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

[Dave WM]

when you are ready....

test yours if its defective you can try this

 

[jonathanrussell]

I have been watching / reading your progress. Didn't want to suggest things already suggested and divert your focus. Early on though I suggested that you remove the air flow meter hoses and do two things.

1) inspect the condition of the hose that connects the AFM and the throttle body. There should be no cracks / leaks.

2) Shine a light into the AFM and view the position of the flap. It should be closed tight and it should not be bent and it should open completely and close completely with free movement. As I mentioned earlier, the worst my 75 280z has ever run was a time when the AFM flap was stuck open. They can bend and get stuck if at some point the car has backfired through the intake. If stuck wide open, the AFM reports WOT all the time.

Anyway, I can't recall reading that you checked this. Maybe you did and I missed it. Keep trying.

And....I know that the tendency is to stay laser focused on fuel pressure. Personally, I don't have great confidence that you are getting meaningful readings.

If AFM checks out, I would look at injector flow and fuel pump.

 

Edited April 13, 2019 by jonathanrussell

[Captain Obvious]

Huh? Someone say cheesesteak???           I've been casually watching the thread, but didn't want to have too many cooks in the kitchen. But since someone promised cheesesteaks...

My thoughts are that you guys are getting out in the weeds with the stuff like leaking EGR valves, bent AFM vanes and brake booster issues*. Of course, all that stuff could need some attention too, but I think you need to focus here first:

11 hours ago, mbz said:

Fuel pressure with only fuel pump on is 40 psi (should be 36 psi).

Fuel pressure while idling is 40 psi as well.

The OP measured his fuel pressure and it was too high. Then he replaced his fuel pressure regulator with a brand new one and it was STILL too high. In fact, the new regulator behaved exactly like the old regulator. That's something that needs to be figured out first and it doesn't sound like it's the regulator.

The 40 psi too high with the pump running and the engine off could easily just be gauge error. I'm not too concerned about the difference between 40 and 36 with the engine off, but the second sentence...... "Fuel pressure while idling is 40 psi as well"?  The engine will drown at that pressure.

So I would pose the question to the collective... Other than a problem with the regulator itself, what could cause the fuel pressure in the rail to be way too high while the engine is running?  Return line plugged? Too much static pressure in the tank?

*About the weeds... The brakes feel pretty much normal, so there may be some leaking at the booster, but it's not catastrophic. The EGR valve might be stuck open a little and leaking some exhaust past, but that would cause it to run lean, not rich. The AFM vane bent a little wouldn't cause the FPR to be non-responsive. And the water temp switch... The engine is designed to run relatively well with the switch in either position. Just with lower emissions on one position or another depending on the temperature.

[mbz]

15 minutes ago, Captain Obvious said:

So I would pose the question to the collective... Other than a problem with the regulator itself, what could cause the fuel pressure in the rail to be way too high while the engine is running?  Return line plugged? Too much static pressure in the tank?

Good questions..... 2 weekends back I checked for blockage in the fuel return line.

With the pressure gauge inline after the fuel filter, I disconnected the fuel return line where it connects to the metal return line running back to the tank, and drained it to a bucket.

While the engine was running and the fuel return was draining to a bucket, I looked at the fuel pressure gauge and there was no change in the fuel pressure.

If I understand this correctly, this tells me that the high fuel pressure is not a result of a clogged fuel return line since the pressure was still high (40+ psi) and the fuel return was functioning properly.

My question is this......

Would a large vacuum leak at or near the air intake manifold cause the engine to get too much fuel, thus resulting in running rich and ultimately flooding and stalling?

It stands to reason that if there is not sufficient vacuum present from the air intake manifold, then the FPR would not function properly.

Any thoughts on this theory?

I'm trying to determine where to focus my diagnostic efforts.

[Dave WM]

there are so many odd readings its hard to answer your question. Logically a large vacuum leak (un metered air) would result in a lean run. BUT 1st things 1st have to get the FPR working like it should. The reason so many odd ball things are being suggested is the illogical behavior seen so far in the test results. Like no change in FPR with vacuum seemingly present. When things like this go on, I find you have to deal with the immediate problem (fuel pressure too high). CO missed the blocked fuel tank line conversation, so at this point its one test at a time, that one item is checked off.

Next up apply a vacuum to the FPR manually to make sure it works. If it does, check for vacuum at the intake nipple for the FPR, There has to be a reason. I try to not speculate (like the brake booster) but it hard with such a frustrating presentation of results.

I hope it not something goofy like a gauge issue.

[mbz]

2 hours ago, jonathanrussell said:

1) inspect the condition of the hose that connects the AFM and the throttle body. There should be no cracks / leaks.

2) Shine a light into the AFM and view the position of the flap. It should be closed tight and it should not be bent and it should open completely and close completely with free movement.

Both good points, and no I have not checked either yet.

Was focusing attention on the electrical (spark plugs, battery, ignition coil, distributor), and fuel delivery (fuel filter, fuel pressure, fuel flow to return, etc).

I'm really starting to think the vacuum leak theory has some credence.

The engine is getting too much fuel and the fuel pressure is too high.

The return fuel lines are functioning, and the FPR has been replaced with a new one, yet fuel pressure is still too high.

The engine is confirmed running rich (new fouled spark plugs and taking oil cap off valve cover have confirmed this), and it is not getting enough air AND/OR getting too much fuel because FPR is not functioning properly due to no/weak vacuum.

Which leads me to believe that there is a vacuum leak somewhere in the air intake system that is substantial enough to cause the FPR to not function properly.

So for today's round of diagnostics I am planning on the following:

1). Check the vacuum at the point where the FPR vacuum connects to the air intake manifold.

2). Inspect and test EGR Valve (apply vacuum) and solenoid for proper function.

3). Disconnect and inspect the hose that connects the AFM & TB.

4). Check TB flap to make sure it is functioning properly.

5). Perform visual inspection of intake manifold for any obvious signs of wear / damage that could result in vacuum leak.

 

Am I missing anything from today's list of diagnostics?

Does this seem like a reasonable / logical next set of tests?

If so, I need to head over to HF and pick up some test gear (vacuum gauge, vacuum puller / brake bleeder, inspection mirror) pronto so I can get started.

Edited April 13, 2019 by mbz
edited for clarity.

[Zed Head]

Get another gauge, even a HF cheapy, or a loaner from OReilly Auto, and confirm the high pressure readings.  Stick your finger on the port that the FPR is connected to.  You should feel the vacuum.  Try another port.  There are a couple that are not necessary for the engine.  The heater control port, and the charcoal canister purge port, for example.

Your collection of things to do is too big, I think, and a bit unfocused.  Some of the things suggested to inspect will actually make the engine run lean.  Vacuum leaks won't make it run rich.

You can see what the AFM vane is doing by watching the counterweight under the black cover.  You can also control it by moving that weight while the engine is running.  So if you just want to hear it run leaner move the weight more closed.  The cover just pries off by hand, there are no clips or fasteners.

Just stuff I would do.

[Dave WM]

5 minutes ago, Zed Head said:

  Stick your finger on the port that the FPR is connected to.  You should feel the vacuum. 

ditto

[jonathanrussell]

1 hour ago, mbz said:

Both good points, and no I have not checked either yet.

Was focusing attention on the electrical (spark plugs, battery, ignition coil, distributor), and fuel delivery (fuel filter, fuel pressure, fuel flow to return, etc).

I'm really starting to think the vacuum leak theory has some credence.

The engine is getting too much fuel and the fuel pressure is too high.

The return fuel lines are functioning, and the FPR has been replaced with a new one, yet fuel pressure is still too high.

The engine is confirmed running rich (new fouled spark plugs and taking oil cap off valve cover have confirmed this), and it is not getting enough air AND/OR getting too much fuel because FPR is not functioning properly due to no/weak vacuum.

Which leads me to believe that there is a vacuum leak somewhere in the air intake system that is substantial enough to cause the FPR to not function properly.

So for today's round of diagnostics I am planning on the following:

1). Check the vacuum at the point where the FPR vacuum connects to the air intake manifold.

2). Inspect and test EGR Valve (apply vacuum) and solenoid for proper function.

3). Disconnect and inspect the hose that connects the AFM & TB.

4). Check TB flap to make sure it is functioning properly.

5). Perform visual inspection of intake manifold for any obvious signs of wear / damage that could result in vacuum leak.

 

Am I missing anything from today's list of diagnostics?

Does this seem like a reasonable / logical next set of tests?

If so, I need to head over to HF and pick up some test gear (vacuum gauge, vacuum puller / brake bleeder, inspection mirror) pronto so I can get started.

To be clear....it is not the TB flap that is the potential problem. There is a flap inside the AFM. it freely opens and closes as air volume passes. When it opens and closes, it moves the electrical connection creating varying resistance values. It is the AFM flap I am suggesting that you test. If it is stuck open or stuck in any position = BAD.

 

[mbz]

1 hour ago, Dave WM said:

1 hour ago, Zed Head said:

  Stick your finger on the port that the FPR is connected to.  You should feel the vacuum. 

ditto 

OK I just did that and there is vacuum present, although I do not know how much.

The engine seemed to idle better when the vacuum hose was disconnected.

Fuel pressure was still very high (40-42 psi).

Edited April 13, 2019 by mbz

[Zed Head]

8 minutes ago, mbz said:

there is vacuum present,

Fuel pressure was still very high (40-42 psi).

Hose on - pressure reading.

Hose off - pressure reading.  Repeat a few times.

Tell us a story. Your pressure readings are so erratic throughout the thread that you need to do those comparison within seconds and tell what happened.

[mbz]

2 minutes ago, Zed Head said:

Hose on - pressure reading.

Hose off - pressure reading.  Repeat a few times.

Tell us a story. Your pressure readings are so erratic throughout the thread that you need to do those comparison within seconds and tell what happened.

Can I just put a valve in the vacuum line between the manifold and the FPR so I can get quick readings without having to replace the hose every time?

That tiny hose is a PITA to get on and off and tears frequently.