Crazy2287

Guide - Troubleshooting fuel level display. Capacitive probe.

14 posts in this topic

Okay guys, due to the simplicity of the system but the frequency at which is comes up im gonna put this to death.

 

Our X-series Falcons and Fairlanes of the same era all use a capacitive type fuel level sensing system. I'd even go as far as saying all the sensing probes are identical (?) between the models.

 

*EDIT*

Information updated, This information extracted from another thread. I have not confirmed the measurements but i have no reason to doubt it.

These are the measurments for the senders:

XD Sedan = 270mm

XE-XF Sedan Carby = 195mm

XE-XF Sedan EFI = 200mm

XD-XF Wagon = 140mm

XD-XF Ute/Van = 210mm

XE-XF Sedan Carb has the same mounting as XD-XF Ute/Van/Wagon and XD Sedan.

XE-XF EFI senders have a different mounting setup where they use 5 studs coming out of the Fuel pump unit, the sender bolts to the fuel pmp unit with these studs.

*/EDIT*

 

After the X-type body was dropped so too was the capacitive method for measuring fuel level. Due mainly too it's incompatibility with alternate fuels. While more accurate and reliable then other methods, if the fuel type is changed or altered it affects the reading and possibly the serviceability of the sensing system.

 

Generally a capacitance system works by comparing the momentary capacitance of the sensing probe with a set capacitance reference inside the display. The resulting output gives the fuel level. The system has no moving parts making it reliable. and the probes contacts surface area can be altered to represent the shape of it's storage tank. so an odd shaped container can have it's quantity measured more accurately as a percentage of its maximum.

 

That's all the boring stuff.

 

I mentioned different fuels can affect the probe.

and along comes ethanol. E10. Ethanol is an excellent fuel. when we drink it, it's called alcohol. making ugly people beautiful and lowering expectations for hundreds of years.

It is a detergent, meaning it's less prone to sludge buildup. it's non-polar, meaning it can mix with water and it can be made from decaying plant matter. (?)

different substances have different dialectic properties. water been a 80.3 . Air is about 1.0, petrol is typically a 2.0 and ethanol 16.2

Our probes work by sensing the difference in dialectic between air and petrol. ethanol has 8 times the dialectic constant of petrol. This is why using e10 will cause your gauge to read full for the first 4/5th's of a thank of fuel.

Notice also, water is 80.3

ethanol absorbs water

water exists in the air.

over time ethanol's dialectic constant increases.

See the problem now?

 

To top that off the water component of the ethanol causes oxidation and corrosion on the capacitive probe's tracks.

Here's a probe that has stopped working, ethanol was used in the tank for some time before it eventually bit the dust:

DSCF2593.jpg

 

That's enough history.

 

Hopefully your stumbling in here because you've got a problem with your fuel sensing system.

There's only 3 things it would be. Wiring. Instrument cluster or the probe. Luckily it's all easy to check.

 

check for power.

Pull everything out of your boot and unscrew the access panel to reveal the top of your pickup/pump and fuel probe.

DSCF2602.jpg

DSCF2600.jpg

unplug the probe and get a multimeter, connect it to pins 1 and 3 of the vehicle side with the ign on, you should get 12V. If you don't check wiring.

The center pin, pin 2 goes to the left plug of the instrument cluster. It's green and gold (auzzie auzzie auzzie)

DSCF2603.jpg

 

Check continuity along this wire. If it's good, plug it back into the cluster and move on.

 

If you have a spare capacitive probe. connect it and submerge in fuel. dose it work? sweet. no? It's your instrument cluster.

If you don't have a spare probe. You can connect a 1000uF electrolytic capacitor across the green and gold (pin 2) and the red (+12v) and cycle power. You should get 2 red and 1-3 green bars on a digital cluster. or at least see some sort of level indication, although it will be low. Good news, your gauge probably is not stuffed.

 

replace your probe.

 

If you want to try to repair the probe then your in luck. because it's easy.

Remove the probe.

Get some pliers and pull the black plastic cap out of the end/bottom of the probe.

Get a flat blade screwdriver and work it down both sides of the bead that crimps the 2 pieces of the shielding/case together. Keep working it till the case can be flexed and popped off. Don't open it more then you have too.

 

You should see the probe. It might look something like this:

DSCF2592.jpg

DSCF2593.jpg

DSCF2594.jpg

DSCF2595.jpg

 

Get a soft abrasive and some isopropanol alcohol or acetone. You can use a pen eraser (the grey abrasive end of a pencil rubber) ,some GREEN scotch bright (its not as harsh as red) or some 1000grit sandpaper. Use the solvent and clean the contacts until they are shiny. clean down the edges too as this track provides the ground to the shell, making the shell work as a 'shield' against interference. don't over rub, you don't want to rub right through the tracks.

 

DSCF2598.jpg

 

you can stop here but you risk it happening again. If you have a soldering iron, some flux and some solder then you can tin the tracks. don't overheat the tracks or you may delaminate the probe. get someone to hold the probe vertical, start at the top and quickly "colour" down. this way gravity helps you, you can be quicker and less chance of putting excessive solder in one spot.

 

DSCF2599.jpg

 

see here these? these are metering orifices. They allow the fuel in and out at a decaying average. this improves the accuracy of the probe. do not damage them. do not remove them. if they are dirty, clean with one of the solvents mentioned above and a toothbrush. also, make sure the bottom plastic piece goes back in or the metering orifices wont do their job.

 

DSCF2601.jpg

 

to assemble, get the case sitting back together and lay one edge of bead on a flat surface. then gently tap the top edge so the edges close up on each other. Once that is done all the way along, give each edge a little squeeze with the pliers all the way along.

 

Re-install and test.

 

Note:

The system dose not 'fill' with power on. you need to cycle power to see filling. sit the probe in, and wait for 1 minute. then turn on power. remove the probe and the fuel will slowly run out of the bleed orifices. you can watch the gauge slowly decrease to zero while this is happening.

dougie77, PH351, Gaz and 5 others like this

Share this post


Link to post
Share on other sites

see here these? these are metering orifices. They allow the fuel in and out at a decaying average. this improves the accuracy of the probe. do not damage them. do not remove them. if they are dirty, clean with one of the solvents mentioned above and a toothbrush. also, make sure the bottom plastic piece goes back in or the metering orifices wont do their job.

 

DSCF2601.jpg

 

 

That was EPIC OVERLOAD LEARNING

 

i think this is extremely valid with the changing fuels of late, my ute came back to normal after one fill with E10 and wierd levels..

 

HOWEVER,  years ago when i got the ute those metering  things were blocked up the wazoo.. i drilled them with the smallest drill i could find(2mm?) and the result is when cornering. braking etc the fuel guage moves due to the chamber level changing rapidly. (did get the guage working initially though)

Share this post


Link to post
Share on other sites

Props for the advice Q, is there anything electrical you can't do?

Yes, Lots. I do, however, have an opinion on everything. No matter how incorrect, misinformed or how many people it pisses off. *tips hat*

 

Also, I spell checked your quote. BECAUSE OCD THAT'S WHY.

Someone buy me a 30c maccas softserve cone... for... science.... and my tummy.

Thom likes this

Share this post


Link to post
Share on other sites
Props for the advice Q, is there anything electrical you can't do?

Yes, Lots. I do, however, have an opinion on everything. No matter how incorrect, misinformed or how many people it pisses off. *tips hat*

 

Also, I spell checked your quote. BECAUSE OCD THAT'S WHY.

Someone buy me a 30c maccas softserve cone... for... science.... and my tummy.

 

Thanks for the spellcheck, the one on my phone is useless, I'll get you a soft serve but it might be a bit melted by the time you get it

Crazy2287 likes this

Share this post


Link to post
Share on other sites

Hey all, sorry to go dragging you all back to 2013. While doing this job I accidentally snapped the 2 wires off so went to solder them back on but while trying to remove a bit of the sleeve over the wires I ended up completely snapping it (idiot right?) anyway I've got some normal speaker wire sitting around could I use that or would the bigger wire thickness cause issues?

 

 

Also a little side question, how does these exposed solder connectors with electrical current in them not cause a fire? I'm assuming it's well above the fuel level?

 

Cheers

 

Sent from my HTC_0P6B using Tapatalk

Share this post


Link to post
Share on other sites

Wire of the appropriate gauge should be readily available from most auto stores, J-car, Bunnings. Although i'm not sure how critical using the correct insulation would be. There are a lot of different insulation types out there and id expect quite a few to be destroyed by submersion in alcohols/fuels.

 

You can use a different gauge (thicker/thinner) it wont affect the reading.

It's intrinsically save, using low voltage/current circuits.

eattsie9 likes this

Share this post


Link to post
Share on other sites

Cool thanks, I test the wire I have in a couple of fuel for about 4 days now and it has been eaten away but I'll go to jacaranda before the weekend and see what they have and try that.

 

Sent from my HTC_0P6B using Tapatalk

Outback Jack likes this

Share this post


Link to post
Share on other sites
On 10/21/2017 at 7:55 PM, Banno said:

Any chance that Crazy can reboot with photos again?

 

47 minutes ago, Valvebouncer said:

+1 for this!

google photobucket fix for (whatever browser you use.. assume chrome, firefox etc.) might be one for tapatalk? 

i can see the pics(with the add on for chrome), i would be able to screen print and re upload but not today, and i'm not a moderator so cant edit the posts with new pics. 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now