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