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

[Zed Head]

If you've already done the other hoses and have already installed new injector seals and don't have any leaks, just do it while it's on the engine.  The key to making it easy is to get the hose lengths right, not too long, then get the rail ends lubed up (gasoline actually works well) before sliding the hoses on.  Slide one short hose length way down as far as it will go, then stick the FPR end in, squeeze the other hose in between the rail and the FPR, then slide everything to the right spots for clamping.  Don't forget to put the hose clamps on at the appropriate times.  It's a pain to get everything right and realize there's no clamps on the hoses.

[mbz]

Yes the hoses all appear to be in very good condition and like I stated earlier in thread, the PO's Mechanic's notes indicate that the fuel injectors, o-rings, gaskets, risers and hoses on fuel rail were all recently replaced. This is what I see upon visual inspection as well. So I concur that there is no need to take apart the fuel rail to service parts other than FPR.

10 minutes ago, Zed Head said:

Slide one short hose length way down as far as it will go, then stick the FPR end in, squeeze the other hose in between the rail and the FPR, then slide everything to the right spots for clamping.

Really good tip.... I hadn't considered sliding the hoses further past where they are supposed to sit when clamped in place. This would make it easier to replace the FPR while fuel rail is in place.

I'll pick up a couple feet of high pressure FI hose before the weekend, just to be sure I have extra on hand if needed.

I think taking the old FPR off should be fairly straight forward, as I am planning on cutting off the hose on the right side of the FPR (closest to windshield) to make removal easier, and then just replace the cut hose with a new piece.

[Dave WM]

any way you go about it, its always tough, like ZH said a little lube goes a long way, I think part of the problem is getting correct sized fuel injector hose. But yea taking the entire thing off is easy getting it all back on, not so much.

One thing to watch for is fuel leaks, anytime you mess with it just make real sure there are no leaks. I generally will pop the hood every time I take it for a drive at the end of the day and while idling do a quick visual inspection.

[mbz]

So do you think 100 PSI fuel injection hose is sufficient?

Or should I go for the 225 PSI hose?

[S30Driver]

A good quality 100 psi hose, (gates for example) should be ok). ***  Its working pressure rating is 100 with a burst rating of around 900 psi.

The higher rated stuff I am assuming is for more modern systems that run at much higher pressure than ours.

*** unless the carb regulations in your wonderful state require the 225 stuff.....

 

[mbz]

7 minutes ago, S30Driver said:

wonderful state

Ugh...! Don't get me started on California!

Thanks for the advice! Much appreciated!

[mbz]

OK, good news first... got the new FPR installed. It was much easier than I thought it would be (took less than 15 minutes) thanks to the hose grip pliers from harbor freight. [emoji3]

The bad news is that it didn’t fix the problem. [emoji22]

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

Fuel pressure while idling is 40 psi as well.

Same problem as before, engine idles rough, lots of dark smoke from exhaust.

Took oil cap off and idle is stable, but fuel pressure is still high = 40 psi (see photo).

If I go WOT engine cuts out at 3000 rpm, stumbles back to idle and either stabilizes at 900 rpm, or it dies.

Then same symptoms present, have to wait about 30-45 minutes to start the engine again because it is flooded.

Stumped again..... [emoji848]

 

Edited April 13, 2019 by mbz
added photos

[Zed Head]

If you want to try something simple just to see what should happen and make sure you're not losing your mind, take your old FPR and connect it after the fuel filter, dumping in to a container of some kind.  You'll need to block one inlet or create a loop, using a T fitting.  Put your pressure gauge in between the filter and FPR.  Pump > fuel line > filter > gauge > FPR > collection container.  Power up the pump and see what you get.  Should be 36 - 38 psi.

Here's a random thought - is it possible that the outlet on your gauge's "T" fitting is restrictive?  Maybe it is restricting flow, causing pressure to rise.  Taking the FPR out of the picture, except as a secondary restriction.

You might have a measurement problem.  Very common, in all engineering endeavors.

[S30Driver]

That is a trick set of pliers!

Have you measured the manifold vacuum at idle?  With the oil cap removed and the motor does not stumble, it indicates a problem there which would explain the high fuel pressure.

[mbz]

1 minute ago, S30Driver said:

Have you measured the manifold vacuum at idle?

I have not.

Would that be just a matter of connecting a vacuum gauge to the manifold where the FPR vacuum line connects?

[mbz]

5 minutes ago, S30Driver said:

That is a trick set of pliers!

https://www.harborfreight.com/3-piece-long-reach-hose-grip-pliers-37909.html

[mbz]

9 minutes ago, Zed Head said:

Here's a random thought - is it possible that the outlet on your gauge's "T" fitting is restrictive?  Maybe it is restricting flow, causing pressure to rise.  Taking the FPR out of the picture, except as a secondary restriction.

You might have a measurement problem.  Very common, in all engineering endeavors.

That may very well be the case (possibly adding 1-2 psi to the readings), however it still doesn't account for the running rich issue (too much fuel, not enough air).

I can take the pressure gauge out the fuel line and see what happens tomorrow morning.