RB26 #6 running lean issue

Anyone have a solution to this problem?

1994 r32, #6cylinder has a tendancy of running lean. so far no problems, but I want to do something about it before i spin a bearing or something.

Have your injectors flow tested, put the best one on number 6.

Or put a screw through the plenum, to imped the flow of air. I have thought about that one, but I just can't do it :)

Or knife edge the intake runners on all except number 6

To tell you the truth, the first one is the best bet, unless you can get your engine flow tested.

I would also say a dirty injector. And you can test that east yo switch with another injector and see how the injector works on the 'new' cil.

Derby

Derby,

All RB26 will run lean on number 6, its a fault with the plenum design, not just his engine ;)

Cheers,
Tony

Derby,

All RB26 will run lean on number 6, its a fault with the plenum design, not just his engine ;)

Cheers,
Tony

See this is what I thought. The intake plenum is deffective from the factory, making #6 run lean. Is there anything I can do to rectify this problem, other then getting an aftermarket unit? And will that even solve this irritating problem? haha.

It hasnt caused me trouble yet, but you know how it is...you drive, skeptical as hell...I just want to know there wont be a problem. Like peace of mind I guess.

Oh thanx for the info, didn't knew that.

Derby

The problem is in order to really correct the issue, your will need a flow bench. The air going into number 6 will need some sort of speed bump, to slow the air down. That is why I had been thinking about drilling the plenum, and put a screw or bolt to impede the air stream going into number 6. That is a shade tree mech type of fix, hence me not doing that. If you had a flow bench, you could actually do it, since you would be able to precisely know how much air you are impeding, compared to the other ports. If this was the case, you could weld some material into port 6, and grind away until you have even flow through out all 6 ports. Or like I mentioned, run your best injector in port 6.

Yeah I'll probably just do the injector thing, maybe even run a larger injector just for #6. I think that should keep me safe since I'm not really pushing this engine to the limits or anything. Over the winter I'm gonna pop in some GT2530's for a little extra boost, but Probably wont even run that much boost except for track days, so The injector idea should take car of it just fine.


SkylineUSA, do you know if this is an issue only for the later R32 models or is it for all GT-R engines?

If your running normal turbo, don't even worry about it.

Do not run a bigger injector, you will get bore wash, then you'll have to rebuild your whole engine.

The problem is with all the RBs

Yeah that was a stupid idea. I will still do your injector idea though. Would an aftermarket plenum help any?

Yes, the aftermarket ones do solve the problem, from what I have been told. The cost for them is outrageous though.

yeah ive noticed...oh well, for the amount of time I'll be running higher boost, i think the injector idea will be fine.

Hello there, I have heard from numerous sources that the cylinder 6 running lean isn't just the intake plenum as RB26 and RB25's both suffer from this problem however they have 2 very different plenum designs. Its actually a combination of several things, the plenum, the fuel rail, and the coolant feeds. The fuel rail because the fuel pressure regulator is at the front of the motor and so this can lead to slight irregularities in fuel pressure at the rear of the engine. Also, the fact that the waterpump is at the front of the engine and by the time the coolant gets to the rear cylinders its been well heated by the front cylinder. Therefore causing the a/f mixture to be heated slightly more = slightly leaner a/f ratio.

On a slightly modified car it's not much of a problem but once you get into things such as the need to upgrade injectors, you might want to upgrade to a fuel rail that is fed on both ends w/ a return in the center. Also, there are some coolant modifications that can be done to help w/ the coolant issues but i'm not very familiar with that. Anyways i figured i would point out that it isn't JUST the plenums.

Hey man i appreciate that. thanks alot!

I have never heard of an issue with an RB25, that is why you can N2O on them without direct port.

That is a good point about the coolant, but not too sure about the fuel rail issue.

I have to agree on the fuel rail being a problem, especially when you want to pump more fuel through it after boosting up. I've seen some with a centre feed to even out pressure across the cylinders. My RB20DET has a rail with two regulators, one at each end. I think the reason is the same - to even out pressure across the rail.