Another_User

I have noticed that my FTs are shooting up on decel, and I got to thinking it may be a vacuum leak. Then I remembered that I have the fixed orifice PCV installed. Could this be the culprit? I am going to put in a new PCV and check all my vacuum lines tomorrow. With my foot on the gas pedal FTs slightly negative, foot off FTs climb to the max, all at the same MAF frequency in Hz. Anybody else think this may be the culprit?

jimmyblue

iTrader: (11)

PCV makeup air should be drawn from after the MAF and
sensed by MAP so I would not think it should matter to
either airflow method. But if you had the makeup air
unmetered then it might.

What about DFCO? Is that out of the picture? Dunno if
fuel cut happens on F-bodies. Can you see anything odd
in the injector pulsewidths, vs CylAir?

Another_User

DFCO and Proportional Idle disabled. Injector pulsewidths seem normal, I think they are slightly increasing along with the trims on decel. I thought maybe it was a trim difference due to timing, so I forced the main timing tables after 4mph and ended up with the same thing. The only thing I can think of is unmetered air after the MAF.

Another_User

Well I just got done with my logs after capping off my PCV port. It looks to have made a big difference. All of the weird positive spikes are down by at least -10 STFTs, and a lot of my positive trims were getting dragged negative on average. I forgot to reset my trims, but I will do that later. From my logs it looks like the fixed orifice flows about .5 g/sec at idle. That's a pretty noticable difference. And my idle was smooth as silk, big difference there. I picked up another stock PCV ($6...seems a bit pricey to me). My old one (taken off many miles ago) does not appear to have been sealing properly anyways. Any thoughts about whether or not the PCV will shut completely at idle? I can seriously deal with the difference it is making. I may need to go back to my VE table to correct the rest of my positive trims (I think I overdid pulling fuel in the "decel" area). After that, all should be well. Sweet. Plus it looks like my MAF table is pretty close to dead-on.

P Mack

iTrader: (6)

Keep in mind, even if you're not getting unmetered air through the pcv, you may be getting unmetered fuel from crank case fumes that would change your ltrims.

Another_User

Yeah, but wouldn't that throw me rich? (and put my trims negative)

Another_User

If you are running the Fixed Orifice PCV and a cam, I recommend you remove the PCV and put in a stock one. It affects FTs, and idle quality a lot. I did a test run (54 miles) today, and cruise is much much better.

P Mack

iTrader: (6)

Stupid question: what is a fixed orifice pcv? If I haven't messed with my stock pcv i shouldn't have to worry about it right?

Another_User

You would know if you changed it. A normal PCV has a spring-loaded valve inside that rattles when you shake it. A fixed orifice PCV has a small hole similar to the little hole in your throttle blade. The difference is a regular PCV closed under vacuum, so it is not a vacuum leak during idle, light cruise, and decel. A fixed orifice is always open, and allows unmetered air in your engine. On a normal vehicle with plenty of vacuum this is not a big deal. With a cam, every little bit helps. Plus I don't think the air flow through the fixed orifice is very steady, I think it probably "pulses" a little bit.