Another Thermotime/Cold Start Valve Issue...Please help

[Captain Obvious]

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.

[Wade Nelson]

My 1980 280ZX developed a problem with extended cranking / complete no start at subfreezing temperatures. Of course it was intermittent, which has made diagnosis a real challenge. Nothing like diagnosis work in a subfreezing garage, eh? Tools sticking to your hand....unable to wear gloves and do fine work...

I eventually found, using a NOID light, that the main injectors sometimes are not firing while cranking at bitter cold temperatures.

I don't know what the cause is, I had to abandon the car to come take care of a sick parent. It should be a fairly simple diagnosis and repair, most likely, a fuel injection main relay failure / dirty contacts.

You might want to CONFIRM yo'ure getting main injection events since you report your problem is temperature related.

I knew it was fuel related because with a big blast of starting fluid she would start immediately no matter what the temperature. You might similarly confirm your problem is fuel, and not ignition related.

W

Edited February 23, 2013 by Wade Nelson

[Zed Head]

The pin 4 theory sounds more reasonable. Maybe pin 21 is an artifact of some idea that didn't pan out. If I had thought more I'd have realized that I already knew there was no pin 21 since I had compared a 76 ECU to a 78 ECU in the past. 76 has more pins than 78 but both work the same in my car. Same exact part numbers. Federal model.

My logic on the what the wiring diagram shows stands though, as far as CSV operation. The diagram shows the normally closed relay to power the CSV, opened either by the resistive heater or the heat of the engine. Both twisting the bimetal strip. That's all that really matters for figuring out how to make the CSV work. The CVS operation stands alone, it has power, a relay through the thermotime switch, grounding through the switch to the block. The wires to the ECU are for something else. You could erase the wires to the ECU and still have a circuit that works, with power supplied through the Start circuit on wire 47. 21 is power to the resistive heater in the TS.

Funny to spend so much time on something that I removed a month or two after buying my car. No problems starting even in low 30s weather. Maybe it's pin 4.

[Captain Obvious]

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

[RPM Resto & Custom]

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

I'm going to have to try and look at it again tomorrow. I had been fighting off a cold all week and it finally caught up to me yesterday. Spent the entire day in bed and all morning today. Have a family function this afternoon so hopefully I'll feel ok tomorrow and check it out more.

I believe you're right and I actually grounded 46 and got the injector to operate in the Start position. Do we really think it's possible for the new CSV to be no good? I remember testing it on friday for continuity to ground (the body of the switch) on both pins. When it was cold I had continuity on both pins and one lost continuity after warming up the switch in hot water. Wouldn't that indicate a good switch? For a system that only has 2 or 3 working parts it sure is confusing. When the thermotime switches to ground it does in fact only ground to the block and not some other wire in the harness right?

[Captain Obvious]

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:

I believe you're right and I actually grounded 46 and got the injector to operate in the Start position. Do we really think it's possible for the new CSV to be no good?

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.

[RPM Resto & Custom]

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.

You're correct I did in fact mean the thermotime and not the csv. I have to cut and buff the freshly painted rear hatch on it in the morning tomorrow and as soon as that's done I'll be focusing on this issue the rest of the afternoon if possible. I'll report back with that I find or don't find. Thanks for all of the help.

[Captain Obvious]

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.

[RPM Resto & Custom]

Ok so I spent the last 2 hours looking this issue over some more and have come out even more confused. Here is what I can tell you for certain. The CSV works since I can get it to spray fuel. And the new thermotime switch seems ok as well. When cold I get about 58ohms of resistance at Pin 45 and ground to the body of the sensor at Pin 45 and 46. If I put 12V to pin 45 I lose the ground connection to 46 after about 6 or 7 seconds and after a minute or so it'll come back...so the heating element and switching seem proper.

Now is where things start to get funky. Remember when I typed a few posts back that if I ground out 45 of the harness at the tt switch I would get fuel and someone said that would yield smoke and 46 would be the correct one to ground for the csv to fire? Well that made sense and I assumed I just remembered wrong. Turns out I'm right.....if I ground out the #45 wire that's when the injector fires. This same wire gets 12V when the ignition is in the Start position.....#46 shows no voltage while the harness is unplugged from the switch. So this being said....just for the hell of it I disconnected the bullet connectors that the tt switch harness leads to and I used jumper wires to criss cross them......sure enough the system seems to operate properly then. When cold the csv sprays for about 5-10 seconds before cutting out and will operate again after a minute or so of cooling down. This makes no sense however as the wiring looks completely untampered with. These are definitely the original bullet connectors and the harness plugs only fit one way onto both the thermotime and csv.

And the last thing I found which I don't think is right is this.....with everything hooked up properly if I probe the back side of the connector at the thermotime I have ground at both wires when cold. As soon as the key hits the Start position I lose ground at both of them....I don't understand why. Maybe this is the key to my entire situation? Shouldn't 45 still always have ground and 46 have ground until the thermotime heats up?

[Captain Obvious]

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.

[RPM Resto & Custom]

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.

Only if they somehow pulled the female connectors right out of the csv connector on the harness side and switched them. The 45 at the tt seems right as it's getting 12V at Start and the 46 doesn't. I'll look the harness over better tomorrow but I'm pretty certain it's original. Is there any way to determing which pin on the csv should get which wire?

I was hoping I was onto something with the loss of ground at both 45 and 46 of the tt as soon as I hit Start.....that sounds proper to you guys though?

[Zed Head]

. So this being said....just for the hell of it I disconnected the bullet connectors that the tt switch harness leads to and I used jumper wires to criss cross them......sure enough the system seems to operate properly then. When cold the csv sprays for about 5-10 seconds before cutting out and will operate again after a minute or so of cooling down. This makes no sense however as the wiring looks completely untampered with. These are definitely the original bullet connectors and the harness plugs only fit one way onto both the thermotime and csv.

Now you're past solving the problem and in to trying to figure out what Nissan or a PO did to the car. Like trying to figure out what Pin 21 does. You have a solution for the problem, you can call it solved. Then spend your extra time on exactly how those wires got crossed. Maybe it's a Monday car.