ISPKI Posted March 16, 2013 Share Posted March 16, 2013 Howdy folks, first post here. I have this same thread running on a couple other sights but havent gotten a whole lot of responses. I have a 1977 280z - that is fuel injected. The vehicle was not maintained well by the previous owners and I am restoring it. At the top of my repair list is the coolant temperature. The needle on the gauge moves to the middle of the gauge when the key is turned to on (or the vehicle is turned on) regardless of whether or not the engine is cold or hot. The needle sits there and does not move from the center of the gauge. This has led me to look at the coolant temperature sensor and senders. I was told that if you ground one of the wires for the coolant temp sender, then the gauge should move to the HOT end and stay there. However, regardless of which wire I ground, the gauge returns to the same spot, right in the middle. I then removed the gauge to check and make sure that it was not jammed, which it was not. As far as I know, there is nothing else on the cercuit between the sender unit and the gauge so what could cause the gauge to not be reading correctly. I tried testing the system with a meter but I can barely get a reading and when I do the reading is rarely consistent. The only consistent reading I got was 512 with the meter set to 20k. The reason I am trying to fix the gauge is because the vehicle slowly develops a rough idle as it warms up and will eventually become so rough that it will not even drive up a hill. There are many other issues that need fixing as well; The fuel pump does not prime the fuel system when the key is turned to "on". The fuel system drains out when the car is turned off. Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 17, 2013 Share Posted March 17, 2013 Fixing the gauge won't make your engine run better. The ECU has its own sensor. 77 does not have a fuel pump priming function. Read the Engine Fuel chapter for how the fuel injection system works, and Body Electrical for the gauge. www.xenons30.com/reference Quote Link to comment Share on other sites More sharing options...
ISPKI Posted March 17, 2013 Author Share Posted March 17, 2013 Here is where I am getting kind of confused. I have been told that there is a temp sender and a temp sensor. The sensor sends a signal to the ECU, the sender sends a signal to the gauge. Reading the manual, it does not say that it has a sender and a sensor, it says that what I thought was the sender for the gauge is the thermotime switch for the cold start valve. So where does the gauge get it's information from? Quote Link to comment Share on other sites More sharing options...
ISPKI Posted March 18, 2013 Author Share Posted March 18, 2013 Well just had a "duh" moment. Tell me if this is correct. There are three sensors plugged in to the thermostat housing; Temperature sensor that sends a signal to the ECU, Temperature Sender that sends a signal to the temp gauge, and Thermotime switch that actuates the cold start valve. The temperature sensor and thermotime switch have the same connector while the sender for the gauge has what looks like a bullet connector/barb thingy. I think I have had them switched around all this time...and the single barb connector is not even plugged in...in fact I cant find the plug for it. Quote Link to comment Share on other sites More sharing options...
EuroDat Posted March 18, 2013 Share Posted March 18, 2013 You are on the right track now. If your working on the temp guage you should be looking in the "body electircal section" of the FSM. Its called a Thermal Transmitter. It should be a yellow wire with a bullet connector somewhere in the area of the thermostat. The two sensors with the square plugs and two small spade terminals are for the EFI system. 1: The Thermotime sensor. Generally the left one when looking from the front of the car. Its also larger then the other sensor units. This is actually a switch and shuts off the cold start injector. It does that two ways. One is if the water temperature is warm it stops the cold start injector when cranking. Second is if you crank the engine too long it will heat up and stop the cold start injector. 2: The temperature sensor to the right of the thermtime switch. This compensates for the engine temperature by adjusting the injector time. The yellow wire is not in the same harness as the other two connectors. Its a part of the body harness. Dont search for it in the EFI harness. It comes from the same harness section where the coil and such comes from. If you are trouble shooting the EFI. Download the 280-Z Fuel Injection manual (Theory and Troubleshooting). It has more detail than the FSM. You might also want to check classiczcars and search their forum " temperature sensor" lots of good threadsabout this stuff. Godluck chas Quote Link to comment Share on other sites More sharing options...
EuroDat Posted March 18, 2013 Share Posted March 18, 2013 Link to the troubleshooting manual http://www.xenons30.com/files/280zfuelinjectionbook.pdf Chas Quote Link to comment Share on other sites More sharing options...
ISPKI Posted March 18, 2013 Author Share Posted March 18, 2013 Well the connector for the thermal transmitter seems to be missing completely. Do you know if the yellow wire routes into the same jacketing as the wires for the water temp sensor? I am guessing that whoever had this thing before me cut the transmitter wire out completely so I may have to run a new wire straight from the gauge in the dash. Does the wire run into anything between the transmitter and the plug for the gauge? Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 18, 2013 Share Posted March 18, 2013 As you're looking at the small wiring diagrams in the Body Electrical chapter, you'll see a legend at the bottom of each that tells what color the letters stand for. Most make sense, except for blue, which is labeled with the letter L. Quote Link to comment Share on other sites More sharing options...
EuroDat Posted March 18, 2013 Share Posted March 18, 2013 Well the connector for the thermal transmitter seems to be missing completely. Do you know if the yellow wire routes into the same jacketing as the wires for the water temp sensor? I am guessing that whoever had this thing before me cut the transmitter wire out completely so I may have to run a new wire straight from the gauge in the dash. Does the wire run into anything between the transmitter and the plug for the gauge? If you mean the water temp sensor for the EFI, then its no. That is a completly different wiring harness. If you look at the wiring that goes to the ballast resistor under the coil, the yellow wire comes from there and its the only wire going to the engine. It also follows a thicker black ground cable that goes from the frame just back a little from the coil and it connects to the EFI manifold close to the AAR. Think of the electrical system as two systems. One for the EFI and one for the rest commonly called body electrical even though it has engine electrical (consider it as everything the caby models had). Goodluck searching Chas Quote Link to comment Share on other sites More sharing options...
Pharaohabq Posted March 18, 2013 Share Posted March 18, 2013 for the link to the EFI theory and troubleshooting guide. I hadn't seen that, its a very good overview of the L series EFI. I am really glad to have read it. If I'd had that back in 88' I wouldn't have been stranded at my girlfriend's house so often when it got cold! Quote Link to comment Share on other sites More sharing options...
ISPKI Posted March 22, 2013 Author Share Posted March 22, 2013 Well, I have scoured the engine bay for several hours but I have not been able to locate the wire for the transmitter. I am going to assume that someone must have yanked the entire wire out for some reason. From reading the wiring diagram in the FSM, the temp gauge has a plug directly behind it that connects it to the instrument harness. There is then another, larger plug connecting the instrument harness to the engine room harness that should be on the passenger side of the cabin. All I should need to do is find the plug connecting the instrument harness to the engine room harness, locate where the yellow wire is supposed to be on that plug and then run a fresh wire all the way to the engine bay. Quote Link to comment Share on other sites More sharing options...
EuroDat Posted March 23, 2013 Share Posted March 23, 2013 Well, I have scoured the engine bay for several hours but I have not been able to locate the wire for the transmitter. I am going to assume that someone must have yanked the entire wire out for some reason. From reading the wiring diagram in the FSM, the temp gauge has a plug directly behind it that connects it to the instrument harness. There is then another, larger plug connecting the instrument harness to the engine room harness that should be on the passenger side of the cabin. All I should need to do is find the plug connecting the instrument harness to the engine room harness, locate where the yellow wire is supposed to be on that plug and then run a fresh wire all the way to the engine bay. Sounds like its the best way to go about it. Just wonder why the PO would remove the yellow wire????? Quote Link to comment Share on other sites More sharing options...
ISPKI Posted March 23, 2013 Author Share Posted March 23, 2013 Well, it was a pain in the ass but I finally found the yellow wire. I started at the gauge and followed it through the dash down to the blue plug that connects the instrument harness to the engine room harness. I cut the jacketing on the harness open at about a dozen spots between that plug all the way down past the alternator, around the front of the car and up the opposite side. The yellow wire seemed to follow the harness for the lights. Anyways I found it plugged in to something underneath what I think is the throttle body. I took photos of it that I will upload when I get back home later tonight. Regardless, I unplugged the yellow wire from whatever it was plugged into, cleaned the connectors and plugged it into the thermal transmitter. Turned the car to "on" and the gauge now reads way down on the cold end. Tested the wire by grounding it and the gauge popped up all the way to the high side. Get to check that one off my list, and add whatever it was plugged into onto the list. Quote Link to comment Share on other sites More sharing options...
ISPKI Posted March 26, 2013 Author Share Posted March 26, 2013 (edited) Finally got these photos uploaded. Could anyone tell me what this thing under the throttle body is? My buddy and I were thinking it was some kind of IACV. This is what the yellow wire for the temp gauge was plugged in to. Edited March 26, 2013 by ISPKI Quote Link to comment Share on other sites More sharing options...
NewZed Posted March 26, 2013 Share Posted March 26, 2013 It's the BCDD. Described in the Emissions chapter of the FSM. Lots of discussion about it aorund the internet. It uses a yellow wire for power, that comes through the same harness section that supplies the AFM. Quote Link to comment Share on other sites More sharing options...
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