LPG Map Analyzer ELM327

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What is LPG Map Analyzer?

In an LPG conversion, the gas ECU multiplies the petrol injection time by a factor from an RPM × petrol time (ms) map. If the map delivers too little or too much gas somewhere, the car’s own petrol ECU knows it best: it watches the mixture with the oxygen sensor and tries to close the gap with a fuel trim (STFT/LTFT).

LPG Map Analyzer reads these trims from the OBD port via an ELM327, collects them while you drive and tells you:

• which cell of the map needs correcting,
• whether to increase or decrease it,
• by how much, and how reliable that suggestion is.

It does not connect to the gas ECU and does not need your current map values. It only reads standard OBD data and never writes to the map — you apply the correction in your own LPG software.

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What you need

• A petrol car with OBD-II (practically any fuel-injected petrol car that reports STFT/LTFT fuel trims)
• An ELM327 adapter (Bluetooth or WiFi)
• An Android phone, tablet or head unit
• Your LPG software, to see the map axes and apply corrections

Which part of the map can be analysed?

Fuel trim is only meaningful in closed loop (oxygen sensor active). During full-throttle enrichment and engine braking (fuel cut) the petrol ECU does not watch the mixture. The app deliberately skips those moments: rather than producing a wrong suggestion, it gives none for that area.

Most everyday driving — and a large part of the map — is closed loop. Tuning the full-throttle area requires a wideband lambda (AFR gauge).

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First-time setup (once)

1. Settings → Map axis: enter the RPM columns and rows (petrol injection time, ms) of your LPG software’s map exactly, separated by spaces.
   500 1000 1500 2000 2500 3000 3500 4000 5000 5500 6000 6500
   2.00 2.50 3.00 3.50 4.50 6.00 8.00 10.00 12.00 14.00 16.00 18.00
2. Petrol injection time at idle (ms): enter the petrol time your LPG software shows at warm idle. Usually 2.5–3.0 ms; leave 2.75 if unsure.
3. Load signal: “MAP/MAF (physical)” is the default and recommended; the app uses MAF if the car has one, otherwise MAP. “Engine Load (PID 04)” is an alternative for cars where MAP/MAF cannot be read.
4. Connection: pair the Bluetooth adapter in the phone’s Bluetooth settings first, then tap Connect in the app and pick it. WiFi adapters usually use 192.168.0.10 : 35000.

How to log

1. Start the engine and tap Connect.
2. Make sure the fuel selection on the main screen is LPG.
3. Tap Start Logging and drive normally. The screen stays on while connected — put the phone in its holder and forget it.
4. No data is taken until the engine is warm (about 60 °C); this is normal.
5. Idling for a few seconds now and then (at traffic lights) is needed for calibration. Once the main screen shows “Calibration ready”, rows are mapped.

The status line on the main screen tells you what is happening: sampling, idle (calibration), transient, open loop, engine braking, engine cold, STFT at limit.

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Filling the map faster: variety, not mileage

The app only records moments where rpm and load stay steady for 2–3 seconds; a trim measured while opening or closing the throttle belongs to the previous operating point. Hours of constant motorway speed keep filling the same few cells. To fill faster:

• Hold the throttle steady for a few seconds in different gears and at different rpm,
• Cruise under load on gentle hills (this fills the middle rows),
• Idle now and then,
• Avoid hard throttle and sudden lift-offs — those moments are not recorded anyway.

Data accumulates across drives — you don’t have to finish in one go. Each reading is shared with the 4 nearest cells by distance, so neighbouring cells get data too.

Reading the results

The View Results screen has “List” and “Grid” views. The number in a grid cell is the measured deviation (%).

• ✓ NOT NEEDED: deviation within ±3%, leave it
• + INCREASE: ECU adds fuel, too little LPG
• − DECREASE: ECU removes fuel, too much LPG
• + Faded cell: low confidence, more data needed
• – No data: no steady driving in this area yet

Tap a cell to see the sample count, confidence and the suggested correction. The suggested correction is three quarters of the measured deviation (e.g. +6 for a +8 deviation), so you don’t overshoot.

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The correction cycle

1. Drive and log.
2. Review the results: high/medium confidence first, and regions of cells moving the same way.
3. Apply in your LPG software: enter the suggested correction in those cells and keep transitions to neighbours smooth.
4. Tap “I applied the corrections to the map” in the app. Old LPG data is cleared; idle calibration, calibration points and the petrol reference are kept.
5. If possible, reset the ECU adaptations (clearing fault codes is enough on most cars) — the long-term trim (LTFT) carries the old value for a while.
6. Drive again and repeat until deviations are within ±3%; 2–3 rounds are enough for most cars.

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Two optional features that improve accuracy

1) Calibration point (recommended for MAP-sensor cars)
When matching rows (ms) to live data, the app uses the idle value as its anchor. For a more precise result, with your LPG software open on a laptop:

• Hold the engine steady at a certain rpm (e.g. loaded cruise at 2000 and 3000 rpm),
• Tap “Add calibration point” on the main screen,
• Enter the petrol time (ms) your LPG software shows at that moment.

2–3 points at different loads away from idle are ideal. Points are listed in Settings and can be deleted.

2) Petrol reference
The car may already have a trim on petrol too (vacuum leak, aged sensor, etc.). To keep it out of the LPG map, log for a while on petrol: set the fuel selection on the main screen to Petrol (reference) and drive a few times. Suggestions are then based on the difference between LPG and petrol. Remember to switch back to LPG when the car changes over — the fuel in use cannot be read over OBD.

Frequently asked questions

Why do the top rows (full throttle) never fill?
That area is open loop; the ECU does not watch the mixture there, so the trim says nothing. The app deliberately leaves it out. You need a wideband lambda for that area.

Why do some cells still show “–”?
There has been no 2–3 second steady driving at that rpm/load point yet. Drive through that area with a steadier throttle.

Is data deleted when I change the map axis or settings?
No. Raw data is stored and recalculated with the current axis and settings every time. Only “Reset All Data” or “I applied the corrections” delete data.

I can’t connect.
Pair the adapter in the phone’s Bluetooth menu first, grant the “Nearby devices” permission and keep the ignition on. With some cheap clone adapters, especially on older (K-line) cars, the first connection can take a few seconds.

Values update slowly on screen.
The app automatically uses a fast query mode when the adapter supports it. Setting “Command delay” under Settings → ELM327 timing to 0 ms speeds things up a bit; switch back if you see problems. K-line cars are inherently slower.

Can I export the results?
Yes. Export CSV on the results screen sends the table by e-mail, WhatsApp or Drive.

Which languages?
Türkçe, English, Deutsch, Français, Русский — choose under Settings → Language.

Important

Web version of this guide (5 languages): www.mscsi.net/lpgmap
Download: Google Play — LPG Map Analyzer
Feel free to post your questions, suggestions and bug reports in this thread.