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David Downs

Delphi Mechanical Fuel Pump stops pumping fuel

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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

 

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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. 

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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.

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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.

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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.

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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.

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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.

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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.

 

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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.

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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.

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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.

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Posted (edited)

I tried to read everything you've done and what others have posted, so forgive me if you've already done this.  Have you fed the intake from the fuel pump directly into a bottle of fuel to test from the fuel pump to the carbs.  When I replaced my pump, I had similar problems.  I ran one 16oz water bottle filled with fuel and everything cleared up.

Edited by wadelester

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Going electric really isn't a big deal. The 240Z's come wired for an electric pump. It's a matter of putting in the jumper at the front of the console area to power the already existing circuit and adding an inertia switch in your jumper loop to kill the pump in the event of an accident.

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5 hours ago, w3wilkes said:

Going electric really isn't a big deal. The 240Z's come wired for an electric pump. It's a matter of putting in the jumper at the front of the console area to power the already existing circuit and adding an inertia switch in your jumper loop to kill the pump in the event of an accident.

I noticed online a factory electric pump upgrade kit to install the pump. It included the small wire harness you mention, pump and bracket, 2 relays, and harness A&B. I would prefer to use as much factory wiring and install the inertia switch near the console. Can you recommend a parts list?

 

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21 hours ago, wadelester said:

I tried to read everything you've done and what others have posted, so forgive me if you've already done this.  Have you fed the intake from the fuel pump directly into a bottle of fuel to test from the fuel pump to the carbs.  When I replaced my pump, I had similar problems.  I ran one 16oz water bottle filled with fuel and everything cleared up.

Yes, I have tested the pump function. I really think installing an eccentric that has more lift would increase the pumping function. Does anyone make an eccentric with more lift? 

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Posted (edited)

My electric pump install is on like the 3rd page in this thread;

There's a ton of good info all through the above referenced thread. The wiring for electric fuel pump was included in the factory harness. There's no need to add additional wiring other than the short jumper loop at the console to power up the existing harness. It turns the pump on when the car is in the run/start positions only. There's no relays to add, just a method for fuel cutoff incase of an accident.

And here's a link to the cutoff switch you can put in the jumper loop.

https://www.amazon.com/Ford-5L2Z-9341-5L2z9341a-Inertia-Safety/dp/B000NTI03C

Edited by w3wilkes

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21 hours ago, David Downs said:

Yes, I have tested the pump function. I really think installing an eccentric that has more lift would increase the pumping function. Does anyone make an eccentric with more lift? 

Have you given thought to installing the mechanical pump without the spacer - just to see if that makes a difference?

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15 hours ago, cgsheen1 said:

Have you given thought to installing the mechanical pump without the spacer - just to see if that makes a difference?

Yes I tried installing the pump without the spacer. The pressure between the pump arm and eccentric was really tight. 

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So you couldn't complete the installation? (to see if it would consistently pump without the spacer) I wonder if anyone has been able to compare the arm geometry between the original fuel pump and these aftermarket pumps. If the arm geometry is the same then GMB and Delphi must be doing something different inside the pump.

Sadly, I guess I'll be playing with this myself. I have a customer bringing in a 72 with similar symptoms. Been pulling his hair out swapping mechanical pumps. He wants me to install an electric fuel pump. I'm an EFI guy - abandoned carbs in the '80's and have avoided them as much as possible since then. While I have the '72 I may look into this mechanical fuel pump issue. I think all the eccentrics are exactly the same but I have a couple of them to compare. Wish I had a Nikki pump...

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Posted (edited)

And My 72 Z was doing the same thing I did about all the same things you did. I bought clear  hoses from Amazon 5/16 and quarter inch and fuel pressure gauge and install them so I could see what the fuel was doing to carbs. If you don’t have clear fuel hoses you’re blind unless you have x-ray vision .I was getting air bubbles to theMechanical fuel pump low Pressure and carburetor float bowl’s making the engine run lean and run hot Hot exhaust manifold  and muffler.Vapor lock in fuel line I check my timing on my distributor it was set to retard.  I advance the timing to 5°or 10• BTDC  now the engine runs a lot cooler and no more air bubbles vapor lock So maybe your engine is running too hot and lean because your exhaust manifold is right under your carburetor float bowls Also check your  Guide  flow valve next to your coil. three-way valve ,blow it out see if you can hear airAnyway that’s what happened to my Z hope this helps..Also it helps to have a half to 3/4 gas in your tank

Edited by tetert1

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On 5/4/2020 at 10:53 AM, cgsheen1 said:

So you couldn't complete the installation? (to see if it would consistently pump without the spacer) I wonder if anyone has been able to compare the arm geometry between the original fuel pump and these aftermarket pumps. If the arm geometry is the same then GMB and Delphi must be doing something different inside the pump.

Sadly, I guess I'll be playing with this myself. I have a customer bringing in a 72 with similar symptoms. Been pulling his hair out swapping mechanical pumps. He wants me to install an electric fuel pump. I'm an EFI guy - abandoned carbs in the '80's and have avoided them as much as possible since then. While I have the '72 I may look into this mechanical fuel pump issue. I think all the eccentrics are exactly the same but I have a couple of them to compare. Wish I had a Nikki pump...

When I purchased the car I replaced the fuel pump without the spacer. I didn't realize the spacer was still attached to the original pump that was covered in grease. The car ran fine for about a month. I thought the pump was damaged from leaving off the spacer. Ordered another Delphi pump with spacer and installed it. Drove it around the neighborhood for an hour until she left me stranded. Towed her home, ordered the GMB pump, and got her running again. I will give her a long test drive after the fuel check valve is installed between the filter and carb. In my opinion, the pump lever needs more lift. It's like pumping up a bike tire and not giving it a full up and down motion. Wish I had a Nikki pump as well so I can compare them.

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You might try some experiments, moving the lever by hand, to see when in the stroke the pump actually moves fuel.  There might be too much play at the beginning of the stroke.  Could also be that the leaky valves inside allow too much fuel past on each stroke.  

If the problem is play, you could stack some gaskets to create a thinner spacer, to take up the play.

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12 minutes ago, Zed Head said:

You might try some experiments, moving the lever by hand, to see when in the stroke the pump actually moves fuel.  There might be too much play at the beginning of the stroke.  Could also be that the leaky valves inside allow too much fuel past on each stroke.  

If the problem is play, you could stack some gaskets to create a thinner spacer, to take up the play.

I removed the valve cover and manually operated the fuel pump arm and was able to pump fuel (full pump motion). Using pump action similar to the eccentric resulted in very little fuel movement. Sometimes after sitting the fuel in the filter would drain back toward the tank. The delay in filling up the fuel filter would cause the engine to starve for fuel (too much air in the system). We could have two issues here. The aftermarket pumps won't hold vacuum keeping the fuel in the filter and the eccentric needs more lift to pull fuel faster to the filter. A new eccentric with more lift may be a solution to compensate for pumps not meeting original manufacture specifications. The fuel check valve will fix the issue with the aftermarket pumps not holding vacuum. Looking forward to an update this weekend after the fuel check valve is installed.

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

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