[Apexslayer]

Three questions:
1) Does it do this on a full tank?
2) Does it do it in left and right hand turns?
3) Does it only do it when WOT?

[GunMetalGrey]

Originally Posted by Apexslayer

Three questions:
1) Does it do this on a full tank?
2) Does it do it in left and right hand turns?
3) Does it only do it when WOT?

1) It does it on 3/4 tank

2) All the long sweeping hard corners at the track are turning right, so is the on-ramp where I test it on the highway, so I don't know

3) I've only noticed it at WOT

[Rodan]

Bumping this, because I believe I'm experiencing the same issue:

Surging / hesitation at full throttle on the straights. Never experienced this on the street, but very apparent on track.

2018 ZL1 A10
Occurred with plenty of fuel in the tank (1/2 to full).
Usually didn't occur on out lap, only when up to speed.
Also much diminished when my wife was driving - she was ~ 6-8 seconds off my pace.
Hot today - mid 90s F
Always in a straight at full throttle.

Definitely not stability/traction control - occured in PTM Sport 1, Sport 2 and Race.

[GunMetalGrey]

Originally Posted by Rodan

Bumping this, because I believe I'm experiencing the same issue:

Surging / hesitation at full throttle on the straights. Never experienced this on the street, but very apparent on track.

2018 ZL1 A10
Occurred with plenty of fuel in the tank (1/2 to full).
Usually didn't occur on out lap, only when up to speed.
Also much diminished when my wife was driving - she was ~ 6-8 seconds off my pace.
Hot today - mid 90s F
Always in a straight at full throttle.

Definitely not stability/traction control - occured in PTM Sport 1, Sport 2 and Race.

What did you mean to write when you wrote "Usually didn't occur on out lap, only when up to speed. "?

Does it happen on all straightaways or only on a straightaway after a long hard corner?

Have you tried to replicate this on the street?

When it happens to me it happens both mid corner and upon exiting the corner if its after a long and hard one.

[Rodan]

Originally Posted by GunMetalGrey

What did you mean to write when you wrote "Usually didn't occur on out lap, only when up to speed. "?

'Out lap' is a reference to the first lap, where you're not going 100%... waiting for tires to come up to temp, checking the track for any changes in condition, etc. I did not encounter the surging on my out laps, usually the 2nd or 3rd lap as I came up to full speed.

Does it happen on all straightaways or only on a straightaway after a long hard corner?

Well, technically all straights come after a corner, and on a track, they're all 'hard', but I experienced the surging on every straight where the car was full throttle in a straight line. After rights, after lefts, and after a right/left chicane.

Have you tried to replicate this on the street?

No. Experienced it for the first time on track yesterday. It only happens when running hard on the track, and I'm not sure I would want to try to replicate it on the street.

When it happens to me it happens both mid corner and upon exiting the corner if its after a long and hard one.

I am not experiencing it in the corner, or on corner exit. Only at full throttle.

I specifically ran the car in PTM Sport 1, Sport 2 and Race to ensure it wasn't some issue with traction control or stability control, and the hesitation was present in all modes. I can feel when the car is pulling power with a heavy foot on corner exit, and that's not what this is. Car is hooked up and going in a straight line, then starts surging like the fuel is cutting out and back on.

I'm going to look at PDR video today, and see if it's apparent on there. If it is I'll try to post a video.

[Rodan]

So here's a clip from the PDR...

https://youtu.be/gVS1bnFQiIo



Turn the volume all the way up. Surging can be seen/heard at 00:16 in 3rd and 00:20 in 4th, but it's subtle.

Very obvious at 00:32 in 3rd.

[GunMetalGrey]

Update; dealership called me and said that GM told them to replace the entire fuel tank and fuel pick up assembly instead of just the fuel pick up assembly.

I sure hope they find some obviously wrong when they pull the tank out in a few weeks so that I can have some confidence that this issue is resolved once and for all.

[GunMetalGrey]

Originally Posted by Rodan

'Out lap' is a reference to the first lap, where you're not going 100%... waiting for tires to come up to temp, checking the track for any changes in condition, etc. I did not encounter the surging on my out laps, usually the 2nd or 3rd lap as I came up to full speed.

Well, technically all straights come after a corner, and on a track, they're all 'hard', but I experienced the surging on every straight where the car was full throttle in a straight line. After rights, after lefts, and after a right/left chicane.

No. Experienced it for the first time on track yesterday. It only happens when running hard on the track, and I'm not sure I would want to try to replicate it on the street.

I am not experiencing it in the corner, or on corner exit. Only at full throttle.

I specifically ran the car in PTM Sport 1, Sport 2 and Race to ensure it wasn't some issue with traction control or stability control, and the hesitation was present in all modes. I can feel when the car is pulling power with a heavy foot on corner exit, and that's not what this is. Car is hooked up and going in a straight line, then starts surging like the fuel is cutting out and back on.

I'm going to look at PDR video today, and see if it's apparent on there. If it is I'll try to post a video.

I wasn’t experiencing it mid corner either until it acted up most recently, now it’s both mid corner and on the straightaway.

Thanks for the responses and clarification

[Yomike951]

I have the same exact issue on higher "g" right turns no matter the fuel level. I'm in China for the week, when I return I'll post a clip of what it sounds like.
In my case it sounds like it's running super rich and sputters until I lift and then get back in the gas and it's ok until the next lap...

[GunMetalGrey]

Originally Posted by Yomike951

I have the same exact issue on higher "g" right turns no matter the fuel level. I'm in China for the week, when I return I'll post a clip of what it sounds like.
In my case it sounds like it's running super rich and sputters until I lift and then get back in the gas and it's ok until the next lap...

Finally someone else!
My car starting doing it at 3/4 tank the last time this happened.
Let me know what if anything you discover regarding the cause and the fix

[Yomike951]

I just returned from traveling and I'll start digging deeper next week but here's a video at the 40 second mark of it sputtering. It happened over and over that day.
Btw, I'm stock except exhaust.
https://youtu.be/0isRI8TDSFw

[Gunkk]

Exhaust pops are usually from spark retard... so why did it pull timing?

Motor mount clang causing false knock?
Loose KR harness?
...?

Did you check the log in the cosworth toolbox?

[GunMetalGrey]

UPDATE: The dealership replaced the entire tank and fuel pick up assembly, they had it all out so I could see it and I now I understand more about the gas tank and fuel pick up assembly;

The two sides of the tank are really divided/segregated and hence there is a fuel scavenger pump in the left hand side of the tank that pumps the fuel on that side back to the main pump on the right hand side, so if this scavenger pump was not working, no fuel would get back to the right hand side of the tank where the main pump is on hard long right hand corners.

Guess what???

The entire time this has been going on, the dealership never thought about replacing the scavenger pump!!! They had only replaced the main pump!!!

I can't believe their lack of logic and thought... If this doesn't fix the problem I'd be shocked.

[Rodan]

Originally Posted by GunMetalGrey

I can't believe their lack of logic and thought...

This is, unfortunately, the norm in dealership service. Especially warranty repair.