Flat Spot @ 3000rpm

[Quinny]

I picked up my R33 Series II GTS-T last night, I noticed it has a flat spot between 3000 - 4000rpm, but goes like a rocket after 4000. What would cause this? How can I fix it? As far as I know, the car is running factory boost, but I am not 100% sure on that. I read that disconnecting the factory 2 stage boost setup can cause a flat spot, could this be it? BTW, I did a search, but could not find anything related to this topic. Any help would be appreciated.

Edited May 9, 2006 by Quinny

[mr_crust]

coil packs

[Quinny]

What is the fix? Retune, replace the coil packs? spark plugs & leads?

[mr_crust]

they normally need to be replaced

[Quinny]

I suspect that the boost has been raised in its previous life. I have read in a few places that if the boost is raised, then you need 0.8mm spark plugs, which is why I asked. I will be getting a full service done next week, so hopefully that will shed some light.

mr_crust: how sure are you that the coil packs would be the problem?

The Skylines run 6 coils don't they? I don't understand how a car with 6 coils could have a flat spot consistantly in the same place. I don't really want to start guessing what might be the problem and spending heaps of money replacing stuff that doesn't need to be replaced.

I should also mention that it does not have a flat spot in first gear, not sure if that makes any difference.

[cry41t]

I have experienced similar problems in the past with my 33, i had new performance coil packs installed prior to that and it turned out to be my fuel pump, as i had too many upgrades for the fuel system to handle. Once i upgraded my fuel pump and installed a fuel reg the flat spot at around 3-4000 rpms disappeared. But your mechanic will know best.

[Quinny]

Is there any reason why the flat spot does not happen in first gear, only in the other gears?

[gtr sleeper]

when the flat spot happens can u hear a popping sound from the exhaust? if so coil packs and plugs. get your mechanic 2 check fuel pressure and check for computer codes/faults and check boost pressure. the reason it doesnt happen in 1st is 1st gear doesnt load up the engine, the other gears load it up.

[Quinny]

The car is fairly quiet, and I didn't notice a popping noise at all when it hit the flat spot. I kind of felt and sounded like the clutch slipping, but I highly doubt that it would be the clutch.

[Munna1]

The car is fairly quiet, and I didn't notice a popping noise at all when it hit the flat spot. I kind of felt and sounded like the clutch slipping, but I highly doubt that it would be the clutch.

I dont know that it would be coils because if it were you would have troubles higher in the rev range as well. Ive got my money on the Nissan ECU over fueling if the plug gapping doesnt fix it a safc or power fc probably will. Make sure you take it to a machanic experienced with Skylines I took mine to a local machanic when I had this problem and he had no idea how to fix it.

[Quinny]

I dont know that it would be coils because if it were you would have troubles higher in the rev range as well. Ive got my money on the Nissan ECU over fueling if the plug gapping doesnt fix it a safc or power fc probably will. Make sure you take it to a machanic experienced with Skylines I took mine to a local machanic when I had this problem and he had no idea how to fix it.

I would have thought that a coil problem would be evident in more than 1000rpm of the rev range. I will try resetting the ECU, and getting 0.8mm spark plugs, if that doesn't work, I will be getting a Power FC & dyno tune soon, so hopefully that will will fix it.

I also need to get a EBC, to make sure my car is running the correct boost. I think I will set it for 8psi until I get the cooler.

Thanks for your help Munna1.

[Quinny]

I took the car for a run yesterday, judging off the factory boost guage, the car is reading about +370mm/Hg (which works out to about 7psi) at full noise, so it seems that the boost is at the factory setting.

I think I might just take the car to a dyno and see what the tuners think...

When I got the car the other day, I put 95RON Premium fuel in by mistake, would that contribute to the problem?

Edited May 11, 2006 by Quinny