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Uneven afr per bank vq35

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Hi.I have a vq35 with lower compression 8:8:1 ,272 cams.running on late model ecu 1995 tuned by nistune on closed loop with a MAF ,set timing mean no vtc.so at any rpm bank 1 is leaner about 20% then bank 2.wat could be causing this?

sounds like a cylinder not firing correctly or at all

I've checked all injectors and coils,nothing wrong with them,and swapped o2 senors as well.

Can you log the fuel trims at all and post them up? If one bank is 20% leaner, you should see the trims maxed out on that bank.

Could you have a leaky exhaust manifold or collector on that bank?

I will postem up later,no leaks on the engine.

You may see this if there is a problem with the cam timing on one bank vs the other. I've had this scenario on a Honda C30B engine. I confirmed it with a compression test and one bank was on average 20 psi lower than the other.

the VQ35 is also very sensitive to fuel pressure oscillations which in stock form are damped by a fuel pressure damper in each fuel rail. These are often removed when swapping to a return-style fuel system and can cause bank to bank fluctuations and weird lean spots. normally this is at select rpm ranges though as opposed to everywhere. In our Z it is very prominent around 3000-4000 rpm where we have bank to bank variations of as much as 25%

I'm using cosworth fuel rails return fuel,I was thinking it could be the cams,but wouldn't that be way off timing if that's the case?this is were i wished I had vtc.

I would definitely start by carefully checking that the cams are degreed correctly. Particularly if you have vernier cam gears that are incorrectly adjusted, it would be very easy to see this kind of situation.

Thx,my next step is to degree the cams.

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