Vapor Lock?

[vercingetorix]

For the last two days every time the temp goes a little above the center of the gauge, I'm guessing abut 195 to 200 or so,the engine quits and won't start again til it cools down. I have never had this problem before and the heat on one trip last year went quite a bit higher than it is now with no problem. I've checked the obvious,water level, fuel filter, fuel pump etc. and found nothing. The outside temps have been a bit higher than normal but nothing serious and heat like this has never been a problem before.

I'm stumped. I am running Z Therapy SU's if that means anything.

Any input greatly appreciated.

Best,

HCH

[naviathan]

Wrap the fuel lines in insulation to stop vapor lock. That's what it sounds like you have happening.

[vercingetorix]

You mean the fuel rails?

[Arne]

Hugh, when it stops, does it stop suddenly, or does it sound like it's running out of gas (stumbling and such before dying)? I can think of a couple other possibilities for temp-related things.

If it dies suddenly, you could be losing ignition. Some ignition parts can be temp-sensitive if they are failing, such as coils or EI modules (if any).

If it sounds like it is running out of fuel, perhaps it is. Fuel pumps (especially mechanical units) can fail when hot, but work acceptably when they are cool. If you are running the stock mechanical pump, check the float bowls for fuel next time it dies.

[vercingetorix]

it seems like its running out of gas, if I stop it will bumble along for a couple of minutes before it dies completely. But wouldnt vapor lock keep the fuel bowls from filling also? The fuel pump is comparativly new maybe 18 mos. or so.

[beandip]

This is the reason Nissan went to the electric pump in '73 , mostly. If you look under your car by the tank sending unit , you should find two wires rolled up and taped with blue tape. These are the factory wires for a electric pump. I don't know about a '70 but the other 240s have them there. Follow the wires going to the sending unit back towards the rear of the car. One thing about the mechanical pump is they do get hot and they do heat the fuel coming from the tank. With the fuel lines running along the engine and over the manifolds there is a lot of heat . This can cause the gas in the lines to boil and this causes what you are describing. The electric pump , being in the rear of the car remains cooler and continues to pump cooler fuel. This pushes the unused fuel that is heated back to the tank through the return line. This helps greatly to alleviate this problem.

[vercingetorix]

I'll check tomorrow.

where and how does the electric pump mount exactly, and is the wiring for it already ignition hot?

[beandip]

No it is not ignition hot. there is a in-line fuse under the dash on the driver side up on the left by the radio. Contact EScanlon he is the guru on all of this. He is the electrical guy and he helped me with my Z. We worked it out and it works great. He can tell you what color wire to fine and how to connect it. The green wire is the hot. I did connect a pressure switch to activate the pump when the oil pressure reached about 6 PSI. this is a safety measure . Only will cost you about $6.00 and may save your engine , car or life.

[beandip]

If needed , send me a PM I still may have pictures of the pump and how I mounted it on my Z . It is no big deal and easy to do.

[toecutter]

I'd be interested in seeing those pics?

[Ramses]

On my '73, the electrical fuel pump is wired to the engine compartment harness in between the harness and the voltage regulator. It was disconnected for the longest time and when I connected it, the noise from the electrical fuel pump was great, but it solved my fuel starving problem. I have since disconnected it and replaced my mechanical fuel pump. The pressure from the mechanical pump kept bouncing from 1 to 5 psi, now I get a constant 4.5 psi. I have no more fuel staving situations.

[vercingetorix]

Just another side note on my fuel system, I need a piece of the smaller braided fuel tubing for the return line from the fuel rails. The dealer here does'nt even list it. Does anyone have a line on it or a replacement for it, mine is cracking and I can't push it up any further.

Gary, Thanks again for the pics and detailed explanation, outstanding!

Best,

H Houghton