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1976 280z engine runs rough then dies, will not idle.

mbz
mbz
in Help Me !!

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comment_572063
6 minutes ago, mbz said:

 

Checking the vacuum on the fuel pressure regulator as it affects the fuel pressure while the engine is running.

0). Take a fuel pressure reading while the engine is running.

1). Disconnect the vacuum line from the FPR while engine is running.

2). Check fuel pressure gauge. If pressure goes up that means _____the FPR is working correctly_________. If pressure goes down that means __magic______________.

3). Suck on the vacuum hose from the FPR. Check fuel pressure gauge. Fuel pressure should go down.

4). Blow on the vacuum line from the FPR. Check fuel pressure gauge. Fuel pressure should go up.

Am I understanding this correctly?

If I am, what do these results tell me?

They will tell you if the FPR is the cause of your engine running rich.  Hopefully you'll get 36-37 psi with the hose disconnected, and about 30 psi with the hose connected.

Then you can move on to other possibilities.


  • Author
comment_572064
10 minutes ago, Zed Head said:

and about 30 psi with the hose connected.

OK but I'm, already getting 38.5 PSI with the vacuum line to the FPR connected. I'm not sure what would change to make that number go down to 30 PSI.....?

I'll run the tests anyway, but just not understanding why it would all of a sudden go down to 30 PSI when it's already been shown to be at 38.5 PSI with the FPR vacuum line connected.

Also, I have the fuel pressure gauge connected just after the fuel filter for easy access..... should I have it connected somewhere else for a more accurate reading?

Edited by mbz

comment_572065
17 minutes ago, mbz said:

 

one last comment on the 36/30 pressures, this assumes a "normal" running engine. for your case I would tend to think the 30 may be a little bit higher (but still less than the 36) since no doubt your engine is not operating in an idle mode. So you may end up with a 36/33 but the running pressure MUST be lower at idle. It may help if you happen to have a vacuum gauge you could hook up at the brake port.

 

comment_572066

We'd like to see if the number rises above 38.5 psi.  Plus it's always good to rerun your tests, to verify results.

Your earlier test with low battery voltage showed about 35.5 psi.  We just want to see consistent verifiable results.

It's sounding like you need a new FPR.  The test will confirm it.  (Assuming that the gauge is good).

comment_572067
5 minutes ago, mbz said:

OK but I'm, already getting 38.5 PSI with the vacuum line to the FPR connected. I'm not sure what would change to make that number go down to 30 PSI.....?

I'll run the tests anyway, but just not understanding why it would all of a sudden go down to 30 PSI when it's already been shown to be at 38.5 PSI with the FPR vacuum line connected.

Also, I have the fuel pressure gauge connected just after the fuel filter for easy access..... should I have it connected somewhere else for a more accurate reading?

we just want to see what happens to confirm the FPR is working at all the way it should.

ZH is clearly a faster typist than me

:)

 

Edited by Dave WM

  • Author
comment_572068
Just now, Zed Head said:

We'd like to see if the number rises above 38.5 psi.  Plus it's always good to rerun your tests, to verify results.

Your earlier test with low battery voltage showed about 35.5 psi.  We just want to see consistent verifiable results.

It's sounding like you need a new FPR.  The test will confirm it.  (Assuming that the gauge is good).

OK So just to be sure I have this right, should I run the tests AFTER installing a new battery, or just when I have them time?

  • Author
comment_572069
2 minutes ago, Zed Head said:

It's sounding like you need a new FPR.  The test will confirm it.  (Assuming that the gauge is good). 

Well the gauge is a Harbor Freight special, so I don't know how "good" it is, but it seems to be functioning good enough.

comment_572070
1 minute ago, mbz said:

OK So just to be sure I have this right, should I run the tests AFTER installing a new battery, or just when I have them time?

With the engine running, doesn't matter about the battery.  Your other voltage test showed that your alternator is providing high voltage.

comment_572071
Just now, mbz said:

Well the gauge is a Harbor Freight special, so I don't know how "good" it is, but it seems to be functioning good enough.

Does it read zero when it's disconnected?  That's always a good first check of a gauge.

  • Author
comment_572072
Just now, Zed Head said:

With the engine running, doesn't matter about the battery.  Your other voltage test showed that your alternator is providing high voltage.

OK Got it.

Will run tests and return results at next opportunity. It may not be until the weekend.

 

comment_572075

you would be alarmed at how often we have gotten post about reading that suddenly are completely different when done again. Just want to make sure. Do exactly has ZH has described. The hardest part of remote diagnostics is generally some minor overlooked observation (wrong line connected, battery cable corroded, volt meter not read properly). trying to avoid rabbit holes is paramount.

hence the need for doing exactly the procedure as asked. Hang in there you will get it worked out, and it will be sweet when you do!

Edited by Dave WM

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