[ZL1 For The Sun]

Last Friday, the dealer’s ZL1 specialist diagnosed my noise per the TSB and ordered the fuel line. Said it was updated to include 2023 models. On national back order! Will patiently wait with all of you and look forward to hearing what a normal LT4 sounds like! At least it can still be driven some and get closer to the break in mileage. They are also replacing the cf heat extractor as I noticed under garage lighting upon arriving home on delivery day that it had several large noticeable hazy areas not visible in direct sunlight. When I showed them they agreed it needed to be replaced under warranty. Thankfully no back order on this!

[Nasty²³]

Went in for my appt today. Gave them the rundown and TSB and everything. Few hours later they say its not the TSB but was due to the exhaust actuator not having the "learn" procedure done on it. To quote my paperwork:
"This concern may be caused by an exhaust actuator that was installed but the learn procedure was not completed. This concern will occur on new vehicles with low mileage. PERFORMED THE RELEARN TO THE CYLINDER DEACTIVATION VALVES USING THE GDS NOISE NO LONGER PRESENT."

I drove it around and the noise at idle did in fact seem gone. I'm still skeptical on whether that was the actual issue since the LT4 doesn't have cylinder deactivation that I know of so take this as you will. I'm gonna keep my ears open and let you all know if it stays fixed or comes back.

[triggerjerk]

Originally Posted by Nasty²³

Went in for my appt today. Gave them the rundown and TSB and everything. Few hours later they say its not the TSB but was due to the exhaust actuator not having the "learn" procedure done on it. To quote my paperwork:
"This concern may be caused by an exhaust actuator that was installed but the learn procedure was not completed. This concern will occur on new vehicles with low mileage. PERFORMED THE RELEARN TO THE CYLINDER DEACTIVATION VALVES USING THE GDS NOISE NO LONGER PRESENT."

I drove it around and the noise at idle did in fact seem gone. I'm still skeptical on whether that was the actual issue since the LT4 doesn't have cylinder deactivation that I know of so take this as you will. I'm gonna keep my ears open and let you all know if it stays fixed or comes back.

That is very strange. Keep us posted.
Mine no longer does it at idle but it does occur once it is warmed up.

[Nasty²³]

I agree, seems odd. Unless two separate issues can result the exact same noise because I was getting the exact same noise as the videos folks posted in this thread. Looking forward to seeing other people's results with their dealers.

[DangerZL1]

If you have an engine stethoscope, place it on the fuel line at the back of the supercharger. If the check valve is not functioning properly, you can hear the noise pretty loud in the line. This is per the TSB and mine is really noticeable. The line runs under the passenger dash which is where the noise emanates.

[ZL1 For The Sun]

Mine makes the noise consistently at idle and low speed once it’s been driven for 15 minutes or so. It started with under 200 miles. I don’t hear it above 2000 rpm but it’s probably being drowned out by the engine & exhaust. The mechanic that looked at and listened to my car thought it was fuel pump or line related from the first check. I’m curios to see if yours stays quiet. Thanks to everyone for keeping us posted!

[SnakeEyeSS]

I'm still waiting until they won't need to hold my car for days to diagnose it. Especially after the newest joyride video of a 2016 Z06. Think I might install an extra hidden dash cam after seeing that.

[triggerjerk]

Well I just dropped my car off at the dealer. Wish me luck. LOL
And today it did occur on cold start.

UPDATE: Dealer ordered the wrong part. They claim the tsb is confusing and the part they ordered fits trucks.
Anyways, the correct part number for ZL1s is 84404473. Apparently the tech has done a ZL1 before. Too bad the
service writer and shop foreman didn't talk to him first! And yes, the part is on national backorder. :(

[DangerZL1]

Thanks for the update. My dealer's lead tech ordered 84404473 after looking into the parts and reading the TSB. It is confusing and applies to all the GM V8s and after looking at it, should be model specific. My part isn't here yet either, but at least they aren't chasing a new problem.

[SoMaR]

Went to the dealership to have this taken care of. Turns out they ordered the wrong part. The part they ordered comes off the hpf and hooks to the main fuel line. They told me the correct line runs almost all the way back to the fuel tank and theyd have to have my car a day or two at most.

[DangerZL1]

If you google GM 84404473 and find a pic it’s almost the length of the car. It’s confusing because the hpfp feed line looks like it connects to 84404473. As long as the line they ordered has the check valve in it. When I brought my car in they had it in the shop for over an hour. I was told most of the time was spent trying to find out which fuel line was the correct one to order.

[h1nch]

Update from my dealer, they said the part now has an ETA of Tuesday 9-5-2023. Once it comes in they'll reach out to me to coordinate drop off of vehicle.

While I had the tech on the phone I had him confirm the part number to me and they did order 84404473, so hopefully they are able to fix the issue.

[triggerjerk]

Originally Posted by h1nch

Update from my dealer, they said the part now has an ETA of Tuesday 9-5-2023. Once it comes in they'll reach out to me to coordinate drop off of vehicle.

While I had the tech on the phone I had him confirm the part number to me and they did order 84404473, so hopefully they are able to fix the issue.

Great info.

[Rogey89]

I go in on the 8th to have the fuel line swapped. I'll post paperwork and verdict once the procedure is complete.