1978 280Z - Won't restart when hot, all interior gauges, fan motor, backlighting not working

[SteveJ]

Could it be the module on the back of the switch? Yep. It could, and I know from helping other people that the symptoms can make it look like a bad ignition relay.

The nice thing is that you can replace the back of the switch with an OEM part.

The part number is 48750-E7705. You can try Courtesyparts.com or Nissanpartsdeal.com. Either site is reliable.

To replace:

1. Disconnect the negative battery cable.
2. Remove the cover from the steering wheel.
3. Unplug the connectors from the combo switch and ignition switch. You may want to label them for faster reassembly.
4. Remove the 4 bolts under the steering column that holds it to the dash.
5. Push down on the steering column so you can access the screws on the back of the ignition switch and remove the old switch.
6. Install the new switch and reverse the disassembly process.
7. Curse under your breath if you didn't follow my suggestion in step 3.
8. Re-attach the negative cable and test.

 

[Zed Head]

Found a good video.  "Break-away" screws.  You don't need the whole assembly.  You might actually be able to fix what you have with a small drift.

 

[SteveJ]

11 minutes ago, Zed Head said:

Found a good video.  "Break-away" screws.  You don't need the whole assembly.  You might actually be able to fix what you have with a small drift.

 

Not needed if you only get the back part. You can get to the screws on the back using the instructions I posted.

[Zed Head]

Are you sure?  I guess we'll find out.  That would defeat the purpose of the break-away screws.  Once you get the electrical part off all you need is a dime or a screwdriver to start the car.

Actually, not sure, my memory is unclear, but there might also be those one-way screws on the electrical switch.  I have a memory of one one-way screw and one regular screw.  Whatever it is, on a factory stock car you had to do some grinding or filing to get the switch off.

[NocturnalEmber]

@SteveJ, While I'm awaiting an ignition switch, I just go out and attempt to repeat the condition again with the car to try and establish it as consistent rather than erratic or coincidental.

Car was cold, it started with a flick of the key (maybe 1/2 a second of total crank time.) The car ran rough, but ran, and I let it sit to see how long it would maintain that, and after about five or so minutes, I went to give it gas, and it immediately died when I tried to give it throttle, and would not restart.  Gauges were working, brake light was on and bright, seat belt warning was on when key was switched to on when I tried to restart it, but the car would crank and sound like it was half firing (very fine lumpy noises if you get what I'm describing, as in it was trying to start but just wasn't managing.)

I did notice the oil pressure gauge was non functional, and the car does have oil in it, I took the connector off and cleaned it and put it back on, but it still wasn't working. Doesn't the oil pressure switch have something to do with the fuel delivery?

 

To summarize:

I. Will start when cold

II. Will run rough when cold and seems to keep running (and running just as rough) if left alone as it attempts to come up to temperature.

III. Will die when throttle is applied (most times, I did have a few times where I tried to apply throttle, I believe when it was cold, and it would only rev a tiny amount, regardless of how much throttle was applied.)

IV. Will not restart when warm.

 

 

 

 

Edited August 30, 2023 by NocturnalEmber

[Patcon]

1 hour ago, Zed Head said:

Are you sure?  I guess we'll find out. 

I believe Steve is correct.

You are correct you could get the car started using Steve's method but the steering would still be locked unless you deal with the anti theft screws

[Zed Head]

Thinking back it might be that I had found that I could not get to the two small screws of the electrical contact portion without removing the whole switch.   Maybe I just didn't have the right tools.  Meaning I had to grind one of the anti-theft screws.

Whatever it was, it wasn't a simple process.   Good luck to NightSpark.

Edit - actually, it might be that I did what SteveJ suggested instead of grinding the screw.  Who knows, can't remember.  I do remember having a switch from a parts car that had a loose pin on the back though.  That's the one that I restaked to fix.

 

Edited August 30, 2023 by Zed Head
have > had

[NocturnalEmber]

I've scoured the 78 FSM, and I can't seem to find anything related to how to test the oil pressure sender, am I going down the wrong rabbit hole while waiting for a replacement ignition switch, or is this something to look into?

The best I can dig up on the FSM is "Clean contacts or replace" (paraphrasing a bit.)

Edited August 30, 2023 by NocturnalEmber

[SteveJ]

5 hours ago, NocturnalEmber said:

I've scoured the 78 FSM, and I can't seem to find anything related to how to test the oil pressure sender, am I going down the wrong rabbit hole while waiting for a replacement ignition switch, or is this something to look into?

The best I can dig up on the FSM is "Clean contacts or replace" (paraphrasing a bit.)

You can actually test to see if the gauge is functioning properly. There is a T shaped 2 pin connector on the oil pressure sender.

The top of the T is the wire that connects to your gauge. You want to measure voltage to ground on that wire with the key in ON. At first, you should see full voltage, then it should start to fluctuate. A while back @Captain Obvious gave a great description of how it worked, and I bought an analog ammeter to demonstrate it. Since voltage and current are proportional, you'll see the voltage reading start to dance after the gauge warms up.

Keep in mind that the oil pressure gauge and temperature gauge use the same voltage regulator, so if you don't see the voltage start to dance when you are checking the wire at the oil pressure sender, you can do the same test at the wire for the temperature sender. If one works, and the other doesn't, my first guess would be that there could be a wiring issue or corrosion at the dash to engine harness connection. Anyway, do this test and report back, and we can figure out if more diagnostics are needed.

[NocturnalEmber]

5 minutes ago, SteveJ said:

You can actually test to see if the gauge is functioning properly. There is a T shaped 2 pin connector on the oil pressure sender.

The top of the T is the wire that connects to your gauge. You want to measure voltage to ground on that wire with the key in ON. At first, you should see full voltage, then it should start to fluctuate. A while back @Captain Obvious gave a great description of how it worked, and I bought an analog ammeter to demonstrate it. Since voltage and current are proportional, you'll see the voltage reading start to dance after the gauge warms up.

Keep in mind that the oil pressure gauge and temperature gauge use the same voltage regulator, so if you don't see the voltage start to dance when you are checking the wire at the oil pressure sender, you can do the same test at the wire for the temperature sender. If one works, and the other doesn't, my first guess would be that there could be a wiring issue or corrosion at the dash to engine harness connection. Anyway, do this test and report back, and we can figure out if more diagnostics are needed.

 

Will do.  I did have one question. Based on your explanation, this test is performed by probing into the harness on that wire with the positive lead and a good ground, can I use the battery for the negative/ground?

Also, in terms of checking the actual sensor itself for functionality, is there a process for that? The FSM just essentially says "does the gauge work? If not replace it."

[SteveJ]

8 hours ago, NocturnalEmber said:

@SteveJ, While I'm awaiting an ignition switch, I just go out and attempt to repeat the condition again with the car to try and establish it as consistent rather than erratic or coincidental.

Car was cold, it started with a flick of the key (maybe 1/2 a second of total crank time.) The car ran rough, but ran, and I let it sit to see how long it would maintain that, and after about five or so minutes, I went to give it gas, and it immediately died when I tried to give it throttle, and would not restart.  Gauges were working, brake light was on and bright, seat belt warning was on when key was switched to on when I tried to restart it, but the car would crank and sound like it was half firing (very fine lumpy noises if you get what I'm describing, as in it was trying to start but just wasn't managing.)

I did notice the oil pressure gauge was non functional, and the car does have oil in it, I took the connector off and cleaned it and put it back on, but it still wasn't working. Doesn't the oil pressure switch have something to do with the fuel delivery?

Yes, the oil pressure sending unit was changed for 78. In previous 280Zs, the flap in the AFM would close a switch to tell the fuel pump relay that the engine is running and kept power on the fuel pump. Nissan moves away from that Bosch fuel pump relay and used oil pressure as a signal that the engine is running.

If you look at the 75-77 wiring diagrams, you see terminal numbers 36 and 39 on the AFM flap. This is how they documented the change on the 78 wiring diagram.

So, yes, the oil pressure sender grounds when the engine is running on the vertical of the T. That circuit is for when the key is in ON.

[NocturnalEmber]

2 minutes ago, SteveJ said:

Yes, the oil pressure sending unit was changed for 78. In previous 280Zs, the flap in the AFM would close a switch to tell the fuel pump relay that the engine is running and kept power on the fuel pump. Nissan moves away from that Bosch fuel pump relay and used oil pressure as a signal that the engine is running.

If you look at the 75-77 wiring diagrams, you see terminal numbers 36 and 39 on the AFM flap. This is how they documented the change on the 78 wiring diagram.

So, yes, the oil pressure sender grounds when the engine is running on the vertical of the T. That circuit is for when the key is in ON.

 

I can't say I've seen the words "useless" in the FSM before, but that gave me a good laugh.  So assuming I text the sensor as well as the harness side of things: 

You mention the vertical pin on the T is grounded by the oil pressure sender when the engine is running,  Would I just set my multimeter to ohms and test between that terminal and the negative on the battery?

Again, much appreciate help so far Steve!