why does my car run lean while excellerating????

[VeloceDrift]

So i have a t25 running around 6psi. I also have an FMU and while boosting i stay in the high 12's for my AFR. the problem is when i accelerates normally just driving around my AFR jumps to 19ish and sometimes up to 21 . . after about 2 seconds or so it will correct itself and jump back to around 15-16. Anyone know the reasoning behind this?? i know that means boom if it runs like that while boosting but how bad is it if it does it for 2 seconds every shift while just normally driving????

[Veriest1]

I'm really not sure but that would freak me out.

Has it any thing to do with the nature of an FMU? If you aren't seeing any boost then I'd guess it's just the way the car runs. Off boost the fuel supply should be the same as stock and with no ECU mods....

[VeloceDrift]

yeah thats what i thought. it suckes but i shall keep trying things til i get it right

[Veriest1]

It's been so long since my bimmers been on the road that I don't remember to clearly but I want to say just puttering around I was reading 17-19ish afr's until I started getting up to speed.

Where are your afr's when you're cruising at highway speeds?

[VeloceDrift]

well for the most part around 16's some times it will go around 18-19 for awhile. its really starting to bum me out because im afraid im close to blowing a ring. is their any alternatives to getting mor fuel without spending much money for now? i forgot to add then when shifting it does lean out so much that my car will start cutting out

[Veriest1]

It should go lean when you close the throttle but cutting out?!?!!?1

I'd go over your fuel system with a fine tooth comb. When was the last time you changed the fuel filter?

And it should be around 14.5ish IIRC when cruising for optimal gas mileage.

[VeloceDrift]

ok. I have a fairly new walbro pump.. but i am going to go get an fuel pressure gauge real soon. This may be a no brainer but would a massive leak before my O2 sensor cause all this rukus?? i Just looked closely today to see the gasket that connects my turbo to my manifold has blown out which means my next day off is pretty much gone........

thanks for your input by the way!

[Veriest1]

ok. I have a fairly new walbro pump.. but i am going to go get an fuel pressure gauge real soon. This may be a no brainer but would a massive leak before my O2 sensor cause all this rukus?? i Just looked closely today to see the gasket that connects my turbo to my manifold has blown out which means my next day off is pretty much gone........

thanks for your input by the way!

Haha, no problem, I'm just sort of shooting in the dark hoping to help out.

As far as your 02 sensor goes I'd say it depends on how dependent the ECU is on the sensor (I'm not familiar with OBDI really).

So I'd start with that gasket if I were you and work from there. If you aren't running a z32 fuel filter this would be a good time to upgrade but I got to thinking about it and I guess it wouldn't make sense for it to be your filter since a clog would effect the car the most under heavy loads as opposed to light loads on the engine.

[VeloceDrift]

sounds good. im going to change it on monday so we will see how it goes. im also changing my plugs today to see if that helps because i have learned that if i ride my clutch when shifting it eliminates the car cutting out. hopefully i just have a couple fouled pluggs.

[ken240sx]

Here's what I've experienced...When just diving normal you should be seeing 14-16's for your afrs, if you let off the throttle a little, it will go to the 17-20's area for a second, then go back down to the 15 range again. If you're giving any kind of acceleration throttle then let off, it should dip really quick into rich then pop up into the lean for a second then even out. When accelerating, even slightly then letting off, it is still giving some gas, so it will run rich for a split second...you may n ot even notice it if you aren't looking, then the fact that the throttle plate is closed abruptly and cuts air off sharply it will go lean on you until it reacts and then goes back closer to stoich. any time the air is cut off somewhat sharply you will go lean. It is like this on all of the stock vehicles w/stock ecu's that I've hooked up widebands to. The 240, acura TL, escort, neon, camaro, saab 9-3, another 240, talon, and the list goes on. I don't think you have anything to worry about, as long as your afrs are under the 13's under acceleration you should be ok.