Hardware Mods for LH2.4 Monitoring and Logging with TunerPro
The factory LH2.4 ECUs and firmware include a simple serial port interface that can read the internal ECU RAM values. To use this interface, you need some hardware mods and a suitable USB-to-serial adapter for your PC. As a bonus, there's an unused ADC (analog-to-digital) pin on the LH2.4 ECUs that can be used for the AFR signal from a wideband oxygen sensor (WBO2).
With these mods, and a custom TunerPro .adx file, you can monitor and log basic ECU parameters in real time using TunerPro. The completed logs can be played back later within TunerPro, or exported to a .csv file that can then be viewed in MegaLogViewer, or similar apps. With a modified .xdf file, TunerPro supports real time table entry tracing using the logged values. Table tracing is also supported during log playback. See the previous posts for some example TunerPro screenshots.
This setup seems to be pushing the capabilities of TunerPro, but is much nicer and more useful than the limited Moates Ostrich address tracing capabilities. I especially like having the VSS vehicle speed sensor (aka MPH) included in the logs. It makes it much easier to match up the log sections to the drive session.
WBO2 Mods
To monitor the WBO2 AFR value, one resistor in the ECU needs to be changed and, for some ECUs, another resistor added. The WBO2 gauge can either be wired in using a newly added pin in the factory ECU wiring harness, or, since you're adding wires already, can be added as a separate wire coming out of the ECU box directly (no need to disassemble the 35-pin ECU harness-side connector to add a pin+wire).
The resistor(s) are on the bottom of the circuit board, so the board needs to be unscrewed from the housing and popped off the plastic standoffs. Be very careful popping the board off the standoffs. I think I bricked one of my ECUs by overly flexing the PCB, and possibly the ceramic hybrid, during removal.
The standoffs have a plastic retention pin within the center of the standoff. To remove these, push down firmly on the top of the standoff using the flat side of a flat blade screwdriver. The center pin should pop down slightly. From the other side, grab the pin by hand and pull it down the rest of the way. Repeat for all 3 standoffs. Next, use a toothpick to lightly oil the crack between the standoff and the PCB. The standoffs become overly stiff after 30 years, so a little oil helps with removal. Using needle nose pliers, squeeze the 2 sides of the standoff together while lifting up on the circuit board. Again, be careful not to twist the PCB too much. Repeat until all 3 standoffs are free. Re-installation is easy, just make sure the retention pins are fully down first.
There are 2 resistors used in the ADC2 circuit, R107 (866ohms gray-blue-blue-black-brown) is a strong pullup to +5volts, and R108 (14700 ohms brown-yellow-violet-red-brown) is a series resistor to the CPU ADC input pin. There are at least 2 different build variations used for the LH2.4 9xx series ECUs. In my stock '937 and '967 ECUs, both R107 and R108 were populated. In my '951 ECU, only R107 was populated.
R107 needs to be removed and replaced with a 100K resistor. This prevents the ADC2 input from floating when the WBO2 isn't connected. [side note: floating inputs are generally a bad hardware design practice, but can be OK with some chips. My '951 ECU did not have R107 installed, so it had a floating input from the factory, but I couldn't find anything in the CPU datasheet to suggest that this was OK. If you don't have a 100K resistor, and will always have the WBO2 connected, then R107 can be left empty.]
If R108 is not populated on your ECU, it needs to have a 10K resistor added to connect the WBO2 signal to the ECU pin. R108 was not populated on my '951 ECU, but was on the '937 and '967 ECUs.
Serial Port Mods
The CPU chip used in the LH2.4 ECUs includes a UART serial port, operating with 5volt signal levels. To connect this to your PC, there are 2 options:
1) wire the CPU 5volt Rx/Tx signals directly to an appropriate serial-to-USB converter module, or
2) wire the CPU 5volt Rx/Tx signals to a RS-232 converter chip wired to a DB9 connector, and then use a standard USB-to-DB9 adapter cable.
Option #2 - 5V Serial to RS232
I chose the 1st option because I had the parts in my closet, but I like the 2nd option better because it can be more robust. There are small RS-232 converter boards available that include the DB-9 connector (
link or search for "MAX3232 DB9").
If this can fit within the ECU box, it would be a clean setup, but I don't know if there's enough room for an external DB9 serial connector behind or on top of the ECU box. It might need an Amazon "90 degree DB9 cable" to fit.
There are also small RS-232 adapter boards without the DB9 connector that could be wired up inside the ECU box, with a small cable to an external DB-9 connector (
link or search for "MAX3232 converter"]. The cable for these can easily come out any side of the ECU box. I still like this better than option #1 because the direct to CPU connections are all kept within the ECU box. Only the converted RS232 signals go out of the box.
For option #2, you must use a FTDI (real or fake) USB-to-RS232 adapter cable (try Amazon "USB to RS232 DB9 serial cable FTDI", e.g.
link). Cables with other chips (Prolific, CH430, won't work).
Option #1 - 5V Serial Direct to USB
For option #1, you need a FTDI USB-to-serial adapter board. They're commonly available with either USB-C or Mini-USB connectors. Note, almost all of the "FTDI" boards on ebay use a fake FTDI chip, but the fake chips seem to work OK for this application (
link )
The adapter board needs to be modified slightly for direct wiring, and to change from USB-provided +5volt power to ECU-provided +5volt power. If USB-provided power is used, the USB adapter can back-power the whole ECU board through the Tx/Rx signals, which is bad for reliability. To modify the adapter, remove the 0ohm resistor by the top of the USB connector, remove the 2 sets of header pins, and direct jumper for +5volt Rx/Tx signal levels.
On the LH2.4 circuit board, the Rx trace going across the pads of B303 needs to cut in half. Use a sharp Xacto knife to cut the copper and dig a tiny trench in the board to break the trace, or you can use a Dremel tool with a small bit, but be careful to not damage anything nearby. Use an ohm meter to confirm the trace is fully cut.
There are 4 wires that go to the USB adapter board: +5volts, ground, Tx, Rx. I used some small stranded 24 gauge wire, and ran the wires through a hole in the heatsink as a strain relief. You can disassemble an Ethernet patch cable, or a fatter USB cable, to get some small gauge wire, but the insulation on those is pretty soft and tends to melt easily when soldering – you gotta' be quick. Or next time you're at the salvage yard, cut off the first ~3 feet of a modern ECU's wiring harness (bring a hacksaw blade holder).
1,2) The easiest place to pick up +5volt and ground is to connect to the ends of capacitor C505. See the green ground wire and red +5v VCC wire in the picture.
3) Rx Signal – there's a PCB via just above the left (CPU-side) pad of B303 that goes to the Rx pin on the CPU. I find it easier, and more robust, to solder in a bit of bare solid wire (aka scrap of resistor lead) into the via, then wire to that via stub instead of connecting to the bare B303 pad. See the yellow wire in the picture, which goes to Tx pin of module.
4) Tx Signal – there's a PCB via just below the bottom right corner of BS203 (near pin 10) that goes to the Tx pin on the CPU. Again, solder a bit of bare wire into the via and then wire to the stub. See the blue wire in the picture, which goes to Rx pin of module.
WBO2 – For the WBO2 signal, I found it easier to solder a wire onto pin 32 of the internal ECU connector instead of adding a new pin&wire on the harness-side 35pin connector. See the white wire the in picture.
Add a zip-tie around the wires by the heatsink to help as a strain relief from any tugging on the external cable/module. Add some shrink wrap around the wires, route them out of the ECU case and to the USB adapter module (hole in the back of the case not shown in the pictures). For protection, wrap the module and USB cable in electrical tape and/or big heat shrink or sleeving.
[continued in next post]
