Datalogging with MHD: channels, pulls, and sharing
MHD turns your phone into a gauge cluster and a recorder. Here's what to log, how to capture a pull worth sending, and what we do with the file.
The flash is the setup; the datalog is the conversation. MHD's Monitor license turns the same phone that flashed the car into a gauge cluster and a recorder, and the file it produces is the raw material for every tune revision we ship. This guide is the capturing side — for how to read what comes out, start with our datalog-reading guide.
The Monitor tab
- Up to **8 live gauges** on screen while a recording runs underneath.
- Logging writes a **CSV with up to ~30 parameters** — far deeper than a generic OBD app, because MHD speaks the DME's native channels, not generic PID translations.
- **Auto-logging** can start recording on a pedal-position threshold, so the pull always gets caught.
- Per-parameter **min/max alerts** with an audible beep — set a timing-correction or fuel-pressure alarm once and the phone nags you before a problem becomes a repair.
The channels that matter
MHD's channel set spans 50+ parameters across platforms. The core, mapped to the four-trace story in our reading-your-datalog guide:
| Channel | What it tells you |
|---|---|
| Boost + boost target | Requested vs. actual — the gap is where problems announce themselves |
| Lambda / AFR per bank | Fueling reality, bank by bank |
| Ignition timing per cylinder + corrections | Knock behavior, cylinder by cylinder |
| WGDC (base / corrected / final) | The effort behind the boost — see the WGDC reference |
| LPFP (low-pressure fuel) + HPFP / rail pressure | The fuel system's two halves, each its own failure mode |
| IAT (intake air temp) | Heat soak and intercooler honesty |
| Ethanol content (flex setups) | What's actually in the tank |
| Oil temp / pressure, coolant, trans temp | The supporting cast — track days care |
Newer DMEs add transmission channels — clutch states, solenoid currents, converter slip on the Gen2 B58 and S58 8HP — logged in parallel with the engine.
Capturing a pull worth sending
A log is only as good as the pull inside it. The protocol we ask for (and MHD's own support asks the same):
- Car fully warm — oil temp in its normal operating band, not just coolant.
- Find safe, legal space; DSC **fully off** (a stability event mid-poll corrupts the pull).
- Stabilize around **2000 rpm** in 3rd (6/7MT) or 4th (8AT).
- **Wide-open throttle to redline**, then hold for 2–3 seconds after shift before you lift fully.
- One clean pull beats five messy ones. Let the car cool between runs if you're stacking pulls.
The default channel set, PSI (not BAR), auto-logging on — that combination travels well between every tuner who'll ever look at it.
Getting the log off the phone
Logs are CSVs on the device. MHD's built-in viewer (Monitor → Graph a Log) pans, zooms, and toggles parameters before you ever send anything. From there: email the file to yourself, or upload to a log-hosting service — SpoolStreet for a permanent shareable link, DataZap for side-by-side comparison graphs. When you're our customer, the revision loop takes it from there: upload through your account, the platform verifies the VIN, and the log becomes the next revision's evidence.
What we do with it
Every revision we ship is built against what the car actually did — that's the whole revision loop. The four-trace story (RPM, boost, AFR, WGDC) plus fuel pressures is what separates "feels fast" from "is healthy," and MHD's logging makes capturing it a button press. Flash, drive, log, upload — the loop closes from your driveway.
What gear should I datalog my pull in?
Third gear on a 6/7-speed manual, fourth on an 8-speed automatic — a gear long enough for the pull to breathe. Stabilize around 2000 rpm, DSC fully off, then wide-open throttle to redline and hold for a couple of seconds after.
How many parameters should I log with MHD?
MHD records up to about 30 channels to CSV, and the defaults already cover the core story. If you trim, keep the four that matter — boost, boost target, AFR per bank, timing corrections — plus WGDC and fuel pressures for anything fueling-related.