Switching from bypass 00 to tunes

[Power Hungry]

Originally Posted by cleatus12r

Normal operation.

The Hydra will not switch to "00" bypass mode without a key cycle. This means a change to "00" needs to be made, wait for the blink, then turn off the ignition. The next power-up will be in bypass. The chip WILL switch from bypass to any of the loaded calibrations without a key cycle...it stalls/stumbles because the calibration on the PCM does not match the calibrations on the chip. This is normal and nothing to worry about - just don't make a habit out of switching between "00" and other calibrations while the vehicle is running. If you must do that switch WITHOUT the engine running turn off the ignition and restart.

An unmolested (not updated by the dealer) VDH4 computer will have a calibration of TNAA5S8. If it's been updated, it's probably TNAA7S5.

You are currently running TNAA4S2, which is perfectly fine and what we normally recommend. However, if you'll notice, the first 5 characters of the calibration are not the same, particularly the 5th digit. The first five characters calibration indicate the Operating System build of the calibration with digits 6 and 7 reflecting the tuning revision. If the first 5 characters are not identical, then the calibrations have structural memory differences and therefore generally cannot be switched between them without causing a computer hiccup. Some calibrations have more changes and may experience more severe stumble or stall while other have fewer changes and may not experience any negative effects at all. It all just depends on the changes.

For all intents and purposes, there's really not any reason to go into [00] unless you need to perform some sort of diagnostics and want the tuning completely out of the way. Outside of that, just keep the Hydra in a tuned level and you shouldn't have any issues.

Take care and Happy New Year!

[deadeye1287]

Thanks to both of you for the quick response and verifying this for me! I absolutely love the chip. This is my first diesel, coming from primarily 350 SBs. I'll never go back! I admittedly didn't read the ECU in Hydraflash and went off the sticker. I'll check and see what is in there and switch to the TNAA5S8 or TNAA7S5. Appreciate it again!

[cleatus12r]

You won't find a myriad of calibrations for either of those. You have "the preferred" set loaded. Is there a reason you are switching to the bypass mode? Like Bill stated, unless you're performing specific diagnostics or troubleshooting there is no reason to run the PCM's flashed calibration. If you need a "stock" setting, flash the chip with the TNAA4S2 "0S" calibration and use it....it won't cause the hiccup.

Also running a calibration on the chip other than TNAA5S8 (provided your original VDH4 PCM hasn't been reflashed) will cause the same stall/stutter you're currently getting.

[deadeye1287]

Sorry, just got around to checking the PCM. PCM shows running TNAA5S8. I double checked and all my tunes are TNAA4S2. The question was prompted due to me coming across the issue when I was getting familiar with the chip. I wasn't doing any specific troubleshooting, just wondered how it operated switching on the fly vs key switched, etc. All is good. Thanks again!