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AU V8 car wont maintain smooth rpm driving 


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 Post subject: AU V8 car wont maintain smooth rpm driving
Posted: Wed Dec 19, 2012 1:10 pm 
Getting Side Ways
User avatar

Age: 28

Posts: 1643

Joined: 8th Feb 2006

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Ride: Ef Ghiaaaaaargh!

Location: Perth
WA, Australia

Cars a 99 au xr8, basically what happens is as i'm driving at any speed the engine will change rpm a small amount, its pretty noticeable and makes driving the car not smooth at all.

Example driving along at any not moving my foot on the accelerator the car will maybe go up and down maybe 50-100rpm, it feels electronic if that makes sense, idle feels smooth and fine.

I'm resetting the TPS and base idle later today, is there anything else i should look at?

Its been doing it since the day i got it. Car has just had leads, plugs, oil, fuel filter, cleaned throttle and new exh with new cats and the problem hasn't changed at all.



Mercedes 500SEC: -- GONE --
Ef Ghia: -- GONE -- Pacie 4480's, 2.5" Redback, custom grille, FTR's.
AU xr8: BA xr wheels, 2.5" custom exh, leather and woodgrain next.
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 Post subject: Re: AU V8 car wont maintain smooth rpm driving
Posted: Wed Dec 19, 2012 10:16 pm 
Parts Gopher

Age: 48

Posts: 54

Joined: 27th May 2009

Ride: Ford TE50 Charged

Location: Melbourne
VIC, Australia

More than likely its probably the torque converter locking and unlocking when cruising at a steady speed. Mine does it as well but you can tune it when it comes in and goes with a quaterhorse chip and BE2012 software.
 Post subject: Re: AU V8 car wont maintain smooth rpm driving
Posted: Mon Jan 07, 2013 3:25 pm 
Tyre Shredder

Age: 28

Posts: 365

Joined: 22nd Nov 2007

Ride: FG MK2 XR6T

Location: Bexley, Sydney
NSW, Australia

I had the same problem with my AU and never really found the problem. I tried adding extra grounds from Block > Battery and Body > Battery.

HOWEVER, i did discover that if I ran it with disconnected O2 sensors it fixed the problem, albeit ran ridiculously rich so I did not keep it like this. Do this temporarily and see if this also works for you and it might give you a better idea of where to look...



Formerly LV XR5 Turbo, AU Fairmont Ghia V8 & EBII Fairmont I6.

Feb 2012 FG MK2 XR6 Turbo
- Manual
- Luxury Pack

 Post subject: Re: AU V8 car wont maintain smooth rpm driving
Posted: Wed Feb 06, 2013 11:22 am 
Tyre Shredder

Age: 54

Posts: 373

Joined: 9th Feb 2006

Ride: AU Wagon

Location: Newcastle
NSW, Australia

The small changes in revs would be adaptive learning going on - the ECU making small changes to spark and fuel to learn optimum settings while in lean cruise mode.

How old are your O2 sensors? They get lazy and slow to respond after 100,000km or so and should be replaced every 100,000km. If yours are old, they are probably not responding quickly enough to changes in fuelling in closed loop, so the ECU is trying another adjustment to fuel before it gets feedback from the first one.

So what the ECU sees is like:
Add fuel... no change
Add more fuel... just right
No change to fuel... suddenly shiftloads rich
Take away a shiftload of fuel... no change
Take away another shiftload of fuel... just right
No change to fuel... shiftloads lean...

...and so on...



AU1.5 Wagon, Raptor ProStreet kit, Pacemaker 4499's with 3" collector, 3" metal cat, 3" pipe, Pex BSO660 & BSO439, BA brakes, Sprintgas mixer LPG system, Airod variable-venturi mixer... stealth FTW Sniper tuned!

To be updated... soon!

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