Engine rough running - at wits end

[Patcon]

On another note, if your alternator is still externally regulated, You aught to see if you can source a voltage regulator locally. Both options on rockauto are out of stock. That would be a cheap first shot at the high voltage

I might have one laying around somewhere ...

[SteveJ]

8 hours ago, Patcon said:

 

Also @SteveJ

Battery is August 2022

At idle

Just after shut off. Where to start??

 

 

High voltage is usually one of two things.

1. The voltage regulator is failing.
2. The battery sense voltage isn't present.

Basically, pull off the connector for the voltage regulator. Measure voltage to ground on the white/red wire on the engine harness side of the connector. It should be battery voltage. That wire comes off the black fusible link, so likely it is the voltage regulator.

[the_tool_man]

From what I'm reading, they switched to internally-regulated alternators mid-year 1977, and it wasn't a clean switch.  So I'll have to take a look this weekend.  Finding a stock regulator looks like a challenge.  And I found a replacement internally-regulated alternator for about the same money as just a regulator.  So I may just swap to that if mine isn't already.

[SteveJ]

18 minutes ago, the_tool_man said:

From what I'm reading, they switched to internally-regulated alternators mid-year 1977, and it wasn't a clean switch.  So I'll have to take a look this weekend.  Finding a stock regulator looks like a challenge.  And I found a replacement internally-regulated alternator for about the same money as just a regulator.  So I may just swap to that if mine isn't already.

Your car has a voltage regulator. I can see the plug.

Frankly I don't trust reman alternators anymore. I have been advising people with bad alternators or regulators to do the Nissan Frontier swap. RockAuto lists "new" alternators for the 2000 Frontier 4 cylinder. You have to buy the plug for the sense and switched circuits. That is readily available on Amazon. I also went the extra step to buy the 6 pin Yazaki YPC male plug to make the jumper to remove the voltage regulator. I haven't had someone come back to me about the RA alternators I suggest failing.

[the_tool_man]

28 minutes ago, SteveJ said:

Your car has a voltage regulator. I can see the plug.

Frankly I don't trust reman alternators anymore. I have been advising people with bad alternators or regulators to do the Nissan Frontier swap. RockAuto lists "new" alternators for the 2000 Frontier 4 cylinder. You have to buy the plug for the sense and switched circuits. That is readily available on Amazon. I also went the extra step to buy the 6 pin Yazaki YPC male plug to make the jumper to remove the voltage regulator. I haven't had someone come back to me about the RA alternators I suggest failing.

Thanks for that info.  I assume https://www.atlanticz.ca/zclub/techtips/alternatorswap/index.html is a good how-to (though it uses a 60A 280ZX alternator instead of the Frontier 70A).

I'd planned to drive the car this weekend to do more diagnosis.  Is there any risk to driving it before correcting the voltage issue?  I don't plan to drive it much, just up the road and back a few times to see if my fuel delivery issue under throttle comes back.

Edited October 6, 2023 by the_tool_man
Added link to how-to article

[SteveJ]

I would advise against it. If the voltage spikes more, you could take out your ECU. 

[Captain Obvious]

11 hours ago, Patcon said:

here is the fuel pressure while warming up and the the vacuum gauge that is plumbed in before the brake booster check valve

Those pressure readings look OK. Manifold vacuum is a little lower than what I would want, but in the ballpark at least.

So what's the assessment of how good or bad the engine runs today? There are 13 pages past in this thread, but what's the latest at this point?

[the_tool_man]

Or I could unhook the alternator and run off the battery.  It wouldn't be the sketchiest thing, considering the 5-gal gas can in the back for a fuel tank.

[the_tool_man]

1 minute ago, Captain Obvious said:

Those pressure readings look OK. Manifold vacuum is a little lower than what I would want, but in the ballpark at least.

So what's the assessment of how good or bad the engine runs today? There are 13 pages past in this thread, but what's the latest at this point?

It idles well and revs when parked.  I won't know more until I can drive it.

[Patcon]

I can not locate a regulator

I think switching to the frontier alternator would be good just for on the road maintenance issues and parts availability

 

[SteveJ]

29 minutes ago, Patcon said:

I can not locate a regulator

I think switching to the frontier alternator would be good just for on the road maintenance issues and parts availability

 

Just keep in mind, @the_tool_man, if you go with the Frontier alternator, choose from the offerings under New.

[Zed Head]

Your number is in-spec for a 77 external regulator.