andy-gts

can you tune , with a catalytic converter in exhaust, for a afr of 12.5 to 13.5 with no problems...or does the richer afr cause over heating of the cat...
this question originates from the sharktuner allowing tuning in open or closed loop mode also referred to non cat mode... is there an actual reason why non cat mode is referred to as is "don't tune for richer afr because of some detriment to the system"

I hope I didn't ramble and not get my question made clear!

what are your thoughts

hacker-pschorr

Start here:

http://www.efi101.com/efi101.html

I'm sure there will be one in your area soon

andy-gts

does the cat overheat with a afr of 12.5 to 13? that is the basic question

worf928

Yes.

andy-gts

that explains it.....!!!!!

thanks

WallyP

Well, yes - the cat will run hotter if the AFR is higher than stoichiometric. But - every 928 runs higher than stoichiometric every time that you go to WOT.

Basically, any fuel that isn't fully burned in the combustion chamber will be oxidized in the cat. The richer the AFR, the more fuel is burned in the cat, so the hotter it gets.

How rich is too rich? When the carpets catch on fire, perhaps. Or perhaps just when the cat biscuits melt and choke the exhaust.

andy-gts

thanks wally!

blown 87

Z

It's not quite as simple as that. It depends on whether the rest of the emissions equipment is still on the car, whether it's been modified, and what the throttle position is. One of the reasons for the stock fuel mapping going as rich as it does at WOT is to cool the cats.

dprantl

The typical lifetime of factory cats in an open-loop CIS 928 is ~6 years. On a closed-loop LH car it is more like 20 years (assuming in all those years the car was always in good tune). The aftermarket metal-matrix cats are more sensitive to this. It's not unusual to have them fail after 2 years or less on a car that is not properly running in closed-loop.

Dan
'91 928GT S/C 475hp/460lb.ft