A/F ratio tuning

[roadboy]

hey, just a question, im starting to tune my car (just a bit before i bring it to the dyno)
so i read the a/f ratio article here:
http://www.supramania.com/forums/showthread.php?14358-A-F-Ratio-Tuning

so does that mean when im cruising or driving normal it always has to be at 14.7?
i know when im at WOT its suppose to be 11.5 or lower.
am i on the right track?

also whenever you downshift or let go of the gas my wideband goes to lean, is that normal?

any input appreciated, Thanks

 

[Supracentral]

so does that mean when im cruising or driving normal it always has to be at 14.7?

No, it will swing around quite a bit during normal driving.

i know when im at WOT its suppose to be 11.5 or lower.
am i on the right track?

Yea, you're headed in the general direction.

also whenever you downshift or let go of the gas my wideband goes to lean, is that normal?

Yes, very. On a long downhill with your foot off the fuel you'll go 20:1 or even leaner at times.

Read this one over too. It's about the MAP-ECU but it applies to just about all tuning. About 1/2 way down there's a section about tuning for vF - very important when tuning these cars:

http://www.supramania.com/forums/showthread.php?39712-MAP-ECU-Tuning&p=545583#post545583

 

[MPR]

Your injectors (should) shut off completely when not on the throttle, unless you're at idle.

You can go as lean as 17:1 under VERY light loads/cruising. This is safe for the engine and will save on fuel consumption.

Try not to go much lower than 11.5 at WOT. Target 11.5-12 at WOT. There is such a thing as too rich...

 

[roadboy]

so i read everything over, i was just wondering if a bit lean at idle is ok, mine is at 15-16afr when at idle, unless if i tune it out. is this normal?
i know vf takes over when trying to tune for but i only need about 10 points on the safc to tune it back to 14.7, should i just leave it at 0 and have a bit lean idle?

 

[jetjock]

Bit lean at idle is fine. I actually prefer it. And just to clarify as long as part throttle operation is steady state the ratio will always be stoichiometric.

 

[roadboy]

awesome, thats true, when im at idle and my safc is set to 0, i have a bit lean idle, but when im driving itl always be at 14.7 and itl mostly be a bit rich, unless im at WOT. thanks guys.

 

[jetjock]

We were talking idle but the truth is the engine can be run lean all the way up to 75% power. By lean I mean around 150-200 degrees on the lean side of peak EGT. It'll run cooler, cleaner, and with better fuel economy. Not so good for emissions though.

 

[roadboy]

well, its only lean idle, when im driving it always goes to 14.7 or lower, which is a good thing. i dont want it to run lean and blow something up, i thought running lean at idle was bad.

 

[Insidious Surmiser]

@ MPR... you do know these cars run 10.5:1 WOT out of the factory? also I wanted to say that my car stayed dead on 14.7 under normal driving conditions.

 

[MPR]

@ MPR... you do know these cars run 10.5:1 WOT out of the factory? also I wanted to say that my car stayed dead on 14.7 under normal driving conditions.

I'm not surprised they run 10.5 at WOT out or the factory. They have to tune them on the safe side. Especially for these cars being sold in various climates. That is part of the advantage of custom tuning. Also doesn't mean they make the best power at 10.5, just that it makes good power at a safe, rich AFR. IMO that is too rich and it'll make more power at 11-11.5 and after dialing in the timing.

We ran our MR2 4agze (converted to turbo) at 17:1 at very light engine load, light throttle input while cruising. Got really good fuel mileage and then spanked the competition on the track running 11-11.5 at WOT.

 

[Turbo Habanero]

My normal driving bounces around quite abit from 14.8-15.7

Idle is very lean around 16-17 sometimes it even spikes 18

 

[destrux]

Someone should make a gauge that can be hooked up to display vF voltage all the time... I bet you could mod one of those cheap O2 sensor gauges to read a 0-5V scale and display vF as "lean-rich". That would be nice for tuning.

Oh and since the OP seems to be tuning an Apexi SAFC (based on his sig), there's a trick with those where you hook the TPS input up to a MAP sensor instead of the TPS and you can tune a little easier because the fuel map will follow engine load not TPS (which is a poor indicator of load). I have my car set up like this and it was alot easier to adjust the SAFC to keep vF steady. When it was set up to the TPS it was constantly going out of tune at part throttle.

It doesn't have the resolution of a MAPECU or a standalone, but if you use the map trick and mess with the high/low throttle points to scale the map up and down it's better than using the TPS and having the vF constantly chasing it's tail. Still crude and a pain to get a nice steady part throttle tune though.

 

[roadboy]

Sorry I meant I have a safcII, just drove my car for the second time today, when it runs lean during idle it seems to almost wants to die is that normal? I see it go to 17.2 and fluctuate lower say 15.0 is this normal? But I mean when I give it gas/driving it will go back to 14.7 or lower.

 

[jetjock]

...Someone should make a gauge that can be hooked up to display vF voltage all the time... I bet you could mod one of those cheap O2 sensor gauges to read a 0-5V scale and display vF as "lean-rich"....

Someone did. Used colored LEDs in a bar graph configuration. Cheap to make too. They were popular in the community around 10-12 years ago.

 

[destrux]

I figured someone would have, it seems everything has been discovered/forgotten/rediscovered 10X over with this car by now.

I wasn't able to find the schematic that guy used, but I found this one which might be the same or very similar if anyone is interested.

http://www.200sx.org/boost_gauge_1.html

The author is using it as a boost gauge, but it's a 0-5V led bar meter so it will work with a bunch of stuff. I'm thinking of sticking two of them in my switch plate above the radio, one for vF and one for the wideband. I'd do a boost gauge too, but my AFC Neo has a fancy peak hold gauge built in.

 

[ifyouaint1sturlast]

In regard to your "lean idle" comment: My general understanding was that lean conditions are generally only dangerous under load. Idle, cruise, and decel do not matter.

Any experts feel free to correct me

 

[jetjock]

^ You're right. Even under power it's not much of an issue until around 70%.

...I figured someone would have, it seems everything has been discovered/forgotten/rediscovered 10X over with this car by now....

Yep, you're right. I chuckle when I read some of Reg Riemer's stuff. Not to take anything away from him but much of what he wrote is lifted directly from the factory TCCS books. Jeff Montigny was the guy with the Vf meter. I'm sure the other old school guys here remember him. Dunno if he is still active though. Probably not since most college pukes eventually grow up and get a real life :icon_razz

 

[Another MkIII]

No, it will swing around quite a bit during normal driving.



Yea, you're headed in the general direction.



Yes, very. On a long downhill with your foot off the fuel you'll go 20:1 or even leaner at times.

Read this one over too. It's about the MAP-ECU but it applies to just about all tuning. About 1/2 way down there's a section about tuning for vF - very important when tuning these cars:

http://www.supramania.com/forums/showthread.php?39712-MAP-ECU-Tuning&p=545583#post545583

That explains why my AFRs act like they're possessed. They are, by the ECM, lol. Don't know why something like this didn't cross my mind, guess I should get on that bus...
-AM3

 

[tmsperformance]

Bit lean at idle is fine. I actually prefer it. And just to clarify as long as part throttle operation is steady state the ratio will always be stoichiometric.

Yes that statement is true. my 7m doesn't like to idle to smooth at anything lower than 14.1 and that is at 10*btdc on a MS1. My map is tuned at 14.5 in the idle range, 12.5 part throttle/light loads, 16:1 lean cruising and 11.7:1 WOT. Hope that helps a little.

 

[mstgeer]

Someone should make a gauge that can be hooked up to display vF voltage all the time... I bet you could mod one of those cheap O2 sensor gauges to read a 0-5V scale and display vF as "lean-rich". That would be nice for tuning.

Oh and since the OP seems to be tuning an Apexi SAFC (based on his sig), there's a trick with those where you hook the TPS input up to a MAP sensor instead of the TPS and you can tune a little easier because the fuel map will follow engine load not TPS (which is a poor indicator of load). I have my car set up like this and it was alot easier to adjust the SAFC to keep vF steady. When it was set up to the TPS it was constantly going out of tune at part throttle.

It doesn't have the resolution of a MAPECU or a standalone, but if you use the map trick and mess with the high/low throttle points to scale the map up and down it's better than using the TPS and having the vF constantly chasing it's tail. Still crude and a pain to get a nice steady part throttle tune though.

This trick apply to the neo?