[RESOLVED] AFC problem

[turboAWDfanatic]

I'm in the process of figuring out why my car is leaning out at 5,500 rpm, and I have a specific question about the AFC. By logging w/ Zeitronix I've been able to see what my true A/F is, but yesterday I started looking at the "cor" display meter on my AFC. I've noticed that during WOT 3rd gear pulls to 6k rpm, the "cor" gauge display peaks at around +7% to +8% even though I've set the 5k, 6k, and 7k points on the air map to +12% and up. I figured that maybe I needed to set my "high throttle" point at lower than 80% so the AFC would correct sooner, but changing that doesn't help.

Why would my AFC only be correcting up to +7% even though I have set the air map to correct +12% and higher in the 5k-7k range?

 

[CTP]

I think the more important question is: why are you adding fuel with your SAFC?

Your car is leaning out because your fuel system can't keep up. Adding all the fuel in the world with the SAFC isn't going to make it run any richer because you don't even have enough fuel in the first place.

The correct way to do things is to get larger injectors and PULL fuel. Then you can worry about your set vs. applied correction.

 

[turboAWDfanatic]

Well, I guess I left out details b/c this thread was *NOT* posted to figure out "why I'm leaning out". It's more or less asking why the AFC isn't trying to compensate the way I'm telling it to. I'm not asking why my AFC settings don't match the true A/F ratio. I'm asking why the AFC isn't lying to the ECU the way I set it to. Correct me if I'm wrong, but the amount that the AFC lies to the ECU isn't dependent on how much fuel you have. The "cor" display gauge on the AFC gauges window tells you how much the AFC is currently compensating as well as what the peak is. This reading is in no way affected by how much fuel my pump and injectors can spit out.

Anyway, so you better understand my situation, I'm trying to get an initial tune done at low boost before I up my injectors and turn up the boost. My fuel system is nowhere near maxed out right now. I'm running very low boost and my logs show that the IDC isn't maxing out yet. I have a re-wired 190 fuel pump with 450 injectors and I'm trying to run 10-12 psi through a 16g GT on a 2.3 stroker.

But, again, PLEASE understand that I'm not asking for help on why my engine is leaning out in this thread. I'm troubleshooting that issue separately. I'm simply asking why an AFC would not apply the proper corrections according to the air flow map at WOT. Thanks!

 

[steve]

The SAFC interpolates between RPM and the low and high throttle settings.
The low and high throttle point set the range between which the SAFC interpolates between low and high throttle settings.

What setting do you have below 5k on the high throttle map?
What are your low throttle maps settings?

 

[CTP]

Well, I guess I left out details b/c this thread was *NOT* posted to figure out "why I'm leaning out". It's more or less asking why the AFC isn't trying to compensate the way I'm telling it to. I'm not asking why my AFC settings don't match the true A/F ratio. I'm asking why the AFC isn't lying to the ECU the way I set it to. Correct me if I'm wrong, but the amount that the AFC lies to the ECU isn't dependent on how much fuel you have. The "cor" display gauge on the AFC gauges window tells you how much the AFC is currently compensating as well as what the peak is. This reading is in no way affected by how much fuel my pump and injectors can spit out.

Anyway, so you better understand my situation, I'm trying to get an initial tune done at low boost before I up my injectors and turn up the boost. My fuel system is nowhere near maxed out right now. I'm running very low boost and my logs show that the IDC isn't maxing out yet. I have a re-wired 190 fuel pump with 450 injectors and I'm trying to run 10-12 psi through a 16g GT on a 2.3 stroker.

But, again, PLEASE understand that I'm not asking for help on why my engine is leaning out in this thread. I'm troubleshooting that issue separately. I'm simply asking why an AFC would not apply the proper corrections according to the air flow map at WOT. Thanks!

Are you watching the "cor" read out while doing a pull and judging by that? Is the correction still off if you do a pull and then use the peak function to display what it maxed at?

 

[turboAWDfanatic]

Are you watching the "cor" read out while doing a pull and judging by that? Is the correction still off if you do a pull and then use the peak function to display what it maxed at?

Yes, I am watching the "cor" display gauge with the peak/hold enabled. Obviously I am looking at my Zeitronix for the actual A/F, but I'm not sure why the AFC won't "lie" to the ECU at the same number that I have dialed in on the air map.

Here's an example of what I would *expect* the AFC to do:
If I set the 6k point at +7, and I do a WOT pull to at 6500, I would expect to see at least "+7%" correction on the peak of the "cor" gauge. I would expect less than "+7" if I did the pull at part throttle and/or only pulled to 5500 rpm. Does that make sense? I just want to be sure the AFC is doing its job properly before I tear into other things.

I do understand the proper use of the AFC, and I have Denso 660's and a 2g MAF at the ready, but I just wanted to see if I could safely do WOT 3rd gear pulls with proper A/F and safe timing at low boost before I started throwing more fuel at it and cranking things up.

 

[turboAWDfanatic]

The SAFC interpolates between RPM and the low and high throttle settings.
The low and high throttle point set the range between which the SAFC interpolates between low and high throttle settings.

True. But once I'm above the "high throttle point" (which I have set at 80%), shouldn't it stop the high/low interpolation, and just gauge its correction off of RPM? I was under the impression that it would only interpolate high/low when you were between the high/low throttle points (30%-80% for me)

What setting do you have below 5k on the high throttle map?

Don't remember off the top of my head, but the 1-5k range was showing good A/F at something in the neighborhood of: +5, +5, +5, +8, +12. Timing was looking good with those numbers as well

What are your log throttle maps settings?

Low throttle maps? Again, don't remember exactly, but to get 100% fuel trims it was something in this neighborhood:
-3, -3, -1, 0, +3, +5, +5, +5

I can see where you're headed with the high/low interpolation, but as stated above I was under the impression that once you're above high throttle point it used stricly the high throttle settings. As for the RPM points, shouldn't the interpolation be between the RPMs, but correct at each RPM point? I.E. if my 5k RPM setting is +12, shouldn't it peak at +12 by 5k RPM (assuming I am at WOT)? When I do a WOT pull to 6k RPM and my peak correction is only +7 I start scratching my head.

 

[CTP]

Yes, I am watching the "cor" display gauge with the peak/hold enabled. Obviously I am looking at my Zeitronix for the actual A/F, but I'm not sure why the AFC won't "lie" to the ECU at the same number that I have dialed in on the air map.

That's very odd. Has it always done that or did it just start recently? Are you sure you have it wired correctly? Maybe try changing the settings to something else and what your actual correction is then?

 

[Steelnation36]

what CTP said on his earlier post worked for me. I was having similar issues then decided to upgrade my fuel system, i got 680cc injectors and a walbro 255 pump plus got my friend to tune the AFC and i had the entire car tuned. Cost me a little bit of money but the car runs so much better now it was worth it.

 

[turboAWDfanatic]

That's very odd. Has it always done that or did it just start recently? Are you sure you have it wired correctly? Maybe try changing the settings to something else and what your actual correction is then?

Yup. Wiring is fine. I just started look at that particular "cor" gauge display. If I enrich it more, the peak number on the gauge will go higher, but not match the settings I gave it.

what CTP said on his earlier post worked for me. I was having similar issues then decided to upgrade my fuel system, i got 680cc injectors and a walbro 255 pump plus got my friend to tune the AFC and i had the entire car tuned. Cost me a little bit of money but the car runs so much better now it was worth it.

Well, I do see your point, but remember I'm running very low boost and my logs tell me I have fuel to spare. I still have other things to troubleshoot, but the point of this thread was to eliminate the AFC itself as the problem. I tell the AFC to "lie" at a correction of +12%, and it tells me that its only "lying" at around +8%. This correction (or lying) is done before fuel becomes a factor...so I wanted to rule it out as a problem.

I'm afraid to try to crank the AFC higher b/c as CTP said the true purpose of the AFC is to lean out bigger injectors. The higher I tell it to correct, the further off my timing gets and the closer I get to fuel cut. I simply want to make sure things are working right and get a basic tune down before I start throwing more mods at it.

 

[Steelnation36]

Ohhh ok sorry about that i see what your trying to do now. Im not sure how much you know about the AFC but it may just be worth taking it to someone with a lot of experience and letting them check over everything. It may be something causing the wrong information to be sent or something along those lines. Ive never had this specific problem i cant even think of why it wouldnt be adjusting at what its set.... when you figure this out please let me know

Ill also ask my friend about it hes the one that taught me how to work mine so ill check to see if hes got any advice

 

[turboAWDfanatic]

Alright, I figured out 2 things today:

1) The AFC correction is NOT instantaneous. It has a little lag time in altering the airflow signal. I realized this when I depressed the throttle with the engine off (but the ignition was on so I could read my AFC). Even though its at zero RPM, I watched it interpolate and change the correction in response to the throttle position. It took longer than I thought. SO, if I set the 6k rpm point to +12, and end my pull at 6k rpm, the AFC doesn't quite have enough time to get to +12 before I lift the throttle....therefore the peak number on the "cor" gauge ends up somewhere around +8. (heh, I'm assuming this is normal of the AFC. If I have a defective unit please tell me)

2) I came across a post on a Lancer Evo forum where a guy stated that if you are gradual and consistent with raising the correction points across the rpm range, it will "ramp up" faster. I was jumping pretty far in my corrections from the 4k to the 6k points. (does that make sense?)

To check all this out, I smoothed out my corrections so that it was more of a linear increase. This meant raising the corrections in some of the lower RPMs. I also raised the higer rpm correction points a little further than I wanted them to be, knowing the correction lags a little and ends up a few ticks below my settings. The good news is...NO MORE LEANING OUT! The correction ramps up quick enough and I was able to stay at an AFR range of 10.5:1 to 11:1 all the way up to 6,500 rpm.

The bad news is...now I really *AM* hitting fuel cut. At least I think so (I haven't logged to be sure of this). I was at WOT in 1st gear from the stop light, and right around 4k rpm *WHAM* the car lurched, mixture leaned way out, and EGTs hit the roof. I let off, eased back on the throttle, and no problem, car pulls just fine. Well, I'm hoping this is fuel cut and that something else isn't horribly wrong with my car. =P

So, in conclusion, I don't believe there's any problem with my AFC. I was simply not anticipating a slight lag in it's correction. I can now pull all the way to 6,500 rpm with a safe AFR, but in order to do so I have to enrich it so much that my timing is being pulled to far and I'm also hitting fuel cut if the conditions are right. I'm fine with that, b/c I simply wanted to rule out any mechanical issues before I started throwing more mods at it. I can install my 660's now, and I'm very close to ordering the Ostrich (a chip emulator), so at that point I'll have full control over fuel maps, timing maps, and I'll have the ability to eliminate fuel cut.

I'm marking this as resolved, but PLEASE feel free to correct me if my thinking is flawed. I'm new to tuning and want to learn all I can. Thanks!