We All Know About Cold Weather Boost Cut, But...

shane02pro5 said:
I tripped a cel this morning at 33 degrees due to maf high input voltage
Click to expand...
This is exactly what happens. It isn't "boost cut" it's "fuel cut" and it's because the voltage the ECU is receiving from the MAF is too high. I'm not sure about the 3s but Protege MAF max out at 5V. Anything higher than that will trigger fuel cut and if you repeatedly encounter it you will through a CEL as shane has mentioned here. It's what you all have been saying: colder air is denser air. Greater density means more molecules per unit volume. So, for a given amount of flow, there is a larger amount of air passing by the MAF on a colder day than on a hot day. The voltage transmitted by the MAF is directly proportional the amount of air it is reading. So more air means greater voltage. Too much voltage means fuel cut. This can be alleviated through the use of a simple MAF clamp.
 
My situation might not be quite as typical with my 22psi but I even have a JoeP FCD MAF clamp. If I gently accellerate and once I get to "traction speed" and hit it hard my WB shows a superquick lean spike from the majorly dense air at well over 500cfm makes it kind of hard to react to. It can also happen if I lose traction and hit high boost with less load than normal and I go rich for a second and cel.

This has been the same occassionally even way back at 8psi.
 
^^^ Interesting. I've actually only hit fuel cut once or twice at high RPM in colder temperatures and that's with a relocated MAF (doesn't actually cause anything though)! For your case though I can see where it would be insufficient injector/fuel pump flow in which case fuel really is running out (well, more that it can't respond quickly enough), not getting cut. I wonder if a too-lean condition read by the primary O2 sensor can also trigger fuel cut?
 
After I got everything tuned near perfect I didn't need the JoeP until after 17psi but i also put in the walbro so...

I'm sure it's a combination of the maf and 02 readings on a stock ecu. Both of my stock 02's are wired to +12v to keep the ecu from complaining since they don't do anything for me using the Haltech.
 
cold weather boost cut

I can't tell if I'm seeing cold weather boost cut or something else.

I have a stock 2008 MS3 and I've noticed that sometimes when hot-dogging into something like a traffic circle or a standard 90-degree turn, I'll get no boost at all while in turn.

example, I'll be hard in 3rd gear, then hard on the brakes, heel-and-toe blip into second, turn-in and then squeeze hard on the gas and...
nothing.

then, when I straighten the wheel I'm usually up at 4K RPM and the boost LURCHES on.

This is NOT the LSD limiting traction, this is simply having no real power for the LSD to have to limit.

thing is, it doesn't always do this. sometimes in a traffic circle (that I entered while in 2nd gear already), I can get the wheels to spin and give the LSD one heck of a hard time until I feather and let the front-end re-bite...

thoughts?
I've only really noticed this lately here in Indiana so maybe it is cold-weather related?
or maybe just steering related?
(dunno)
 
rednofive said:
I can't tell if I'm seeing cold weather boost cut or something else.

I have a stock 2008 MS3 and I've noticed that sometimes when hot-dogging into something like a traffic circle or a standard 90-degree turn, I'll get no boost at all while in turn.

example, I'll be hard in 3rd gear, then hard on the brakes, heel-and-toe blip into second, turn-in and then squeeze hard on the gas and...
nothing.

then, when I straighten the wheel I'm usually up at 4K RPM and the boost LURCHES on.

This is NOT the LSD limiting traction, this is simply having no real power for the LSD to have to limit.

thing is, it doesn't always do this. sometimes in a traffic circle (that I entered while in 2nd gear already), I can get the wheels to spin and give the LSD one heck of a hard time until I feather and let the front-end re-bite...

thoughts?
I've only really noticed this lately here in Indiana so maybe it is cold-weather related?
or maybe just steering related?
(dunno)
Click to expand...

It should always do this, our speed3 actually lower the boost when the steering is turned past a certian degree to limit wheel spin, we get max boost in a straight line, but when turning, you won't get max boost. It's actually a pretty cool feature for street driving, but at the track, I can see how that gets annoying. Does this answer your question?
 
Alexsered said:
It should always do this, our speed3 actually lower the boost when the steering is turned past a certian degree to limit wheel spin, we get max boost in a straight line, but when turning, you won't get max boost. It's actually a pretty cool feature for street driving, but at the track, I can see how that gets annoying. Does this answer your question?
Click to expand...

Yeah, thanks!

How did you know that?

I assume they did this to keep us from killing ourselves with hellacious "push"?
 
I remember reading about it when the car was first coming out. It's pretty good because turning the wheel and having all of the power would just cause a FWD to slide.
 
Alexsered said:
I remember reading about it when the car was first coming out. It's pretty good because turning the wheel and having all of the power would just cause a FWD to slide.
Click to expand...

I mostly agree, but I'd rather let my foot and the mechanical LSD decide that more than the ECU. I'm not saying that because I think I'm some kind of amazing driver or anything, but it seems like they drew the line in the sand pretty close to the kiddie's sand box.

No boost at all is what it feels like and I have no gauge to confirm that. Its pretty obvious that the car could handle more boost than none while turning, especially with the stock summer tires and an excellent LSD.

What is the boost curve for the MS3 in each gear, BTW? Is there a FAQ on this site for the MS3 that shows me things like that?

thanks again,
Pete
 
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