The engine electrical in these cars runs off magic and fairy dust, it scares me

[ShiRen]

I don't really have any problems with the electrical, but I am a bit scared of moving forward with the build because I have no plans on messing with the systems that work for what I need them to do, those just happen to bee the last few remaining components and I have no idea why they still work. This is mainly just a discussion to shed some light on these if anyone knows how or why they work on a stripped engine, its hard to dig through a 1000 page manual to figure it out. To preface, my engine is a completely stripped, carbureted engine, no OBD, stock carb. I have no black box or any of the original engine management hardware, no vacuum rats nest. At least, if the og black box fails, my car is a testament to how little is required to keep it running.

I will go over these systems in order of severity, literally everything that is plugged into my engine still because there is not much.

• Reverse lights

I am pretty sure there is noting fancy here, just a switch in the trans. If your car has 12v it should work.

• Ignition

Surprisingly, the ignition is of very little concern to me. As far as I can tell if your ignition tumbler is good and you have 12v then there should be no issue sending 12v to the distributor. The only problematic part here is the ignitor. You can still wire up an MSD box here like I did.

• Oil pressure sensor

I think this is the sensor threaded into the top of the oil filter housing. I think it should work no problem, I only put it 3rd because I don't think it should be relied on, it would be best to install a mechanical gauge. The dummy light comes on for a second after a cold start though, so I think it works. There may actually be a buzzer to go along with it, but I have never heard it.

• Fuel pump

The stock fuel pump is ran on a pulse signal from the tachometer in the distributor, there is a relay that sends power to the pump from the tach. It is a bit strange and I do not like it. I have only kept it this way to prevent flooding. I think relay failures are the biggest problem overall here. It might take some tuning, but with a new low pressure fuel pump and a low pressure fuel pressure regulator I think the relay can be bypassed.

• Mixture cutoff solenoid

For those of us still on the stock carb, we have a solenoid on the back of the carb that opens when the ignition is turned on. If it is unplugged the car dies (at idle). Its original function, with the black box, was to shut off above a certain rpm, temperature, and speed. Its hard to tell if it is still doing that when the only way to find out would be to remove it from the carb and visually check it under those conditions, or wire up an elaborate test light and go for a drive. It is hard to say if the orifice it blocks has gas or air running through it, but my guess is gas. The orifice is somewhat of an equivalent to a pilot jet and the screw that controls it is the small one on the back, right at the base of the throttle plates. I run almost full lean under decel, so I have to assure that is solenoid is doing something and that if it was not working it would cause some performance issues like dying on low idle or backfires (with flames!) on decel. Replace the carb with something else and you don't have to worry about it.
Edit: Forgot to mention it will shut when the car is turned off, so mixture can't be pulled from the orifice. Might be a cause of dieseling, but in my experience sometimes these cars don't need an excuse to diesel, especially on 87.

• Cooling fans

This is a strange one. Not actually integral to the car running, but your fans need to run periodically if you are sitting at an idle, it would be bad if they didn't and you did not know it. Coolant no longer runs through my intake and I just installed an aftermarket radiator from an Integra. As far as I know, the only probes in the cooling system are in the intake for the temp gauge, the one in the lower tank of the radiator, and maybe one on the back of the block, I don't remember, I only see a picture of it in the manual. I do not have the probe in the lower tank of the rad anymore, but I think my fans still kick on, I probably need to pay more attention, it is hard to hear my flexalite fans running. The probe from the intake is not required for anything beside the gauge and its a pos, I have mine in my lower rad hose and after several minutes of sitting it does rise from 0 to about 3/8 the way up, so I can monitor that. The A/C button will turn the fans on and with the basic climate control package they will run all the time, so that is there, no need to install a manual fan switch if you have A/C. The temp switch can be replaced with a simple aftermarket solution, but being a Honda, the engine severely lacks locations to add anything to the coolant system and sometimes they are strange threads like BSPT.

• The "ECU"

There is a box under the drivers seat that the manual calls, and picture this with big air quotes, the emissions control unit. The carb engines actually have some sort of computer control. I have no idea what it does, the manual glosses over it from what I have seen, and I would like to unplug it at some point just to see if anything stops working. Maybe it will mess with the mixture cutoff solenoid if I unplug it who knows. The only reason I have not done it yet is I loath the thought of how much cigarette dust I will have to vacuum from under the seats.

In the end, I think everything is fixable, the carb engines are extremely dumb and my concern stems from that because it should have almost no idea what is going on. The FI cars have their own set of electrical issues, but they are actually computer controlled and it makes a bit more sense in a way.

[ShiRen]

So, I have a bit to add to this I guess.

The cooling fans are driven off a sensor in the bottom of the rad, at least in an 87 DX there is no sensor on the back of the block and I know the sensor is in the t-stat housing for EFI cars. So yeah, I currently have no way of running mine, I just turn on the AC when I see the temp gauge rise, but my gauge reads low.

The emissions control unit does run the mixture cutoff solenoid. It may control other things like the fuel pump, but my car died immediately due to the jet closing, same as if I unplug the solenoid, it did not run until the float bowl was empty. However, the right plug does nothing that I can tell with a full vacuum delete.

[Dr_Snooz]

You sure the mixture cutoff solenoid isn't there to stop the car from dieseling when you turn the key off?

[ShiRen]

You sure the mixture cutoff solenoid isn't there to stop the car from dieseling when you turn the key off?

Yes it does, but as far as I can tell from the manual it shuts off above idle too. I was not sure it functioned whatsoever on my car until I unplugged it. But yeah, it closes when the emissions control unit powers down via switched ignition, so no pilot mixture as the engine is shutting down. I will add that.

[ShiRen]

I've decided to just include some general information in this thread... Weird title, but I'm trying to dissect it.

Distributors

These cars come with 2 distributors, one made by ToyoDenso (TEC) and another by Hitachi. The TEC seems to be the more common, there is a good rebuild thread here: https://www.3geez.com/forum/3geez-ac...light=lazy+man The Hitachi is a bit more modern unit and parts are much cheaper, it has an igniter integrated into the pickup coil instead of a separate unit like the TEC. For comparison, current Rockauto prices on the Hitachi pickup is $12, the igniter and pickup for the TEC is $68 and $25 respectively. The internal unit of the Hitachi is likely to run cooler and is never exposed to the elements, however I can not say anything about the reliability at this time, but the TEC has failed on many, including me.
The way these distributors work is very similar to a points style ignition. There is a 4 sided reluctor pulsing the pickup coil sending signal to the igniter, which is basically just a transistor, the igniter outputs a 12v waveform to charge and collapses the ignition coil very similar in the way that points arc every time a cam lobe opens and closes the contacts when a piston is at TDC.
There are 3 wires, a black ground for the radio condenser, a black/yellow for the coil positive, and blue for the coil negative. On the stock coil you may notice there are 2 plugs with the same colors, these are separated for ease of connectivity, but the same colors are joined together internally, on aftermarket coils and MSD ignition these can be joined together. The blue wire is also used to drive the tachometer, so in the case of removing the stock ignition and replacing it with something like a Megajolt, connecting your tach signal to this wire will give you a tach reading and restore operation to the stock fuel pump relay.

[carotman]

I had a problem with the fuel cutoff solenoid. The "ECU" stopped sending power to the solenoid for a reason I wasn't able to pin point. I finally used a temporary fix that was simply to connect it to a 12V source when the car was running. This way, the solenoid remained open and I was able to have a proper idle speed. When I shut off the ignition switch, the solenoid closed and the car wouldn't diesel.

Since the diagnosis procedure didn't reveal anything, that "fix" is still there, though I haven't started or driven the car for years.

I might do so soon enough. I wonder if it will still start after sitting for so long.