I fixed a boost leak and now A/f's are off the wall?

[hottscennessey]

So i had a boost leak, so then i fixed it. I took my car out for a run and my car backfired in higher RPM's. I logged it with my laptop and I dont know what the hell my A/f's were doing.. they didnt dip down at all in boost.. i mean LEAN LEAN LEAN (18 at one point). WTF, i had tuned out my A/f's pretty well before i fixed this boost leak. Is this normal? It wasn't a huge leak or anything..

 

[supra87t/t4]

You were most likely seeing misfires as a lean condition on your wideband. What is the rest of your setup?

 

[hottscennessey]

mainly.. maf-t, sp61gt, fmic + hardpipes, walbro, 550's.

acceleration was pretty smooth when i took the logs, no big misses.

 

[GrimJack]

Not good, but expected.

You see, you had a boost leak, so your ECU had 'learned' that the amount of air your turbo was pushing only needed a certain amount of fuel to get a decent AF ratio.

Now, you have fixed a boost leak - which means that all of a sudden, your engine is still reading the same amount of air going in, but now it's all going in, instead of some of it leaking out. Voila, seriously lean conditions.

Your ECU would figure it out again in a while, but you are better off to just reset the ECU and let it relearn again from it's hardcoded baseline. Pull your EFI fuse for a couple minutes, plug it back in, and I'll bet you'll go back to the usual rich condition.

 

[hottscennessey]

yea, i understand grim, but the only thing is, you might remember, but I run a MAF-T in blow through.. the leak was before the MAF.. does what you were saying still stand true?

 

[boost fiend]

if your leak is pre maf, i would think that is not the problem. not too sure though.

clear the ecu and try again. see if it does the same thing.

 

[GrimJack]

boost fiend is correct, if your leak is before the sensor, it shouldn't have any effect.

 

[hottscennessey]

i cleared my ECU, riched up my WOT and tried again.. it dipped down nicely into the 10:1 ratio before i hit fuel cut, i leaned it out, more and more, got it to 11.5:1 range and still hit fuel cut.. i was about to up the fuel pressure before my laptop died and i had to go to work for 11 hrs. BTW whats the max base FP i should run (vac line off/plugged)?

 

[hottscennessey]

mmm nobody?

 

[boost fiend]

iirc, its 30 psi. not too sure though. i dont have it installed yet

 

[hottscennessey]

I thought base FP was just under 40psi?

Edit: you must mean with the vac. line connected, right?