Zed Head

Is the T plug at the alternator plugged in? Check for continuity to ground through the bottom leg of the T on the alternator pins if it is. The alternator is the ground for the two circuits.

I've heard it as GIGO. Garbage in, garbage out. When I think of "shite out" it starts with food. AI plus the Google ad algorithm will be when things get really bad. Artificial people talking about crap you really don't care about. Can't wait!

There is a fuse that is on the supply wire to the charge lamp circuit. Seems like the most likely place to start. Does the Brake light light up when you turn the key on? That is the other part of the circuit. Don't forget to check your grounds too.

Weird that you said Amp light and not Voltmeter. USA cars from 1976 on had Voltmeters, not Ammeters. Maybe you meant the Charge lamp in the Voltmeter. Is it a USA market car? You didn't say if it has EFI or not either. The more details the better. Maybe @EuroDat is out there and can help out in Dutch, if it makes a difference. No offense intended.

Is it a 1975 280Z? Is it fuel-injected? It could be the power supply to the ECU. There is a ground wire and a power wire, both at the battery terminals. The power wire has its own fusible link. Don't get them backward.

Did things work correctly before? Supply some history of the vehicle. What is it? Did you disconnect the battery before doing the work?

Found it. This is from the 1982 FSM.

The AC belt idler pulley bearings are known to go bad. AC compressor clutch is a possibility. If you have AC. Your video was pretty short. Couldn't tell if it happened on every rev or only the start up. Seems to be starting on just a few cylinders too. Thumpa thumpa thumpa...

I thought that there was a flashing light involved on the ECU somewhere. Vague memory. Might be mentioned in the FSM troubleshooting section.

The auto parts store refrigerant cans are a gamble. I'd take it to a pro. Or at least buy the proper gauges, high side and low side so you know what's what. https://www.amazon.com/Orion-Motor-Tech-Conditioning-Maintenance/dp/B08V5JWJSB/

The pump power probably doesn't matter at Start since the bowls should be full.

The test is best done with all of the plugs out so that you get good engine speed from the starter. If you have a slow cranking speed you'll get lower numbers.

His problem seems to be oil-fouling of the #4 spark plug. And maybe #6. His pressure numbers don't show that #4 is different from any of the others. #3 and #4 are 19% higher than #1, which is at 73 psi. But #1 spark plug and cylinder work okay, apparently. #1 plug actually looks very clean in his picture above. Not sure that anything will become obvious anytime soon. Cylinder #4 has the highest pressure of all, along with #3.

jalex should put the engine specifications in his signature. Carbs, ignition system, etc. Can't remember the details. A multi-spark ignition system might help for something like this. MSD. Cheaper than an engine rebuild. The low cylinder pressures could also be caused by an adapter on the gauge. But those are very low, as stated. I think that I used an adapter once and got 125 instead of 175. 80 psi is waaaaay low. I thought the numbers were higher, in past posts. If those numbers were found with a good gauge on anybody's factory stock engine you'd say that the engine was worn out and needed a rebuild.

Have you examined the voltage regulator? Just to be sure that nobody has messed with the wiring. It should be under/inside that shelf that the fusible links blocks are attached to, protected. A small metal box.

Did you verify proper mechanical and vacuum advance operation? Ha ha. Just messing with you. But you were right there... Ignition system complete. On to the next...

Did you guys reset ignition timing after installing the new distributor?

Sounds more like the pickup coil / reluctor system in the distributor. The TIU doesn't know which cylinder is which. But the distributor does.

Could be just bad oil rings. Might be possible to just hone the bores and change rings to stop the fouling. It is an old California Datsun engine. Who knows what he put in there.

Thanks Patcon. My mistake. I saw the word "order" and my brain went to firing order.. #6 doesn't look very good either.

In the correct firing order 4 is next to 1 and 2. There is nothing to argue about. It's either wrong or right. The engine will still run with the wrong firing order. It will just run very poorly. Oops.

Are you sure? It should be 1-5-3-6-2-4. Counterclockwise. Error. Here's an old CZCC thread with pictures.

It's just a bad engine. Bad rings or cylinders or valve seals/guides. You've got many miles out of it. Consider finding a replacement. Or run hotter plugs in the bad cylinders and hope the plugs stay cleaner.

That list is nice but it doesn't tell much about what the component does. Also leaves some things out like the fact that the (L)amp pin is also the field pin. It's dual function. I think that the "tachometer" label is also kind of confusing. My vague memory is that it is meant for sensing proper operation of the alternator components. Pulse counting. Not 100% sure on that. Looks like it can be used for diesel applications also. http://www.vermontficks.org/pic/dtachd.htm Like those old databases that show CV axles for 240Z's once somebody creates the database and everyone starts using it the mistakes last for decades.

I think that they all come from the same place. That number is probably attached to that alternator across sellers. Napa has something different. https://www.napaonline.com/en/p/RAY2138114?impressionRank=1 The problem with reman alternators is that you often have to return 2 or 3 before you get a good one. So Rockauto could cost you a lot of time and shipping costs. Better to buy local. I had a salvage yard 280ZX unit on mine and a new reman on the shelf.