MAF is bouncing all over? Can someone look at the log/tune?

[Time2Kill]

I've got a Silverado SS that I just put a 414 into, and when I took it the dyno, the tuner cannot get the AFR to stay where he wants it (12.8~13.0). He will make one pull, and it will be dead on, but then make another pull without touching the tune and the AFR will lean out to 15 or 16. When scanning the MAF during the pull, it will just all over the place, as much as 40~45 g/s throughout the entire pull. He thinks that there is an electrical problem or interference with the MAF. Is it normal for the MAF to fluctuate that much during a pull?

We have tried several MAFs, moved the MAF farther away from the intake, tried a stock truck intake tube with baffles in it, and nothing seems to make a difference.

The only thing I can say, the tuner did not adjust the P0101 max delta airflow or the MAP max error tables. The MAF and MAP codes were being thrown on the dyno, but I have since fixed that on my own and the MAF still acts the same way on the street when I log it. The tuner also did not disable STFTs during openloop, so I'm not sure if those could of been throwing the tune off that much or not. I have since also disabled STFT during open loop to try and figure out whats going on.

When I do back to back runs on the street, the O2s can be at .930mv for one run, then I can stop, do another run, and they will only be at .880mv. Seems kind of odd to me that they flucuate that much from back to back runs during openloop with both LTFT and STFTs disabled.

If anyone has any ideas, please post as I need to get this truck running ASAP. I've been to the tuner twice already with no luck.

Two log files are attached along with the tune. For both logs, the truck was locked into 2nd gear for the WOT pull. One log is with the stock truck intake tube on, the other log has a 4" intake tube with a K&N air filter on the end with the MAF right next to the filter.

Engine mods: 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.

[bigbrian442]

Was there a screen in the MAF that has been removed?

[Time2Kill]

No, its a stock truck 85MM maf. Not ported or descreened. I have also tried two other MAFs besides this one.

I have also already tried another PCM. Forgot to mention that in the original post. I checked all the wires of the MAF, all are less than 1 ohm resistance. I also took the plug apart and pressed the pins down to ensure a good connection when connected to the MAF.

Does everyone agree though that there is a problem with the MAF bouncing, or is that normal with this large of an engine? I've had multiple 408s tuned and as far as I know, its never been a problem before.

[RWTD]

40-45 bouncing really isn't all that bad. I'll take a look at your logs in a few.

BTW, did he disable VE before attempting to calibrate the MAF in?

[Time2Kill]

40-45 bouncing really isn't all that bad. I'll take a look at your logs in a few.

BTW, did he disable VE before attempting to calibrate the MAF in?

He never calibrated the MAF. He left the stock MAF tables in. He had the tune dialed in to a good AFR at 12.8, but then the next run with the exact same tune would be extremely lean at 15 or 16 AFR. He was fighting this the entire time while tuning the truck. The AFR would be spot on, then the next run would go really lean.

Although he did forget to turn off STFTs during open loop, so I don't know if the STFTs could make the AFR vary that much from run to run or not. The tuner is trying to blame the supposed erratic MAF on the varying AFRs from run to run.

[Dozer]

What I see that has been done basically is the VE table below 1600rpms has been lowered and the the Power Enrichment Eq vs RPM has been set to 10.78 AFR (1.36) from 0 rpm to 4400rpm then it set to 10.95 AFR (1.33) from 4400 rpm up to 7200rpm. This is is the problem. Dont tune it by jacking the EQ table. Get a wideband on this thing and tune the VE table and then the MAF. Or just set it to be MAF only and tune just the MAF.

[Time2Kill]

What I see that has been done basically is the VE table below 1600rpms has been lowered and the the Power Enrichment Eq vs RPM has been set to 10.78 AFR (1.36) from 0 rpm to 4400rpm then it set to 10.95 AFR (1.33) from 4400 rpm up to 7200rpm. This is is the problem. Dont tune it by jacking the EQ table. Get a wideband on this thing and tune the VE table and then the MAF. Or just set it to be MAF only and tune just the MAF.

This is how the tuner normally tunes his vehicles. I doubled checked it in several other vehicles that he has tuned (including two previous vehicles that this exact same motor has been in). He normally tunes via the IFR and PE tables instead of dialing in the MAF/VE tables.

He is considered one of the best tuners in the area and I have had horrible luck with the other tuners in the area also. I don't agree with the way he tunes, but it has always worked on every other vehicle I have brought to him.

I'll bring it up to him next time I talk to him and see if he can dial the VE/MAF tables in. At this point in time, I'm considering driving out of state to see another tuner.