I bought a used 2008 G37s from Car Max with 70k miles and it's been a great car. It was stock as far as I know and I have not made any modifications.


I took it to a southern California dealer for a 120k service and afterwards the engine and exhaust were much quieter, with no throaty sound, the loose baffle in the muffler no longer raddled, and there is significantly less power.


I took it back, went on a test drive with the mechanic, and showed him that the time to accelerate in 3rd gear from 3k to 4k RPM was about the same as from 4k to 5k and from 5k to 6k RPM, and much longer than normal.


He reprogrammed the ECU and you could hear the improvement in engine and exhaust noise immediately after starting the car. The acceleration in 3rd gear from 3k to 6k RPM was noticeably better but not back to normal. When driving uphill in 5thgear at 60 MPH (3k RPM) there is hardly any acceleration at full throttle - much, much less than normal.


Reprogramming the ECU made a significant improvement and suggests that it was affected during the original service but the dealer swears it was not altered then, which is difficult to believe.


At this point, I’m not confident that the dealer will be able toget the performance back to normal and am not sure who can be trusted to dothat.



Comments and suggestions please! Thank you.

 

What exactly did they do at 120k

 

1. Maybe your ECU was just reset that first time and it was re-learning your driving patterns.

2. Maybe you have improvement after ECU reprogram because you received newer firmware.

I really don't feel like there would be a difference in sound from ecu reprogram. Maybe one time was a cold start?

The car can also feel different depending on the weather. That is normal. Hot weather = more slugish.

 

They claim just a Major Service including fluids (oil, trans, diff), filters (oil, air, cabin), coolant flush, and front brakes but I can't imagine they did not reprogram the ECU.

 

Thank you for your thoughts.


1. It was performing poorly for a couple weeks and seemingly learned nothing during that time.
2. I assume just the software was reprogrammed. The improvement was significant but not back to where it was before the original service.


They claim that all they did was reprogram the ECU but they may have done more or corrected other problems caused by the original service and not wanted to mention it.


I don't think cold vs. hot starts or temperature are factors - the car was warmed up both times and the temperature in our area has not changed significantly over the last couple weeks.


I bought the car used from Car Max and am wondering if it had an after-market tune and now it has a stock tune.

 

They didn't change your plugs?

 

There was no explicit charge for plugs on the Invoice and changing them is not listed on their Standard/Schedule 1 for 120k mile service, so I assume they were not changed.

 

If your performance is close to what it was before, then my best guess is just ECU reprogram. I doubt they did more to fix your car without telling you. Unless they had your car for a while (more than 1 day), you have very little reason to suspect.

Why don't you go test drive another G37 and see how it feels? It's not a rare car, so just find a similar year/package and give it a test drive.

But all the same, even if you had a tune before, it doesn't really matter because you can't get it back without buying it again. Not like you have the license.

 

Well thinner older fluid will give less resistance is the only thing I can think of