Originally Posted by
MeentSS02
These PCMs are temperamental - you need to turn the key on and let it sit for about 60 seconds before trying to connect to do anything. Even then, sometimes you have to connect a couple of times (especially with the scanner) before it will finally function properly.
As for what you have, there are 4 options (and I think you've already ruled out one of them):
1. OEM PCM with the stock tune
2. OEM PCM with HPTuners
3. Mopar PCM
4. Mopar PCM w/ Arrow reflash
Since you couldn't read out the PCM, you likely don't have #2 (stock PCM with HPTuners). Since the car has headers, you also likely don't have #1 - most Gen 4 (2008-2010) Vipers running headers with the stock PCM will throw codes. If the car runs fine and doesn't throw codes, they likely did something with the O2 sensors (like anti-foulers).
Most Gen 4 guys went with the Mopar PCM when they added headers. There are some tell-tale signs that you are running this, including a bump in idle RPM from 700 (stock) to 750, and a bump in the rev limiter from 6,400 to 6,500 RPMs. The most noticeable difference will be the behavior on decel - when you let off the gas, you should hear no exhaust burble/popping at all. This was disabled, and is unique to the Mopar PCM.
Some guys with the Mopar PCM had their PCMs reflashed by Arrow Racing - this did a couple things in the performance category, including raising the rev limit to 6,600 RPMs. The most noticeable difference with this configuration is also the behavior on decel, but for a very different reason - when you let off the gas under 2,000 RPMs or so, you should hear some very loud popping on decel. There should also be a very noticeable increase in throttle response - with the stock PCM, pushing the gas pedal for the first half inch or so does little to nothing. This was supposed to have been eliminated with the Arrow reflash, but I've never been able to verify that in person.
Bottom line: have the owner go for a drive, and note the behavior on decel. If it doesn't pop, you likely have the Mopar PCM. If it pops ridiculously loud, you likely have the Mopar PCM with the Arrow reflash. Both PCMs eliminate the skip-shift feature as well, although you could do the same thing by installing a resistor in the wiring harness going into the transmission.
If you have the Mopar PCM (with or without the Arrow reflash) and you choose to overwrite the calibration, you'll be back to a stock calibration, and you'll have to go from there. There's no reversing it once done, so keep that in mind. It wouldn't be too hard to recreate, but it also won't be a carbon copy.