BD125-8 ZS190 swap and EFI conversion

[glavey]

Taking a break from stuff like a rats nest of a wiring harness and settings like crank trigger offset angle to doing something comparatively mindless like painting is a welcome reprieve. I took all of the angle brackets I used for the license plate holder and the exhaust hanger bracket outside (it happened to be a warmer-than-average day), ground them down to bare metal and primed, sealed, painted, and attempted to clear-coat. All of the paint I am using is left over from previous projects, and all of the cans were at least half-empty. I had enough primer and primer-sealer and EXACTLY enough black paint, but just a few spits of clear coat. I don't think any of these pieces will see any real abrasion except from being bolted/unbolted, so no real worry there.

Next I tackled getting the two holes drilled in the dash for the two newly found indicator lights. What a perfect job for a drill press! The previous day, I traced the outline of the white plastic light guide piece of the dash with all the indicator light holes. I then taped the outline to the front of the dash and lined it up as best I could. The drill worked as it should and gave me two very straight, smooth-ish holes where I needed them.

I wanted to keep the dash as water/weather-resistant as possible, so I needed to seal up the holes I just drilled with something that would let light pass through it. I would have liked silicone, but 1. it is too viscous to settle into having a flat surface and 2. it isn't completely clear, it's more like trying to look through a few mm of milk. I settled on epoxy; it flows well enough to have a smooth-enough surface and dried clear (but with lots of tiny bubbles). I put a piece of scotch tape over the top of the drilled holes on the front of the dash to keep the epoxy from leaking out, then flipped the dash over and filled each drilled hole to the point where the surface of the epoxy was flush with the plastic of the dash, and let it set for a day. You can clearly see the indicator light's color, although the "icons" in the dash are distorted. That doesn't really matter to me, I use the color and location of the lights for recognition; red light on the right side of the dash? temperature. Red light on the left side of the dash? engine is still warming up (or whatever condition I set for that light).

I attempted to make a engine block temperature sensor using one of the 10k thermistor and a ring terminal crimp (pictured). It did not work. I did successfully solder the ring terminal to the temp probe, but the probe short-circuited internally when I tested it afterward. I made another one that I jb-welded on. I'll let you know how it works once it dries.

I was trying to use the 10k thermistor instead of the 100k one that came with the aliexpress kit because when using the 100k one, the difference to the ECU between 60F and 100F is only 0.127 volts .With the 10k thermistor, the difference between 60F and 100F is 0.757 volts; greater resolution in the range we need it. The ECU can detect (I'm kinda guessing on the exact numbers) 0.005 volts change on the temperature input; each 0.005 v is one "step" of resolution. If there is only 0.127 volts between the numbers we gave earlier, the ECU only has 25 steps of resolution, or a resolution of (100-60)/25 = 1.6 degrees F per step. Whereas with the 10k thermistor, using the same 0.005 v step and 60-100 range, the ECU has 155 steps of resolution or 0.25 degrees F per step.

I'm still going to try and use the GM temperature sensors; they are much more robust than the quite-flimsy thermistors, but they are also MUCH bigger. I was intending to put one of the thermistors in the air filter to measure the IAT (intake air temperature), but there is just no way one of the GM temp sensors would work there. I asked on the megasquirt forum about remotely mounting the IAT sensor since I have essentially NO intake plenum or piping to speak of, it is literally air filter -> throttle body. I was told that remote mounting of the IAT sensor would work in my case (no under-hood area to trap heat and increase charge temperature; IAT essentially always equals ambient temp).

The place I have ear-marked for the IAT sensor is around about where I put the CDI when I had the aliexpress ECU installed. It shouldn't get heat soaked from the engine back there, and it will get some airflow over it when riding at speed. As for the engine/coolant temp sensor, I have three possible places in mind:

1. The same location the 100k thermistor is bolted to (look at my previous posts to see where I installed it). Problems with this location are I would have to drill out the threaded hole in the cylinder to a larger size to fit the tip of the temp sensor in, and then I would have to hold and secure the sensor there somehow. I really don't want to jb-weld anything to the engine. I could also make a ring terminal fit the sensor's tip and NOT SOLDER, but epoxy or jb-weld it on there. I would still have to secure it in place somehow; the sensor is too heavy to be left secured at only one point, especially on something as violently shaky as an engine. Pros are easy to access and replace, and reading the temperature of the cylinder, not the oil.

2. The oil channel access bolt next to the position mentioned in place 1. Problems with this location are having to thermally connect the temp sensor to the bolt, having to thread the tip of the temp sensor (I don't even know if there is enough meat on the tip of the sensor to be safely threaded), or having to find and buy multiple pipe thread adapters to go from the threads on the engine block to 3/8 NPT on the sensor, while having enough clearance for the tip of the sensor. Pros are easy (though not quick) access and replacement.

3. The spark plug hole. Make a CHT sensor with a ring terminal and put it between the cylinder and the spark plug. Problems with this location are, again lots o' vibration, having to jb-weld a ring terminal to a sensor, rendering it useless in any other situation, and lots of airflow over the sensor body while riding at speed, possibly cooling it below the temperature of the cylinder head. Pros are this would probably be the most accurate reading of the temperature we want, it can aid in tuning, and easy (though not quick) access and replacement.

I'm really not sure which location I'm gonna go with. Maybe a slight lean toward the current temp sensor location.

There were quite a few wires left over, unused coming from the ECU. Since I installed it (the ECU), I had a plan to wrap the unused wires together in a circle and tuck them behind the ECU. I tried to do this once by just stuffing the wires into the plastic wire loom sleeve in a circle, but that didn't work well. I had straighted the wires and tape them together about every 6-8 inches, then wound them on top on one another and taped them to each other, then finally putting the plastic sleeve over them. I seat does slightly press on the sleeve when installed and with a person sitting on it, but no where near enough to damage the wires inside.

I have been (and still am) wondering if the 125's and the 190's CDI is DC or AC. I can easily see that the 125's CDI got its power from the black switched +12v wire, but it is also comparatively smaller than most DC CDIs I have seen (from what I have read, DC CDIs need to be bigger because they need room for additional circuitry). It is only 1mm smaller than the 190's CDI. The 125's CDI has four wires/pins; trigger, ground, power, and output to coil. The 190's CDI only has one more ground pin. The wiring harness that came with the 190 would have the CDI getting AC power, and the 190 stator has a high voltage winding, the 125's stator (pictured) does not. At this point, since the 125 stator didn't have any HV windings, I am relatively certain the 125's CDI is DC (or at least works with DC). The 190's CDI... the wiring harness connections point to AC, but being the same size as the 125's CDI points to DC. I guess I'll have to try the 190 CDI on DC first (DC first because I am guessing that feeding 12 volts into something that usually needs 100+ won't hurt it, but doing the opposite will make the magic smoke escape). If it doesn't work on DC, then its on to AC. If that doesn't work, then I screwed something up.

I think I broke my cat.