Delphi Mechanical Fuel Pump stops pumping fuel

[HappyZ]

@David Downs would putting the check valve on the other side of the fuel filter allow you to retain that fuel too?  Just a thought.

[dutchzcarguy]

9 minutes ago, wadelester said:

putting the check valve on the other side of the fuel filter allow you to retain that fuel too?

Sorry to but in but yeah i think so..

My early 240z starts when warm in a little kick from the starter but when cold i Always have to start a longer time, he Always starts but it needs to suck some gas.. i think.. on the other hand there should be enough gas in the carb bowls.. never realy investigated it but always started that way.. (Mine has no check valve )

[w3wilkes]

I've removed my mechanical pump and have gone electric at the tank. When cold I apply full choke, turn on the key and let the pump run for a few seconds until I hear a slight change in the pump sound which I think is when the system is fully "charged" with fuel. Then holding gas peddle to the floor it always takes 5 to 10 seconds of cranking before it comes to life. Once it fires up I can reduce choke to almost nothing and by the time the oil pressure comes up I can eliminate the choke. When the car is warm I just bump the key and it starts right up.

On my '73 it was about the same story as my current early '71. I had the full dealer stuff on the '73 to address vapor lock so it had both electric and mechanical pump.

[David Downs]

1 hour ago, wadelester said:

@David Downs would putting the check valve on the other side of the fuel filter allow you to retain that fuel too?  Just a thought.

I installed the check valve between the fuel filter and metal fuel rail to the SU carbs. 

 

[David Downs]

On 5/9/2020 at 11:17 AM, w3wilkes said:

I've removed my mechanical pump and have gone electric at the tank. When cold I apply full choke, turn on the key and let the pump run for a few seconds until I hear a slight change in the pump sound which I think is when the system is fully "charged" with fuel. Then holding gas peddle to the floor it always takes 5 to 10 seconds of cranking before it comes to life. Once it fires up I can reduce choke to almost nothing and by the time the oil pressure comes up I can eliminate the choke. When the car is warm I just bump the key and it starts right up.

On my '73 it was about the same story as my current early '71. I had the full dealer stuff on the '73 to address vapor lock so it had both electric and mechanical pump.

I'm going to add the electric fuel pump soon.

 

[Zed Head]

You could plumb one of these up in to the cabin.  It's funny, but I had to do a similar starting routine on my EFI engine after I removed the cold start valve.  Crank for a couple of seconds, wait for fuel to vaporize around the intake valves., then fire it up.  That was only after it had sat for a couple of weeks.

https://www.dhgate.com/product/fuel-pump-hand-primer-bulb-all-fuels-length/404919119.html#seo=WAP

[rosaaen89]

have you figured out the issue ? i’m having similar problem. if i prime the fuel system to get fuel in the filter it’ll run. once it sits the fuel drains out of the filter back to the tank and won’t start. i’ve replaced the pump twice and redid the fuel hoses and blew air threw the hard lines to ensure it’s all good. i’m thinking of dropping the tank to clean it out

[AK260]

I know we’ve gone off topic a little, however, permit me to add to the chorus ....

 

I was going to fix this issue with a non-return valve, however, as my incredible mechanic of a father in law pointed out: if the engine has been standing for a while, there is a benefit to cranking for 10-20 seconds without it firing, as it gets the oil around first. On my engine, the oil pressure starts to rise on the gauge just before it fires. So I’ve stopped worrying about it when I crank and instead enjoy the thought of all that lovely oil covering the cam and the bores before the revs arrive. ;)

 

If you use the original style filters, they have a simple and effective non-return built in, by having the vertical inlet pipe inside the filter housing higher than the normal height of the fuel in the filter. So it “shouldn’t” be drying out unless you live somewhere mega hot and / or have an air leak somewhere.

 

 

Despite the fact that the float bowls and fuel lines have fuel in them, if there is air in the pipe work, the pumping action is just compressing the air and you’re not building sufficient fuel pressure as a result; until it’s blown out of the return line’s restrictive orifice on the fuel rail and the float bowls (depending on where the air is). I would imagine that when standing, the floats in the bowls aren’t fully closed and over time, air is very slowly sucked through them back into the fuel rails.

 

After stopping the car, heat soak will warm up the float bowls and the pressure from the fuel vapours will blow some fuel out of the bowls through the jets, or indeed evaporate through the jets, thus marginally reducing the volume of fuel and the floats dropping. Remember, when the engine is off, the jets are still somewhat open. The fuel then cools, the floats drop further and hey presto, you have a way for air to enter the feed lines. Notwithstanding of course that the fuel in the rails also heats, pushes through the return line, then cools and sucks air from anywhere it can.

 

So in short, even with a return valve you’re not totally going to fix this issue and frankly, it’s a benefit in getting the oil going after a long period of standing; replacing what gravity and heat soak took off the areas it needs to be, before the straight 6 warbles into life!

 

 

 

You could plumb one of these up in to the cabin.  It's funny, but I had to do a similar starting routine on my EFI engine after I removed the cold start valve.  Crank for a couple of seconds, wait for fuel to vaporize around the intake valves., then fire it up.  That was only after it had sat for a couple of weeks. https://www.dhgate.com/product/fuel-pump-hand-primer-bulb-all-fuels-length/404919119.html#seo=WAP

 

 

Finally, under pain of death don’t EVER plumb this into the cabin!! There are very good reasons why fuel lines are not routed inside the cabin. The last thing you need is to be the meat in a car-b-q with its own fuel source, or should that be sauce? Dad joke alert!!!!!

 

 

Essay over - Less of a chorus, more of a bohemian rhapsody I fear! ;)

 

[David Downs]

7 hours ago, rosaaen89 said:

have you figured out the issue ? i’m having similar problem. if i prime the fuel system to get fuel in the filter it’ll run. once it sits the fuel drains out of the filter back to the tank and won’t start. i’ve replaced the pump twice and redid the fuel hoses and blew air threw the hard lines to ensure it’s all good. i’m thinking of dropping the tank to clean it out

I rebuilt an original pump and it seems to have fixed my issue. The check valves in the aftermarket pumps are junk. I would take apart one of your failed pumps and look closely at the check valves. It was obvious my check valve failed.

[Zed Head]

On 5/10/2020 at 10:06 AM, Zed Head said:

You could plumb one of these up in to the cabin.  It's funny, but I had to do a similar starting routine on my EFI engine after I removed the cold start valve.  Crank for a couple of seconds, wait for fuel to vaporize around the intake valves., then fire it up.  That was only after it had sat for a couple of weeks.

https://www.dhgate.com/product/fuel-pump-hand-primer-bulb-all-fuels-length/404919119.html#seo=WAP

This was meant as a joke.  Thanks AK for clarifying.

[AK260]

This was meant as a joke.  Thanks AK for clarifying.

ROFLMAO - I did wonder how someone as wise as you had made that suggestion! [emoji1787] I need to sleep more and regrow the sense of humour!