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

[SteveJ]

3 minutes ago, NocturnalEmber said:

 

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."

Yes, you can use battery negative for ground. (Also, if you look through my YouTube channel, you'll see a video where I show how to check the quality of your grounding. Bad grounding can cause some perplexing problems.)

Yes, you can check the functionality of the sensor. You measure resistance to ground at the top of the T at the sending unit.

1. Remove the connector from the sending unit.
2. Get your baseline resistance reading between the top of the T and ground. It should show very high resistance.
3. You will need to ground the pin on the connector that connects to the fuel pump relay so you get fuel to run the car.
4. Have someone start the car while you continuously measure resistance to ground at the sending unit. Resistance should drop.

[NocturnalEmber]

8 minutes ago, SteveJ said:

Yes, you can use battery negative for ground. (Also, if you look through my YouTube channel, you'll see a video where I show how to check the quality of your grounding. Bad grounding can cause some perplexing problems.)

Yes, you can check the functionality of the sensor. You measure resistance to ground at the top of the T at the sending unit.

1. Remove the connector from the sending unit.
2. Get your baseline resistance reading between the top of the T and ground. It should show very high resistance.
3. You will need to ground the pin on the connector that connects to the fuel pump relay so you get fuel to run the car.
4. Have someone start the car while you continuously measure resistance to ground at the sending unit. Resistance should drop.

Awesome, sounds like I have my tests planned out.

 

For step 3 with testing the sensor itself, grounding the pin on the connector that connects to the fuel pump, is this the vertical connector?

[SteveJ]

11 minutes ago, NocturnalEmber said:

Awesome, sounds like I have my tests planned out.

 

For step 3 with testing the sensor itself, grounding the pin on the connector that connects to the fuel pump, is this the vertical connector?

Yes, the vertical is for the fuel pump, and the top of the T is for the gauge.

[SteveJ]

12 hours ago, Zed Head said:

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.

I don't recall ever seeing security screws on the ignition switch module, and that includes 2 new Beck Arnley full switches that had Nissan part numbers on them. (I never knew Beck Arnley was a Nissan supplier until I bought them.)

On the other hand while it's security via obscurity, it is not a trivial task to get to those screws. It would be a determined thief doing that, and at that point he's going to take your car pretty much any way he can. 

I have replaced the ignition switch module on a car just as I described. It helps to have a stubby screwdriver or a mini ratcheting bit set like pictured below.

[NocturnalEmber]

Just an interim update:  Ignition switch and oil pressure sensor did arrive.  However, the oil pressure switch was rounded off, and trying to use vise grips made it shear off, leaving me with a partially exposed stud ouside of the block and whatever threads are inside the block.  

As a result I am currently trying to tackle that issue, as I need a working oil pressure sensor for the engine to run being that it's a 78.

I did notice there was a small amount of oil on the wire connection when I unplugged it, and it spun almost freely, so the sensor was likely bad.

 

[SteveJ]

Take a photo of what's sticking out and post it here.

[SteveJ]

If you're near a Harbor Freight, you could get these:

https://www.harborfreight.com/screw-extractor-and-left-hand-drill-bit-combo-set-10-piece-63987.html 

https://www.harborfreight.com/3-piece-t-handle-tap-wrenches-38560.html

Also 25% off coupon that's good today and tomorrow: (https://www.harborfreight.com/promotions)

BTW the coupon will work for jack stands. I wanted to get a set of 6 ton stands, so it worked for about $20 off today.

[siteunseen]

You could also drive a flat screwdriver in there and gently turn it out.

[SteveJ]

9 hours ago, NocturnalEmber said:

Just an interim update:  Ignition switch and oil pressure sensor did arrive.  However, the oil pressure switch was rounded off, and trying to use vise grips made it shear off, leaving me with a partially exposed stud ouside of the block and whatever threads are inside the block.  

As a result I am currently trying to tackle that issue, as I need a working oil pressure sensor for the engine to run being that it's a 78.

I did notice there was a small amount of oil on the wire connection when I unplugged it, and it spun almost freely, so the sensor was likely bad.

 

Of course, that would explain fuel pump issues.

[Zed Head]

1978 uses the oil pressure switch or the alternator current to power the fuel pump relay.  Or Start.

[NocturnalEmber]

5 hours ago, Zed Head said:

1978 uses the oil pressure switch or the alternator current to power the fuel pump relay.  Or Start.

So based on that chart the fuel pump would still work even if the oil pressure switch was bad assuming the alternator was working? I figured if the oil pressure sensor was bad that would cause an issue with running when key was on.

Also - I pulled the plugs to try and remove that oil pressure sensor when it was still whole.  The plugs (that have maybe fifteen minutes of runtime) are black, so somethings making it run rich.

 

Also @SteveJ Pictures as promised...It's not pretty. I'm not sure if I can get the drill bits or tap wrenches in there with any kind of accuracy. I did see a stud extractor socket that Performance Tool has (available at advance auto parts, depending on your location) that I was going to consider, but I honestly don't know if there is enough stud left sticking out of the block for that to work. 

 

Here's what I was considering - https://shop.advanceautoparts.com/p/performance-tool-stud-extractor-w83203/11931907-P?searchTerm=stud+extractor

 

It's a bit hard to see in the first picture, so I held a light up to the block, you can see the silhouette of what is left remaining of the stud.

Edited September 3, 2023 by NocturnalEmber
Added link & pertinent info

[SteveJ]

The extractor kit I linked goes inside what's left if there is a hole in it.