i have a FMU and i run 8 psi but during accelleration when im not flooring it fully maybe only 3/4 of the way m y air fuel reads way lean till i let off gas then it quick goes to rich for a sec or two. at full throttle it reads all rich but i just dont wanna damage anything if this is a prob. if i spool up gently or full throttle its ok though??

sounds normal to me. as long as its not dangerous lean you should be ok.. you should have a wideband to know for sure. don't tune by an idiot light.

^^^what he said.

Thats the ECU staying in closed loop during boost, and its still reading off of the o2 sensor to keep the A/F around stoich(14.7:1). There really isn't much of a way around this with that setup.. Either boost it a bit lighter, or put it to the floor, to kick it into open loop. As long as you are not getting any detonation, and you dont go though all the gears like that, then it should be fine. This is another reason I'm really going to like the Megasquirt.

I always found this to be extremely annoying. It always made me nervious seeing the stock ECU trying to lean things out if I didn't have my foot mashed into the floor while in boost.

A long time ago I cooked up a quick and dirty solution to the problem - a relay that clicks on at atmoshperic pressure and switch the TPS signal wire to a ~3.8 volt (100%) refrence. This makes the ECU think you are at full throttle and will start open loop operation. My little gadget worked, but not as well as I hoped so I stopped using it. I was too lazy to perfect it. When I picked up my 034EFI a while back it partially solved this problem, however, the real solution is to stop using the stock ECU entirely.

I've thought about this question alot. I don't think it's as much of an issue because it's at part throttle. Remembering that it's really about how much air gets pumped into the cylinder and not what the pressure in the manifold is at, with the throttle partially open we are substantially limiting the amount of air that can make it into the cylinder during the intake stroke. Since the amont of a/f mixture is considerably less, we should not be seeing obscenely high cylinder pressures. With the low load being placed on the motor at the same this should be safe.

Now I could be way off. This is just how I've rationalized it. This also depends on what you mean by "lean". Is lean like 15:1 or is lean like 13:1 to you? I do think there could be issues when you ride the line between high load and low load conditions. Basically when the car goes from open to closed loop operation (or is that the other way around ... I can never get that straight), there might be some points that you'd like it to be a little richer than it is.

Now I'm curious as to what a stock turbo car's A/F curve is at partial throttle experiencing positive pressure.

ok well it reads all the way lean on a/f gauge so i dunno. why does ecu stay in closed loop mode any way? cant i somehow make something to stop that? i dotn like running lean at all .

Yeah I hate that lean thing too. I wonder if it is like that all all non-turbo cars with an aftermarket kit?

I was wondering, if it says "lean" on you cheap regular a/f gauge, will it say "lean" on a wideband?

The ECU is still seaking to 14.7:1 A/F becuase its in closed loop. at partial throttle load levels, this is 100% a non-issue and if any of you had the resolution of a real wideband, you'd see what it's doing and realize the same thing.

Lean != knock. Not always. High EGTs != knock. Not always. Boost and 14.7:1 A/F in closed loop may look lean on your Gadgetseller gauge, or your blinky Autometer, but i'd bet money it's not knocking and you don't have anything to worry about.

hmm.. all this happened cause i fixed a boost leak i found i had. i never knew ... oh well as long as it dont hurt it, this is my only car. Why does ecu stay in that closed loop during boost anyway? what makes it do that.

cuz our PCM doesnt know what boost is, and you prevent the PCM from seeing boost, so it doesnt even know its boosting.

The inputs required for open loop operation are not met at a part throttle cruise, boost or no boost. Boost is not part of the equation at all.

Originally posted by DarkOne
The ECU is still seaking to 14.7:1 A/F becuase its in closed loop. at partial throttle load levels, this is 100% a non-issue and if any of you had the resolution of a real wideband, you'd see what it's doing and realize the same thing. Lean != knock. Not always. High EGTs != knock. Not always. Boost and 14.7:1 A/F in closed loop may look lean on your Gadgetseller gauge, or your blinky Autometer, but i'd bet money it's not knocking and you don't have anything to worry about.

Oh good. I'm gonna bust out the wideband this week and see what the values as.

ecu definately seeks 14.7 afr like dino said, proven with a wideband

the thing i cant figure out is why it never did this before. ive ran 8 psi for a while now and it never did this. it feels like its weaker to. . i dunno. at full throttle its ok but not at half throttle. the only time it felt like this was when my fmu gas hose had a small leak and gas was pouring out into my rug.. but i fixed that and it was better. now i changed my piping and fixed a boost leak and it feels like less power. and reads lean . .

Originally posted by 97grnRS
when my fmu gas hose had a small leak and gas was pouring out into my rug..

so you run your fuel lines through the interior of the car???
you're kidding right?

Originally posted by djtrickee

Originally posted by 97grnRS when my fmu gas hose had a small leak and gas was pouring out into my rug..

so you run your fuel lines through the interior of the car??? you're kidding right?

maybe his garage is carpeted? :shrug

Originally posted by BlackMagic

Originally posted by djtrickee

Originally posted by 97grnRS when my fmu gas hose had a small leak and gas was pouring out into my rug..

so you run your fuel lines through the interior of the car??? you're kidding right?

maybe his garage is carpeted? :shrug

we can only hope he has rugs in his garage.

this pisses me off alot... losing power

I would recommend getting yourself a datalogger...you are now at the crossroads I have come too as well. I just recently had a turbo installed and I am having similar issues, except I am only leaning out for a breif second or 2 and then back to rich. Also when I let off the gas completely my car goes all the way lean not rich like you stated yours does. But I just ordered a datalogger to get figure out what is really going on. I think you would benefit from one as well. There are some for sale on dsmtuner.com for a good price that comes with everything you need.

Just something to think about, because if you are like me at all you do not want to take any chances. Maybe this lean spike during closed loop is normal...but more then likely it isn't!

Good luck, and I hope you get things figured out. I will keep you posted on mine as well.