MAF reading lean and low flow amounts

[davepl]

I've been chasing a MAF issue for a while on my new LS3/eRod. Both banks go way lean when the MAF is connected (like 17:1 or leaner). That means to me there is a problem with the MAF or there is other air getting in that's not being metered.

Other things I've done:

- Runs fine at 14.7:1 when MAF is disconnected
- New MAF, no difference
- Tried a straight 4-inch pipe with MAF as intake, no difference
- Verified 30ohms to ground from ground pin at MAF
- Verified IGN voltage present at MAF
- Yes, MAF is facing the right way :-) Presuming arrow shows direction of flow...
- It meters and runs OK up at 3000rpm when more air is flowing, making me think the MAF is OK except down low.

Today I found one of my PCV intake ports on the valve cover was uncapped, which I thought for sure was the problem, but capping it doesn't fix it. Temporarily I've got the PCV sealed so I can confirm vacuum in the crankcase (so I know it's not pulling in unmetered air through it). Confirmed lots of vacuum in crankcase, so no leaks to speak of.

There are only three vacuum ports on the intake:
- One connected to the valley, and the PCV is closed off, so it's not through there (vacuum builds in crankcase quickly)
- One connected to the power brakes, which I have plugged off, so its not through there
- One aux vacuum to the accessories, but I've not even opened that nipple yet, it's still sealed, so not through there
- I can't think of anywhere else that it could pull unmetered air from!

Can anyone else think of anything that would make a functioning MAF take the engine lean? Clearly it's not reporting enough air, which is why everything goes lean, but why????

Thanks,
Dave