New fuel tank and sending unit weirdness (Questions)

Steve83 wrote

What do the battery terminals look like?

Battery terminals are good. The gauges (oil, temp, fuel) all work and I tested each with 10, 22, 75 ohm loads at the end of the cables to ensure that the were no high resistance links in the circuit.

Gary Lewis wrote

The schematic below shows the senders grounding via ground G701, which is on the firewall behind the radio.  So I was wrong about checking the tank for being grounded as the ground comes through the cable.  Sorry.

Do those codes on the EVTMs translate to physical locations?

Randy wrote

How did it work before the last few weeks? I ask because I installed a new tank and the same sender that you installed. The first fillup took a full 16 gallons (the 5ish were put in at my friend's hangar and the 10ish we put in when we drove to town) but the gauge didn't read. I was not as smart as you and didn't test it before I installed it. So I managed to remove it without dropping the tank thinking I'd confirm that the sender was bad. But it worked just fine outside the tank. I bent the wire a bit to get it to register higher; now it reads 1/2 tank when I fill up, but I never put more than about 7 gallons in because it feels so weird driving on E, even though I suspect that when I get to E I still have another 8 gallons.

Hi Randy,

Everything worked fine before the tank and sender swap, so it has something to do with the new setup.

I was thinking about it some more, and with you mentioning the bending of the float arm I am convinced that is what is wrong with mine. I did test my new sender before installation, but something I did not do was put the new sender beside the old one to compare the height and bends of the new float arm.

My tank fills just fine...I can run the pump on full speed (or at a decent speed at least) the same as with my old tank. I think the problem is simply that the range of my new sender is -50% to +50%...instead of 0% to 100%. If the tank fills fine at the beginning, then it should also fill fine at the end...at least I think it should.

My plan is...when I get my truck back from the body shop I need to rectify this before I reinstall the bed. I'm wondering if, with the fuel filler hose removed if I can reach in there with a rigid wire (like a metal coat hanger) and operate the float while it is installed? I'll have to try and figure out where full is, and then bend the float arm to suit that.

Further adding to this theory is that when I really stuffed the tank full last time, every time I came to a stop (and the fuel in the tank came forward) the gauge would momentarily read full. So either the arm needs to be bent, or I need to rotate the sender in the hole?

Cory, I'm pretty sure the sending unit is clocked by the tabs at the bung

ArdWrknTrk wrote

Cory, I'm pretty sure the sending unit is clocked by the tabs at the bung

Yes sir, absolutely, but with aftermarket parts it doesn't mean that the clocked location is 100% correct. I remember the fit being a bit sloppy, so maybe it's not kosher...

Randy wrote

Do those codes on the EVTMs translate to physical locations?

If by "those codes" you mean something like G701, no they don't translate to a physical location.  But, there are tables that tell.  In fact, there's usually a page of the EVTM in the same section that tells the location of most of the grounds (GXX), splices (SXX), and connectors (CXX).  In this case it is the very next page, shown below.

But, if the thing you are looking for isn't listed you can go to the Grounds page to find a complete listing of those.  However, splices and connectors can be a bit difficult to find if not on that page.

Randy wrote

Rembrant wrote

Gentlemen,

I installed a new fuel tank this past winter (Spectra Premium # F14A 16.5 Gallon), and a brand new sending unit (Spectra Premium FG75A). I tested the sending unit before I installed it in the tank, and it stroked the fuel gauge with no issue. So now for the past few weeks driving the truck, the gas pump cuts off and the fuel gauge only shows 1/2 tank. I don't know how much fuel is in there...I drive it until I hits Empty, and then refill it...today it took 8 gallons.

How did it work before the last few weeks? I ask because I installed a new tank and the same sender that you installed. The first fillup took a full 16 gallons (the 5ish were put in at my friend's hangar and the 10ish we put in when we drove to town) but the gauge didn't read. I was not as smart as you and didn't test it before I installed it. So I managed to remove it without dropping the tank thinking I'd confirm that the sender was bad. But it worked just fine outside the tank. I bent the wire a bit to get it to register higher; now it reads 1/2 tank when I fill up, but I never put more than about 7 gallons in because it feels so weird driving on E, even though I suspect that when I get to E I still have another 8 gallons.

A week or so ago I put 5 gallons of gas in each dry tank with new senders (16 gal side tank / 19 gal rear tank) and found the needle came up to the empty line for both tanks so I was happy to be on EMPTY and have 5 gallons left.

Being I don't know when the truck will be on the road and not wanting to spill gas from a can on fresh paint I added another 5 gallons to each tank and found the 16 gal tank not reads full?
The 19 I think was about half and think that is about right.
As long as they read good when close to empty I am happy.
Dave ----

FuzzFace2 wrote

A week or so ago I put 5 gallons of gas in each dry tank with new senders (16 gal side tank / 19 gal rear tank) and found the needle came up to the empty line for both tanks so I was happy to be on EMPTY and have 5 gallons left.

OK, I am getting my truck back in a few days and I need to rectify this fuel gauge issue before I reinstall the bed, so I need to come up with a plan. Dave, you mention that yours is reading empty with 5 gallons in it, and that's cool, but I believe my original tank was reading empty with more like 2-2.5 gallons in it. The few times I drove it any distance, I drove it until it was empty (on "E", or below) and to fill it took 14 gallons.

I guess to start I'm going to drain as much gas out of it as I can, and then put 2-3 gallons in it and then bend the sender float arm until it reads "E" on the gauge. Would this be a reasonable or unreasonable thing to do?

Anybody?

My issue is that I really won't have much time to play with this before putting the bed back on.

I'm also going to check and adjust the plastic vent tube if required. I know this thing will work, I just need to hold my tongue right.

I think it’s a reasonable thing to try. I don’t have any faith in these fuel quantity systems. I go by mileage.

My rear gauge kind of works. The front gets to around half a tank and dives to empty.

I agree that it is a reasonable thing to do.  But if you have 1 or 2 gallons left when it hits empty then you can loan it to someone and they won't run out.

Dad didn't tell me about his '72 Mustang - until I ran out.  I drove home and the gauge was just starting to touch the E.  Shut it off and came out the next morning and it wouldn't start.  THEN he told me.  

Ok go I got my old Bullnose back late today.

Fuel gauge was sitting between “E” and 1/4 tank, so at the 1/8th mark more or less. I removed about 42-43 litres of fuel...about 11 gallons I guess.

Interesting to note I found the filter sock had fallen off the end of the sender. I had to fish it out of the from the front of the tank with a piece of wire. No biggie, I’ll fix that.

I bent the float arm but couldn’t get it to read past 1/2 tank, even with the 11 gallons in there. So after I drained it, I put 2.5 gallons back in, and the gauge goes to “E” when I turn the key on. I don’t really know what it will do until I fill it back up. The way it was, I think the float would have had to almost hit the top of the tank to read full, which makes sense based on how it was working.

The sender looked fine, it just almost seems like it’s too short for the tank.

Does anybody know how far the pickup tube is supposed to be from the floor of the tank? I’m trying to tweak everything to get the right balance.

Right now the pickup tube is just barely submerged with 2.5 gallons in it. I can’t tell if the float is floating or if it’s bottomed out. I will check that tomorrow.

PS: I think the original tanks were specified at 16 gallons ya? My usually fillips used to be about 14 gallons so that makes sense.

This new aftermarket tank is advertised as being 16.5 gallon. I don’t know if it is actually different or just the same and labeled different.

Ignore my awful spelling lol working on my phone tonight...

I don't "know", but I'd think that the pickup tube should be almost to the bottom of the tank.  Otherwise the gas at the bottom of the tank can't be used.

And while that means you'll also potentially suck up some sediment, that's what the fuel filter is for.

Gary Lewis wrote

I don't "know", but I'd think that the pickup tube should be almost to the bottom of the tank.  Otherwise the water at the bottom of the tank can't be used.

FIFY...

I hope this hijack isn't inappropriate, but I want to say that I changed both tanks and senders about four years ago.
I could not find the one year wonder '87 senders, so I went with '86 mechanical pump senders.
These read completely wrong, so I've been just watching mileage with fill ups and figure I need gas around 160 miles per 19 gallon tank.
Gary has mentioned an Arduino workaround for this.

This has been working fine for five years.
But now, the rear tank runs dry seemingly at a random mileage between 120-150.
At first it thought it was because I'm pushing the truck so hard, or my speedo/odo was dying.
So I've been using Google maps to follow miles and check speed.
BUT when filling up I can only get 13-17 gallons into the tank.
I can see the fuel in the fill neck, so I know it's full.

If it was consistent, I would say the pickup had fallen off.
I can leave the gas cap loose and it still happens, so not a vacuum problem.
Tanks are fairly new, and clean according to borescope inspection. (Dont send a cheap $15 cellphone borescope into whatever they call gasoline these days )

Hard to imagine there's a random 2-6 gallons of water in there,and I didn't see any phase separation with the scope, but my next 'experiment' is to dump a couple of gallons of toluene in with my next fill up.
That's miscable with water and pretty difficult to separate.
It will burn in its equilibrium state and has a good octane #.

Can anyone see something I'm missing?
Any other ideas to fix or figure this out?

Hijack/

How much does the rear tank hold? Or, how much is it supposed to hold?

Cory, i have 19 gallon tanks both side and rear.

At 160 indicated miles I used to fit around 18.3 gallons, and I hadn't run it dry.
Now it 'runs dry' when it feels like it.
Hopefully while I'm rolling, not stuck in traffic, as it takes a lot of cranking to prime the pump.
I now have to remain vigilant to the hint of starvation, since it is so random

You said you went with '86 mechanical pump senders.  Does that mean you either have a mechanical pump or a frame-mounted electric pump.  If so I'll guess that you have a bad hose that's leaking at times, perhaps as the body twists, and allowing air into the system and killing the vacuum the pump is creating.

But yours should have the plastic hose, and they don't seem to age.  Maybe a connection is leaking or loose?

I have a pump on the timing case.(two pin connector on the bung)
There are no fuel line leaks, and the switch valve is good.

It ONLY does it towards the bottom of the tank, not randomly.(but at a random fill level)
The senders look 'new' when I scoped it.
I don't see, nor could I understand a hole in the pickup tube.
Because one day it will take 13, and the next 17, but never the full 19 like it did before (if I ran the tank dry)

You have it in the right thread - weird!