overrun fuel cut is driving me nuts
 

No matter what I do, I always get lean spots between shifts. Seems overrun fuel cut kicks in almost instantly (PW drops with TP) although it's turned off. My AFR calibration doesn't go leaner than 19.5 BTW.
Weird thing is that PW / dutycycle don't drop entirely to zero, suggesting it's not overrun fuel cut? Is there some other setting that I'm overlooking?
Autotune always leans out the bottom row, but adding fuel there, doens't make a difference.

http://img15.imageshack.us/img15/6442/leanshift.png

http://img143.imageshack.us/img143/4895/leanfuel.png

Weird, have you tried increasing the MAP and RPM thresholds to something very high(110kPa, 10000rpm) to at least disable it that way?

Dimitris

yup, I have 3 seconds delay and only > 100°C and that makes no difference.
Weird thing is that sometimes overrun does not kick in.
This is a bit earlier in that same log.
Overrun is turned off during the entire log.

http://img375.imageshack.us/img375/8273/leanshift2.png

What is your decel fuel amount set to?

100%

Sounds like you need to post a datalog at msextra.com...

good suggestion, will do.

Is there an indicator for overrun fuel cut that I can add to the dashboard?

Overrun fuel cuts always drop to zero. That is running off the VE table and possibly the acceleration wizard.

that's what I found weird, that it doesn't drop to zero. The VE table has no lean spots though and decel fuel is 100.
To rule out msq errors, I reflashed to 3.0.3u and started a new project from default.
I'll turn on decel fuel and do some more logging.

your MAP is dropping down to 13ish kPa? what's your fuel there look like?

It would just fuel whatever is in his bottom most cell at that rpm on his ve table.

Well, it's not overrun. Switched on overrun and duty drops to zero.
So it must be something else. My bottom fuel row is only 2 points leaner than my idle row. Autotune always leanes it out to 30ish, but raising it to where it is now does not seem to make a difference. I'll try raising more.

That is strange. Are you sure it's leaning out and not dumping too much fuel? It drops to full rich and then goes lean. Your cells are 2/3 the fuel they are at 60kpa. That sounds like a ton of fuel to me. Increase it more and I'd bet you'd start getting backfires. What does your timing map look like? When autotune leans it out to 30, does it run the same?

I have lots of backfire. Nearly between all shifts a fat fart (especially hi rpm) and a rumble when coasting. Thought that was because of running too lean, is it not?

http://img64.imageshack.us/img64/9697/ignition.png

are you using EAE? Is your sucked-from-walls too aggressive?

I thought backfire was from unburnt fuel, not lack of fuel.

Frank needs to post his MSQ and logs

logfile here. Look at 1018s
msq here

it is odd that your PW goes to 1.2 and isn't completely cutting. what would happen if you added 10 points to your 20kPa row on your VE fuel table? My logs look similar, but the leanness doesn't kick in right away, think it's cause my lowest kPa row in my VE table isn't so leaned out like yours...it hovers at 1.3PW, fully lean, and then kicks off completely with overrun.


Have you tried using EAE? Looks like you're really not getting much reacting from the TPSdot, dunno why you arent using EAE, should really help improve the AE between shifts.

Try taking some % away on your decel enrichment and lean out the lower cells in your table a good bit. I bet you'll stop getting backfires. It'll at least get rid of that huge AFR drop. I had this happen when I was tuning, then I realized you can't keep a high AFR during decel unless maybe if you have a huge spark gap and strong coils. I think there's just not enough oxygen to burn the fuel. High vac has been the hardest part for me to tune and I still haven't gotten it perfect. You also may need to play with spark timing so it's under enough compression to ignite.

Also, as an FYI, if the fuel isn't burned, you will have oxygen in your exhaust, which looks like a high AFR to the WB sensor. It detect the amount of oxygen still in the gases. Let autotune do its work and just slowly lift off the gas from high RPM until your foot is completely off the gas and see what it figures out. That way it'll tune the cells above and the WB won't all the sudden start thinking it's lean when fuel stops being burned.

I never backfire or have poppy exhaust between shifts...



Actually, notice at sec: 1044, the AFRs start to richen up during decel...looks like overrun still hasn't come on and you're getting to a better spot on your VE table to get back to stoich, but the map was too lean prior. Overun never kicks on there, you have it set to come on below 20 kPa and after 2 sec, and RPM greater than 1750, but you don't even pass those triggers.

I have mine set to above 1700rpm and active below 29.5kPa (I idle at 33kPa, so anything below is decel) and only under 0.8% TPS, only returning fuel once it's around 1100rpm. I bet your pops will go away if you actually get overrun to activate. in fact, now that I've seen MS3 has the return fuel at X rpm, might be why in this heat i've stalled onve or twice, looking at logs, it's returning fuel a little too late and not getting fuel back in time to stabilze idle.

lots of good info, thx guys.
Overrun was turned off in that log to make sure it wasn't related to it. Forgot to mention that, sorry. There's actually less backfire with overrun turned of.
I agree the logs look as if I need more fuel in my 20 kPa row, but I cannot grasp that I would need more fuel in my 20kPa than in my 29kPa row. I noticed the weird rich / lean thing as well. Each time I shift, it goes very rich for a split second than very lean. I was thinking of lowering decel fuel and addding fuel in the 1400 to 2800rpm cells.
TrickerZ's explanation makes sense as well though. It would explain the rich / lean thing.
I'll play with it some more using more extreme numbers (add / remove 10 points or so) and do some more logging.
I haven't turned on EAE because I figure I need to solve this first.

it'll always go a little rich when you lift from residual fuel and what not vs. closed throttle.


you may want to turn EAE on and see if tuning the sucked-from-walls correction table helps in this situation. This curve assumes that some fuel gets stuck to the cylinder walls when you lift so you can control how fast the ECU pulls fuel when you lift, and you can control it vs rpm and clt temp as well.