This was the pump that originally failed before, but started working again intermittently. I have since replaced it with one of 6 new spares I now have . It seems that you cannot buy the cheap "tin top" pumps anymore, even though Rock Auto and AutoZone show pictures of them, what you end up getting is the same Delphi pump. Delphi, Carter and Spectra all label the same pump.

I started the car up yesterday. It started and ran fine but still had a large air gap at the top of the filter. When revving the engine you can see actual surging of air going though the discharge connection on the pump and the level in the filter drops down to the bottom of the filter element. I have to be sucking air in from somewhere.

I plan to run a vacuum test on the line from the pump suction connection all the way to the tank with the rubber hose plugged at the tank end. If no vacuum leak, then the air MUST BE coming from the metal suction tube inside the tank above the fuel level. This would make sense as I have never detected any dripping gas from a steel line or defective hose. Remember, we inspected this suction tube earlier as best we could with a mirror and flashlight, looking though the level gage hole but could not see all of the tube clearly. Replacing the tube will require removing the tank again (third time), and bringing it to the tank repair shop (again) to have the tank suction tube removed and replaced. So, it may not be the pumps fault. We shall see. Stay tuned.

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John Kish
1971 240Z - original owner

OMG. My hat's off to you for being the proverbial Z pitbull to find the cause of your ongoing problem. Another thought.... If there is a rubber connector by the gas tank would it be possible to disconnect it from the gas tank completely? Then fabricate a temporary line that you can put into a gas can/ plastic jug, start the car and see if you're still sucking air. Cut the end of the temporary fuel line at an irregular angle with some notches so that it doesn't "stick" to the gasoline container when you start drawing a suction. If you still see the air in the lines then you'll know that it's NOT the pick up tube and you won't have to remove the gas tank a third time.

I too remember that the clear gas filters that I've installed over the years never ever filled completely.

Good luck John.

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1985 300ZX- GLL Dark Pewter Metallic - Survivor

Thanks Howie. Good suggestion and I tried that once before and again today with my neighbor holding the portable can with the filter suction line dipped into it and yes, there is still air in the top of the filter. The level in the filter does drop down when the engine is revved up just as it does when connected to the car's gas tank lines. I even checked all the lines and the filter with my vacuum pump before hand to make were no pinhole leaks in the test line and filter. NADA

So, my current thinking is this: that the filter element itself may be too restrictive for the mechanical fuel pump, causing the level in the clear filter to drop under higher load conditions. When the level drops to the bottom of the filter element, the engine gets fuel starved and quits. As I'm writing this, my neighbor just called and suggested that I turn the filter upside down to ensure that the filter element and discharge connection is always below the fuel level. The only drawback to this other than hose routing is that the inlet tube stand pipe then serves no purpose. I believe it is meant to spill incoming fuel to the bottom of the clear filter container so you can see any debris collecting at the bottom. Let's see what happens.

More later.

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John Kish
1971 240Z - original owner

So I ran the Wix filter attached to both the car's fuel tank line (normal connection) and then from a portable container to compare filter gas levels and to again, isolate any possible issues with air leaks or blockages in the car's fuel lines. Both times the filter level dropped to the point where the engine started to skip. See video links below.

I have contacted WIX to see if the filter element may be too restrictive for this application and questioned why the top discharge connection does not have a suction line down to the bottom of the filter. I am still waiting for a response. I think we need a higher flow rate/low pressure drop filter to allow these new fuel pumps to pump strong enough to supply full flow and pressure to the carbs.

Any of you guys still running carbs and mechanical pump see the big air bubble in your filters? If not, whose filters are you using?

https://youtu.be/hpLNXidQrNM
https://youtu.be/SfDAHMZ7J1g

Haven't given up yet!

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John Kish
1971 240Z - original owner

These fuel filters aren't like the old glass-bowls we are used to on our father's Oldsmobile. These feed fuel in from the top, flows thru the inside of the cone-shaped filter to the outside, then is pulled out the bottom from 'vacuum' (no such thing, really) and into the fuel pump.

In order to make the fuel actually flow thru the filter element itself, it has to be designed to have slightly more pressure "Inside" the cone-shaped filter than outside it. If the fuel level on both sides of the filter cone were equal, fuel wouldn't flow as well. Therefor the bowl should never appear "full". To accomplish this, I suspect they make the exit route slightly larger than the inlet route. You should always have an airspace in these filters so the fuel can flow freely from the inside of the filter cone, to the outside, trapping all the dirt on the inside of the filter.

If you have suspicions about the filter, eliminate it for a drive around and see how it performs.

ALSO, if you have one of those winter/summer air cleaner intake necks on your car, remember what Zeason this is. Also check the air cleaner itself and remember to replace the batteries in your fire alarms.

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1970 240Z

The Fram, Hastings and Wix fuel filters for the Z do not operate the way you are describing Frank. Fuel is "drawn in" the bottom of the filter and spills over the little stand pipe, filling the filter container. The fuel pump sucks the fuel from the top of the filter though the inside of the filter element. The decreased pressure inside the filter element then draws the fuel from the container through the element and out through the top of the element and out the filter discharge connection. What makes things worse is there is no little discharge tube dipping down into the filter element so if fuel does not flow fast enough to maintain a full volume within the element the level in the filter element may drop which I fell causes the pulsing and cavitation that we are experiencing.

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John Kish
1971 240Z - original owner

What it sounds like to me is the suction tube in the tank has lost its soldering bond and now sucking air.

Hi Paul, I was hoping to hear from you on this.
I had suspected that tube to be the possible cause for a while now, but then why the continued air gap in the filter even when it is drawing air from a portable tank as shown in the video? I do plan to get back under the car again and draw fuel though the filter when it is connected right at the tank to see if I am drawing air bubbles. This would bear out your theory but I am still baffled by the results I got when recording the operation from the portable tank.

Do you and Big Al still run a mechanical fuel pump? If so:
1)What style pump do you run?
2) What fuel filter do you use?
3) Is there an air bubble in the filter when the car is running?
4) Can you see the fuel pulsing out of the filter discharge connection, meaning that air is also being discharged to the pump?
4) Does the level in the filter ever drop near or below the actual filter element?

One theory I now have is that these aftermarket mechanical fuel pumps made in S. Korea which look like OEM pumps cannot pull enough fuel though the dense filter elements creating a "vacuum void" at the top of the filter.

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John Kish
1971 240Z - original owner

As Frank suggested, would you feel comfortable bypassing the fuel filter completely using a rubber fuel line and two worm screw clamps? I believe one of my past Ford SUV's had an all metal in-line filter back by the fuel tank mounted horizontally. Might this be another way to avoid the fuel having to "waterfall" into/out of the filter? Maybe installing a clear generic in-line filter with entry and exit ports on the same plane in a horizontal position?

Sorry if this does not make any sense! I'm just releasing some more brain spasms. Older people seem to have this condition.

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1985 300ZX- GLL Dark Pewter Metallic - Survivor

Can your existing filter be held or temporarily mounted so that the inlet and outlet ends are on the same horizontal plane? This way there is always fuel in both of the fuel lines.

Maybe a couple of Rolaids will help me with these brain spasms! ??

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1985 300ZX- GLL Dark Pewter Metallic - Survivor

Ha!Ha! I need to buy more Rolaids too.

Howard, your idea of using an inline filter near the tank looks doable. I may try that as I am waiting for a low restriction inline filter to arrive shortly. I may first try it at the original filter location then see what happens.

I still feel that there are major issues with these aftermarket fuel pumps. Just yesterday, I tried manually operating the last pump I had in the car while it was pulling gas from a gas can and discharging gas into another container all on my workbench. Again, it only works intermittently. No line leaks possible, no restrictions from a filter.

I plan to start the Z up again today, and monitor the "return" fuel line flow to see how much gas is returning to the tank giving me an indication if the installed "Carter" labeled version of this style pump is providing enough flow.

BTW, how is your Z running these days? Have you had a chance to stretch it's legs? The weather is supposed to break later today.

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John Kish
1971 240Z - original owner

Yes John the Z has been "stretched" only two times so far. I don't want to say how it"s running because I don't want to jinkZ anything. With all the car shows and meets being cancelled on Lawn Guyland my only options are to drive nomadically around with no particular place to go. Hey... I think I have that song on one of my cassette tapes. I'll make sure to turn up the volume.


It sounds like you're honing in on the problem. Good luck. Let us know the outcome.

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1985 300ZX- GLL Dark Pewter Metallic - Survivor

So, this past weekend, my son Mike and I have been tinkering with the Z and completed the following "tasks"

1) Fuel Flow check - Checked pump flow while cranking engine so see if there was return fuel flow coming from the fuel rail which returns gas to the tank. Good flow was observed. Return line to the tank is clear.
2) Line Leak test 1 - Blew fuel out of the entire fuel line back to the tank with compressed air until air was bubbling in the tank. No drips were observed anywhere under the car. Good!
3) Line Leak test 2 - Performed a vacuum leak test using a hand held vacuum pump on the entire fuel line from the "plugged" rubber hose tank connection (back) to the fuel filter (in front). No vacuum leaks observed. However, when disconnecting the rubber hose clamp connecting the rubber fuel line to the tank for this test we found that it was not very tight and could possibly be pulling in air. Replaced the 3-prong tension clamps with stainless screw type clamps.
4) Fuel Tank outlet tube check - Checked for pinhole air leak in metal "outlet" fuel tank line. Accomplished this by pulling fuel from the less than 1/4 filled tank though a clear length of 5/16" plastic tubing to see if any air bubbles were in the fuel flow while using a hand held fluid pump. No bubbles were observed. This was my biggest worry as any entrained air bubbles would mean that there was a tiny leak in the tank outlet tube INSIDE the tank. This would require the tank to be removed a third time and sent to a repair shop to have the tube assembly cut from the tank, replaced and re-welded to the tank. At least there are no more tank worries for now.

I took the car for a quick test run with Mike following me in his 370Z. I filled the tank up to 3/4 full at the local gas station and ran the car hard back home, up and down hills. She ran great, no hiccups.

We plan a few more longer test runs soon before signing off on this project. I'm still not sure if the replacement fuel pump will hold up. Time and more miles will tell I guess. The other issue is if I need AAA to flatbed the car home they will not allow passengers in the cab due to Covid 19. I would need someone to pick me up.

Again, thanks to my CTZCC buds for the technical and moral support. Hope to Z ya soon!

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John Kish
1971 240Z - original owner

So what did you install/reinstall to get it running satisfactorily? Did you eliminate the gas filter? Put in a straight in-line? Pay-off one of the Z gods? Either way, I'm glad it's running well and hope it stays that way.

Clear skies and smooth roads.

Howie

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1985 300ZX- GLL Dark Pewter Metallic - Survivor

Howie,

I see my first "task description" got fragmented some how, but to answer your question, I am running a new replacement "Carter" labeled pump of the same design along with a CarQuest fuel filter from Advanced Auto. The filter is "advertised" as having low restriction making it easier on existing mechanical fuel pumps. Well, for $4 I put it on.

Just today, I received a response from an email I had sent to Carl Beck (THE Z guru in FL) who, although had not had first hand experience with fuel pump failure (is still running an OEM pump!), has heard of others that had issues with them, seemingly with the fuel flow valves which we have also suspected.

Fingers crossed.

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John Kish
1971 240Z - original owner