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KiileZ

My 240z has fuel problems!

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So most of this year I have been dealing with a fuel issue. I have done so much research and googles just to come up with dead ends and references to threads that don't seem to exist, so I am ready to ask!

My 72 240z runs great, when it stays running. I can go out and fire it up no problem let it warm up and it idles pretty good and has good power everywhere. My problem is when I let the car sit at idle for longish periods of time. Say 5-10 minutes or so. I do this when I want to drive the car and I let it warm up in the driveway. Basically, it will start and run good. After a few minutes it dies. The fuel filter is empty and the carb bowls are dry. I can crank on it for a long while and it will eventually start, but it's easier to fill the bowls up. Once the bowls have gas the car fires right back up and no problem. This same problem occurs after I shut it off for short periods of time. I can turn it off to get gas and then when I start it back up and leave the gas station, it will die just minutes down the road. Then I am stuck and have to use my gas can I keep with me to fill the bowls up on the side of the road. Once I do that and take off, it's fine. This same issue also occurred the weekend before last when I went to Deal's Gap and when going uphill for long periods of time it starved and died like 5 times in 11 miles.

I have checked my float levels and they seem right. I have had the tank cleaned out, but it still get small particulates in the fuel filter and no place nearby will line or really clean my tank. Believe me, I have called everyone and anyone to fix it. I have replaced the hard lines going from the tank with new stainless lines and all soft lines are new.The fuel pump is new and just this spring completely disassembled my carbs and cleaned everything and replaced all the necessary components. I really feel like my tank is the culprit here. Maybe a pinhole in the pickup? My concern is that if it's full of gas this shouldn't happen, but it does no matter what really. I drove all the way from southern indiana to Deal's Gap and it was absolutely fine on the interstate except when I would stop for gas. I just started preemptively filling the bowls after getting gas so I wasn't stuck on the side of the interstate.

I pulled the tank yesterday and am sending it to zcarsource for a refurb. It's expensive, but I am fed up with this. If anyone can shed some light on this, I would much appreciate it!

Thanks!

Edited by KiileZ

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It seems like it started after I messed with all that stuff, but I bought it in October of last year and didn't really drive it a whole lot until I did the carbs this spring. It never ran very good until I took the carbs apart, but I don't recall it ever really leaving me on the side of the road fixing it either other than when the old fuel pump that was on it stopped working.

On a side note, when I did the carbs I used a kit from Zcardepot for gaskets and such. I also replaced the needle jet with the ones that came with the kit. After doing so I saw a post on facebook regarding the needle jets from that kit supposedly being trash. I am stilling using those jets though because they seemed alright.

Edited by KiileZ

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From reading your last post, I get the sense that you may have replaced the fuel pump recently as you mentioned "other than when the old fuel pump that was on it stopped working."  In your opening post you say that the float bowls keep going dry which would suggest that either the fuel pump is not working properly or the float valves are getting stuck.  Based on your comment that the fuel filter was also dry, that would suggest that the fuel pump may not be working.  What is your fuel pump setup, original mechanical style or electric?  If mechanical, and it was replaced recently, what did you replace it with.  I had a very similar problem recently when I got my old garage stored '71 Z back up and running.

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So last fall the mechanical fuel pump died on me. I got it back in the garage and bought a new one. It wasn't an original Nikki, but some aftermarket model. I just replaced it with one from ZCarDepot. Then I ordered the same one from ZCarDepot before going on our trip to Deal's Gap just in case. When we got to our cabin my buddy thought maybe my new pump was just bad, and wanted to try and put the spare on to see if it would help and that way when we stopped for gas I wouldn't need to fill the bowls. That didn't change anything.

Quote

 I'd test the fuel pump for proper pressure and volume first.

I will attempt to test the pump more thoroughly. It's just strange that it will do it at idle, but doesn't have issues at higher RPMs unless I am going up hills. That's why I was thinking it might be more related to the fuel tank.

Another note: This is just a stock L24 with stock SUs.

Edited by KiileZ

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 It's weird that it's running out of fuel at idle and climbing a hill. The two scenarios are at opposite ends of the fuel usage spectrum. Assuming we're dealing with a mechanical pump, I think I'd pull the valve cover, take a look at the eccentric fuel pump drive on the end of the cam (it could be loose) just to rule out that possibility. Where is the fuel filter that runs dry located?

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When I got my Z running a few years ago (after sitting for 28 years), I replaced the fuel pump before I ever tried to start it (original Nikki pump).  After removing it, I opened it up to check it's condition and sure enough the rubber diaphram was cracked and broken.  I replaced it with an aftermarket pump that had an "original" look.  It worked, but within days (I don't drive the car much) I started have issues where it would die and then not start.  I noticed that the fuel filter would always go dry when the car died or the engine was off.  I used a pressure gauge to check the fuel pump and quickly discovered that the fuel pump valve (inlet side that draws fuel up from the gas tank through the fuel filter) wouldn't hold a vacuum.  So I tested the valve on my old Nikki pump that I just replaced and sure enough it would hold a vacuum.  I went and purchased another aftermarket pump (same exact model) and it did the exact same thing, worked briefly and then the inlet valve started leaking (would not hold a seal) so I took it back for another replacement.  About this time I starting thinking that the new aftermarket pumps were of poor quality so I decided to try something.  I mounted the top of my old Nikki pump (which contains the 2 one way valves) to the bottom half (containing the rubber diaphram and lever arm) of one of the new aftermarket replacement pumps and lo and behold, it worked.  I have been running this setup (old original top half of Nikki pump with bottom half of aftermarket pump) for over a year with no problems (granted I don't drive it much).  Try using a vacuum pump on the inlet side of the new fuel pump, you should be able to create a small vacuum that holds.

Do you have any pictures or a make and model of the aftermarket pump you used?  I'm really curious if it's the same one I've had problems with.

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1 minute ago, Mark Maras said:

 It's weird that it's running out of fuel at idle and climbing a hill. The two scenarios are at opposite ends of the fuel usage spectrum. Assuming we're dealing with a mechanical pump, I think I'd pull the valve cover, take a look at the eccentric fuel pump drive on the end of the cam (it could be loose) just to rule out that possibility. Where is the fuel filter that runs dry located?

It is a mechanical pump. So at idle it runs out and climbing a hill runs out, but when I am doing 70 down the interstate I have no issues until I pull over and shut it off. The fuel filter is just a glass dorman filter located in the engine bay about a foot from the pump.

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6 minutes ago, 240Znomad said:

When I got my Z running a few years ago (after sitting for 28 years), I replaced the fuel pump before I ever tried to start it (original Nikki pump).  After removing it, I opened it up to check it's condition and sure enough the rubber diaphram was cracked and broken.  I replaced it with an aftermarket pump that had an "original" look.  It worked, but within days (I don't drive the car much) I started have issues where it would die and then not start.  I noticed that the fuel filter would always go dry when the car died or the engine was off.  I used a pressure gauge to check the fuel pump and quickly discovered that the fuel pump valve (inlet side that draws fuel up from the gas tank through the fuel filter) wouldn't hold a vacuum.  So I tested the valve on my old Nikki pump that I just replaced and sure enough it would hold a vacuum.  I went and purchased another aftermarket pump (same exact model) and it did the exact same thing, worked briefly and then the inlet valve started leaking (would not hold a seal) so I took it back for another replacement.  About this time I starting thinking that the new aftermarket pumps were of poor quality so I decided to try something.  I mounted the top of my old Nikki pump (which contains the 2 one way valves) to the bottom half (containing the rubber diaphram and lever arm) of one of the new aftermarket replacement pumps and lo and behold, it worked.  I have been running this setup (old original top half of Nikki pump with bottom half of aftermarket pump) for over a year with no problems (granted I don't drive it much).  Try using a vacuum pump on the inlet side of the new fuel pump, you should be able to create a small vacuum that holds.

Do you have any pictures or a make and model of the aftermarket pump you used?  I'm really curious if it's the same one I've had problems with.

https://zcardepot.com/collections/fuel-pump/products/fuel-pump-mechanical-240z-260z-70-74

This is the pump that I used both times. Sadly, my car didn't have the original Nikki but some aftermarket model. I would have tried to rebuild the Nikki, but seeing as it was just an aftermarket I just replaced it with new. I will attempt to check the seal on the inlet valve and see what happens.

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That model number on ZCarDepot is different than the aftermarket one I tried using but it looks very similar, ie. has the OE look.  The specific model that I've had problems with is a GMB brand, and the number on the box is 550 8040, I still have the box with the top half of the pump sitting in it.  I'd definitely spend a little time checking the fuel pump as your problem sounds eerily similar to mine.  If the fuel filter is going dry, it's got to be either no fuel coming from tank (ie. no fuel, blocked line, etc.) or fuel pump not drawing fuel.

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I was thinking a hole in the pickup tube in the tank, honestly. That's why I decided to ship my tank off to be refurbished. However, I think I will also spend some more time checking out my fuel pump. I wonder if there is a better aftermarket replacement for the Nikki, I mean other than running an electric pump.

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I came here to post that I'm having a very similar problem getting my '71 back on the road. Everything worked great when I took the car apart to do the body work. I also get a stream of bubbles coming up into the (new) fuel filter. I tested the pump off the car, and it works fine. I used a vacuum pump to draw fuel through the filter, and no bubbles. The filter level drops as the car runs, until it runs poorly and dies, and will slowly rise back to full when the engine is off. Runs great when it runs. I have about 5 gallons in the tank. I see no leaks that might indicate a place for air to enter. I did read about the possibility of the inlet tube damage in the tank, but don't think that's it. Weird.

Edited by ByStickel

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I installed my refreshed tank this past weekend. I've been driving the car each day and so far have not had any issues since. I haven't had a chance to check fuel pressure, but so far so good. I believe the bad pickup was my problem. I have yet to call zcarsource to verify if that's what they found or not.

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1 hour ago, ByStickel said:

I came here to post that I'm having a very similar problem getting my '71 back on the road. Everything worked great when I took the car apart to do the body work. I also get a stream of bubbles coming up into the (new) fuel filter. I tested the pump off the car, and it works fine. I used a vacuum pump to draw fuel through the filter, and no bubbles. The filter level drops as the car runs, until it runs poorly and dies, and will rise back to 2/3-3/4 when the engine is off. Runs great when it runs. I have about 5 gallons in the tank. I see no leaks that might indicate a place for air to enter. I did read about the possibility of the inlet tube damage in the tank, but don't think that's it. Weird.

That sounds like a leak somewhere. Could be a pick up problem but my first suspect would be all the connections or a cracked hose or filter

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Thanks Patcon.

I ended up putting a bicycle pump on the outlet of the filter and blew back toward the tank. There was a blockage somewhere, probably at the fuel pick-up. Problem solved.

Now, onto the OTHER problems (;

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