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Engine rough running - at wits end


the_tool_man

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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 ...

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  On 10/6/2023 at 1:36 AM, Patcon said:

 

Also @SteveJ

20231005_200404_resized.jpg

Battery is August 2022

20231005_195749_resized.jpg

At idle

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Just after shut off. Where to start??

 

 

20231005_201740_resized.jpg

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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.

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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.

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  On 10/6/2023 at 11:35 AM, 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.

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

image.png

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.

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  On 10/6/2023 at 11:58 AM, SteveJ said:

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

image.png

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.

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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 by the_tool_man
Added link to how-to article
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  On 10/6/2023 at 1:36 AM, 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

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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?

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  On 10/6/2023 at 12:50 PM, 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?

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

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