Worsening vapor lock problem.........

[justinr54321]

Richard, with that, sounds like the electric fuel pump may be going bad. Check its electrical connections first, and the wiring to it. If not, then replace the pump.

Justin

[Mat M]

With all the trouble you have been having...how do you KNOW the mech pump is fine?

Have you actually pulled the mech. pump and opened it up to see:

A) if the diapragm is actually intact; (one of mine was torn)

the one-way valves are functioning properly;

and C) the return spring hasn't dislodged (l also has a pump return spring diengage)????

[richard1]

in very warm temperature my deduction it is coming from the rear.

I may also suspect that the mechanical pump may have a problem because it doesn't seems normal that when the engine his hot and turn off, there is a low "eesssss" noise coming from it. I don't know if it is the diaphram or a valve inside the mechanical pump that does this noise when the engine cool down.

Anyway, I replaced the electric pump and put the car at idle in the sun for 15 minutes without the electric pump. It died as before in the same period of time. I started the car again and put the electrical pump on.

Runs rough when on for a minute or so but better after for about ten minutes with all accessories on. I stopped the testing short because the new pump started to be very noisy.

I brought the car back in the garage and checked the gas flow in the line. It seems to be OK.

I now have to go for a replacement electric pump.

Conclusion: The problem seems to be the electric pump but I am not sure if the mechanical pump is not also a problem because the engine doesn't idle smooth when very hot.

Again the temperature is normal.

[justinr54321]

With all the trouble you have been having...how do you KNOW the mech pump is fine?

Have you actually pulled the mech. pump and opened it up to see:

A) if the diapragm is actually intact; (one of mine was torn)

the one-way valves are functioning properly;

and C) the return spring hasn't dislodged (l also has a pump return spring diengage)????

Matt, that sucks when that happens. When I'm finally able to afford it, I'm gonig to be picking myself up an electric pump, and get rid of my mechanical pump, and just put a block off plate there, for I eventually plan on going with a triple mikuni set up.

[Mat M]

in very warm temperature my deduction it is coming from the rear.

...snip...

Anyway, I replaced the electric pump and put the car at idle in the sun for 15 minutes without the electric pump. It died as before in the same period of time. I started the car again and put the electrical pump on.

Runs rough when on for a minute or so but better after for about ten minutes with all accessories on. I stopped the testing short because the new pump started to be very noisy.

...snip...

Emphasis mine.

DING DING DING, we have a winner. Have you had your fuel tank 'boiled'?

These are THE EXACT symptoms I was having before I bit the bullet, dropped the tank, and had a radiator shop boil the thing out.

My diagnosis: there is crud either in the pick-up tube, or on the pick-up screen, that when left alone, settles out of the way enough to begin letting fuel through, then eventually jams itself in the pick-up tube when the flow lifts it back into place.

The givaway is the elec. FP, quiet at first, then when the restriction hits, it gets noisy. It can't overcome the clog, and the mechanism starts to cavitate.

[edit] I should also add that my car was dying wether or not I had my elec. FP installed, and wether or not I had my in-line regulator at 2 PSI or 5. [/edit]

[Mat M]

Besides, as I recall, vapor lock is defined as the fuel heating up over the exhaust manifold to a point where it begns to disassociate.

[Mat M]

...snip... I'm gonig to be picking myself up an electric pump, and get rid of my mechanical pump, and just put a block off plate there, ..snip...

Why wait? If you have an elec. FP, you won't need the mechanical one. Electric PFs are literally only $30 bucks, new, $5 at a P&P. Do you have a grinder, or a Dremmel type tool and a drill motor with a set of bits?? If you can find some plate stock, even if it's from an old file cabinet, you can make a template out of the mech. FP gasket, get some RTV, and make your own block off plate.

*It's sad that in this day and age, one must succomb to doing the following:*

WARNING- IF you DO decide to go with an elec. FP, please go the extra mile to ensure you have some sort of automatic shutoff device, wether it be a relay connected to the oil pressure sender, or otherwise. I for one, and I am sure others on this site, would not want to have you and your car engulfed in flames fed by an electric FP that did not disengage in the event of an accident.

[gogriz91]

I have similar problems with a new electric back at the fuel tank. I'll probably just relocate it to the engine bay, the thing seems to work better when it pulls the fuel than when it pushes it.

[Derek]

I had similar problems with my 73 and SUs. I tried everything I could think of including adding an electric pump. I ended up switching the fuel pickup to the drain plug on the tank and all my problems disappeared. This may not help you but I thought I would throw it out there.

Derek

[jtl260z]

Has been redone three years ago but no filter between the tank..... and the electric pump.

My best bet is to change the electric pump and install a filter at the inlet.

Richard,

Provided you electric pump is defective... try bypassing it. Your electric fuel pump is only for priming.

I have a 1974 260z with the same set up. My electric fuel pump failed and I removed it and reconnected the lines. I haven't had a problem since. The mechanical fuel pump is all you need for that car.

Hope this helps,

[Mat M]

I have similar problems with a new electric back at the fuel tank. I'll probably just relocate it to the engine bay, the thing seems to work better when it pulls the fuel than when it pushes it.

This is contrary to everything I have ever read about elec. FPs.

[Weasel73240Z]

FWIW, I run my 73 (new ZTherapy SU's) with the mech. pump only, no problems at all. I have the factory-added elec. pump at the tank also, but I bypassed it. Of course, MA is a bit cooler than NV.