Captain Obvious

The 58 Ohms makes perfect sense. Thats the resistance of the heating element in the thermotime. In fact, pretty much everything you have tested and posted makes sense with the exception of the grounding 45 thing, and the swapping the wires thing. One last thing before I throw in the towel and just revel in your success... Do the pins on your thermotime line up like the picture on EF-32 in the 78 manual?

Don't know if this is old news or not, but I've turned up a mistake in the pre-78 service manuals pertaining to the resistance readings from the air and water temperature sensors (Pages EF-52+53 for 1976 and Pages EF-53+54 for 1977). Similar mistakes are in the FI "Bible" as well. Apparently there was some difficulty translating from degreesC to degreesF. Add a language translation to that, as well as a positive to negative conversion complication, and you've got issues. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ To start, here's the 78 air temp sensor chart as a reference. The math works out as do the thermister resistances: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ But in the previous years, the temp vs resistance charts are wrong. Here's air temp: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ And here's the water temp sensor on the next page: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Similar mistakes in the Fuel Injection "Bible". Here's the air temp sensor test: ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ And here's the water temp sensor test:

45 should be 12V to engine block when the key is in START and 0V to engine block at all other times. You should get these same readings regardless of whether the connector is clipped on the thermotime or not. And 46?... 46 is a little more complicated, but if you have the thermotime unplugged and the CSV connected, then you should see the exact same thing on 46 as you see on 45 - 12V at START and 0V at all other times. If you have both the thermotime and CSV unplugged at the same time, 46 should be always 0V regardless of key position. It makes no sense to me that it would work if you ground 45 and smoke if you ground 46... Are you sure you're not mirroring the numbers when you spin the connector around?

Haha! You must be in Marketing or Sales. :laugh: Seriously though... There's no way I would guarantee the performance of the ECU would be dead-nuts identical today as it was the day it left the plant almost forty years ago. No way. Things are better than vacuum tubes and oil filled paper caps, but we haven't figured out how to get all the long term drift out of everything yet.

Yeah, the vehicles voltage will mess with continuity and resistance measurements. You can not trust that tone to provide accurate results on anything that's powered. If you start adding voltage to a resistance or continuity measurement, seemingly unpredictable things can happen. So about that short to ground... Is this what made it work? Because I still can't explain it: Depending on the quality of the ignition switch and all the connectors between the battery and the thermotime connector, you may have gathered up enough resistance along the way such it wouldn't draw enough current to actually smoke, but there's no way putting a ground there as drawn should make the system work as intended. I'm an hour away....

Yeah, that mess is an indication of how well the anti-drainback feature is working. Here's a couple of my dissected filters. Old style AC Delco before they switched to the plastic filter support cage: (Notice the little split where the filter media was never connected properly at the factory.) Typical Purolator. Been this way for at least ten years:

And about that shorting to ground to get the CSV to spray with key in START... Is this where you connected to ground? Because if this is what you really did, then something should have smoked. If it didn't, I have no explanation other than someone has messed with the system somehow.

The CSV should be polarity and connection independent. I haven't taken one apart, but I expect it doesn't matter which connection goes to which prong. You could probably swap the two wires right there at the CSV and I don't think the system would care. The thermotime on the other hand is most definitely connection specific. I clipped the 1978 cold start stuff out of the wiring diagram and added a few notes: The connector pin on the tt which gets 12V on START should be 45 The connector pin on the tt which is connected to ground when the tt is cold should be 46. I'm not sure what you mean when you say "loss of ground at both 45 and 46". Without more specific measurement definitions... Are you measuring voltage, or resistance? The reason I ask is because you can measure 0V between two things, but that won't necessarily tell you if they are connected together or not.

Sounds like the CSV and the thermotime are both functional, but the rest of the stuff has me confused as well. I know you said it looks like all the original wiring, but maybe someone swapped something and then wrapped it back up again? Give me a little bit... I'm gonna make a picture.

Depends on the design of the oil passages and the position of the oil filter. I guess your truck likes the anti-drainback. On a different, but related note... I've had some filters that DO include that anti-drainback feature where the valve does not work. You can tell when you take the filter off the car that the inner portion has already drained out past the valve. It's not supposed to, but I've found that they sometimes do anyway. Maybe one in twenty?

"Oh, that's very different.... Never mind."

I had mine completely apart a few months ago, but I don't remember. I would assume it only goes together one way.

The ECU output stage uses open collector Darlington transistor drivers to pull the low side of the injectors toward ground in order to open them. That open collector style of driver is sometimes referred to as "floating" when it's OFF. Ummm... I'm assuming that has absolutely nothing to do with what you're talking about? If that's the case, then I've never heard of it. Give me just a little hint (PM if you don't want to influence the results from others) and I'll see if it rings any other bells?

My pleasure. And if all else fails and you're ready to throw in the towel, I'm about an hour south of you. Once you get over the cold start hump, I'm sure your car would make the drive.

Nothing jumps out at me as being out of the ordinary. I was half expecting to see the #1 wire on the rear side of the cap back by the carbs. I can't really explain how yours works fine with the small half moon to the rear when my car (and all the service manuals) say to put the small half moon to the front, but whatever works. Only other thought I have is that what you were thinking was TDC on #1 was actually TDC for #6. I remember you said that you pulled the valve cover to verify that you were, in fact, on TDC#1, so other than that, I got nuthin'. Anyway, like I said, whatever works. If it's running fine now, then I say don't mess with success, right? Unless someone else has a theory... Great pics by the way.

Yeah, a clear head is a requirement. Let us know what you find when you get back to it. But in the meantime, something to think about: You said CSV above, but I'm guessing you meant thermotime? You verified that the CSV is fine when you grounded 46 and it sprayed when you hit START. I'm thinking that the thermotime or a wiring issue may still be suspect, but I believe you have verified that the CSV good, right? The thermotime has two connections to it: One of them should go to +12 in START (just like one of the CSV connections). The other will be (depending on temperature) either a no connect, or a connection to the body of the thermotime. The body of the device is supposed to connect to ground through the thermostat housing. So, to answer your question... Yes, when the thermotime switches to ground, it grounds connection 46 through the mounting threads where it screws into the thermostat housing. It does not make a ground connection using another wire in the harness. It GROUNDS one of the wires in the harness.

:paranoid:

What an annoying, wretched, painful, dangerous, stressful pain in the arse. Sure glad that's over. Have you cleaned up the bore in the bottom of the strut knuckles yet so you can see what it's supposed to feel like? A little sandpaper wrapped around a gun swab chucked up in a drill does wonders.

Pump never ran? Any idea what was the threshold temp for the ZX fan switch? What other supporting data might I be able to help with? I won't be in any position to further investigate until it warms up, but once that happens, I'd be glad to do what I can.

The ever persistant 280 hot restart issue..There are lots of threads about it and lots of things people have tried to fix it. Here's mine... I put a 10K resistor across the contacts of a normally closed push button switch and then put that switch in series with the water temperature sensor. With the switch not pushed, the resistor is shorted out by the switch and it's as though it's not there at all. However when you push the button, the switch opens, and now you've now go a 10K resistor in series with the water temp sensor. The resistor adds to the water temp sensor, and presto... Your ECU thinks your engine is very, very cold and supplies the "appropriate" amount of fuel to start a frigid engine. Worked so well for me that I even disconnected my cold start valve. I just push my "electronic choke" button. Supporting info? Here's resistance measurements I took last fall from my air and water temperature sensors after shutting down my motor. All measurements are in Ohms. 0 minutes after shutdown: W=250, A=1900 2 minutes after shutdown: W=226, A=1640 4 minutes after shutdown: W=231, A=1530 6 minutes after shutdown: W=245, A=1450 8 minutes after shutdown: W=268, W=1350 Some conclusions? a) The temperatures of both sensors goes up after the motor has been shut off. No surprise there. The water temperature seems to crest somewhere between 4 and 5 minutes after shutdown. c) The air temperature sensor temperature is still rising even after eight minutes of shutdown. My theory, which is mine, is that the ECU is seeing the temp sensors and injecting a very small amount of fuel because it thinks that's all the engine needs. On edit - Forgot to mention... This coming summer, my plan is to refine the system a little and use a relay instead of a push button switch. Wire it such that when the key is in "START", the additional resistor will be inserted in series, but once the key moves to "RUN" the resistor would be shorted out and the WTS readings would be normal. That way I won't have to push the "choke" button. It will all be automatic.

I hope the OP comes back after looking into it some more. (I hope that all our chatter hasn't scared him off! )

Not buying it. I just took a look at my ECU notes, and pin #21 is not populated. The ECU has absolutely no idea what's going on with the thermotime or the CSV or pin 21. There are two "power" signals into the ECU. Pin 10 which is hot in "RUN" and "START", and pin 4 which is hot in "START" only. We're getting a little off topic here, but here's my full read on what happens when starting the engine. All engines need a richer mixture in order to start, "irrespective of the cooling water temperature". They use pin 4 to tell the ECU that the engine is attempting to be started, and the ECU responds by injecting more fuel than would normally be required based on the current AFM, WTS, ATS, and TPS signal inputs. That's the phase "Start Enrichment" referenced in the pictures and text you posted. Since this signal to pin 4 will be present irrespective of the cooling water temperature, it will cause the ECU too add some enrichment even if the engine is hot enough that the thermotime and CSV will not operate. After the engine starts and the key is released from "START" back to "RUN", the 12V on pin 4 goes away, but the ECU continues to hold the injector pulse widths longer than would normally be required based on the current AFM, WTS, ATS, and TPS signal inputs. This is the phase "After Start Enrichment" referenced in the pictures and text you posted. This "After Start" phase gradually decreases from the time the key is moved off "START" until this enrichment is completely gone. At that time the injector pulse widths are based solely on the AFM, WTS, ATS, and TPS signal inputs.| I haven't traced the signal, but I would assume there is a simple R-C circuit on pin 4 that performs this gradual decrease feature. As for pin 10, it's the power to run the ECU. That's where it get's the energy to operate.

And even after all that typing I did earlier (certainly too much), I didn't address this issue... If you did in fact connect the thermotime 45 wire to ground and then hit START, something should have gone up in smoke. I suspect that you grounded 46, not 45. One small digit. Big functional difference. And if in fact that's what you did, it points to a problem with the thermotime switch. I know you just replaced it, but if the CSV opens on START with 46 grounded, then the problem is on the ground side (thermotime side) somewhere.

I don't believe so. I suspect the pin you are thinking of is pin 4 which goes hot in START. That would be the signal to the ECU of how long ago the engine was started. And The ECU already knows when the engine is cold due to the water temp sensor. I'm no expert, but that's my read.

Wade's info is from a 1980 ZX, not a 78, and while the concepts of the cold start system are the same, I wouldn't assume that the systems are identical. For example, things that caught my eye in his thread... a) He drew in a relay between the ignition switch "START" signal and the cold start system. You don't have that relay. You're "START" signal comes straight from the ignition switch. No relay. There might be a relay on the ZX, but you don't have one in that location on your 78. He referenced wire colors in his text that may or may not apply to you. Looking at the 78 diagrams, seems all the cold start wiring is green or black. Both sides of your thermotime sw are black and everything else is green including both sides of your CSV. The point is not to get hung up on wire colors like the yellow/white that are referenced in Wade's ZX thread. You don't have a yellow/white. So while the system concepts are the same, I'm not sure you can count on the specific details. You have a yellow/black wire coming off the back of the ignition switch that goes hot in "START". That wire goes to a bunch of things including the starter and the fuel pump relay. It also goes to a connector at which point it changes color and becomes G-4 (green number four) in the EFI system. Once that wire gets into the EFI system, it splices a few times after which, G-4, G-45, G-47, and B-45 (black number 45) are all connected together. Simply put - When you turn the key to START, you should have 12 volts on G-4, G-45, B-45, and G-47. G-47 goes to one side of the CSV and should have 12 volts when cranking. B-45 goes to one side of the thermotime and should also have 12 volts when cranking. The other side of the thermotime is B-46 which connects to G-46 and G-21 (the mystery connection to the ECU). This set of connections (B-46, G-46, and G-21) will be connected to ground when the thermotime is cold and becomes a no connect once the thermotime has warmed up and opened. This ground connection is made through the thermotime body where it is screwed into the engine. Operation goes like this: Key in START - 12 volts connects through the ignition switch to one side of the CSV (G-47) and the heating element side of the thermotime (B-45). If the thermotime is cold and it's internal switch is closed, it connects the other side of the CSV (G-21) to ground. If the thermotime is warm and it's internal switch is open, the other side of the CSV is connected to nothing, and the CSV will not open. So, about that pin 21? Why does the thermotime switch feed back to the ECU? I got two possibilities. a) First is what Wayne mentioned in his thread... That Bosch wanted the ability for the ECU to activate the CSV instead of (or in addition to) a thermotime switch. If they would switch pin 21 to ground inside the ECU, it would activate the CSV while cranking. I don't remember what, if anything, that pin is connected to inside the ECU, but it may have been or a future enhancement. Second theory is that it is simply a test point for being able to check the function of the thermotime switch. Seems Datsun wants you to do all of the diagnostic testing right there at the big ECU connector, and they provided that wire just to allow you to have the ability to measure the thermotime switch function. Without that connection, you would have no insight into the cold start system from the ECU connector. Remember, I wasn't there when they designed the thing, but those are my guesses.