TRWeiss1

iTrader: (20)

...in terms of AFR? I fired up my 7 today and let it warm all the way up while keeping an eye on the WB. I'm idling right around 11.5 @ 1000 RPMs with the parking lights on. As it's warming up I'm right around 10.8, then it leans out to around 11.5 once warm. Is it necessary to have this rich of an idle? Just curious.

Montego

iTrader: (1)

I'm right around 12.9

arghx

iTrader: (3)

It's not necessary to have it that rich. Typically you can run at least as lean as 12.5:1 . The higher the idle speed, the leaner a mixture it will tolerate. What's tricky is that you have air and water temp correction tables that need to be adjusted. The idle AFR is always going to fluctuate. You just need to have it in an acceptable range. On the factory computers the ECU will idle as lean as possible until misfire occurs.

TRWeiss1

iTrader: (20)

Thanks guys...I thought that was a tad rich. I'm tuned by Dave, so I'm not surprised by the conservative idle. :P I think I'll lean it out a bit...really no reason to have it idle that rich, other than to suck down fuel faster.

94touringFD

iTrader: (30)

Funny, my idle is right around 13.0-13.2 as advised by Dave

TRWeiss1

iTrader: (20)

Not sure...he tuned my car and set my idle where it's at right now...

Jobro

iTrader: (2)

Tuning the idle based on AFR is wrong. Tune the idle by the following process.

Normal process is to tune idle to fastest idle (slightly above what you want) for a given throttle setting and then bog it down slightly by adding fuel. Thats how you get a stable idle.

If you do it any other way it will be prone to stall or too high.

I once tried to tune my idle when I had dirty primary injectors. It wouldn't idle nicely and it needed more fuel PW that it should have. AFR gauge was reading around 10.5-11:1. Anyway after I had the injectors cleaned I removed a lot of fuel to make it right again. This time checked AFR's and it was 12-12.5:1. Basically if you can get a good slow idle all the way lean back to stoich (14.7:1) do it.

I don't find that very likely on a modified rotary.

t-von

iTrader: (8)

Your not going to idle anywhere near stoich on a peripheral exhaust port rotary. If that was possible, Mazda would have never had to go the Renesis route. I use negative split and idle my 20b at 13.7@750rpms. My ports are still stock though. I can go leaner but it starts hunting a bit. You can also save some fuel by adjusting your injection angle once you get to your ideal idle AFR. AFR doesn't tell you everything because if the injectors aren't pulsing at the correct timing, you will have more fuel hitting the rotor on a closed port. Any fuel that gets by to be burned will still register your tuned AFR. But the reality is you are using way too much fuel to get that reading.

This is what I do when I tune for idle.

I run negative split values just like the Rx8. Then I start pulling fuel out till I get to 13.7. Then I go to my injection angle tables and start raising or lowering the values till the AFR start getting rich again. When your AFR goes up WITHOUT you adding more fuel, this means your injection timing is near perfect because you obviously now have more fuel entering the combustion chamber. Now you can go back and start pulling more fuel till you get back to your desired AFR. Saving fuel is all about pulsing the injectors at the lowest MS values possible for any given rpm. I have to thank Judge Ito for that knowledge.

TRWeiss1

iTrader: (20)

Thanks for the input guys. Also, FWIW, my injectors are pretty much new (850 primaries/1600 secondaries), and I have a moderate street port. I'll consult Dave this spring and see what he has to say on the subject.

arghx

iTrader: (3)

having spent many hours tuning idle on different cars, I will say that you can't expect a tuner to have one or two sessions with a car and get every parameter set right so that idle is stable and lean under every condition. That includes every weather condition, cold start, hot start, different electrical loads, etc.

What makes it worse is that most modified FD's are running a PFC and PFC's have a single air temp correction table that applies for low and high load. So that requires compromises.

TRWeiss1

iTrader: (20)

Agreed...Also keep in mind, I've visited Dave quite a few times, so this is going far beyond one tuning session. I understand that there will be compromises, and air temperature/oxygen density will fluctuate. I was just curious what other peoples' FDs were idling at, that's all. I'm fine with it idling this rich, to be honest...was just wondering if anyone else was seeing similar AFRs.

j9fd3s

iTrader: (3)

yes AFR is a ratio, but pulsewidth is um volume?

the P port idles @900-1000rpms, at about 14.5:1 on the wideband...

arghx

iTrader: (3)

yes but 3 milliseconds pulsewidth at 3 bar static fuel pressure (43.5psi) is more fuel than 3 milliseconds at the factory 2.5 bar (36psi) pressure.

As for the injection timing, most modified FD's are running a Power FC which has no way of changing the injector phasing.

j9fd3s

iTrader: (3)

true, i played with injector phasing on the 20B with almost no results, although i should have taken more time. the phase map is actually in the cosmo training book, so we started with something decent.

back then it idled around 12.2-12.5 afr @ about 2.2 ms.

if i had that car today, i'd be looking for a STABLE idle closer to 2ms, prolly remove the converter (yes i ran a cat), remove the boat anchor turbo system; i think 20B Na might be lighter than 13BT. the car only lost like 40lbs going from 20B-REW to 13BT. we KNOW the 20B turbos are like 100lbs...

and just tune the **** out of it and enjoy it NA