High AFR readings at idle, Running lean?

[944Scott]

Guys I need your help here.

I have installed my promax level 2 kit, tial wastegate and 55lb injectors. I have the FQS set at 3 (I did start at 2 but the afr at idle was even higher) Currently the afr at idle is hovering around 16.3 which seems a bit of high figure to me, can anybody give me some advice?

 

[Lowtimer]

I can't speak to what the AFR theoretically ought to be at idle but I'd be looking to the CO2 reading as a confirming measure of whether your idle mixture is correct or not In case you're worried, it is impossible to damage an engine by running it lean (numerically high AFR). Generally as long as it idles smoothly and picks up cleanly when you brush the throttle, it's not idling too lean. Lean mixture only becomes a potential issue for engine damage once you are developing more than about 50% of normally aspirated power (i.e. 50% of the available power at zero boost, 1.0 bar absolute). On a 2.5 944 Turbo, given its low compression, that equates to around 75 bhp. This is roughly the most power you will be developing when drifting around with slowish-moving commuter traffic, up to a steady cruise of about 85-90 mph on a level road. The sort of power we tend to use when warming up the engine, revs below 3000, engine kept off-boost.

 

[944Scott]

Idle mixture was ok before and its not something I have touched. I have re checked and cable tied the vaccum lines which made no difference. I have also set the FQS back to zero and now I get a reading the flutters between 12.7 and 13.

 

[Lowtimer]

So what is the CO2 reading now at idle?

 

[944Scott]

Erm don't I don't know, I have no way of testing it.

 

[Lowtimer]

Actually, apologies, I shouldn't have said CO2, I should have been talking about CO and hydrocarbons as an indicator of idle mixture. Might be worth running it round to whoever does your MOTs to see what their emissions gear says. The main point I wanted to make is that providing it's capable of an MOT pass, and actually running nicely, with clean idle and good off-idle throttle response - not stummbling or sooting up - then AFRs are important once you are developing meaningful power, but not very important at idle and near idle power settings. So if they are where you want them to be during the boost transition and on-boost then I wouldn't worry too much about the idle setting. Nevertheless as you are using Promax kit I'm sure they would offer a useful view if you put in a call in the morning.

 

[944Scott]

Ahh with you now. I could possibly get it down to the garage at somepoint during the week, they are not too far away and I had been thinking about ringing promax in the morning[]

 

[Frenchy]

Scott, i adjusted my AFR to 14.7 (ideal stoich) by using the adjustment available on the air flow meter.

 

[944Scott]

Food for thought, thank you []