Soarer Central: Starting problems with 98 RON

Soarer Central Mechanical - V8 Starting problems with 98 RON

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Clayton Webb
TryHard
South Australia
'31 V8

Posts: 414
Reg: 09-2005

Rating: N/A
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Friday, October 06, 2006 - 04:13 pm, by: Clayton Webb (Clackers)

This is really starting to confuse me. For the last 12 months I have been using Ultimate as a preferred fuel but have been having troubles starting from cold in the cold weather. I have recenlty put 95 into it and it's starting fine in the cooler weather and it seems to be running a bit leaner. Does anyone have a clue why this would be?

Ben Socratous
DieHard
SA
Iv'e started to put my interior back together!!!

Posts: 866
Reg: 07-2005

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Friday, October 06, 2006 - 05:05 pm, by: Ben Socratous (Socrates)

Ahahahahahaha, the mystery of why my car does bloody weird and un-describable things must be contagious!

Greg Badger
Newbie
NSW
V8 UZZ31

Posts: 3
Reg: 07-2005

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Friday, October 06, 2006 - 07:13 pm, by: Greg Badger (Baldas)

Clayton - Try resetting your ECU. If you haven't reset your ECU in a while it's worth a try - certainly won't hurt.

Tim Appleton
TryHard
QLD
UZZ31

Posts: 332
Reg: 07-2005

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Monday, October 09, 2006 - 07:40 am, by: Tim Appleton (Timbo)

I have the same problem. A fuel with a higher RON makes it harder to ignite. So it could be ignition related, but I think it's more likely to be the slow reaction of the idle air control valve. I'll try replacing the bearings in it in the near future.

Daniel Clarke
DieHard
NSW
TT 2.5L 6 cylinder

Posts: 695
Reg: 03-2006

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Monday, October 09, 2006 - 04:06 pm, by: Daniel Clarke (Dieseltrain)

I thought HIgher RON fuel was MOre explosive and easier to ignite? Hence making better power? Thats why 91 fuel to 98 fuel = more power? If it was harder to ignite it would make less power would it not? Or am i going to sound like a total noob here?

David Vaughan
Goo Roo
ACT
V8 Ltd manual

Posts: 2565
Reg: 07-2005

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Monday, October 09, 2006 - 04:18 pm, by: David Vaughan (Davidv)

quote:
Or am i going to sound like a total noob here

Yep

This reference is actually a site for FC/FE Holdens but it says some useful things. There will be other and probably better references on the net.
http://www.fefcholden.org.au/techinfo/tech003.html

Among other things, it says

quote:
Higher octane fuels burn more progressively, rather than explosively. A high octane fuel can be compressed more without detonating, ignited earlier to reach full burn intensity at "top-of-stroke" ... A low octane fuel goes "BANG" once the spark is introduced.

Edit for more explanation: A low octane fuel, exploding more readily under pressure and heat, requires the ECU to retard the spark to avoid pre-detonation or pinging, reducing power. Higher octanes allow that turbocharged engine of yours to spark a little earlier for more power.

Both of my cars became harder to start after I added timing with Unichips, especially the IS300. It takes a few moments for the ECU to work out that more than expected fuel is required to kick things off from cold.

David Vaughan
Goo Roo
ACT
V8 Ltd manual

Posts: 2566
Reg: 07-2005

Rating: N/A
Votes: 0 (Vote!)

Monday, October 09, 2006 - 05:51 pm, by: David Vaughan (Davidv)

Here are a couple of other articles which you might find interesting on the subject.

This one is long and appears fairly comprehensive, although I read only a part of it:
http://www.turborx7.com/fuel.htm

This one directly addresses the question "Will I get more power using 98 than 95?":
http://autospeed.drive.com.au/cms/article.html?&A=0429

Note the comments in both that you will not improve power if the current octane rating is already as good as the timing/compression of your car will exploit. However, Soarers are understood to exploit up to 100 RON even though the ECU will manage down to 95 or even 92. Many of us have tuned specifically for higher ratings anyway.