Cold start valve problem?

[spklaus]

Hello, gang. I have a 77 280z , efi, that bogs, sputters, and stalls after it's warmed up for about 10 minutes. I think the cold start valve isn't shutting off, but my repair manuals don't address troubleshooting this specific behavior. My understanding is that this could be caused by any number of things, from the water temp sensor or thermo-time switch, to the ECU, or even just a bad wire/connection somewhere. How do I go about testing the various components of that system, to find out for certain what the problem is?

[datsunaholic]

Easy way to test to see if the cold-start valve is getting left open is to start the car, then unplug the cold-start valve.

 

To check the temperature sensor, I was taught at one point to take the wires running to the temp sensor and unplug them (that makes the system think it's cold, otherwise it won't start very well) then as soon as it starts to warm up and get too rich, plug the 2 wires together (not the ones going to the sensor but the ones headed into the harness) which makes it act like it's warmed up. It's hard to describe without pictures, but in the wires leading to the 2 sensors there'll be a pair of bullet connectors about 1/3 the way back from the front of the engine, in the harness.

 

Hopefully you don't have my old '77. That's exactly the symptoms I had. All the time. In addition to a billion other EFI problems. But the sensor bypass usually made it run for a couple days between ECU failures. The ECUs are very sensitive to proper grounding, and because mine was stolen and recovered after being partially gutted the wires were a mess.

[spklaus]

Easy way to test to see if the cold-start valve is getting left open is to start the car, then unplug the cold-start valve.

 

To check the temperature sensor, I was taught at one point to take the wires running to the temp sensor and unplug them (that makes the system think it's cold, otherwise it won't start very well) then as soon as it starts to warm up and get too rich, plug the 2 wires together (not the ones going to the sensor but the ones headed into the harness) which makes it act like it's warmed up. It's hard to describe without pictures, but in the wires leading to the 2 sensors there'll be a pair of bullet connectors about 1/3 the way back from the front of the engine, in the harness.

 

Hopefully you don't have my old '77. That's exactly the symptoms I had. All the time. In addition to a billion other EFI problems. But the sensor bypass usually made it run for a couple days between ECU failures. The ECUs are very sensitive to proper grounding, and because mine was stolen and recovered after being partially gutted the wires were a mess.

 

Thanks, D. That's more information than I've been able to gleen in two weeks of research. Will give it a shot soon.