Ls2SilverBullet

So, I have been messing with installing a FAST 90mm intake manifold on my ls2 camaro for a week now. First I installed it just like FAST recommends without any rtv or anything. Once installed I fired it up and it ran, but began surging at idle.

I figured it had a leak somewhere so I pulled it back off, opened it up, and RTV'ed over the gasket from the inner manifold to the top portion of the manifold, put it back together and reinstalled it back on the car. Started right up but it still surged at idle.

It seemed to run the exact same after the RTV as it did before. So I was thinking, since it ran the same before and after the RTV, it probably wasnt leaking at all if the leak didn't at least slow down..?

This makes me think the manifold is not leaking at all and its in the tune.

So my question is.... Could upgrading from a ls1 intake with 78mm tb to a F.A.S.T. 90 with a 90mm tb cause this?

My car is Speed density tuned.

tdevil55

iTrader: (23)

I would say yes it would confuse the PCM on a SD tune. With the extra amount of air and no maf to adust tables, that would be my guess. Im not a tuner, but im sure someone will tell more on this.

Ls2SilverBullet

Yeah, thats what I was thinking. I havn't actually looked into the details of sd tuning, or tuning at all really, until recently because of this. But thanks for the input, hopefully others will know more

Ls2SilverBullet

anyone?

C5kid

iTrader: (12)

yea, you need to get that retuned.

There is alot more air moving through that 90mm TB and your idle air tables probally need some adjustment. The surging sounds like the idle air because it is trying to add or remove air to find idle, but is having a hard time because there is more flow from the 90mm TB.

Ls2SilverBullet

Ok, cool. thanks for the help man. I need to talk to my tuner then.. Wish i would have waited and kept the damn thing on the car now

Ls2SilverBullet

Bump

for some info from someone with tuning experience please

DrkPhx

iTrader: (15)

Without a doubt it to be to be retuned because of the FAST 90mm. As mentioned above the increased airflow is causing problems, but It's easily corrected by retuning.

bayer-z28

iTrader: (14)

I'm not fluent with tuning, but I do know that an SD tune is a set parameter. If you change the airflow, the parameter is still set to the old value.

Higgs Boson

iTrader: (3)

base running airflow needs to be tuned. did you change your TB size? may need to adjust the scalar.

Ls2SilverBullet

Yes. Went from a factory ls1 manifold and 78mm tb to a FAST 90 and 90mm tb.

and scalar? Whats that?

redtan

iTrader: (5)

Like it has been said, an SD tune assumes certain airflow and gives fueling for that.

If you change the airflow, the PCM does not know how to compensate for that...so it will still be dumping the same fueling as before. But now there is more airflow but not more fuel, so the trims and AFR are off.

Higgs Boson

iTrader: (3)

adjust the tb scalar in the tune (there is a spot for it) to the right size for a 90mm tb.

then run a scan to help you dial in base running airflow (and then dial it in).

tune your VE table properly.

retune base running airflow.