It seems since I had my HFC's put on the car sometimes not all the time would hesitate when I am on the freeway in sixth gear between 60-70mph, and push on the gas it would hesitate for a second or too then go. What do you think it could be? I have changed my plugs and still the same. Do you think it's the fuel filter or fuel pump? Oh by the way, I had it dyno tuned and the graph on the dyno was so erratic.

 

This has happened to another member here... and he had Berks as well.
The thread is around here somewhere, but if I remember correctly, the problem was finally reslved after moths of battling the dealership, by removing those Berc HFCs.

I'll go digging now and look for the thread

 

Here's one...
https://g35driver.com/forums/v36-gen...eistation.html

I also found your thread from back in March of 2009 where you were asking this same question. You were pointed to the same thread above.
Have you been living with this for over a year now?!?!?
Your thread:
https://g35driver.com/forums/v36-eng...ion-berks.html

 

LOL sucks.

And wow good memory.

 

Yeah I am still with that problem. At that time i was waiting for my Uprev tune to come in. they said that it would take care of it, but it didn't. Yeah so I got a second dyno tune and the tech guy had me look at the screen and the graph was all over the place up and down. You think I should take my cats off before I go to the dealer?

 

Whats weird is that it seems it happens usually on my way back home from work when it's warmer. In the morning the car feels so much stronger.

 

The hesitation issue in this link is because one or both wideband sensors installed on the manifolds are damaged due to installation. Those sensors up there are very sensitive and easily get damaged if you remove the cat bolts with air tools or use a hammer to loosen the bolts up. It's a pretty common issue because a lot of shops have difficulty getting the cat bolts off and use force to take them off.

https://g35driver.com/forums/v36-gen...eistation.html

 

I guess the best thing is for me to take the car to the dealer and have them check the o2 sensor. Right?

 

You'll probably have to pay for the replacement sensors but yeah.

 

I took my car in finally and had them check everything, and surprisingly the o2 sensors were okay, so I had them change back to the stack cats. Guess what the car is fine now. I do notice a power loss after the cats were taken off but since I had the car tuned with the cats on I might need to take it back to get it retuned with the stock cats. The best thing is there is no more hesitation. Do you think I should call Berk even though it's been a year and tell them the story because I even changed my spark plugs thinking it was that but it wasn't. Maybe they would refund me or send me a new set?

 

What exhaust system are you running? My friend is having a similar issue.

 

^ looks like he had the stock OEm exhaust with Berk CATS, and it were the Berk CATS that were the problem, which means no problem with the OEM catback