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HOWTO: LH2.4 Injector Driver Replacement

Replacing the injector driver on an LH2.4 ECU.


ecu_on_bench.jpg

If you accidentally use low-Z (low impedance) injectors without a resistor pack, the injector driver will supply too much current and subsequently cook itself. Symptoms of this are a car that won't run (or only runs briefly with the injectors disconnected) and a crankcase full of gasoline.

Tools needed:

Driver with T-10 Torx bit
Driver with T-20 Torx bit
Soldering Iron
Desoldering braid or solder sucker
Needle-nose pliers
Wire snips

Parts needed:

TIP-122 or equivalent in TO-220 package (try DigiKey)
Solder (I've used radio shack 60/40 .062 diameter with success)


Remove the case from the ECU.

clip_on.jpg

To gain access to the injector driver, remove the metal clip from the heatsinked power components.

insul_on.jpg

Remove the plastic insulator as well.

driver_marked.JPG

You should now be able to see the injector driver. It is the one closest to the main connector on the right-hand side (with the connector pointing down).

Remove the board from the case. There are three nylon standoffs in addition to the four torx screws holding everything in place. The nylon standoffs must have their retaining pin pressed out before they can be removed.

spacer_removal2.jpg spacer_removal.jpg

To remove the driver you must desolder the three pins holding it in place. Rotate through the pins with the soldering iron and braid, or with the solder sucker. While doing this, gradually remove the driver from the board.

I have found that it is easier to heat the pins of the old driver from above using a fine-tip soldering iron. Make sure that the joint is fully melted before you begin pulling the component from the board or you risk lifting a trace.

Once the faulty driver has been removed, throw it away! (Or, alternately, mix it up with your replacement and put it right back in... sigh.)

Next, make sure that the solder holes are clear and free of solder. The new driver should slide in easily, with minimal resistance.

Insert the replacement into the board. It helps to bend the middle pin slightly outward, matching the layout on the board. Ensure it is facing the correct direction (the same as the others). Push the replacement through until it is in line with the other transistors on the heatsink.

trim_leads.jpg

Flip the board over and solder the three pins, making sure solder flows into the holes and that no brdiges are formed. Once it has cooled, clip the spare leads from the driver.

That's it! Replace the board, install the plastic insulator and metal retaining clip over the new drivers and test it out. But make sure you have a resistor pack installed first!

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