1978 280Z Runs rough? - Page 2 - Nissan : Datsun ZCar forum :Nissan Z Forum: 240Z to 370Z
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post #11 of 56 (permalink) Old 06-26-2019, 11:46 PM
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as mentioned before, the CTS, get the FSM read how to test, if bad replace. Super easy 5 min fix.
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post #12 of 56 (permalink) Old 06-27-2019, 08:58 AM Thread Starter
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Just noticed your response. I will check out the coolant temperature sensor per your advice. thanks
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post #13 of 56 (permalink) Old 07-01-2019, 03:32 PM Thread Starter
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Need help with testing results - what do I do next?

7-1-19Update
  • 1978 280Z (California model) Car starts and runs well for 15 mins, as soon as it gets to running temp it starts running really bad and stops running after 35 mins.
Did several tests based on the “Engine Fuel” service manual.
The following check points all passed – Throttle valve switch (idle & full), Thermotime Switch, Ground Circuit, Altitude Switch, Revolution trigger signal, Powerline circuit and Injector and resistors (all 6 cylinders)

I need helpon the following:



Check Item #1-(3) Air Flow Meter
  • Terminals 6 & 8: Got reading of 182.2, but I did not get a Continuity audible beep like I did on other terminal checks. Is this ok?
  • Terminals 7 & 8: Got readingof 183.6, but I did not get a Continuity audible beep. Is this ok?
  • Terminals 8 & 9: Got readingof 101.5, but I did not get a Continuity audible beep. Is this ok?
Check Item #1-(4) Air Temperature Sensor
  • Terminals 6 & 27: No reading and no Continuity audible beep.
Check Item #1-(5) Water Temperature Sensor
  • Terminals 13 & Body Medal: No reading and no Continuity audible beep.
Check Item #1-(6) Air Regulator
  • Terminals 34 & Body Metal: Got reading of 63.0, but no audible beep. Is this ok?
Parts I checked are:
  • Air flow meter – everything checked out ok including the “Air temp sensor”
  • Water Temp Sensor – tested ok, but still replaced with a new one I had just purchased (new unit also tested ok)
  • Thermotime Switch – passed butI had a challenge getting a 56.2 ohm reading.
So, FSM says if the continuity does not exist to trace the circuit. Sorry I’m not sure what that means. Do they want me to follow the wire from the EF control unit to the sensor? If the sensor is not the problem, then what am I looking for in the wiring?

Thanks
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post #14 of 56 (permalink) Old 07-01-2019, 03:50 PM
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Originally Posted by ctfisher View Post
7-1-19Update
  • 1978 280Z (California model) Car starts and runs well for 15 mins, as soon as it gets to running temp it starts running really bad and stops running after 35 mins.
Check Item #1-(5) Water Temperature Sensor
  • Terminals 13 & Body Medal: No reading and no Continuity audible beep.






Thanks

what was the resistance reading in ohms at the 36pin connector pin 13 and chassis ground. What was the temp of the engine.
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post #15 of 56 (permalink) Old 07-01-2019, 09:41 PM Thread Starter
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For 13 and ground I could not get a reading. The engine had not ran for a couple days at the time so I assume the motor temp was about 80 deg F
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post #16 of 56 (permalink) Old 07-02-2019, 08:09 AM
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if you have no resistance that is the problem. You will need check at the temp sensor next. take a pic so we know you are testing the right one. The problem will have to be the sensor or the wiring to it. No resistance is telling the ECU you live in the artic circle.
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post #17 of 56 (permalink) Old 07-02-2019, 01:42 PM Thread Starter
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checking no continuity in water temperature sensor

Dave - thanks for all your help so far. Sorry I lack automotive knowledge but I'm slowly learning and I will also have this car for the rest of my life.


Ok I know the new water temperature sensor is good. So I must have a problem with the wire or the electrical connection.
- Any tips on how I go about testing the wire so I can figure where the problem is?
- can I assume I have a similar problem with the air temp sensor since I also did not get a reading at the 6 & 27 terminals?
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post #18 of 56 (permalink) Old 07-02-2019, 03:52 PM
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simple wire tracing. Start by making sure you multimeter is working, some that are not auto ranging can lead you astray. Get the known good one out of the T stat and start checking it, BTW NEVER assume a new part is good, check before installing.


Once you are sure you know the new part is testing good, then its time to inspect the wire harness. Here continuity testing with a tone function of the multi meter is important. You know one side of the sensor connector is ground so test that. One lead of the meter to the chassis ground then the other lead to the sensor connector. ONE of them must have continuity, if neither do then follow the sensor harness to the 1st break point, a bullet connector test there. Use logic to find the break in the circuit.


Do all this testing with the 36 pin connector disconnected and the battery disconnected.
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post #19 of 56 (permalink) Old 07-02-2019, 03:54 PM
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also make sure you have the right sensor plugged into the right sensor plug and the right bullet connectors hooked up to the right bullet connectors (sub harness to main harness)
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post #20 of 56 (permalink) Old 07-02-2019, 04:47 PM
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I just check mine, the bullet connector sub harness is marked with some red tap wrapped near the bullets. that is the THERMOTIME harness, the other sub harness wth NO RED TAPE is the CTS. You can just disconnect there leave the sensor plug attached to the sensor, and get a reading off the bullets (the side that is plugged in) you should see somewhere around 2k-1.2k (2000 to 1200) ohms, depending on local temps (cold motor). Once it has warmed up you should see around .3k or 300 ohms. that would be around 180f water temps. Trace the wire harness from the CTS and follow it back toward the firewall along the top of the engine. You should be able to find the bullet connectors. Make sure you don't break the wires when you disconnect it, they will prob be stuck. again you should see a RED piece of tape wrapped around the harness near the bullets, that is the harness for the thermotime, it matches the main harness also marked with red tape. You want the NON red tape for the CTS wires.
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