33 replies to this topic

[stevelane]

Following on from another thread I have identified that there is an issue with the wiring, somewhere between the two wires on the sender, through to the back of the cluster, that is giving me inaccurate fuel readings.

I have today free to try and investigate but this is a little out of my comfort zone and knowledge.

I see the two wires go behind the tank so do I need to remove this to start tracing back or can it be found elsewhere?

I have a multimeter, but again only basic knowledge on how to use it.

Can anyone give me any guidance on where to go from here?

[Dan]

What car is it?

[ibrooks]

Assuming it's a classic Mini........ One of those wires is just an earth. I haven't seen the other thread so I'm not sure how you've come to the conclusion you have but.....

 

Check the earth wire is really earthed. Put the meter on resistance (Ohms - looks like an upside down horseshoe) and if you touch the leads together you should see a reading of zero on the scale. The earth wire on the sender is the un-insulated connector (welded to the plate of the sender) and probably black. Touch the earth wire from the tank and since it's conveniently close touch the -ve terminal of the battery. You should see zero again or at least a very low reading. Make sure the terminals are clean and re-connect it. Leave the battery connected for this one.

 

The wire on the insulated terminal (goes into a bit of plastic through the sender) is the signal wire and goes to the rear of the gauge. Before you go stripping things out repeat this test between the ends of the wire. Pull the wire off the sender and connect it to a length of known good wire (anything you have kicking around) shove that wire through a hole in the parcel shelf so you can reach it inside the car. Now pull the signal wire off the rear of the gauge and connect the meter (still on resistance) to each of these wires. Again you should see zero or a very low reading. Again making sure the terminals are clean re-connect. Should be fairly safe with the ignition off but disconnect the battery just in case of shorting the wires to anything whilst you are fumbling around with them.

 

You might find that the act of pulling the terminals off, cleaning them and re-connecting them will solve the problem.

 

I assume you have been told to just pull both wires off the sender and connect them with the ignition on to see the gauge go right up and that this isn't working? If it does then all this is a waste of time as the wiring and gauge are almost certainly fine and it's the sender that's at fault.

 

Let us know how this goes.

[Dan]

There's more to it than being a classic Mini. The wiring changed more than any other part of the car over the years and if we know what car it is we can give more specific help.

[ibrooks]

But the basic principle of the fuel sender and gauge never changed - in fact these steps would work with probably 90% of cars whether they are British or foreign and new or old.

 

Iain

[dklawson]

Oh... the gauge system did change... in late 1964.  However, Steve's car is much later than that and has the Nippon Seiki gauges.

 

Speaking for Steve until he returns to his thread, he has removed and bench tested all the parts.  The problem is that the fuel gauge reads low when it is in the car (temperature gauge appears to read correctly and the fuel gauge works properly on the bench).  He has tried multiple sending units (in the car but not installed in the tank).  Electrically he has bypassed the earth wire and gone straight to the battery (-) terminal.  He's done quite a lot really.

 

Steve, did you make sure this is the correct arm style sender for the tank?  I mentioned in the other thread that the arm shape did change when injected cars were introduced (even if your car is a carb model... I think it was in/about 1992 when the tank and sending unit changed).

 

If you determine it is the sending unit wire, you will need to pull an new green/black wire from the boot to the back of the gauge cluster.  Hopefully your headliner is not installed.   

[Dan]

Iain I think you should read the other thread. He's already done more adventurous testing, this thread is for more specific help.

This is why it's best to stick to one thread for a problem

'92 is around a change point in the wiring and I was trying to find out which side of the change this car is. I'll just do it the long winded way. Lift the left side of the carpet, does the main loom run front to rear in one of the floor channels here? If not it's in the roof. The problem is most likely to be at the front to rear loom connection. If the harness is in the roof the connection point is in the engine bay by the wiper motor (RHD car). It's a bundle of bullet connectors and they get corroded and dirty, especially if the rear bonnet seal is missing. They may start to snap off the wiring when you handle them. Clean it all up, remake the connections and replace any that are too far gone. If the wiring is stiff and cracking around them then chase out the damage, cut off as much as you can get away with and still make the joint. If the wiring is inside then you should find a multi plug if you follow the harness up to the dash. These can pull apart or again just be generally dirty. You could continuity test the cable first, but a visual inspection is quick enough to do.

Edited by Dan, 26 March 2014 - 12:42 PM.

[stevelane]

Sorry guys, I haven't been ignoring you, the forum kept saying that I had no new content so I presumed no one had answered

Am out and about now but will have a look at your suggestions in a bit

[stevelane]

Ok home now, not sure if I'm gonna get much done today but still helpful to get as much info as possible.

Firstly, apologies if the new thread caused confusion, I only did this as, to me, it was a different problem now, the other thread was about the voltage stabiliser and I now know that isn't a problem so I thought if I was more specific I'd have more chance if the right answer.

The car is a 1992 city, the year that you guys remarked that was the change year. Dklawson, I hadn't investigated the sender any further as the bench test had worked, I presume the only other issue would be it fouling in the edge of the tank and I can visibly see that it isn't yet I have an empty reading again. If there is any other electrical difference then please feel free to correct me but then I would've thought the bench test wouldn't work

Unfortunately the headliner is in and as I'm on a bit of a time restraint I don't really want to take it out. Can I simply run a wire through the inside of the car to the back of the cluster/gauge as a quick temporary fix until I can get back into this again? Just to check I'm right, I was expecting to run this off the same connecter as the green/black wire but not sure where to then attach at the other end.

I can see the cluster of wires but there are no bullet connectors, there are more permanent looking rubber connectors so I don't want to start them out unless I have to.

One other bit I information that I don't know if it's relevant, when I started all this earlier today I checked the voltage at the sender then the two screws that connect the fuel gauge on and at both points the voltage was up and down like a yo yo. Don't know if that helps any diagnosis?

[Dan]

The rubber connectors are bullet joining sleeves, there is a bullet on each side of them. You won't hurt them, or if you do it was time to replace them anyway. The voltage will be up and down, that's the stabiliser working. If you used a less responsive meter it would look like 10v but if the meter is very quick it will show the fluctuations. Unless you are using a slow meter, in which case there could be a problem! Try setting it to AC and see if it shows 10v.

[stevelane]

Ok will take another look tomorrow night, they looked like solid units but I could be wrong, thanks for your help

[KernowCooper]

Yes by all means run a test wire from gauge to the cluster, have you tested the continunity of the original cable between gauge and gauge?

[stevelane]

I haven't, I'm a little out of my comfort zone here

[KernowCooper]

You put your multimeter on ohms and touch the 2 probes together and the lcd reading should read 0 or 0.00, then you put one prob on the wire coming from the gauge behind the dash, use a extender wire and put this on the wire off the sender in the boot, touch the other probe on the extender wire, it should read 0 with means there is continunity on the wire and its nor broken.

 

Go to this post http://www.theminifo...starter-course/

 

 

and download the elictricians course which will help you get to understand the multimeter

Edited by KernowCooper, 26 March 2014 - 11:11 PM.

[dklawson]

As mentioned above, you can check the resistance (end to end) of the green/black sending unit wire.  To elaborate a bit on Kernow's advice above, first set the meter to measure Ohms, then touch its probe tips together.  While the meter should read "zero" it may not.  A non-zero reading is indicating the resistance of your meter probes.  If you don't get "zero", write down what that value is.  Now hold the meter probes to each end of the disconnected green/black sending unit wire (in all likelihood you will need a helper).  Again the reading should be close to zero.  Whatever the reading is, subtract the value you measured when you held the probe tips together.  The remaining value after subtraction is the resistance of the sending unit wire and this should be close to zero.

 

If you measure a non-zero value for the wire resistance... start by removing the wire ends, cleaning the bare copper wire, and crimping or soldering on a new wire end.  Then repeat your measurement.  While the wire could have failed along its length, that seems unlikely.  If the wire with new ends still has bad resistance, go ahead and run that new wire from the back to front.  For speed, if you can figure a way to run that wire inside the car... that should be fine.