S14 Fuel Tank Information

[ixfxi]

I am doing an overhaul on an S14 fuel tank and was curious if anyone has a proper understanding of what some of these components are and what their function is:





There are some differences between the earlier 95 fuel tanks & components vs the later 96+. In particular, the fuel bulkhead has a 4-wire connection for sending unit whereas the older 95 models have a 3-wire connection.

With that said, it appears that all tanks have a component at the bottom right (shown in my first photo) that is not accessible. Inside the tank you will notice a small 3-wire connector that goes all the way to the bottom corner. FSM does not mention this, but I am guessing its part of the low-fuel indicator. Anyone ever cut apart an old tank to see what this is?

Also above, the second and third photos show the differences in the sending units between 95 and 96, the later models having an additional component on the side of the housing.

One of the major problems we will all be facing is that these components are old and no longer available. The fuel tanks are still available, but the fuel level sending units are now NLA. All of the components are 20+ years old and the plastics are falling apart. I figure I would make this post to help open up some discussion. I would imagine that the wiring & connectors would need to be replaced soon if not now.

[Agamemnon]

If I remember correctly, there are two fuel warning lamp sensors in the tank. The first one being on the fuel level sender and the second in the bottom right corner.

As for the black component on the 96 year pump, maybe something for the OBDII system? It looks like it's spliced in to the fuel lamp sensor.

[bfellini]

96 up added a Fuel Tank Temperature Sensor for OBD2 compliance. The ECU compares fuel temp with IAT and ECT as another indicator something is up with the evap system I believe. That will be your extra wire. I know other mfg's and standalones use fuel temp in the fuel modeling calcs to derive fuel density, but not sure if it's something Nissan implemented with ECCS back then, and judging from the sensor, I doubt it!

[ixfxi]

Originally Posted by bfellini

96 up added a Fuel Tank Temperature Sensor for OBD2 compliance. The ECU compares fuel temp with IAT and ECT as another indicator something is up with the evap system I believe. That will be your extra wire.

^ Bingo!

I wonder what the other silver metal canister is, maybe thats one of the low fuel indicators.

I did some more digging and it appears the other part DEEP inside the fuel tank (and non-serviceable) is called the FUEL LEAD SWITCH shown here:


http://zilvia.net/f/showthread.php?t=404055

Not much info on the web other than the above thread. Anyone?

[bfellini]

This is awesome... over 20 years later, finding new stuff! Yeah there's practically zero info about it... Judging from the table in the FSM for the 3 states it can be in, looks like it's probably a sanity check for the fuel level, or used in conjunction with the float because of the issues with saddle style fuel tanks?

[ixfxi]

Thats what I am thinking too, I think its a supplementary for the low fuel indicator due to the design of the tank. I want to try to test all of this on the bench before assembling.

Problem is, and this goes for everyone, is that all of these components nowadays are so damn old and rotted. I mean, how often are guys examining the internals of their fuel tank to check all of this? Never. The last tank I took apart had fuel pump wiring with numerous cracks in the insulation and a semi-dissolved rubber insulator:



After restoring both S13 and now S14, you can see just how much cost-cutting NISSAN did with the later model. Lots more plastic. Best thing about the S14 is the subframe, thats about it.

[bfellini]

How about consolidating some info for drop in fuel pumps, and where to source a proper fuel sock/pre-filter? There's so many new pumps out now, and more are now e85 compatible... although, I have no clue if the tank would hold up to e85?

[cdlong]

Originally Posted by bfellini

I have no clue if the tank would hold up to e85?

I'm curious too. Well, the entire fuel system actually.

[russian]

you can use factory tank with e85 100% fine, but your better clean it out first because all that crap and sludge will come off and come in to the fuel lines and clog and we seen that happen.
also check to make sure the fuel hoses in the bay are rated for ethanol.

[ixfxi]

i'd be concerned about the wiring and sending unit. ethanol seems to destroy everything.

[fatduece]

Thanks for creating this thread. I'm subscribing!

[Yellow4g63]

That's probably why my low fuel light led doesn't work.

[2_Liter_Turbo]

Anyone know what the fuel lines running across the tank are for by chance? I'm thinking to equalize the two sides or something of that sort. Also would like to know why the line from the bottom goes back to the fuel pump bulkhead.

[tb13]

Originally Posted by 2_Liter_Turbo

Anyone know what the fuel lines running across the tank are for by chance? I'm thinking to equalize the two sides or something of that sort. Also would like to know why the line from the bottom goes back to the fuel pump bulkhead.

Those hoses running across the top are ventilation hoses according to Nissan's catalog. The lower hose that leads to the bulkhead is labeled as a fuel hose, it looks like its connected to the fuel pump, look at the diagram and find 17051 below the fuel pump bulkhead.

[2_Liter_Turbo]

Yeah, I looked again and the two hoses Y'd into one are definitely for venting. Just trying to figure out exactly how the one that goes down to the bottom corner works. That third line T's into the return line underneath the bulkhead (I'll post pics soon), so I'm wondering if it uses vacuum generated from the return line to pull fuel from the bottom corner to dump it on the side the fuel pump side of the tank.

Originally Posted by tb13

Those hoses running across the top are ventilation hoses according to Nissan's catalog. The lower hose that leads to the bulkhead is labeled as a fuel hose, it looks like its connected to the fuel pump, look at the diagram and find 17051 below the fuel pump bulkhead.

[2_Liter_Turbo]

The green arrows are the typical fuel pump outlet and return lines. The red is the line from the opposite side lower corner.


I'm trying to figure out how this union works. Is there any sort of check valve integrated or is it just a union? This part of the bulkhead will tell us how exactly it works, ha ha.


Exterior shot of routing just because:

[tb13]

Originally Posted by 2_Liter_Turbo

Yeah, I looked again and the two hoses Y'd into one are definitely for venting. Just trying to figure out exactly how the one that goes down to the bottom corner works. That third line T's into the return line underneath the bulkhead (I'll post pics soon), so I'm wondering if it uses vacuum generated from the return line to pull fuel from the bottom corner to dump it on the side the fuel pump side of the tank.

Actually it looks like that line is connected to the return line, maybe it somehow uses the return to pull fuel from the bottom of the tank?

[2_Liter_Turbo]

Originally Posted by tb13

Actually it looks like that line is connected to the return line, maybe it somehow uses the return to pull fuel from the bottom of the tank?

That's what I was thinking. Just curious how exactly it works. Seems there may be some sort of check valve or something integrated in the union.

[LoSt180]

Originally Posted by 2_Liter_Turbo

That's what I was thinking. Just curious how exactly it works. Seems there may be some sort of check valve or something integrated in the union.

Looks like it would create a vacuum and suck fuel from that corner of the tank to keep the fuel pump happy. Showing my age here, but that setup looks a lot like the venturi valves used to drain old water beds. You basically hook the valve to the faucet outside, run a suction hose to the water bed, then turn on the water. The water coming out of the faucet will create a vacuum and drain the water out of the bed.


Ninja Edit: Tried to find a picture and found this part is very common in saddle tank design. It's called a siphon jet pump. It uses the pressure already provided by the fuel pump to power the suction jet pump to pull fuel out of the other half of the tank.

Cutaway pic to give an idea:

[Andy’97]

I have a sending unit I’m installing but the small cylinder sensor on the outside (it’s a 1995 unit) is broken off. Can anyone confirm if this piece being broken will render the faulty gauge? Just trying to figure out if I must have this piece connected on the outside. Thank you!

[Andy’97]

I've learned there are two exterior sensors on the '96 and up sending units, the lower is the secondary fuel gauge sensor and the upper is the added fuel temperature sensor for OBD2 compliance.