Fuel pump on 72 Z

[richard1]

It may be a stupid question but I have an argument with my son.

Last year I installed an electric fuel pump to supply the mechanical one when the temperature in Las vegas goes up to 100F because of vapor lock and gas evaporation.

He is the primary user of the car that is fully original with A/C.

Since I have never been able to fix the problem of the electric pump to works without at least the parking lights being on, he tells me that the gas consumption is a lot higher.(there is something weird in the wiring harness to add this optional electric fuel pump that was part of the 73 set-up but optional on the 72)

It seems that the gas consumption with the A/C on without the electric pump is better than 200 miles for a full tank of gas but when the electric pump is on it goes under 200 miles.

The car is mechanically perfect and we are aware of top maintenance in the warmest months here.

Who is right?

[hls30.com]

Sounds like the perfect mechanical shape would warrant spending the energy to correct the electrical system-it could be that the lights, fuel pump,and AC clutch are enough load to tap out your alternator, and thereby max out its parasitic drag. The AC clutch is enough to dim the lights and seriously impede the windshield wiper action in every stock 240z electrical system I have encountered. The easy test, Start the car with nothing on, one at a time turn on the required lights and then the AC, all while watching the AMP gage. You have the straw that maxes the drag from the camels alternator!

Will

[Arne]

There's another possibility as well. What if the addition of the electric pump is pushing the fuel pressure over 5 PSI? Get much over that and the needle jets in the float bowls might not close tightly, pushing the float level up, and richening the mixture.

[EScanlon]

And by all means get the Electric Fuel Pump onto the circuit it belongs to and not with the lights, which due to the inherent resistance in the wiring, AND the A/C, AND the lights themselves, are undoubtedly causing the alternator to work overtime as Will has pointed out.

Look behind the Fuse Box, and locate a 2 wire connector with a Green and Black with a White Stripe pair of wires. That's where you can plug in a 20 amp fuse and have power at the terminals for the factory wiring for the fuel pump. This will power the fuel pump once the engine starts and run it off the ignition switch (that's why it needs it's own fuse).

Then take her out for a spin and check mileage.

But Arne's point may be very valid. There is a valve at the front of the engine compartment that regulates how easily the "overflow" of fuel is allowed to return to the gas tank, but as far as I know, this is not adjustable.

Is this "vapor lock" an ACTUAL problem, or a perceived / read about problem? I can understand that Las Vegas gets VERY warm, (read that HOT!), BUT dual fuel pumps seems like something needs to be addressed. You might be, literally, pouring fuel down the drain.

2¢

E

[EScanlon]

I was visiting NWCubsman to help him remove the dash from his car, and we discovered something of direct impact on this thread.

Take a look at the pictures below; in them you'll see a Fuse Holder with a Green and a Black/White wire going to it. That is the OEM Fuse Holder for the Fuel Pump. The White Clips on the side of the Fuse Box is where it is clipped onto.

As an aside, if you look at the last picture, you'll see a 2 wire connector that's taped to the harness with blue tape. Take a look at the colors of the wires. They are Red and Green/White. That is the connector that goes to the Fog Lamp Switch, and presumably a fuse could also be installed there, but none of the schematics show an inline fuse for the fog lamp. All you need to do is to insert a switch here to control the Fog Lamps plugged into the original wiring connectors up at the front of the car.

FWIW

E

[richard1]

So, if I understand, the blue taped female connector would be for the fog lamps but why did I found a male connector and it relies to the electric fuel pump?

Also, it means that the fuse holder that you are speaking about must be hidden far under the dash. Did you found a fuse in it and is the car a 72?

I have not these white fuse brackets on the side of my fuse box.

[EScanlon]

So, if I understand, the blue taped female connector would be for the fog lamps

That's Picture #4, and I included it ONLY to show how people would find it. It has nothing to do with the Fuel Pump. It was a point of interest picture only. And ONLY because we were in the same area and the connector was immediately to the side of the Fuel Pump Fuse.

Don't read more into it than that.

...but why did I found a male connector and it relies to the electric fuel pump?

Also, it means that the fuse holder that you are speaking about must be hidden far under the dash. Did you found a fuse in it and is the car a 72?

I have not these white fuse brackets on the side of my fuse box.

Male/Female Connector labels can get confusing when you're referring to the METAL or to the PLASTIC. Typically SPADE connectors are mounted such that the MALE METAL spade ends up MOUNTED in the FEMALE PLASTIC connector and viceversa.

So take a look at pictures 2 and 3 and you'll see that the In-Line Fuse Holder is connected to a Female Plastic housing that holds two Male Spade connectors.

Since you do NOT currently have the fuse holder connected and in the circuitry (because you connected to the light circuit), you would have a Male Plastic Connector holding two Female Metal Spade connectors in it.

Hopefully this clarifies rather than creating more confusion.

That you don't have the white fuse holders is because you didn't have the Fuel Pump Relay Fuse mounted at a dealer back in the day. I mention what it's for for those people that have the white clips and don't know what they're for.

As far as locating that connector, it should be right behind the Fuse Box, and should be easily located. At worst, you might have to move the fuse box by unscrewing it from the hump bracket, but that should really be all it should take.

E

[Arne]

Also, it means that the fuse holder that you are speaking about must be hidden far under the dash. Did you found a fuse in it and is the car a 72?

The car those pictures are from (nwcubsman) is a '73, which came with the electric pump from the factory. My early '71 has the wires and connector, but it is unused and there is no fuse holder or clips on the side of the fusebox.

[richard1]

Thanks to Escalon and Arne for the clarifications.

Next weekend, i will investigate further about the hidden wiring and connections as told by arne and i will come back with my comments.

As for the eletrical pump pressure mentionned in one of the posts above, it is rated beetween 2 and 5 PSI.

I have a 160 thermostat but in very hot days after shut off and start up, I have the feeling that the engine is starving in traffic or at stop lights and idling a lot lower than when the engine is cool. The temperature is always normal no matter it is 100 0r 115 in the traffic at idling but my feeling is the gas is evaporing during the time it goes from the tank to the carb bowls.

I am pretty sure that it is a percolating problem because I have owned a fully restored 1949 Buick Riviera until two years ago and I discovered after many years that my problem during the summer was the gas percolating in the filter bowl causing the carburator to get "dry".

For the Z, I observed that the electrical pump helps during the hottest days and when I start the car after a stop of ten to fifteen minutes beetween errand, it is easier for the engine to iddle smoother.

[Rick Bolus]

If its a late 72 it should have the extra fuse conector and if it has not fallen off look for a silver decal, I have seen some that said fuel pump on them.