Tuning Question

[Jez]

Hi guys first post for me.

Have an AU3 with a 5 litre. Recently got a set of extractors and 2.5" twin exhaust which made a bit of a difference in low end torque. I then got a custom CAI run off the front of the airbox and a performance filter. The airbox mods made the engine come to life it revs a lot quicker now.

Only trouble is now I seem to have a flat spot in the rev range around 3000 rpm. Would this be a tuning problem? I find it strange that the power drops out just below 3k and then boots back in at about 3500

Is it true that the computer is self tuning? Someone told me if I disconnect the battery to reset the computer it might rectify itself...?

[richo77]

dunno about the flat spot mate but if you go to www.aufalcon.com it gives instructions on how to correctly reset your computer after disconnecting the battery.. worth a try!

[xr8ute]

Auto or manual? Sounds like the factory EEC torque "control"...

[12]

Firstly.. Jez.

Is it AU3 XR8 or other? Might be the exhaust system. What type of headers you got? 4-1 (tuned), or 4-2-1 (tri-Y)? What brand name? Also.. is it a twin 2.5" from the headers right to the tips, or 2.5" into a Y connection and a single pipe under the diff?

4-1 headers and twin 2.5" from start to finish is not the best system for a standard 5.0 AU. You will loose power down low in the rev range. That system is more suited to a stroked or supercharged 5.0.

[Jez]

xr8 ute: it's manual (its a ute too : )

012: cheers! AU3 XLS... They're pacemakers, pretty sure they are 4-2-1...
it's 2.5" from cat back twin system straight through
are you saying there might not be enough back pressure in the exhaust?



i drove it for a couple of weeks with no problems after the exhaust was done it was only after airbox mods that the flat spot appeared. I'm going to reset the computer and see how that goes...

[Jez]

double post

[parawolf]

money is on torque control from the ECU...

[12]

Originally Posted by Jez

012: cheers! AU3 XLS... They're pacemakers, pretty sure they are 4-2-1...
it's 2.5" from cat back twin system straight through
are you saying there might not be enough back pressure in the exhaust?

Yeah. 2.5" twin system is too big. 2.25" is better suited. Hell.. the 5.6 250kW T3's I think had 2.25" twin system from factory. XLS had a 175kW V8 if I'm not wrong.. I'm not sure. All your power is down low in the rev range. No doubt torque trunication is also a part of it, but your computer has had plenty of time to re-learn the new exhaust and is now working at it's best range for the exhaust.. which is 3000-3500rpm and over. I'm no expert.. this is only my understanding and opinion. Try to find out exactly what headers you have.

The computer takes a while to re-learn after a exhaust system is fitted to your engine. So you will not feel an instant rush just after fitting a sports exhaust system.

[Stav]

Firstly..welcome to the forums...its always great when we get new people posting .

I have been to quite a few dyno days and the typical air fuel ratio is similar in both au v8 's and 6 cylinder models.

If you have a look at my old curves you will see that they go really rich and finally start to get a bit leaner.This would explain the flat spot.

Get a unichip to fix the problem.I recommend Spiro at AUTOTECH ENGINEERING IN Sydney

Here is a before and after for you to look at

http://photobucket.com/albums/y119/u...t=Scan0001.jpg

[xr8ute]

Originally Posted by Jez

xr8 ute: it's manual (its a ute too : )

Pretty good looking yoot at that ;)

Is that a VN SS in the driveway? I have very fond memories of one of them...

[Jez]

cheers bro, where can i find a pic of your beast?

good spotting, have many fond memories in that car also.

[FTE217]

Originally Posted by useless

Firstly..welcome to the forums...its always great when we get new people posting .

I have been to quite a few dyno days and the typical air fuel ratio is similar in both au v8 's and 6 cylinder models.

If you have a look at my old curves you will see that they go really rich and finally start to get a bit leaner.This would explain the flat spot.

Get a unichip to fix the problem.I recommend Spiro at AUTOTECH ENGINEERING IN Sydney

Here is a before and after for you to look at

http://photobucket.com/albums/y119/u...t=Scan0001.jpg

useless is the man !! you're spot with your comments above.
Mine had the same flat spots which peeeved me off, chip sorted it out.

[Jez]

seems he's not so useless after all then
I'm not in Sydney unfortunately but I'll go back to the place who did my intake and see about a unichip

cheers
Jez

[xr8ute]

Originally Posted by Jez

cheers bro, where can i find a pic of your beast?

No pictures yet, I dont have a digi camera.

But close your eyes and magine an immaculate AU1 XR8 ute in black, with factory sportsbar, and otherwise completely stock.

Well mine is like that....only covered in dirt, some paint chips/scratches, a dent in the bonnet from when the engine mount broke, a bunch of gutter scrapes on the stock 17" rims, clear side indicators, and a bit of rubber on the rear guards from last time at the track (over 2 months ago!!)

I'll clean it up and post some picks one day

[lotus]

Since you have played around with your exhaust,check that your oxygen sensors are ok. Had this problem (though I think the flat spot came in a bit earlier than 3000r.p.m.). Could be too much gasket sealant used. Also could be fuel used. Mine gave me hell when using Vortex,changed to Optimax and no problems since.
Just a couple of other things to think about!

[Jez]

Well we can put this one to rest... Give lotus the prize for the check oxygen sensors option. One of the guys who fitted the CAI disconnected the air flow sensor cable and forgot to put it back when he finished.

Not suprisingly it was running like S**t in comparison to now with the sensor working again. Case closed!

[Stav]

So your air fuel ratios would have been totally stuffed

[xr8ute]

Originally Posted by Jez

Well we can put this one to rest... Give lotus the prize for the check oxygen sensors option. One of the guys who fitted the CAI disconnected the air flow sensor cable and forgot to put it back when he finished.

You mean the MAF sensor? When that is disconnect the computer defaults to some very safe fuel tables (a limp home mode for the MAF).

As useless just said, your AFR's would have been e. Glad it's back on track