Hey guys,

So I just installed stock injectors on my car to start diagnosing my hard starts and rough idle, when I put them in with all the rest of my settings returned to stock I got a +20% fuel trim at idle, so the car is running way lean. I have no boost leaks or vacuum leaks.

Tonight I was playing around with my MAF and I decided to pinch off the PCV line that runs from the valve cover to the intake pipe, my trims immediately dropped 15%.

Now the line itself isn`t leaking and its connected after the MAF so logic tells me that the air is metered but how can it be effecting the fuel trims then? Please chime in and let me know if this is normal behaviour or not.

So what is left on your car that's not stock?

The car still has HKS 272's which I'll be changing out for stock cams shortly, Aeromotive AFPR, walbro 255, Injen Intake with K&N filter, e316g, RTM FMIC, greddy BOV, L19 head studs, and full exhaust with cat.

So I've been reading about the PCV system, I think I'm going to install a check valve in the line between the intake pipe and valve cover that only allows air to flow towards the valve cover. I think that currently both the line from the VC to the manifold and the line from the VC to the intake pipe are sucking air out of the crankcase, maybe because of the low vacuum in the manifold caused by my cams. What should be happening is the manifold line should be sucking fumes out through the PCV valve and the line from the intake should be drawing metered air into the crankcase but I think that line is flowing the opposite way, a check valve will fix this.

Makes sense in my head, can anyone see an issue with this?

Edit: I'm also going to tee another check valve into this line that flows the opposite way so it will be sealed when the line is in vacuum and will vent excess crankcase pressure to atmosphere when in boost.

No that's wrong.
Your pcv system pulls from your intake plenum when you are idling and pulls from your intake when you are in boost.

If you are expecting stock values from your logs your car should be completely stock. I think you need to do some reading about what happens when you have 272s, the short version is your intake valves are open at the same time as your exhaust valves for a period of time.
As for the rest of the stuff on the list you should be fine with leaving those on.

Okay so with my idea the only functionality I would be losing would be that under boost the pcv line doesn't have a vacuum source connected to it so I'd be losing the suction effect from the -2 psig that is seen in the pipe at WOT but I would still have a vent to atmosphere for that pressure to disappate. I think I'm still going to give this system a shot to see if it improves my starting and go from there, I guess I'll know if its not working well enough if I pop my dipstick.

Well you still have MAF so in theory this would mess up your idle even more, but will be curious to see what your experience will be.

I'll give it a try, for $10 of check valves and vacuum hose its worth it. I'll post up with the results when I get it in on the weekend.

Hello Chris. I see that you have ECMLink. Shoot me an Idle Log and I'll have a look at it.

Check your pm.

Ghislain

Did you ever figure this out Chris?

Well my trims sorted themselves out when I put the stock cams back in, actually all of my problems were fixed by doing that. I believe that the 272's which actually turned out to be regrinds were severely worn, I'm going to measure them in the near future to confirm.

As for the PCV system it still messes with the fuel trims when you pinch off the line but I believe this is mostly due to the airflow changing through the MAF, I think it is normal. I got my fuel trims within +/- 5% on the stock injectors / stock cams after I installed them and fixed a few very small exhaust leaks.