Lower Boost Cut When Cold?

[rico05]

I have noticed a trait on my new motor that is odd. When my motor is cold, it will hit boost cut at like 5-7psi. When warm, I can run ~1bar and never hit cut. I have rationialized this all to hell, but just wanted to hear some thoughts on the subject.

[fabio240]

I have noticed a trait on my new motor that is odd. When my motor is cold, it will hit boost cut at like 5-7psi. When warm, I can run ~1bar and never hit cut. I have rationialized this all to hell, but just wanted to hear some thoughts on the subject.

I have the same problem with my ca too I believe that its because its sucking in colder air and more dense air and Im using a z32 maf and an afc to tune my car.

[Ca_Silvia]

Yes, this has happened to me as well, even after my tune. Rico are you running a manual boost controller?

[float_6969]

Remember, the stock ecu measures air MASS. The density of air increase considerably when it is cooled. This would cause the same MASS of air to be consumed at a lower pressure.

Now whether cold temps are enough to increase the mass so much that it causes you to hit boost cut is another story. It's hard to tell for sure unless you are able to monitor the voltage output from the MAFS when this cut occurs.

I would be more inclined to think that the MAFS is failing.

[rico05]

I get the idea Ryan, I just asking for some verification. You really think the MAF is failing? I could pick up another one sice I run a KAE unit. It never did this before and it is the MAF from my old setup.

[Ca_Silvia]

I think its MBC related, when its cold you just get a big nasty spike. I ran 12 psi just off the wastegate before this, never had an issue. But as soon as i went to a MBC i now have this problem.

[float_6969]

Is it spiking?

[Ca_Silvia]

I don't know for sure, it only happens when i am full throttle and i'm not about to glance down at my boost gauge to look. I will have to wait till Wednesday, once i'm back on the track, to find out for sure.

But it definatly seems temperature dependant, its never done it before at the track when its hot as hell. Only later at night when its cold.

[ca18detgabby]

But it definatly seems temperature dependant, its never done it before at the track when its hot as hell. Only later at night when its cold.

he is talking engine temp wise not ambient temp.....

[float_6969]

Holy crap, I totally mis-read your post. I thought you meant cold ambient temps, not cold engine! Sorry dude.

In that case I would suspect a failing engine temp sensor. Maybe it's pulling too much timing or adding too much fuel?

[rico05]

Now I get why you were playing Cpt. Obvious lol. I may have found the issue in shot plugs and a vac leak (hence the shot plugs...). I fixed the leak and threw in some NGK IXs that I had squirreled away for a sunny day.

[Ca_Silvia]

Holy crap, I totally mis-read your post. I thought you meant cold ambient temps, not cold engine! Sorry dude.

In that case I would suspect a failing engine temp sensor. Maybe it's pulling too much timing or adding too much fuel?

I meant cold ambient temps, i see how in that one post its a little confusing. Anyways, i went to the track last night and yes my car was cutting out. Its was only above 6500rpm, motor running 190* coolant temps. It happened a few times, like 3 times in 4 hours of drfiting. Im going to seafoam the motor and change out the plugs and see what happens.