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David Downs

Delphi Mechanical Fuel Pump stops pumping fuel

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On 4/25/2020 at 1:20 PM, Zed Head said:

This is the bothersome part.  I'm not an SU guy.  But the float bowls should not be siphoning empty with the filter's emptying.

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The car should run as long as there is fuel in the fuel bowls. Every time the filter runs out of fuel the car will keep running until the carbs are dry.

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Posted (edited)

oops

 

Edited by Zed Head

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14 minutes ago, David Downs said:

The car should run as long as there is fuel in the fuel bowls. Every time the filter runs out of fuel the car will keep running until the carbs are dry.

Does the filter run dry while the engine is running?

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31 minutes ago, Zed Head said:

I think that the heart of the problem might be the bad valving.  Have you checked pressure, and capacity?

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I have not performed the specific test. However, I think it's clear the Delphi fuel pump is the issue. Maybe the non original pump design is actually a better design.  

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5 minutes ago, Zed Head said:

Does the filter run dry while the engine is running?

Only if the car was parked for a little while. After restart she will run on the fuel that is in the carbs and filter until its dry.

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I think that this was a good idea, below, and it's telling about the valve quality.  Maybe you can find an old Nikki pump.  Pretty common to have to fix new aftermarket parts.

 

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Posted (edited)

When I was a kid, my first car was a '73.  Flat top carb issues aside, periodically my fuel filter would run dry and the engine would stall.  I disconnected the fuel line from the filter and put a long hose into a glass jar of gas which eliminated the tank and lines as being the problem.  Periodically, it wouldn't draw fuel. So I concluded it was my factory pump.  I replaced my pump and had the exact same result. At the time, I was told it was vapor lock which was common with that year but the behavior acted like it was the fuel pump. 

Today, I have a low mile '71.  It runs very well.  But I only drive it once per month during the summer. A year or two ago, if it sat, gas would drain from the fuel filter.  I would need to crank it for about 20 seconds or so to get it started.  My son would witness gas coming back into the filter which resulted in it starting soon after.  That made no sense to me since I knew there was gas in the float bowls regardless of what the filter looked like.  I installed a different pump and made sure the fuel line clamps were tight so no air could get in and allow the fuel to return to the tank.  Now the fuel remains in the filter but I still crank it 20 seconds or so if it has sat for a week or two. So the bottom line is there was no noticeable difference in how quick it started based on how much fuel was in the filter.  I will be curious if that check valve makes a difference.

Edited by 87mj

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2 hours ago, 87mj said:

When I was a kid, my first car was a '73.  Flat top carb issues aside, periodically my fuel filter would run dry and the engine would stall.  I disconnected the fuel line from the filter and put a long hose into a glass jar of gas which eliminated the tank and lines as being the problem.  Periodically, it wouldn't draw fuel. So I concluded it was my factory pump.  I replaced my pump and had the exact same result. At the time, I was told it was vapor lock which was common with that year but the behavior acted like it was the fuel pump. 

Today, I have a low mile '71.  It runs very well.  But I only drive it once per month during the summer. A year or two ago, if it sat, gas would drain from the fuel filter.  I would need to crank it for about 20 seconds or so to get it started.  My son would witness gas coming back into the filter which resulted in it starting soon after.  That made no sense to me since I knew there was gas in the float bowels regardless of what the filter looked like.  I installed a different pump and made sure the fuel line clamps were tight so no air could get in and allow the fuel to return to the tank.  Now the fuel remains in the filter but I still crank it 20 seconds or so if it has sat for a week or two. So the bottom line is there was no noticeable difference in how quick it started based on how much fuel was in the filter.  I will be curious if that check valve makes a difference.

Clearly I'm not the only one having these issues. The only difference we are having is my car will start right away if fuel is in the float bowls. The problem for me is when the fuel drains back to the tank and my car burns all the fuel in the float bowls before fuel returns to the filter. I'm assuming by installing the check valve my fuel will always be in the filter and eliminate the air gap between tank and float bowls. Looking forward to a fun day of driving and not being towed. 

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@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.

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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 )

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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.

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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. 

 

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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.

 

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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

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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

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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.

 

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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

image.png.558e1c9e7d3ae8eac24142f40e48fbc9.png

 

 

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! ;)

 

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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.

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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

image.png

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

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


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

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