Lack Of Power

[IanB]

Hi all

Bit of background info first:

Car: R32 GTR (RB26DETT)

Turbos: R34 N1

Compression: 175, 170, 170, 168, 170, 170 (cold) (done tonight)

Oil Preassure: Fine - Electronic sender was replaced recently and stock gauge works quite well, reports normal oil pressure

Water Temps: Normal

ECU: PFC

AFMS: Stock

Other power mods: Minimal. Blitz SBC2 controller, light mods such as oil cooler catch can etc

Boost: 16.5 PSI 85% inj duty

Injectors: Stock

Recently out at the drags I ran some rather disappointing times. The problem is the car seems to be developing less then normal power. Normally I run around a 12.9 however on my first run I ran a 14 flat. I put it down to the fact that I hadnt dragged in a while, and there was a open lane, so I did another run, which was a 15.0. The car started to develop some noises so I parked it and watched for the rest of the night.

The noises turned out to be several of the nuts on my exhaust flange on the front turbo (between the turbo and 02 sensor) missing - I replaced 2 and the noise has gone away, however the problem remains. It is possible that there are more nuts missing from this flange as I have to get under the car and have a good look to be certain.

On the way out to the drag strip I wasn't pushing it overly hard (it would be rather ironic to be fined for speeding on the way to the drags) however on the few pokes I did give it, I thought it felt a bit slow, so I think the problem has developed either on the way their or shortly before hand.

The problem seems to be that the car simply isnt pulling hard enough for the level of boost its getting. Its still boosting up cleanly and as quickly as normal, and holding boost at the right levels, but it just seems to lack urgency. Is a exhaust leak post-turbo enough to cause this? I have had conflicting opinions, one mate of mine who studys mech. engineering says any leak after the turbo shouldn't effect it however ive had others tell me that backpreassure is required and that this leak will be sufficent to slow the car down.

What I want to know is should I be hunting for more problems? What could the effects of a exhaust leak here be? I also noticed very poor economy on this tank of petrol since the problems developed, this may be however because I am pushing the car harder to get the desired result from the motor, however the leak is pre-o2 sensor, and I am curious as to if this could effect it? I have been told that the PowerFC's dont adjust AFR's on the go and that the o2 sensors are only for idle. o2 sensor voltage remains constant at 5.xx volts (im not entirely sure of the decimal, however it never changes) for both o2 sensors for both turbos, if this is of any help.

Thanks for all the help and if i have left out any details you need please ask.

Cheers

Ian

[R31Nismoid]

Had it on a dyno yet to see what the AFR's are doing?

Could be fuel pump failing, fuel filter perhaps could be blocked up

Clutch perhaps slipping a bit

Maybe a split vac line/cooler pipe somewhere that isnt dropping boost much, but would affect things possibly

Maybe its due for a plug change

Lots of things, AFR's are a good place to start

[IanB]

Not bad suggestions. I dont know if its the clutch,it may be but it doesnt really feel like clutch slip. The fuel filter is a good point its quite old, ill replace it tomorrow. How do you tell if the plugs are dead or not? Plugs arent terribly cheap, however the other night we put copper standard plugs in a mates RB25 and it runs fine, so maybe they might be worth giving a go.

I got under the car today and found another 2 missing nuts (again on the exhaust flange of the front turbo), I replaced one however the other is prooving rather difficult to get to and ill have another go tomorrow. The car sounds much smoother and seems to rev nicer now with the exhaust leak (nearly) fixed up however it still just doesnt feel fast enough. The boost controller reports only -17 or -18 in.HG vacume, when i thought it should normally report 20? Could this indicate a boost leak? ive been over the intake side of things pretty throughly and cant find anything, and boost seems to be holding strong.

I'll replace the fuel filter tomorrow and then see how we go, if its still not feeling right ill get a power run and see what that says.

[R31Nismoid]

Plugs should be less than $20 Iridi/Plati are a waste of money, coppers all the way.

[IanB]

Ok new fuel filter and plugs tomorrow, car needs new oil in 1000k however I dont want to change it now cause then the oil changes will be out at weird numbers :|. Hows that vac reading sound to you? Fine or too little?

[IanB]

Ok, i put coppers in and they seem to run fine, old plugs were quite worn and have gone in the bin. New fuel filter as well.

Initially I noticed a power gain and it almost felt normal, now im not so sure. It seems to be running very rich, much more then normal? Im on half a tank from a full tank and ive only done 120 k's (with a spirited, but boost turned right down run up and down my local hill), and there seems to be alot of black spray on the ground around near the exhaust pipe where the car is normally parked. Could over-fueling be causing the problem with the power? Theres been no changes in the cars setup for a while now, what would cause it to run richer all of a sudden?

Im tossing up if I should shell out the coin for a retune before I go blowing nearly 100 bucks on just a power run. However im thinking there might be a leaky injector? I cant smell any fuel when I open the bonnet, what else could I look for? The car pops and backfires alot, more then normal, could this indicate that there is still an exhaust leak I have not found? Would this affect preformance and economy?