2015 ZL1 RPM surge in every gear while driving at 1250 RPM

[mixitup]

My 2015 ZL1 automatic, experienced a 219B air fuel mixture imbalance and at the same time every time and in all gears when I reach 1250 RPM under light throttle it surges from 1250 to 1400 indefinitely. Above 1500 RPM it drives normally.

The 219B turned out to be a bad injector and I purchased a new set of FIC1000. I had the car re-tuned for the new injectors and cannot fix this RPM surge. I even disconnected the JMS fuel max to see if it was responsible, no luck. Even smoked the engine looking for vacuum leaks, none found. Cleaned the MAF and throttle body. Any thoughts.

Car is stage 2, DSX, JMS fuel max, Kooks with cats, pulley, etc..

Any help would be much appreciated.

[70T/A400]

These cars do not like after market throttle bodies. Your troubleshooting looks

I assume it is not setting a service engine soon light and there are no codes to pull.

You may have to look at the spark and fuel tables.

When you modify a car you have to accept the consequences that it is not going to run like stock.

Check out this link for what happens when you modify a Gen 6 ZL1 and the consequences.

https://www.camaro6.com/forums/showthread.php?t=490819

[acammer]

When you say stage 2 - does the car still have the factory camshaft, or is it stock? There is no reason a stock car cannot be smooth there. If it's got a significantly more aggressive camshaft that might be a natural side effect that is a by-product of increased overlap and decreased stability in the airflow at very low RPMs.

[mixitup]

the cars has a BTR stage 2 cam, Roto Fab CAI, 10% over drive crank pulley, 2.39 super charger pulley, DSX flex fuel, JMS fuel module, Kooks headers and cats.

I drove the car 7000km's last year with no issue until this spring with the 219B air/fuel mixture imbalance code. Turned out I had 1 bad fuel injector flowing at 900 instead of 1000. At the same time I started to experience this 1250 - 1400 rpm surge/fluctuation at light throttle in all gears (automatic). Tuner re-tuned for the new set of FIC1000 injectors, and can't fix this idle surge.

[acammer]

Originally Posted by mixitup

the cars has a BTR stage 2 cam, Roto Fab CAI, 10% over drive crank pulley, 2.39 super charger pulley, DSX flex fuel, JMS fuel module, Kooks headers and cats.

I drove the car 7000km's last year with no issue until this spring with the 219B air/fuel mixture imbalance code. Turned out I had 1 bad fuel injector flowing at 900 instead of 1000. At the same time I started to experience this 1250 - 1400 rpm surge/fluctuation at light throttle in all gears (automatic). Tuner re-tuned for the new set of FIC1000 injectors, and can't fix this idle surge.

If it wasn't a problem, then had a mechanical issue followed by a retune and now the mechanical issue is resolved and now it has a driveability problem I think that probably points at the tune. I assume you've discussed with your tuner? What is there explanation for the change in behavior?

[mixitup]

My tuner says he has lots of cammed cars that exhibit the same issue, and to live with it. It never did it last year

[acammer]

Originally Posted by mixitup

My tuner says he has lots of cammed cars that exhibit the same issue, and to live with it. It never did it last year

That sounds like a cop-out. You KNOW it doesn't have to do it, because it didn't always do it.

There are characteristics of increased overlap with more aggressive aftermarket camshafts that will impact driveability, and that does show up the most from idle to ~2000rpm.

BTR loves to mask the complete specs of their cams for some unknown reason - so it's hard to know the exact valve events of your camshaft. I guesstimate with the BTR Stg2 PD blower cam you've got somewhere around 5-8 degrees of overlap. This is enough to get some very minor disruption to driveability, but with proper tuning should still be very smooth.

It sounds like your next upgrade might be a personnel change, not a part. If you've got other good, local, trusted resources that's always your best option. Otherwise, if you're interested, we can talk directly about remote tuning options with us at GPI. Feel free to email me directly if you want to chat - andrew@gwatneyperformance.com

[1JEWLDSSRS]

I have to agree with Andrew on this one! When a tuner tells you THIS....
My tuner says he has lots of cammed cars that exhibit the same issue, and to live with it. It never did it last year

It's time to move on to a different tuner/shop. It is saying that whatever the issue is with your car, and the others, the tuner just doesn't want to dive into researching what the issue is. Personally, if it was me, I would be working with Andrew/GPI to get it sorted out, they know these platforms better than anyone!

[Ashen L99]

You need to look at TPS on a log. It might be tune related, but the fact that it didn’t do it last year, and the only change you did was injectors, so your tuner put in the corresponding injector data, leads me to believe it’s probably the throttle body fluttering.

On the other hand, if it is tune related, get with Andrew and the guys at GPI. They are some of the best in the business hands-down.