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

[BR3W CITY]

I don't have a good mechanical explanation. Tune-wise the Airflow Vs Frequency table under MAF calibration would be the first place I'd look, but why that would have been played with is beyond me.

[aknovaman]

Read and post your file. Who flashed the file? Swap ecu out with another. Download a stock erod file and do a write entire. See if that helps.

[davepl]

Originally Posted by aknovaman

Read and post your file. Who flashed the file? Swap ecu out with another. Download a stock erod file and do a write entire. See if that helps.

Stock tune, no changes, so no point in posting a file. This isn't a calibration issue, as it's all bone stock.

I have no means by which I can swap in new hardware like a new ECU, but I have no diagnostic info that would indicate there's anything wrong with the ECU.

[BR3W CITY]

Did you verify the harness wiring on the MAF plug pigtails?

Dave, can you refresh my memory on the e-rod ECM situation. I know we talked about it before, but its running on the GenV ECM stuff right? Is it throwing codes for the MAF or the lean condition when it happens?

[davepl]

Yes, short of tracing each line back to an ECM pin, I've verified the pinouts and that the correct voltage and ground are present. Since it reads something, the other pins must be working....

Both banks go way lean, and I get codes for those two. I also get a code for MAF Voltage Low, but I can't tell if that's a symptom or a result of it not seeing enough airflow to be reasonable.

[BR3W CITY]

Have you tried running it with the MAF on but the air filter off (or were you already?). Most MAF don't "sorta" fail, the either do or they don't. I have seen MAF codes as a result of oiled air filters, or in some cases tiny bad flowing filters...running it without the filter would obviously verify that in a second.

[ls1nova71]

Is this a new engine? I am assuming so since a used e rod engine isn't too common. Also assuming it's always done this? Are you sure its a MAF problem? If you're running lean on both banks, I would be checking your fuel delivery, enough pressure/volume. I'm thinking that when you unhook the MAF it's going to a set set of values and maybe lengthing the injector pulse width and that's making it not run lean. Not positive, just thinking out loud.

[BR3W CITY]

^^interesting thought dude. Unplugging the MAF puts it into fail, which can trigger the low octane tables (at least on GenIII).

[Hart_Rod]

Quick question, do you have your exhaust on? Are you running both cats and 4 O2 sensors? Have you verified your fuel pressure (should be 60 PSI)? Also, I would recommend hooking the PCV as the instructions recommend.

https://www.chevrolet.com/content/da...nd-17tooth.pdf

Positive Crankcase Ventilation System (PCV)
How to set up your PVC system:
There are three ports on the engine that make up the PCV system.
There are two possible foul side ports. One or both of these ports
should be connected to the intake manifold and be exposed to vacuum
at idle. If you choose to use only one of these ports, and the other
one is part of your engine, make sure it is capped off. The ports on
the engine are 1) Front port on the valley cover(LS3 only). 2) Left
rear (driver side) valve cover. 3) Top center of the inlet manifold (LC9
only). The ports with silver tubes may look simple but, they should
not be modified. The tubes have a small orifice within them that is
used in place of a PCV valve of earlier designs.
There is one fresh air port which is on the front of the right (passenger
side) valve cover. Again this is a silver tube that faces forward on the
valve cover. This port should be connected to filtered clean air. This
connection must be within the engines air cleaner system and must
be between the MAF (Mass Air Flow Sensor) and engine’s throttle
body. The engine burns the air that enters the PCV system so, if the
fresh air port is prior to the MAF then, this air will enter the engine
without being measured by the MAF and adverse engine operation
may occur.

[Hart_Rod]

Also, where is your MAF loacated?

Here's a guy that had similar symptoms as you:

http://www.norotors.com/index.php?topic=14610.75

[solidaxel]

So the 90* fitting in FRONT of the MAF was the lean problem?

[davepl]

I have only a gentle 30 degree in FRONT of the MAF, and I tried adding a 4-foot extension to it, which didn't change anything, so it's possible that the tube is the problem, but I don't think so.

I might try running the pipe backwards just to make 100% sure I don't have the MAF backwards, but its arrow is aligned with the direction of flow, so doubt that's it (unless the arrow points at the filter, but that'd be weird).

That picture is my car, BTW! So as you can guess this isn't for my truck but since the LS guys here know as much as the Camaro guys, I just asked here.

I connected vacuum to the engine (like a PCV but I plugged the intake ports on the valve covers) and it generates and holds a ton of vacuum in the crankcase, so I don't think I have a vacuum leak (it didn't change much). I also pulled off the vacuum hoses and plugged the brake booster line to rule out other leaks. Really feels like a vacuum leak, which is what the other guy thought too, but I can't find one.

Given that when you bring the revs up it reads OK, I think it has to be either a vacuum leak or a problem with the MAF's mounting. Can't find evidence of either though.

[BR3W CITY]

Did you see if there is a worn o-ring seal or crack in the intake?