When should fuel pump begin operating?

[ea6driver]

78 280Z. Fuel and electrical systems are totally stock. Car runs fine.

Should I be able to hear the fuel pump working when the key is turned to "on" or just when it's turned to "start"?

Currently the fuel pump does not operate until I turn the key all the way to "start" (starter motor engaged). Search function revealed conflicting answers - perhaps the answer is different depending on year model.

It seems to me that I used to could hear the pump come on when placing the key to "on" (years ago) and so I'm wondering if something has happened that only allows it to operate when engaging the starter ("start" position of key).

Any help is most appreciated.

[TomoHawk]

The fuel is turn on when the key is on Start. After that, the fuel pump stays on because of a set of contacts onide the Air Flow Meter.

[sblake01]

I've said this before but not louldy enough apparently so I'll try this:

78'S DON'T HAVE FUEL PUMP CONTACTS IN THE AIR FLOW METER!!!!!

Bob your car is working correctly. After a 78 starts it the fuel pump runs basically from a signal from the oil pressure sender. Look it up Tomohawk. No fuel pump contacts in the air flow meter after 1977.

Edited October 21, 2008 by sblake01

[beandip]

Good one. Once again.

[TomoHawk]

Sorry, you must have inaccurate or incomplete information. My engine, the wiring, and all the relevant literature I have all confirm a set of contacts in the air flow meter. Otherwise, I would not have said so.

Edited October 21, 2008 by TomoHawk

[Walter Moore]

Not to get into the fight, but the parts CD lists two fuel injection systems for the L28E. One from December 1974 to July 1977, and another for cars made after August 1977. Wouldn't a car made in Japan in late July of 1977 have been sold in the U.S. as a 1978 model?

(The U.S. automakers start production of the "next" year's model in July, so it seems logical that U.S. car dealers and BMV's would make the same assumption.)

I don't mean to start a fight. I am try to end one...

[TomoHawk]

This might be another of those peculiarities I've found on my car since I got it. Some look like factory things and some are from a PO.

thxZ

Edited October 21, 2008 by TomoHawk

[sblake01]

Sorry, you must have inaccurate or incomplete information. My engine, the wiring, and all the relevant literature I have all confirm a set of contacts in the air flow meter. Otherwise, I would not have said so.

If yours is a 78, you will note that the harness that plugs into the AFM doesn't have terminals on the side where the fuel pump contacts would be in the 75-77 models. I'm not here to argue with you but my 78 doesn't have them, the FSM says it doesn't have them and no 78 I've ever worked on had them unless the AFM had been changed and, even then, they didn't work because there is no circuit for them in a 78. It is you that is providing the inaccurate information. Edited October 22, 2008 by sblake01

[sblake01]

This might be another of those peculiarities I've found on my car since I got it. Some look like factory things and some are from a PO.

thxZ

That would be quite the set of peculiarities considering the amount of work it would take to put the earlier setup in a 78 and actually have it work. So you say that your 78 has fuel pump contacts? Does it have an externally regulated alternator? Is you fuel injection relay above the steering column (75-77) or under the hood(78)? Those are pre-78 items. What's your build date? Edited October 22, 2008 by sblake01

[ea6driver]

OK. Thanks for the responses. So the fuel pump shouldn't begin operating until I begin cranking the engine (key in "start" position). Sounds like that's what mine is doing.

Now it seems to me that this would imply that the fuel system should maintain pressure even after the engine is turned off. However, in my car that is not the case (I have a fuel pressure guage installed downstream of the fuel filter). Additionally, when I try to start the engine it doesn't start up immediately. I usually need to crank the engine 3 or 4 seconds (or maybe 2 or 3 seconds, haven't actually timed it) before it fires up. To me it seems like this delay is due to the fuel system repressurizing once I begin cranking.

What might be the most likely causes of the fuel system losing pressure when the engine is turned off? I was thinking fuel could be leaking past the cold start valve. The only real "problem" I'm having here is the additional cranking required to start the engine. But, hey, if it ain't right I'd like to try and fix it.

Thanks again for your ideas.

[sblake01]

The most common cause of this is a leaking check valve at the fuel pump outlet. It could be other components leaking such as injectors, cold start vavle, etc. but you don't seem to have any of the other symptoms, such as richness or black smoke, that go alon with that.

[Jeff G 78]

The most common cause of this is a leaking check valve at the fuel pump outlet. It could be other components leaking such as injectors, cold start vavle, etc. but you don't seem to have any of the other symptoms, such as richness or black smoke, that go alon with that.

Where exactly is the check valve and what does it look like? Is it part of the pump or between the pump and the metal fuel line? Mine has been losing pressure as well and I haven't taken the time to look around for the check valve.