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

[Dave WM]

Test your setup by just seeing if you can blow thru the feed line and have flow out the return before engaging the pump to be safe. again with no restriction it should flow pretty easy.

[mbz]

3 minutes ago, Dave WM said:

You will have to rig up some way to bypass the FPR, so the fuel goes from the injector rail then directly into the return line where the FPR sits. Remove the FPR and rig up some pluming.

You mean something like this diagram?

[mbz]

Is it possible to just use a plastic T with hose barbs? Like something from a plumbing store?

[Captain Obvious]

Anything look wrong? I think so.

2 hours ago, mbz said:

Anything look wrong with the AFM?

I don't like the looks of the clear silicone blob on the big gear at the 2:00 position. I suspect that blob was originally at the 11:00 position over by the locking screw (hidden by the big silver metal counterweight). If my suspicion is correct, then it looks like someone rotated that gear way leaner (looks like close to 20 teeth) than factory. An indication that they were fighting a severe rich condition and decided (incorrectly) that adjusting the AFM was the way to fix it.

That black silicone that was holding the lid on is another indication that someone has been in there poking around.

Of course, none of that explains why your fuel pressure is wrong, but it's something that you'll have to look into as well.

[Dave WM]

what ever you can righ up should work, again the presssure should be low, but yes that diagram is correct.

If CO is right it would be classic, too rich mess with the AFM... as if it just suddenly got way out of spec.

[Dave WM]

you can prob just connect one side of the T to the return line with a short lenght of hose, then plug the other side of the T with a hose with a bolt in it. as long as you can flow back thru the return line, you should be able to test.

Edited April 13, 2019 by Dave WM

[Zed Head]

1 hour ago, mbz said:

Regarding the fuel pressure gauge, I'm not defending it, however at worst I think it's maybe 1-2 psi higher than it should be.

That last set of fuel pressure data was pretty consistent (albeit high).

44 - 36.3 = 7.7 psi.  That is not 1 - 2 psi higher.

I don't think that you're understanding how the FPR works.  With no vacuum on the FPR port the pressure is supposed to be 36.3 psi. It doesn't fluctuate.  Some of them are apparently set for about 38 psi.  But none of them are set for 40 psi or above.  No matter what they are set for, with no vacuum on the port the reading should be the same every time.

[mbz]

OK so I'm getting a little twisted up here.....

Should I focus what is left of the time today to trouble shoot this on checking for a clogged return line?

Or should I focus on testing the vacuum at the FPR and the manifold?

[Dave WM]

the FPR seems to be reacting to the vacuum (it drops) you may have a weak vacuum for a lot of reasons, #1 is a poor running engine (under ideal settings of the A/F ratio at idle you will get about 17-18"). I think the bigger issue is as ZH noted there has to be a explanation for the high no vac readings.

its got to be:

1. gauge not right
2. FPR bad
3. restriction somewhere higher that it should be

assuming 1 and 2 are not the issue (and the only way to know for sure is more testing and checking of calibration), that leaves 3 If 3 checks out (no significant restriction with FPR out of loop), then you will have to reconsider 1 or 2. That's it bottom line. What ever you do its important to stick with one issue at a time, Fuel pressure now, the AFM adjustment later (if needed).

So I would focus on item 3 connect one side of the T to the return line, plug the other side of the T and see if you can blow thru the fuel rail, if so hook up the fuel pump and get another reading, fuel pressure MUST be lower by a lot if there are no internal hard line restrictions.

For some reason I thought we were at about 40psi with no vac at some point and chalked that up to a calibration issue, but 44 no vac is just way to high and needs to be addressed.

 

 

 

 

 

Edited April 13, 2019 by Dave WM

[mbz]

DaveWM, what about a set up like this....?

And, if this will work, let's make sure I understand the test and the potential results.

Without the FPR in the way of the fuel return line, the unrestricted fuel flow should go right back to the tank and the fuel pressure on the gauge should drop.

If the fuel pressure does not drop, then I have a CLOG somewhere in the metal fuel return lines going back to the fuel tank, which is causing the high fuel pressure.

Do I understand this correctly?

[Dave WM]

see pic

[Dave WM]

as you can see the fuel will flow along one side of the rail and return to the tank with no restrictions, should have very low recorded fuel pressure. Two pieces of hose one for bypass one with a bolt in it to plug is all you need.