Fuel sender

[Caulky]

Hi all,

Anyone know what the resistance of the mk2 diesel 100, tank unit is?
I have problems with the fuel gauge.
Short of taking it out, I am guessing. It is difficult to make an estimate of the range if there`s an unknown quantity of fuel in the tank (it reads quarter full, when empty

[Gunslinger]

i have the sender unit from my lwb 1984 diesel tank in the garage i'll see if i can dig out the meter and get you some readings (i think the tanks were the same)

will get back to you later tonight or early tomorrow morning

[Caulky]

Thankyou Gunslinger.
From the web (different make), the fuel sender should be >250 Ohms float down and <60 Ohms float up. This doesn`t make a lot of sense to me.
I presume it means the total resistance is more than 250 Ohms (tank empty).
And less than 60 Ohms (tank full).

[Caulky]

In addition, I`ve got the instrument cluster on my table. There seems nothing wrong with the gauges.
The original voltage stabilizer was definately duff.
Just trying to make a reliable/accurate replacement.
I have a new temperature sender, but setting-up the gauges is difficult, without knowing the fuel sender resistance. They work in tandem with each other.

[Gunslinger]

ok ... forgot to say before, my tank is from a 1984, lwb, 190, twin rear diesel minibus (but i think the sender units are the same if from the same mk of van)

1) if the voltage stabiliser was naffed, then ALL readings etc on the gauges would have been
a) wrong and
b) would have changed with the engine speed

2) the readings from mine are as follows (i had a little trouble as it seems i need to clean the resistive track in mine as it was super sensitive when moving it,

float all the way down (empty tank) = 80 ohms
float all the way up (full tank) = 12 ohms

this is wildly different to the figures you gave above, as far as i know it was working fine when i took it out, i am due to strip and clean it, if i find any major difference in the readings after this i will report back,

for setting it up, i have not played with the instrument cluster yet in mine so dont know what options are available to you (posting back some info or pics would be good) but as a general rule there are 2 methods used by many for which point to use as your reference point.

Some will say fill the tank, but not right up the filler neck and set the gauge to read full at that point, others will say put 1 gallon of fuel in and set the gauge to read empty at that point as its more important to know where empty is, or put 1 gallon in and run it till it runs out and cant pick up anymore and use that point as empty

personally i would put 1 or 1 1/2 gallons in and use that as your empty level, because the fuel is never still in the tank and is likely to run away from the pickup tube while your moving, so if you set a lower level as empty, you may find while this is fine stationary, as soon as you move you have fuel pickup problems

better to fill up sooner than needed that to walk 5 miles in the pissing rain

[Caulky]

Thanks again Gunslinger. That info is invaluable....didn`t fancy getting into the fuel tank .
Perhaps I should explain the situation.
Without boring you with a long-winded story, I`ll give the present facts.
The vehicle has a 2.5Di engine...was a 2.4 York. After it was fitted the fuel gauge read quarter full when the tank was empty.
I had problems previously with the heating/cooling, which destroyed the old York engine.
All summer I have been renovating the van. It hasn`t done more that a few hundred yards, with the `new` engine.
When I found the voltage stabilizer was u/s, I was informed they were obsolete. So I decided to make one.
Now bench testing it with the instrument cluster.

I see what you mean about setting the minimum on the fuel gauge, good idea to set it reading low

Regards,
Dave.

[Luke]

The vehicle has a 2.5Di engine...was a 2.4 York. After it was fitted the fuel gauge read quarter full when the tank was empty.

how did changing the engine affect the fuel gauge?

[Caulky]

The vehicle has a 2.5Di engine...was a 2.4 York. After it was fitted the fuel gauge read quarter full when the tank was empty.

how did changing the engine affect the fuel gauge?

I can only presume it is because the wiring and various devices are for the old York engine. except those that came with the engine. The temperature sender springs to mind.

I have also ripped-out various relays and yards of wire/cable.
There was a `birds-nest` of someones efforts to wire-up a radio under the dashboard.....mostly all the same colour (red), and not a mechanical fixing to be seen....a sticky mess of insulating tape. Lots of wires going nowhere, which had to be `chased` out.
I had no idea if any of these wires were required or not.

This nausea began, because in the past, the water pipe connector from the engine to the heater matrix had been broken off, and plugged with a piece of wood. It was professionally finished off with a shiny new jubilee clip.

Then, the water-pump failed whilst moving, it got very hot
The fuel/temperature systems have never been much good.
I am informed that the York heater was never any good anyway!

[Luke]

hmmm strange!!! must have somehow disturbed some wiring or the instrument cluster itself!!!
The wiring for the fuel sender is un-connected to the engine, however the temp gauge is obviously not - i dont know if they share any componants in the instrument cluster!!!

When i swapped my perkins 4-108 to a Di the temprature needle only used the bottom half of the gauge!! i put it down to the Di runs colder!!

[Gunslinger]

dam .... i had overlooked the temperature sensor (i have fitted a 2.5di too)... hhmmm, i have a digital readout unit that is designed to control fans, i think i am going to be using that if i didnt keep the temperature sensor from the 2.4 diesel lump

either way the only thing it might do is read wrong, they are afterall nothing more than resistive bi-metalic switches that change resistance with temperature, so it shouldnt have damaged anything, the reading 1/4 full when empty, sounds like the voltage stabiliser to me was your main problem

[Caulky]

I have now just about finished the construction and testing of the new `electronic` voltage stabilizer.
As the info maybe of use to others at a later time, I thought that I would share the stuff that I have found out.
This has been a steep learning curve.

The old electro-mechanical V/S is quite a clever device.....not just a mechanical switch.
I noticed in the fuse-box that F11 was marked red and labeled 5V. This is the fuse that supplies the instruments.
Operation of Voltage Stabilizer
This rather ancient device supplies a switched voltage to the fuel and temperature gauges and their respective senders. On my model of Transit, it is housed in a small metal box, mounted on the back of the instrument cluster. 12V is supplied from F11 to the `common` inside this box. This voltage ( battery voltage) goes through the bi-metal strip to the normally-closed contact, and on to both the F & T gauges. Also, it supplies the heating element wound around the bi-metal strip.
As the bi-metal strip heats up it bends, away from the n/c contact, cutting the supply to the gauges/senders and the element.
The bi-metal strip then cools and resets to `normal`. Hence, constantly switching the supply.
The rate of switching is dependent on various factors: battery voltage, battery load, ambient temperature, engine speed, etc.
So, the average output voltage to the gauges is dependent on the rate of switching and battery supply.

The stabilizer tries to compensate for the variables by varying the speed of switching. E.G. if the supply voltage (battery) is low, the heat output from the element is less, and the longer it takes to break the contact. In effect the average voltage supplied to the gauges, is greater (bearing in mind it was low to start with).
And vice-versa.

The gauges themselves are heavily damped, to compensate for short duration variations, such as fuel slopping about in the fuel tank.

This said, how Ford came to figure of 5V is beyond me.

The `new` voltage stabilizer needed to allow for all of these problems, and hopefully be more accurate and reliable.

The variation of battery supply was easy, use a constant voltage regulator.
But, I needed to know what value of voltage to use. This is why knowing the resistance of the gauges and senders was important.
Both meters themselves measured 13 Ohms, each.
A new temperature sender was dunked in water and heated to boiling-point. I noted the change in resistance with temperaure. From the web, the normal coolent temperature is between 88 (thermostat opens) and 99 degrees C. And it MUST be within these limits....lots of nasty things can happen if not. (although 99C appears to be a bit close to boiling, it must remembered that the system is under pressure, and should have antifreeze).
Figures:
Water at normal pressure boils at 100C
Water at 15psi boils at 120C
Coolant with 50/50 antifreeze boils at 106C
Coolant with 50/50 antifreeze at 15psi boils at 129C
Coolant with 70/30(max) antifreeze boils at 113C
Coolant with 70/30 antifreeze at 15psi boils at 132C

Armed with this info revealed: T sender 894 Ohms at 20C
T sender 54 Ohms at 88C
T sender 48 Ohms at 99C
T sender 46 Ohms at 100C
T sender 41 Ohms at 110C
T sender 38 Ohms at 120C
T sender 35 Ohms at 130C
T sender 32 Ohms at 140C
All at normal pressure! (maybe this is an inaccurate method).
Obviously I couldn`t reach the boiling temperature at 15psi resistance, without some fancy test gear.
But this showed the range at working temperatures.

Now using Gunslingers fuel sender info, I was able to set-up and balance the Fuel and Temperature gauges, AND find a regulated voltage value to run my stabilizer.

Not really knowing if a constant DC voltage would stress the gauges (heat/ overloading?), I decided to use a switched supply [square-wave].

At 2Hz and a 4:1 duty cycle it was found that setting the regulator at a value between 9 and 10 Volts was good. Final build and set-up now in progress.

In order to fix the fuel-gauge offset(????), a shunt (22 Ohms) was connected across the meter terminals.

This stuff is probably of little interest to anyone without F & T problems, but maybe it will be of use as a reference. It would have been easier with diagrams.



Bye for now,
Caulky.
P.S. *Due to both gauges being supplied from the same source, a variation in one affects the other....but not any more!

[Luke]

Caulky and gunslinger in one thread!! you both love your long posts!!!
but seriously some good info there - just need to get a more comftable chair before i start to read it!!

[lincolnimp]

Hi,
Old post I know, but I am having fuel guage problems. I changed my tank to a proper Transit one, the old 'un came appeared from a car and was :
a) Ridicously low (Ilegal)
b) Small
c) Connected to the filler with some 'marley' guttering downpipe and gunk which leaked diesel on the forecourt when filling.
Anyway, having put in anew tank and lines the fuel guage now reads full all the time. I have got similar readings to Gunslinger of 66 Ohms float down (tank emtpy) and 9 ohms, float up (tank full).
The fuel guage is non origional

I am right in thinking that if I get the right combined speedo, fuel and temperature guage, my fuel gauge should read okay?

[FredTransit]

lincolnchimp did you fit a sender from a later (Mk3/4, 86-91) transit? They will physically fit, but just won't read right. We tried it, so I would know. You need a Mk2 one, they do come up on ebay from time to time.

[lincolnimp]

Hi Fred,

The sender was already in the replacement mkII tank.