Need help diagnosing noise

[BJG32]

Last weekend i installed bellanger headers. In the process i replaced the spark plugs.

I have the arrow pcm.
Intake air temps are below 60 degrees.

Normal driving no issues or noises. Car sounds great and accelerates normal. If i hit redline at 80% throttle nothing sounds/feels wrong.

But when I am 100% throttle at high rpms the exhaust rapidly pops and sounds like what i think a missfire would sound like. . Acceleration is minimally affected if at all...

Any ideas on what this is and what i need to do to resolve?

Video below captures some of yhe popping. Best i could do with one hand and cold weather.


https://youtu.be/gqaSKTy-xs0

[PRVT JET]

Detonation?

[Martin]

Kind of sounded like your PCM needs to learn the new exhaust. That sound, at least as I remember it, is an open-loop fuel management system dumping a rich mixture into the exhaust which is popping off in the cats. I'd give it a few days to learn your driving style with the new exhaust and creep up on those full-throttle accelerations and the system will likely figure out how to adjust the fuel mixture at open loop.

Keep in mind that when in open loop, all the normal fuel management tables go out the window. There's basically one setting that the PCM thinks is "right" for wide-open throttle and it spits a ton of fuel into the system to avoid detonation. Too much extra fuel, and you get fuel ignition in the cats, which cause that backfiring sound.

Just my .02 - I don't know a lot about how these PCMs handle WOT fuel delivery nowadays.

[BJG32]

I should add i have arrow pcm. Not sure if that matters? Will add to 1st post.

Thanks for the insight!

[Jack B]

Here are some thoughts:

1. I would verify all the plug wires are properly attached. You can also pull the plugs to check if they all look the same or similar. In addition, look at each plug wire, look for a black tracking mark.

2. Make sure you do not have an exhaust leak at the header gasket. Look for a black line on the header flange.

3. At WOT (open loop), there is no learning. those are fixed tables, however, they are affected by the IAT and the ECT.

4. Use a scan tool and see if you have any misfire codes or pending codes.

5. The exhaust is under both positive and negative pressures, if there is an exhaust leak on the engine side of the cat, strange things can happen. Look for a leak on both sides of the turnout.

[7TH_SIGN]

Jack's advice above is exactly what you need to do. Hard to tell from the video as it could be anything. I would start by checking to make sure all plugs and wires are properly attached. After this if the problem still occurs pull each plug and inspect them. Make sure when you reinstall them you make proper connection.

You did mess with the spark plugs last week so I'm almost certain it has something to do with your ignition.

[BJG32]

Thanks for the guidance Gentlemen!


If anyone else experienced this, then please chime in and let me know what the problem ended up being........

[texasram]

This honestly sounds like my factory exhaust but amplified

[BJG32]

This honestly sounds like my factory exhaust but amplified

Video doesn't do it justice. This is Belanger headers with cat and muffler delete. Popping is like a machine gun at like 4k to redline at WOT.

[BlueAdder]

If when you accelerate the car seems to misfire, gets kind of jerky etc, I would check the TPS.
I had a problem with my Elise and it was a lot worse than what you have. the car was fine under 4K but once I'd be between 4K and 6K the motor was not happy at all.
I thought, that it could be the spark plugs but nope. Then I left it at the shop (which I no longer go to...) and the dude kept the car for 10 months and when he gave it back, the problem was still there.

I gave the car to the guys who tuned the EMS and they found out what the problem was the next day: TPS was bad and thus causing me grief. $50 part :furious:
I would do all the stuff Jack B mentioned and check the TPS and the spark plugs.

Edit: TPS -> Throttle Position Sensor
Not everyone is familiar with the acronyms, so just in case...

[BJG32]

Thank you! Im going to run through Jacks list since i touched all of those items in the install. TPS is on the list if all else fails.

I did get a blob of anti sieze on the electrode of a spark plug. I only whiped it off. Im going to clean and reinstall all plugs first. I'll report back....

[Jack B]

I would throw that plug away. The torque value on G5 plugs is 13 ftlbs. With antiseize it will be close to 10 ftlbs, be careful or you may be pulling a head. Fyi - I believe the G2 was 18 ftlbs for the plugs.


Thank you! Im going to run through Jacks list since i touched all of those items in the install. TPS is on the list if all else fails.

I did get a blob of anti sieze on the electrode of a spark plug. I only whiped it off. Im going to clean and reinstall all plugs first. I'll report back....

[7TH_SIGN]

It's your car but I'd recommend not to use antiseize on the plugs. Just hand tighten. That's how I've always done my cars.

[nx91notch]

Also when you install the plug wires make sure you hear and feel the audible "snap" it makes. If you don't feel/hear that click it may look like the plug wire is seated but it actually isn't.

[BJG32]

Great tips guys. Will do!

[BJG32]

Narrowed the problem down to the driver's side. Replaced all 5 plugs after confirming connections were ok. That fixed whatever the issue was. Thanks for all the replies!

[RdyPlr1]

This is why we love the forum, glad you found a fix!

[7TH_SIGN]

Narrowed the problem down to the driver's side. Replaced all 5 plugs after confirming connections were ok. That fixed whatever the issue was. Thanks for all the replies!

Just like we suspected. Now get out there and hurt some Vette feelings.