Project Cappuccino: Testing the Kei Sport USA PNP ECU
Suzuki Cappuccino ECU Cover Screws
Once on the bench, remove the four screws that secure the cover.
Suzuki Cappuccino ECU PCB Screws
Six screws secure the PCB to the bottom half of the case: one in each corner, and two for the high side driver heatsink.
Suzuki Cappuccino ECU PCB Detail
Goodness, this ECU is a fossil! The PCB is a single sided design (components only mounted on one side of the circuit board), whereas most modern ECU have components on both sides of the board. All of the components are through hole design whereas every modern ECU uses surface mounted components which are easier to robotically pick, place, and solder. Modern components are also much smaller in size and typically leadless. The heat sink is especially hilarious as it’s basically a block of cast aluminum with no fins. The fact the CPU requires no heat sinking shows how underpowered it is. Worst of all, this ECU uses leaded solder, a fact I can tell from the lack of conformal coating.

I’ll let you in on a little secret: the primary reason modern PCBs are conformal coated is to prevent dendritic growth between pins on fine pitch components and NOT for weatherproofing.  This is a consequence of modern recyclability regulations which prevent the use of leaded solder in automotive electronics.  Unleaded solder is mostly made of tin and copper, two metals that are notorious for ionic diffusion, especially in the presence of electrical charge.  This creates material growth between two pins, similar to the formations in caves, eventually creating a short circuit condition between adjacent pins.  My chemistry is really bad so I am probably explaining this wrong, but suffice it to say, lead free solders require conformal coating to prevent internal short circuits.  Lead is not a reactive metal so it does not require such coatings.  This is why our 30 year old PCB looks brand new despite being completely exposed to the interior elements of our car.  

Conformal coat can be used as a waterproofing agent, but the correct coating has to be used.  Most conformal coats are acrylic and therefore brittle when cured.  Micro cracks will eventually let moisture in and cause corrosion.  Certain components are also thermally incompatible with conformal coatings.  Non-acrylic coatings are more expensive and require longer cure times so most OEMs do not use them.  Instead they fully seal the ECU case.  This also protects the PCB from debris, salt, and other engine bay chemicals.

Suzuki Cappuccino OEM & PNP ECU Comparison
The Kei Sport USA ECU is designed to drop right back into the original case. The two screws for the old heat sink are no longer needed, but aside from that the installation is the reverse of the removal. With the two PCBs side by side you can really see how electrical design has changed over 20 years.  Once installed, we followed Kei Sport USA’s instructions for start up and checking sensor calibrations.


Leave a Reply

Your email address will not be published. Required fields are marked *