DIY 4A-GE Smallport EFI Wiring Pt.4: Harness Done

After a few weeks of this..

.. took me a while to finish it, squeezing time between office work to solder, cut and measure the cables but finally the EFI harness is done. Here's the end result.

That noodle spread across my room is what will be seen on The Dog in a few weeks from now. It will be wrapped in spiral wrapping so as to keep it neat but first i have to make sure that it works. Not much to say about how the harness-making goes except you have to have lots of cables in different colors. I used about 25 different colors. You don't have to follow exactly the cable colors mentioned in the diagram but try to get as many colors as possible. It'll help you one day when you troubleshoot. Take your time and triple check every connection. I work on the harness only 2-3 hours per day at a very slow pace. Use heat shrink tubes, avoid electrical tapes at all cost. You will forget to insert the heat shrink tubes BEFORE soldering but try to keep that minimum.

Gee, what's to share about harness? Cable harnesses aren't exactly interesting to make a story about. Anyway, at least i can show you this modification i did.

See the two connectors on below right? The first one on the left is a cut i made on the engine Coolant Temp Sensor wire (CLT) so that i can insert a variable resistor. The purpose of this is to "fool" the ECU into thinking that the engine is colder than it actually is. If the ECU thinks that the engine is cold, it will control to injector to put more gas and advance the timing.. thus increasing the horsepower, claimed to improve off-idle and midrange RPM response. There are lots of sensor that can be modded this way like the Intake Air Temp (IAT) sensor but CLT has more weight for the injector pulse width calculation. The idea is taken from yotatech here.

Here's diagram which shows the relation between engine coolant temperature and CLT sensor readout.
See that at low temperatures, the CLT has higher resistance? Now what i did is insert a potentiometer or pot which will add to CLT's own resistance. This way, ECU will think that the CLT is reading lower temperatures. This is basically what i did.

It's better to use 500 ohm pot but i can't find one so i went with 1 kohm. This will make a slightly coarser control over the CLT manipulation but will do just fine.
Right now i have the connector jumpered but if i want to insert the pot, i just unplug the jumper cable and connect the pot.

The second connector, on the right, is a splice i did on the Oxygen sensor wire. This way i can add the Air/Fuel Ratio meter i have without damaging the cable.

Did the harness work? I can't say right now as the engine is not ready to run yet. Harness comes later when all parts like the fuel pump are installed properly. So for now, i can only hope for the best. Wish me luck!

Oh by the way, it would've taken me longer time to finish it if i didn't have an assistant to accompany me. Here's my lovely assistant slash girlfriend..

Cute pose.. LOL. That's what you call maximizing your resource. All limbs are used just to solder two wires together. I was surprised that my girlfriend could do such a neat soldering all by herself and all the soldering lesson she had was back in junior high!

It wasn't just me who was relieved to see that the harness has been completed. My girlfriend was as excited as well as she had been aching to clean the mess that is my room due to all the wire cutting, soldering and measuring i did. Here's the aftermath of all those things.

I used only around 50% of all the cables i bought and left with the cables shown above. I have no idea what will i do with those leftovers but considering that i only spent a third of the price i was charged if i let the workshop do the cabling instead, i really don't mind.