Delphi Mechanical Fuel Pump stops pumping fuel

[David Downs]

57 minutes ago, siteunseen said:

My cruddy tank would let me drive about a mile before clogging up the fram g2 I had right out of the tank. Took the front hose off at input of that filter. Blew like crazy with my mouth until it was gurgling in the tank then I could get back home, barely.

 

It's possible my tank has debris. However, I can use a vacuum pump and suck fuel to the filter. I can remove the Delphi pump and hand pump fuel to the carbs as well. 

[Zed Head]

2 hours ago, David Downs said:

Also, I removed the pump and manually pumped fuel back to the carbs to see if she would start.

My impression is the fuel pump is not getting enough motion. I believe the pump should pump on a 7mm lift. I think it needs more lift to get a full pumping stroke. Time to add an electric fuel pump.

Seems like you have it narrowed down pretty well.  A bad aftermarket product is not uncommon.  You could just return it and get a different brand.  Delphi looks like a run of the mil auto parts store brand.  No offense.

https://www.rockauto.com/en/catalog/nissan,1972,240z,2.4l+l6,1209169,fuel+&+air,fuel+pump,6256

 

[David Downs]

1 minute ago, Zed Head said:

Seems like you have it narrowed down pretty well.  A bad aftermarket product is not uncommon.  You could just return it and get a different brand.  Delphi looks like a run of the mil auto parts store brand.  No offense.

https://www.rockauto.com/en/catalog/nissan,1972,240z,2.4l+l6,1209169,fuel+&+air,fuel+pump,6256

 

Which pump would you purchase? I purchased my Delphi from RockAuto and they stopped selling it. Makes me wonder after installing 2 of them. The same pump was installed on a friends car and he is having similar issues. 

[Zed Head]

I don't know the mechanical pumps well.  Airtex makes some good products.  Carter has been around for a while.

The carb'ed guys would know better.  If you go electric then you need to think about safety shutoffs and proper pressure regulation, and wiring and other odds and ends.  It's simple in concept but takes some work.  There are threads on the site about problems trying to go electric.  There's always something...

Or, and if you can't return that pump it might be worth a shot, maybe adjust the arm.  You seem to think that it works if it gets proper stroke.  Maybe the first part of the stroke is dead and if you get the arm closer to the eccentric it will work.

[David Downs]

3 minutes ago, Zed Head said:

I don't know the mechanical pumps well.  Airtex makes some good products.  Carter has been around for a while.

The carb'ed guys would know better.  If you go electric then you need to think about safety shutoffs and proper pressure regulation, and wiring and other odds and ends.  It's simple in concept but takes some work.  There are threads on the site about problems trying to go electric.  There's always something...

Or, and if you can't return that pump it might be worth a shot, maybe adjust the arm.  You seem to think that it works if it gets proper stroke.  Maybe the first part of the stroke is dead and if you get the arm closer to the eccentric it will work.

Funny you mention adjusting the arm. I tried on one of the other two pumps and damaged the arm. The arm cracked. Probably needs heat but fuel residue and heat don't mix to well. I ordered the least expensive GMB pump just in case it's not the Delphi pump. Thank you Z friends for all the support. I will let you all know the results next weekend once I install the new pump.

[David Downs]

Update on my mechanical fuel pump issues. I received a replacement pump (GMB brand from RockAuto) that is the same style as the Delphi. Installed the pump, cranked the engine for 10 mins plus until fuel filled the carb bowls. Once I had fuel in the carbs she ran really well. I let the car sit overnight and noticed the fuel in the filter had drained back to the tank. She fired up with ease but the fuel filter was slow to fill and the engine experienced hesitation. Today, I started the car on the first crank but there was no fuel in the filter. While running you could see the fuel begin to fill the filter but the pump could not keep up with the demand and she ran out of fuel. Is there a fuel pump eccentric with a larger lift (more than 7mm) that could increase the pump lever action (Manually you can pump plenty of fuel.)? My factory cam eccentric has been inspected and looks to be functioning as designed. I ordered a fuel check valve to install between the fuel pump and filter. I'm hoping this will keep the fuel filter full so the fuel is closer to the carbs and less work for the mechanical fuel pump.

[siteunseen]

I always use full choke on the first crank and let it run until it starts to stumble. This fills my filter everytime.

Have you checked float chamber height lately? Before my filter was always filling, never full. Adjusted the floats and now it fills completely up within a few seconds. This is observed at idle of course.

Glad you found a good pump! I run a cheapo GMB too without issue.

[240Znomad]

When I got my 240Z running a few years ago (after sitting for 28 years), I replaced the original Nikki pump (mechanical) with a new GMB pump as the rubber diaphram inside the Nikki pump was dried and cracked.  The new GMB pump worked initially, but soon (just a few rides) it stopped pumping fuel and I saw the same issue you did, after turning the engine off, the fuel in the fuel filter would slowly drop.  I purchased a new GMB and the same thing happened, it worked for a few rides, then quit holding a vacuum (ie. sucking in fuel).  I figured the one way valves on the new GMB pumps were failing so I took the bottom half of the new GMB pump (side with the rubber diaphram) and the top of my old original Nikki pump (side with the two one way valves) and mated them together.  It has so far been working well.

[David Downs]

6 minutes ago, siteunseen said:

I always use full choke on the first crank and let it run until it starts to stumble. This fills my filter everytime.

Have you checked float chamber height lately? Before my filter was always filling, never full. Adjusted the floats and now it fills completely up within a few seconds. This is observed at idle of course.

Glad you found a good pump! I run a cheapo GMB too without issue.

I started my car with full choke as well. My float bowls should be fine but I'm going to get some clear fuel line to confirm. 

Just now, 240Znomad said:

When I got my 240Z running a few years ago (after sitting for 28 years), I replaced the original Nikki pump (mechanical) with a new GMB pump as the rubber diaphram inside the Nikki pump was dried and cracked.  The new GMB pump worked initially, but soon (just a few rides) it stopped pumping fuel and I saw the same issue you did, after turning the engine off, the fuel in the fuel filter would slowly drop.  I purchased a new GMB and the same thing happened, it worked for a few rides, then quit holding a vacuum (ie. sucking in fuel).  I figured the one way valves on the new GMB pumps were failing so I took the bottom half of the new GMB pump (side with the rubber diaphram) and the top of my old original Nikki pump (side with the two one way valves) and mated them together.  It has so far been working well.

I just read your post and sent it to a friend that is having the same issue. We both have the same fuel pump (on our 3rd each). Went with the GMB to confirm if the Delphi pump is bad. Wish I had an original pump. I tried the vacuum on the previous pump don't remember the results. I'm hoping the fuel check valve will solve the issue.

 

[Zed Head]

6 minutes ago, 240Znomad said:

I figured the one way valves on the new GMB pumps were failing so I took the bottom half of the new GMB pump (side with the rubber diaphram) and the top of my old original Nikki pump (side with the two one way valves) and mated them together.  It has so far been working well.

That is actually a good analysis, I think.  The valving should hold a vacuum, it's essentially a check valve, preventing the fuel from exiting the filter and lines because no air can get in to replace it.  Like when you pull soda from a glass in a straw by holding your finger over the end of the straw.

You might be able to cobble up a fix for the leaky valves with a real check valve between the filter and the pump.  Ideally the pump would work correctly but that's life in aftermarket world.

[David Downs]

4 minutes ago, Zed Head said:

That is actually a good analysis, I think.  The valving should hold a vacuum, it's essentially a check valve, preventing the fuel from exiting the filter and lines because no air can get in to replace it.  Like when you pull soda from a glass in a straw by holding your finger over the end of the straw.

You might be able to cobble up a fix for the leaky valves with a real check valve between the filter and the pump.  Ideally the pump would work correctly but that's life in aftermarket world.

I will update the group next weekend. Amazon Prime is not on the 2 day schedule.

[240Znomad]

3 minutes ago, David Downs said:

I just read your post and sent it to a friend that is having the same issue. We both have the same fuel pump (on our 3rd each). Went with the GMB to confirm if the Delphi pump is bad. Wish I had an original pump. I tried the vacuum on the previous pump don't remember the results. I'm hoping the fuel check valve will solve the issue.

I tried a similar test myself using a vacuum pump when the new GMB pump was failing.  I hooked up a vacuum pump to the GMB inlet side (side coming from fuel filter and tank) and when I applied a vacuum, it would not hold.  I took the GMB pump back to the store where I purchased it and showed the test to the guy at the counter.   He exchanged the pump for me.  Much like you, I went through 2 GMB pumps and still have the 3rd (brand new) sitting in my garage as a spare.  I tried the Nikki/GMB clone idea before installing the 3rd GMB pump and so far it has worked so I haven't had to try my spare GMB unit.