What maintains the fuel line pressure when the care is off?

[Gary L]

When I rev it up a little, the fuel pressure does jump from 28 to may be 29 for a second or two. But why isn't it closer to 36 as specified in the FSM?

 

When I put a vacuum gauge on my engine, it does read a steady 17 and when I flick the throttle, it drops to zero then up to about 25 and then settles back to a steady 17, so I do think I have a "healthy" engine.

 

Gary

[Zed Head]

You need to either remove the vacuum hose from the bottom of the regulator, or measure the pressure without the engine running by removing the yellow wire from the starter solenoid and turning the key to Start.

 

The purpose of the vacuum hose is to maintain a constant fuel pressure from one side of the manifold to the other.  So if pressure inside the manifold increases (vaucum drops), pressure inside the fuel system increases.

 

You can also convert inches of vacuum to pressure.  17" = 8.3 psi.  28 + 8.3 = 36.3 psi.  Looks good.

[EuroDat]

+1 on Zed Heads description. Sorry for not mentioning the lower pressure with manifold vacuum. My bad.

The jetronic system calculates fuel mixture based on a constant 36psi across the injector tip. If the manifold has a negative pressure (vacuum) the fuel pressure regulator will adjust the pressure accordingly. Hence the vacuum hose connected the the FPR.

Certainly looks like your FPR is causing your pressure loss.

[Captain Obvious]

You must have lovely spark plug insulators! 

 

I bet you say that to all the Z's.

[Gary L]

I put a new Bosch FPR on it a couple of days ago and now it starts right up after cranking for only a couple of seconds.

 

Thanks everyone

Gary

[Martzedcars]

My (Longago sold..) 1980 280zx fuelpump started right after putting contact to on.. you could here it run and stop when pressure was high.. my 1979 280zx (currently in restauration.) does not do that.. the fuelpump starts together with the cranking of the engine.. they altered this in the early 1980's...

 

One could change the wiring from a 280z or early 280zx to the better configuration..

 

fwiw.

Mart

[Gary L]

Hi Mart, I've thought about doing that. It seems some of my other newer cars are set-up like this. However, I think they also have an inertia switch in case of an accident. Datsun set it up that way for safety. I'd like to change it so that the pump starts when the key is in the on position, but I'm not very good at wiring stuff. If someone else has done this and has some nice, easy to follow instructions on doing this, that'd be great.

 

Gary

[Consigli]

I have a 1978 280Z with a leaking Fuel Damper. Does anyone have a NOS one for sale? Its part number 22675-N4200 or 22675-N4205. Thanks! 

[Redwing]

Reading all this. So what it is saying is:

FPR'S should hold pressure overnight.

Is that right?

Thank you,

Jai

Edited November 25, 2015 by Redwing

[siteunseen]

I have a 1978 280Z with a leaking Fuel Damper. Does anyone have a NOS one for sale? Its part number 22675-N4200 or 22675-N4205. Thanks! 

You can try zcarsource

 

http://www.zcarsource.com/fuel-damper-280z-280zx-75-83-new_8_77824_52489.html

[siteunseen]

Reading all this. So what it is saying is:

FPR'S should hold pressure overnight.

Is that right?

Thank you,

Jai

Yes, a good FPR will hold pressure indefinitely.  My '77 will crank right up after sitting for a week, leave it a month and I have to turn it over a few times before it cranks.

[siteunseen]

I can't edit that post but this thread talks about the check valve in the original fuel pump.  It works like a valve stem for a tire but backwards, it lets fuel leave but not flow back in.