Cold start problems on '78 280Z

[nkgreen]

When my engine is cold I have to usually floor it before I crank and keep throttling it for a minute or two before the engine will run. Once it gets warmed up, it's runs and idles no problem.

I'm thinking it's the cold start valve or thermotime switch, is there anything else I need to look at?

[sblake01]

Those are the first two things I'd look at. BTW, flooring a vehicle with EFI before cranking does nothing.....

[nkgreen]

Those are the first two things I'd look at. BTW, flooring a vehicle with EFI before cranking does nothing.....

Ahh, I mean I just have to be on the gas hard nearly as soon as it starts up.

From what I understand, the thermotimer changes resistance as the engine heats up, and that opens the CSV, injecting fuel. Also looks like the water temp sensor could be the problem.

A question about the CSV/thermotimer though, is it based more on relative engine temp or weather temperature? The service manual says,

It causes fuel to be injected into the intake manifold independently of the injector operation so that the engine can be cranked smoothly during cold weather.

It's definitely not cold here, and probably 110 degrees in my garage.

[sblake01]

I doubt that the water temp sensor would be the problem. When they go bad, it's usually the opposite-run fine cold; bad warm. The thermotime switch operated based on engine (coolant) temperature.

[Zed Head]

When my engine is cold I have to usually floor it before I crank and keep throttling it for a minute or two before the engine will run. Once it gets warmed up, it's runs and idles no problem.

I'm thinking it's the cold start valve or thermotime switch, is there anything else I need to look at?

If your water temperature sensor, or the power wire to it, was shorted, the ECU would see a fully heated engine, all the time. I've never seen anyone describe it but that might be a possibility (assuming the short doesn't fry the ECU). You can check what the ECU is seeing at the ECU connection in the cabin. You should see somewhere between 1 and 3 k-ohms between pin 13 and ground (according to pages EF-22 and 53). If you get an open circuit, then your engine is showing as "very hot" to the ECU.

I think that the CSV only opens when the key is turned to Start (cranking the engine). So once the engine starts it should not be in play, unless it was leaking.

[sblake01]

But, on the other hand, if the temp sensor had a bad connection or was non functional, the ECU would see a cold engine, all the time which I've seen and even experienced on my own vehicles. That's what I described in my last post and why I don't think you have a temp sensor related problem. The CSV only opens when the temperature is low enough and then only for a maximum of 9 seconds (I believe) which is how long it takes for the coil in the thermotime switch, which gets its signal from the starting signal, to heat up and break contact.

Edited July 20, 2010 by sblake01

[Zed Head]

I agree. I was just pointing out a far-fetched possibility that fit the symptoms, of "won't idle until it's warm".

I have never seen a description of a shorted water temperature sensor or wires, or its symptoms, which is kind of surprising considering the location of the sensor and all of the bending and abrasion the wires can see over 30+ years. But I've only been reading the forums for less than a year.

[sblake01]

You might want to hook up a fuel pressure guage between the outlet of the fuel filter and the fuel rail. If the pressure is bleeding down between starts that could make it difficult to start is completely cold.