75 280Z - Starter Motor intermittently clicks when restarting after car has been driven for several miles/in town driving

[SteveJ]

Now I have a few minutes for the long-form answer.

For the 240Z, the ammeter measured the full current between the battery and the ammeter. If there was a short in that area, the full ammeter current would feed the fault. The battery was limited by the fusible link. (Don't be fooled, while the FSM wiring diagram shows a fusible link off the alternator, I've never seen a car equipped with one.) Also, if the ammeter failed, the car was dead. If it was running when the ammeter failed, it might keep running, but as soon as you turn it off, the car would not restart since the battery was now isolated from the majority of the electrical system.

For the 260Z, the design was improved by using a shunt to limit the current flowing through the ammeter. Also the failure of the ammeter would not strand the car. Less of a fire hazard and eliminated a single point of failure. That's definitely an improvement. The 75 carried on this design, and the 76 introduced the voltmeter.

[Zed Head]

Nissan put the relays in an area that gets wet if the windshield leaks.  If a crusty relay is causing excessive draw the extra bypass relay might just be delaying another problem.  They're by the fusebox.

I don't know if Nissan just changed names or did not use a standard ignition relay in 75.  The 1976 BE chapter shows one but 75 only shows an "igntion interlock relay".  They don't include the small diagrams either.  75 is one of the difficult years.

This is the 75 drawing -

 

Here's 1976, where that rusty picture above came from -

 

[Zed Head]

I missed the part above where you already installed the relay.  Oh well.

Don't overlook this part.  Part of it is only in use at Start.

 

[HusseinHolland]

8 hours ago, Zed Head said:

I missed the part above where you already installed the relay.  Oh well.

Don't overlook this part.  Part of it is only in use at Start.

 

Unless I'm mistaken, that resistor's only purpose is to drop the voltage to the ignition coil. Mine is wired slightly differently further down the road, but the resistor itself is the same for CA versions.

 

I'll check the relays & panel. There is no evidence of any water ingress on the passenger side, I have all the carpeting out. Also, the car was never driven or left in the rain for the first 46 years of its life.  One of the reasons he never bothered to fix the wiper pivot when it seized 30+ years ago. He did say it saw a little snow when he used to ski, but that was also in the first 15 years of its existence.

Edited June 8, 2023 by HusseinHolland

[Zed Head]

The premise of the added relay is that something along the circuit to the starter solenoid is drawing so much current that the solenoid can not actuate.  The circuit has worked just fine for over 40 years I'd guess.  Something is different now.  The wire from R to the resistor bypass circuit is one of the few things that are different during Start.  You have a "key at Start" voltage drop problem.

Just offering troubleshooting paths to check.  As far as the relays, there are several pictures on the forum of burnt/baked relay coils.  They just get old and crusty with time.  It's not just water that causes problems.

How has it been starting with the new relay?

[Yarb]

Has anyone measured the current draw on this rebuilt starter to determine if it’s overloading the circuit? I had mentioned in an earlier post that I had  the same issue. I mentioned the resolution without adding a relay into the mix. I struggled with this for over a week and found that starter itself was the issue even though I could crank the car with my remote starter. As Zed mentioned that the harness is old and breaks down over time. My solution was the later model gear reduction starter. After the issue was resolved I took the original rebuilt starter to a alt./starter rebuild shop that confirmed it was pulling way to much current/amperage.

[HusseinHolland]

1 hour ago, Zed Head said:

The premise of the added relay is that something along the circuit to the starter solenoid is drawing so much current that the solenoid can not actuate.  The circuit has worked just fine for over 40 years I'd guess.  Something is different now.  The wire from R to the resistor bypass circuit is one of the few things that are different during Start.  You have a "key at Start" voltage drop problem.

Just offering troubleshooting paths to check.  As far as the relays, there are several pictures on the forum of burnt/baked relay coils.  They just get old and crusty with time.  It's not just water that causes problems.

How has it been starting with the new relay?

 

21 minutes ago, Yarb said:

Has anyone measured the current draw on this rebuilt starter to determine if it’s overloading the circuit? I had mentioned in an earlier post that I had  the same issue. I mentioned the resolution without adding a relay into the mix. I struggled with this for over a week and found that starter itself was the issue even though I could crank the car with my remote starter. As Zed mentioned that the harness is old and breaks down over time. My solution was the later model gear reduction starter. After the issue was resolved I took the original rebuilt starter to a alt./starter rebuild shop that confirmed it was pulling way to much current/amperage.

Thank you, gentlemen.

The PO said that it has had the hot start/no start condition for quite some time (years). His mechanic suggested a new solenoid to solve it, after he installed the reman (I removed) some years back. I have not tested the new reman. The car has started every time so far with the relay in place.

I'm going to a Fiat Club gathering in NH tomorrow, so it will be a few days before I can do further testing. 

[HusseinHolland]

A related question - looking at the motor I don't see a chassis ground strap from the block. Since the main ground cable goes from the starter to the battery, there must be a ground somewhere, besides the EFI leg going back to the battery (page EF-45-48 in FSM). Everything works as is, it just seems odd as one would imagine the drivetrain is pretty much isolated from the chassis through all the mounts. 

Edited June 8, 2023 by HusseinHolland

[Captain Obvious]

The wiring diagram shows three connections to the negative battery post... 1) To starter. 2) To EFI system. 3) To body.

So I don't know if the wiring diagram is "literal" or "really how it came from factory", but that's what it shows.

I also took a look at the 77 diagram (my year) and they only show two connections to the battery negative. My year does NOT have a dedicated connection right from the battery to the body. And now you have me thinking that maybe I should add something like that. So thanks a lot... 

[HusseinHolland]

1 hour ago, Captain Obvious said:

The wiring diagram shows three connections to the negative battery post... 1) To starter. 2) To EFI system. 3) To body.

So I don't know if the wiring diagram is "literal" or "really how it came from factory", but that's what it shows.

I also took a look at the 77 diagram (my year) and they only show two connections to the battery negative. My year does NOT have a dedicated connection right from the battery to the body. And now you have me thinking that maybe I should add something like that. So thanks a lot... 

Yeah - that would definitely make the EFI ground back to the battery less critical, I want a ground from battery to chassis, and chassis to block. Every Volvo & Fiat I've owned has that setup. This is what I used on the Fiat w/Honda drivetrain&EMS: AC Delco EGS18

 

Any idea where that grouped ground is located? I'm assuming inside the cabin under the dash somewhere...

Edited June 8, 2023 by HusseinHolland

[Zed Head]

On a 76 one would be right around where the yellow is in this picture.  An eyelet with a screw through it in to the manifold.  The ground wire is in that harness.  The alternator also has a dedicated ground wire which would provide grounding through the mounting points, assuming contact was good.  Poking around with a meter is always fun.  You could also use a headlight bulb to pull some amps through the various ground points.  I like to measure things, but, adding a redundant ground wire won't hurt anything if you don't trust your measurements.

https://bringatrailer.com/listing/1975-datsun-280z-45/

[HusseinHolland]

@SteveJ - thanks for the reference pic. My 75 doesn't have a manifold ground. I do have the dedicated alternator ground - I replaced it recently- the original was fried, probably due to poor grounding in the original main battery cable if I had to guess. I'm going to add a block-to-chassis ground to make sure there is abundant path to ground.