Major MAF Problems in '03 Silverado SS

[Time2Kill]

We're trying to finish up a 2003 Silverado SS here in the shop with a 414 in it. We had it on the dyno last week, and the MAF was reading all over the place. The tuner could hold the truck at 45 mph on the dyno, and it would read 420 g/s on the MAF. We would make a pull with the AFR at 12.8, shut the truck down, restart and make another pull and the AFR would lean out anywheres from 15 to 19, and the MAF would now be reading 350 g/s at 45 MPH and the same RPM. There AFR readings are changing even though we have not touched the tune. Everytime we flash a new tune, we will get one or two ok pulls, and then they will start going extremely lean again.

We have tried switching MAFs, trying MAF Cleaner, and have also switched out the PCM. When loggin the truck, the MAF is not a smooth curve, it curve would be very jagged and look similar to an O2 that is switching on/off, just not as severe.

The truck has also started throwing a MAF Performance code which we cannot figure out. Sometimes it will set as soon as we start it up, other times during the run. Now that I have back at the shop though, we cannot get it to set off again, but we are letting it idle as we try and figure it out.

The tuner also said that the STFTs are active/adjusting during open loop when they should not be. When we swapped PCMs, the first pull with the new PCM the STFTs were not active during open loop, but as soon as we turned the truck off and back on, the STFTs were active again in open loop.

I'm about to switch the engine harness to another one that we have here in the shop to see if that somehow affects it as the harness currently on the truck is a used harness that we bought for this project. It was a stock '03 Silverado SS harness and as far as I could tell, nothing was wrong with it. We have checked out grounds on the harness that is currently on the truck also, and everything seems to be in check.

Does anyone have any ideas on what we can check as we are completely stumped and need to get this truck running ASAP.

Cam Specs: .635/.630 246/252 +4 112 lsa & Custom ported TEA AFR Heads

[WS6FirebirdTA00]

Make sure STFTs are disabled in OL.

As for the MAF, my first guess (since you changed sensors) would be to check the wires for the MAF

[5_Liter_Eater]

you may also try clocking the MAF.

[Time2Kill]

Attached is the hptuners bin, and three log files. The log files show how the MAF is reading anywhers from 2.9 to 3.25 lb/min on the MAF at 2000 rpms on different startups.

This is after taking the MAF Connector apart, and pressing the pins down so they make better contact. I also cleaned them to make sure there was no corrosion/dirt etc.

The truck is still throwing P0101 MAF Sensor performance and also P0106 for the MAP.

[Time2Kill]

Scanning the truck, and holding idle at 2000 rpm, it would read from 3.0 lb/min to 3.25 lb/min but when I go to scan a stock Escalade with a 6.0L, and do the same test, it reads 4.0 to 4.1 lb/min on the maf. Shouldn't the 414 in the truck be reading more through the MAF at the same RPM? My tuner told me I should expect about 20 g/s with the truck at 2000 RPM, and I believe 3.0lb/min is right around 22 g/s.

[Programmer]

Have you rescaled your P1514 airflow table for the change in engine displacement and expected airflow ? Your Max delta airflow looks stock also.

[Time2Kill]

Have you rescaled your P1514 airflow table for the change in engine displacement and expected airflow ? Your Max delta airflow looks stock also.

I was actually just checking this last night and saw that the MAP/MAF error tables are stock. I'll ask my tuner whats up with them.

I'm normally don't touch anything with my tunes since my tuner handles it, this is the first major problem we have had with tuning. He's even tuned this exact motor in a different car two times before.

[Time2Kill]

Attached is a log of a WOT run locked in 3rd gear to prevent wheel spin. I only made it to about 45 before I had to let off.

Do the MAF readings look ok to everyone? The MAF bounces around quite a bit and the tuner told me that should not be happening.

[Programmer]

Can you make a list of all parts that are not original.
Engine new size, injectors, etc....

[Time2Kill]

Can you make a list of all parts that are not original.
Engine new size, injectors, etc....

Engine is a 414 (Iron block, 4" stroke), 246/252 .630/.635 +4 112 lsa cam, Edelbrock Pro Flow XT intake (http://www.edelbrock.com/automotive_...f-xt_ls1.shtml), 42lb GM Marine Injectors, 4" Intake tube (90* off of the intake and runs over to the fender with a K&N cone filter with the MAF attached to the Filter), AFR Heads ported by TEA, flow right at 340 at .600 lift, 1 7/8 LT Headers.

I have also attached two better log files with pulls on the street with the trans locked in 2nd gear. One log is using the 4" intake I made, the other log file is with the stock truck intake tube with baffles. The tune is also attached.

[Eagle]

Attached is a log of a WOT run locked in 3rd gear to prevent wheel spin. I only made it to about 45 before I had to let off.

Do the MAF readings look ok to everyone? The MAF bounces around quite a bit and the tuner told me that should not be happening.

I would say it definitely does NOT look right. Way too much bouncing around considering how steady everything else is... however your cam is fairly large so you could be seeing reversion... but I wouldn't expect it to be there that far into the RPM range...

Have you checked for any leaks after the MAF?

You also have ~3* knock logged in that baffled-intake scan... might want to look into that.

[pdsq98gt]

I would add a lenth of tubing between the filter and the maf to straighten the airflow. Maybe having the filter connected to the maf is causing turbulance in the maf housing. Do the mafs that you tried have the screens on them?