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

[richard1]

It is not even 110 degrees yet here and I am starting to have more serious vapor lock problems than the years before.

1-All my lines are wrapped with insulation.

2-I have an electric pump at the gas tank.

3-Fuel filter is clean.

4-Mechanical fuel pump has been replaced last winter.

Here my questions:

1-Is it possible that the gas could be in vapor from the gas tank (electric pump) to the front filter? I removed the filter and there is no gas coming just from the electric pump. The pump works.

2-Could it be possible that the electric pump could be partially clogged not delivering a proper flow of fuel to the filter?

3-The front filter has never more than half of gas in the bowl. Is it normal? In the vapor lock situation, the filter is completely empty.

4-After one hour, the engine can be started again but the filter doesn't fill more than one quarter of its capacity which seems to me very low.

Thanks for any suggestions.

[DeesZ]

Is this on your '72? If so, I guess the electric fuel pump was an add-on, correct? I'm guessing here, but your 'vapor lock' situation sounds to me more like 'fuel starvation'.

#1 - The gasoline should not be getting hot enough from the tank to the mechanical pump to vaporize. I don't quite understand what you mean by "I removed the filter and there is no gas coming just from the electric pump. The pump works." If you are not getting gas, there is likely a clog somewhere.

#2 - Yes, that could be clogged. Does your electric pump have a filter on it? If so, I'd take a look at it.

#3 - My front filter often runs at about 1/2 or more full. If the car is not starting and the front filter is empty, it would appear to be lack of fuel.

#4 - After an hour it will start & the filter is still 'low'.... so, fuel eventually gets there after sitting a while. I had two situations similar to this..... one was a clogged fuel filter (in a GM car), and the other was crud from the tank floating around and blocking the inlet.

Generally, I would be seeking a resolution to the issue of getting too little fuel through the system, not vapor lock. I'd suggest starting at the back (the origin of the fuel flow) in the tank and working my way forward. FWIW, I have never had an issue with vapor lock with my '72. I hope that this helps.

[richard1]

The car is full stock original and has never been modified.

The problem occurs only in very hot climate situation during the day. Morning and evening, the car runs just fine with no problem and full power.

[richard1]

Deez, Thanks for your comment. My feeling is also that something is going wrong at the back because when the hose in remove from the filter and the rear pump is on, no fuel is coming to the filter for a very long time.

[DeesZ]

I think that you are narrowing it down.... The electric fuel pump should have things squirting pretty good up front very quickly. I'd suspect an obstruction or failure of the pump. I'd probably start with cleaning up the electrical connection and ground to the electric pump. A long shot, yes, but easier than the next steps that require removal and inspection of parts... Please keep us posted... Hopefully someone else will chime in here with a silver bullet!!

(As an aside, what's the build date of your Z?)

[richard1]

4/72, #78117

[richard1]

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.

[DeesZ]

That sounds like a plan.

Mine is not far from yours .... although no electric pump.

05/72 - 84646

[d240zx2]

You could have a kink (dent) or other obstruction in the line from the electric to the filter. If your pump is running and not delivering gas, you've two options: clean the lines (via air or other chemical means) or replace a pump that is running but not performing.

Have you run the pump directly into a container (short of the main fuel delivery line to the front)? This may help you determine whether the problem is a line blockage or a pump problem.

Frank

[Arne]

Also, check to make certain the hose connections between the electric pump and the tank are tight and well sealed. If these connections aren't tight, the pump can suck air and not pump fluid. I've seen it happen on one of my Zs.

[richard1]

1-Checked the rubber hose from the metal pipe and connecting to the filter. Looked OK but I replaced it and the filter also.

2-Disconnected the fuel line at the electric pump. Blew air from the fuel filter. Looks OK.

3-Blew air in the fuel pump. Looks OK.

4-Started the fuel pump. Good flow of gas.

5-Installed a filter between the tank and the electric fuel pump.

6-Checked all clamps.

7-Checked the flow of the electric pump to the filter. Its OK.

I put the car in the sun (110 degrees now) and started the engine and let it run for 15 minutes without the electric fuel pump on. The engine idled rough after 15 minutes and died. I adjusted the throttle for 1000RPM with all the accessories on including A/C and I engaged the fuel pump.

With all the accesories and electric pump on, the engine run for another 10 minutes and died without being able to start it again.

The engine temperature is normal.

I removed the filter from the hose coming from the line: the filter is dry.

I started the electric fuel pump alone and nothing is coming from after two minutes.

To conclude, the problem happens when it is very hot. When cold, the electric pump give gas supply but when it is very hot it fails.

[z74z90]

Not offering a solution to your particular problem, but I am the original owner of a '74 that has always had vapor lock issues. I added a "fuel injector fan" from the '79-'83 years that has proven quite helpful. I have it on a manual toggle switch and only use it when it is very hot and humid. It definitely helps. Just a thought for consideration.