cant raise afr under boost

SupSay Z · Post by **SupSay Z** » Wed Apr 02, 2008 10:32 pm

hey guys, whats up? basically my problem is that my car, z31, runs stoich at cruise with less than 0 psi, once i hit positive pressure the afr's drop to low 10's and sometimes even 9s. bellow are my current fuel settings. also, i do have a stock AFM and i think this may be part of the problem, but would it max out as soon as i go to boost? this may be something simple, but i cant think of anything now. thanx for the help guys.

alex

Matt · Post by **Matt** » Wed Apr 02, 2008 11:10 pm

If the MAF tops out around 5 volts then you have problems. However you are saying that its running too rich, usually when the MAF tops out it should read too lean

You can use the logger to monitor the AFRs vs the input voltage from your MAF sensor when its on boost

Hendrick301 · Post by **Hendrick301** » Wed Apr 02, 2008 11:54 pm

what injectors are you running?

Bernardd · Post by **Bernardd** » Thu Apr 03, 2008 2:19 am

I've mapped a bunch of stock afm's to over 300hp, it's most likely a kvalue, latency issue.

post a datalog with afr's, and the binfile along with your injector size

SupSay Z · Post by **SupSay Z** » Thu Apr 03, 2008 3:24 pm

thanx guys, i thought that when the afm maxed out it defaulted to rich. anyways, i am running 550cc injectors. i will try to upload a datalog with any more info i find relevant.

Hendrick301 · Post by **Hendrick301** » Thu Apr 03, 2008 11:05 pm

im sure someone will chime in, but your k-value seems too high for 550 injectors...

im running 420cc's and im at 376 k value

i believe 286 is in the ball park.

SupSay Z · Post by **SupSay Z** » Fri Apr 04, 2008 11:55 pm

well, i adjusted the k to 300 and adjusted the idle enrichment and so far it looks good. i have not, however, gone out to do a run yet. in the meantime here is the bin...

Bernardd · Post by **Bernardd** » Sat Apr 05, 2008 12:54 am

if those are rx 7 550's the latency should around 75 hex;
for some reason your latency change is 255, you should leave that as stock;
your fuel and timing maps have differing scales, why is that?
there are other things that could be changed but the main thing is get your k value and the latency adjusted and set the latency change back to B8.

the k value is used to calc an injector pw with the latency added to the inj on time. with shorter on time like at idle the latency value plays a larger role in the overall on time. i will usually set my k value old inj/new inj, then adjust latency to get a proper idle, then reset the k value at about 3k moderate load, then reset latency at idle until i get the afr's close to what the map is calling for. you should also disconnect the o2 sensor or disable it in the software for initial tuning.

SupSay Z · Post by **SupSay Z** » Sat Apr 05, 2008 5:06 pm

Bernardd, thanx a lot for all your help. i will work on these things tomorrow and give you an update. as far as the scales being different, i changed them at some point and never changed the other to match, thanx for catching that too.

SupSay Z · Post by **SupSay Z** » Mon Apr 07, 2008 5:00 pm

BERNARDD, i made the scales match and brought the k-value to 290. the car still idle fine like this. however, bringing the latency to b8, which is 3680 or so i believe, made the afr to drop to ~10 at idle.is this what you are referring to? and yes, these are rx7 injectors. once again, thanx for all your help..

alex.

Bernardd · Post by **Bernardd** » Tue Apr 08, 2008 12:40 am

sounds like you changed the wrong latency. the one referred to as injector latency change should be b8, the other one is called injection latency, that one should have 75 hex or 2340. the injection latency is a starting point and may or may not be your final value, but that is what several tuners have come up with and it matches the latency value for that injector on spec sheets. the fuel/timing scales should end at 60 or so to start.

SupSay Z · Post by **SupSay Z** » Wed Apr 16, 2008 4:13 am

alright Bernardd, once again, thanx for your help. i went to the injector resize and i see how that one could be b8 and how the injection latency is 75 hex. where i was confused was with the injector and injection latency. i think ill be able to get these in order today. as far as the scales, do you recommend i start at about 5 or so and go up to 60 at ~equal intervals? i thought a higher number was better, guess not.

on z31performance you mentioned moving the stock afm element to a 4" pipe. is this what you are running? how hard was it to tune for this and how accurate can you get? prices for the z32 afm are a little out of reach right now and unless i find one at the junkyard i wont be able to afford one for a while, so i'd be willing to try this. thanx again..

alex

Bernardd · Post by **Bernardd** » Wed Apr 16, 2008 8:20 am

As long as the tp scale is just below the calculated tp value you should be good at the low end. The top of the tp scale should be determined by max calc'd tp via dataloging. You don't want to go off scale.

Regarding the maf, yes you can install it into a larger pipe and increase it's flow rate. I would only modify if you are reaching the end of the vq map. I have only changed the k value by the same amount I've increased the maf area and it usually works out fairly closely.