Clarification on Vf signal and tuning.

[IwantMKIII]

I understand the voltage steps with the Vf signal. ~2.5V is where the ECU is 'happy' and not pulling or adding fuel.

My question is lets assume you are tuning for part throttle boost with some type of SAFC or something similar. Part throttle is much harder to tune since the ECU is still making a lot of adjustments vs. full throttle when it goes open loop.

So lets say you want rich AFR's at part throttle where boost may most likely kick in. Wouldn't you want the Vf signal to be attempting to max out its pulling fuel ability so it wouldn't try to lean the AFR back out? In other words with SAFC you are maxing out the ECUs ability to subtract fuel to the point it can't anymore and your AFR's stay rich (if thats even possible). Or would is it possible to stay rich and still have a 2.5V reading?

 

[GrimJack]

Personally, I've found that the stock ECU wants it to be rich pretty much all the time, unless you're cruising on flat ground or decelerating in gear.

I haven't had to mess with the partial throttle tuning to keep it rich at all.

 

[IwantMKIII]

I just always get worried since that's when most problems occur on boosted cars from what i read about.

 

[grimreaper]

I think your referring to the lean condtion with boost building in the 25-3500 rpm range right? If so then yes you'd have to max out the fuel trim (VF) so the ecu had no more room to pull or add fuel. Youd have to peg 0.00V or 5.00V in that range.

Doward wrote a tutorial on how he did this using the maftpro VE table. IIRC he hits more on the transistion from cloed to open loop while building boost as he was lean at first.

 

[mkIIIman089]

0v is open loop and decel.

You're worrying too much, the ECU kicks in to open loop way before you'll do any damage.

You aren't going to make it run any richer unless you go sky high on the SAFC, and even then the ECU may recognize that something doesn't add up and throw a code or do something else undesirable.

Overall, it's a bad idea and a losing battle to fight closed loop operation.

 

[IwantMKIII]

calling isnms, any input?



So two of you make it seem useless to tune. So what should I tune for? 2.5V and let the ECU have its choice with what it wants to do?

Grimreaper, you say to tune way rich.

Which is it....

 

[mkIIIman089]

What do you have that makes you think you need to tune at all?

 

[adampecush]

calling isnms, any input?



So two of you make it seem useless to tune. So what should I tune for? 2.5V and let the ECU have its choice with what it wants to do?

Grimreaper, you say to tune way rich.

Which is it....

There is not a lot of use fighting the ecu in closed loop operation. Are you actually seeing a lean condition, or are you attempting to fix a problem that might not be there?

 

[isnms]

There is not a lot of use fighting the ecu in closed loop operation. Are you actually seeing a lean condition, or are you attempting to fix a problem that might not be there?

+1

You are not going to be able to tune closed loop with an SAFC that's why it's only suggested tune 3000~3500rpm and above, ~70% throttle, with a piggyback. If you want more control than that you'll need a stand alone or possibly MAFTpro.

 

[grimreaper]

You can adjust idle pretty easily with the safc (in regards to pleasing the vf's) but because its base on rpm and not load it gets hairy trying to adjust in closed loop above that. You will "chase your own tail" using the safc in closed loop...

I was giving an example. To affect A/F ratios in closed loop you have to peg either 0.00v or 5.00v and continue to add or pull fuel after that. Other wise get everything as close to 2.5 v as possible...

 

[IwantMKIII]

I don't see any huge problems happening, its relatively lean in the 13's sometimes more rich at part throttle i notice. Just want to prevent any problems. I've had enough. I don't need a blown engine in my future.

ok. Just trying to avoid any lean conditions at cruise. I easily boost in the mountains of WV cruising and want to be safe. I'm always very worried and keep a very close eye on whether i'm boosting or not. Maybe i'm just being over protective/worrisome

 

[TurboStreetCar]

Most likely over thinking it. Safc has no load input for tuning? you should consider a maft gen2 if the answer to that question is a no.

 

[mkIIIman089]

To affect A/F ratios in closed loop you have to peg either 0.00v or 5.00v and continue to add or pull fuel after that. Other wise get everything as close to 2.5 v as possible...

Again, 0v is not closed loop.

iwant - Again, you're worrying way too much. You're likely in some degree of enrichment at anything over 35% throttle and 3k RPM. Unless you screwed with something, it's virtually impossible for you to do engine damage due to a lean condition with the stock ECU.

 

[grimreaper]

Again, 0v is not closed loop

I understand that your saying it indicates open/closed loop as well. However it IS in closed loop.

 

[IwantMKIII]

^thats what i thought grim. I didn't thing it came out until about 65-70% throttle.

 

[GrimJack]

I understand that your saying it indicates open/closed loop as well. However it IS in closed loop.

0v can mean two things, unfortunately. It can mean it's in closed loop like you've shown, OR it can mean it's in open loop, like after initial startup while it's waiting for the o2 sensor to heat up.

It's a bit of a PITA to deal with, you basically have to make an educated guess based on whether it should be running open or closed.

 

[TurboStreetCar]

Using something to log the VF to a line graph makes easy work of being able to tell open or closed loop and how your tune is. I have mine logged with Zeitroniz and you can tell as soon as rpm and tps is up the VF would drop off sharply.

 

[Doward]

Nosechunks is correct.

Tuning VF with an SAFC would be a PITA, imo. I used the VE table of the MAFT-Pro to make everything great, with the exception of high load, low rpm usage - I forced the TCCS to dump some extra fueling in at that point.

I also logged my Vf with the ZT-2

 

[isnms]

I too log VF with my ZT-2

Some of you may know that you can use the zt-2, to display user input i.e. VF (if that's the 5v input you choose to monitor). It displays where boost normally shows if you log psi. I have wired a toggle to switch on the fly. If you are displaying user input on the display boost will not be logged. If you have boost displayed then both user input and boost will log.

I added some wiring information on my Zeitronix install write up -
http://www.supramania.com/forums/showthread.php?p=1365315

 

[IwantMKIII]

^i also use ZT-2

And tune thanks to your spread sheet. makes it a lot easier. You should try to incorporate Vf signal output with the tuning

I see you have input on it but i don't know if that effects your settings