance engines are more susceptible to damage when they run lean than normal engines, it isn't like a corolla you can just let it go lean and expect to engine to survive for a while. You need to know instantly the engine is lean- you MUST have a wideband.
Drifting
Joined: May 2008
Posts: 1,693
Likes: 490
From: Denver, NC
This is the clamp design that you should use to replace the crimp on clamp
The crimp on clamp has been removed from its location. On the left you will notice the crimp on clamp laying on the ground. You will notice it beside its position and intake tube. This thing does not seal the system
Very interesting. That is the clamp I have found loose and used a cv joint clamp tool to tighten. I have always disliked that clamp.
Race Director
Joined: Oct 2004
Posts: 12,860
Likes: 4,661
