YellowFever Posted February 19, 2008 Share Posted February 19, 2008 Last weekend I pulled the original N42/N42 engine out of my 1976 280Z (non-California). The car will be non-op for approximately 3 months while it is being painted and a replacement engine is built. While removing the engine the wire leads on one of the thermostat housing sensors broke off due to corrosion. The other 3 sensors ("thermal transmitter" for temp gauge, "water temperature sensor" for ECU, and "thermotime switch" for cold start valve) are all okay. I did a little research on the broken sensor and found that it is the "Water temperature switch". Further investigation shows that this switch is used to control the EGR valve... which my car doesn't have... since EGR was California only in 1976 280s. Would Datsun really have used this switch when a pipe plug would have worked just as well? Is there any other purpose for this sensor, or has it really been on my car for 32 years for absolutely no reason other than to plug a hole in the thermostat housing? Someone please correct me if I am wrong, but I am not going to replace this sensor since it appears to serve no purpose on a non EGR engine (the replacement engine will be non EGR as well). Quote Link to comment Share on other sites More sharing options...
Tony D Posted February 19, 2008 Share Posted February 19, 2008 Original Non-EGR cars (like non-USA) will not have the switch, they will have a plug. I forget what it is for, but there is another circuit it disables... Cold Start Valve is a thermotime and crank signal kind of thing. The 1975 EFI Bible shows the Water Temperature Switch, and does not tag it as California Only, but also shows in most of the diagrams and photos a PLUG in it's place---which I what I have seen on Non-Catalyst cars. (Home Market JDM L20E's had EGR from day one, they had stiffer regulations than California at the time!) There is a harness for it, and a function it does, but other than turning on the solenoid to allow EGR to work...hmmmmmm.... Quote Link to comment Share on other sites More sharing options...
naviathan Posted February 19, 2008 Share Posted February 19, 2008 That's odd...I've never seen an EGR solenoid before... The vacuum for the solenoid pulls from a ported vacuum on the bottom of the throttle. This only activates vacuum when the throttle is open. When the throttle is open is the only time you want the EGR open. I'm confused now because I've never seen that setup, mine has always been just a vacuum line from the ported throttle port to the EGR directly, nothing in the middle. Must have been a short lived control. Quote Link to comment Share on other sites More sharing options...
YellowFever Posted February 19, 2008 Author Share Posted February 19, 2008 It looks like the switch was only used in 75 and 76 models. The top picture that I posted came from the 1976 service bulletin which outlines all the changes between the 75 and 76 models. I see the "water temperature switch" in the 1976 wiring diagram but I can't find it in the 1977 wiring diagram. I guess they dropped it for 77 and went to a vacuum only EGR system. Quote Link to comment Share on other sites More sharing options...
naviathan Posted February 19, 2008 Share Posted February 19, 2008 I guess so, which tells me it wasn't a necessary setup and you should be able to eliminate the temp switch and the egr solenoid then just run straight to the EGR if you so desire to keep the egr connected...I wouldn't. Quote Link to comment Share on other sites More sharing options...
Tony D Posted February 19, 2008 Share Posted February 19, 2008 Solenoid... The EGR is disabled when the engine is cold. This is what the solenoid does. Until the engine reaches 120-130 degrees, EGR is disabled by the water temperature switch. On the 74's, there is a third gear switch, and a speed switch, AND a water temperature switch (vacuum switch that is thermally activated). The speed sensor and the transmission switch complete the circuit to let the EGR solenoid open to allow vacuum to be ported to the amplifier/diaphragm, and the thermal vacuum switch acts as a mechanical block until the engine is warmed. The amplified and non-amplified EGR's have different switching scenarios. The later 77/78 had a back pressure transducer and delay thingie in the hose for California to stop tip-in stumble inherent in the lean operating conditions of Cal Calibrated cars, the Fed calibrated cars were richer to begin with so they just had a thermal vacuum valve like on the earlier 74's. Basically, if you aren't pulling at least 2" Hg on the manifold, the EGR will not be open. So any sort of full load condition will stop it from recirculating. This is all from memory, but it all goes back to the fact that the cars had a plug if they didn't use a switch. What is the manufacture date on your car it is possible someone has swapped parts, you know! Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted February 19, 2008 Administrators Share Posted February 19, 2008 This switch is also used to switch pick-ups on dual pick-up dizzy's. Quote Link to comment Share on other sites More sharing options...
YellowFever Posted February 20, 2008 Author Share Posted February 20, 2008 Solenoid... The EGR is disabled when the engine is cold. This is what the solenoid does. Until the engine reaches 120-130 degrees, EGR is disabled by the water temperature switch. On the 74's, there is a third gear switch, and a speed switch, AND a water temperature switch (vacuum switch that is thermally activated). The speed sensor and the transmission switch complete the circuit to let the EGR solenoid open to allow vacuum to be ported to the amplifier/diaphragm, and the thermal vacuum switch acts as a mechanical block until the engine is warmed. The amplified and non-amplified EGR's have different switching scenarios. The later 77/78 had a back pressure transducer and delay thingie in the hose for California to stop tip-in stumble inherent in the lean operating conditions of Cal Calibrated cars, the Fed calibrated cars were richer to begin with so they just had a thermal vacuum valve like on the earlier 74's. Basically, if you aren't pulling at least 2" Hg on the manifold, the EGR will not be open. So any sort of full load condition will stop it from recirculating. This is all from memory, but it all goes back to the fact that the cars had a plug if they didn't use a switch. What is the manufacture date on your car it is possible someone has swapped parts, you know! Wow, that's a lot of stuff to pull out of memory. I assume you're a bit younger than I am... 'cause at 43 years old my memory doesn't work quite as well as it used to! If I remember correctly my car was built in 6 or 7 of 1976. My buddies car, which is only 3 months newer than mine, is a 1977 model. Quote Link to comment Share on other sites More sharing options...
YellowFever Posted February 20, 2008 Author Share Posted February 20, 2008 This switch is also used to switch pick-ups on dual pick-up dizzy's. Hmmm... very interesting. That may just be the reason for this silly little switch to be there. Last year I swapped the dual pickup distributor for an early 280ZX distributor. So I guess the wires from the temp. switch eventually lead to the ignition box on the passenger kick-panel... which is no longer in use on my car. Thanks for all the information, guys! Quote Link to comment Share on other sites More sharing options...
Administrators RTz Posted February 20, 2008 Administrators Share Posted February 20, 2008 So I guess the wires from the temp. switch eventually lead to the ignition box on the passenger kick-panel... which is no longer in use on my car. Sort of. They go to a relay, and the relay feeds the ignition module. Quote Link to comment Share on other sites More sharing options...
Tony D Posted February 20, 2008 Share Posted February 20, 2008 THANK YOU RON! I knew that damn switch did something else! For the life of me I couldn't remember. Old age (4X... what year is it again? 2008? Oh yeah, 44 this September!) is a bitch. I could remember a lot more useless trivia when I was younger. Ever watch Bill Murray in 'Groundhog Day' while he watched Jeopardy? That was me when I was 26...same hair, too! LOL Quote Link to comment Share on other sites More sharing options...
tworkman Posted March 16, 2009 Share Posted March 16, 2009 Just acquired a 1975 280Z for my son...little rust (floorboards). It runs but we still have alot of work to do. Among these, the Water Temperature Switch discussed in this thread has both wires broken/missing. Haven't been able to find the PN (E-Fast doesn't work with my Vista) and our local auto parts dealers keep coming up with the Water Temperature Sensor. Does anybody know where we can get the Water Temperature Switch...or suitable replacement? Thanks in advance. Quote Link to comment Share on other sites More sharing options...
darom Posted March 16, 2009 Share Posted March 16, 2009 tworkman, have you tried rockauto.com? Quote Link to comment Share on other sites More sharing options...
tworkman Posted March 17, 2009 Share Posted March 17, 2009 darom...thanks for responding. Using Xenon's microfiche, I was able to locate the PN...and that led to this thread... http://www.zcar.com/forums/read/1/646924/646999 . It looks like Nissan can get me this switch. Couldn't find it at rockauto.com but I'll keep their link handy. Quote Link to comment Share on other sites More sharing options...
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