Faulty Fuel Gauge

The tank sensor seems to be working OK... No resistance when full and .82 ohms when empty. It is currently
registering .62 so seems to be OK.

Jeff.
We may have a problem here. With the sensor removed from the tank, the right way up, ie:- float at the base or
empty tank...you should get a reading of around 85.5 ohms, inverted, the float going to the top, or full tank,
reading should be around 2.6 ohms. These readings refer to the later unit which you should have fitted. Can you
give us the Pt.No. of the sensor as well.
I read your figures as being 0.82, and 0.62, which are not correct.
Can you please recheck with unit removed.

Cheers

John

John,

It was probably the scale on the meter that I used, I had it on the range 20K?? The results will translate to 82 OHMs when the float was on the bottom, and zero full scale when I inverted the tube ie. as far as it would go. I know that you mentioned that it should be 2. something but I turned it fully upside down which may be further than where it should have been?
The resistance was progressivley changing as I moved the float from the bottom to the top which I thought should indicate that it was reading OK.

Is there anyway to check the TSU unit out? Do you know what voltage it should send to the tank sensor?
I assume that the resitance in the tank sensor is then calibrated by the TSU and feeds the a variable voltage back to the gauge depending on the level, or am I oversimplifying things?

John, another thing to consider...you said that my sensor should be the later one? My tank is not the very late one and does not have the later filler cap. I know because I bought the later cap expecting to fit it to my tank only to find that the later tank has a different neck arrangement, so probably it also has a different sensor??

The results will translate to 82 OHMs when the float was on the bottom, and zero full scale when I inverted the tube ie. as far as it would go. I know that you mentioned that it should be 2. something but I turned it fully upside down which may be further than where it should have been?
The resistance was progressivley changing as I moved the float from the bottom to the top which I thought should indicate that it was reading OK.

Is there anyway to check the TSU unit out?

...you said that my sensor should be the later one?

Jeff.
It looks as if the sensor is in fact OK, which is good news. However to check the TSU you need to use an oscilloscope, but I doubt if you have one of those. There is another way with an LED and a resistor, but you will have to tell me if you feel comfortable playing around with that type of thing. The only other thing I can suggest, apart from substitution, is for you to send it to me and I can check it over internally, for broken print or other damage, and I can check it out in my Alp. I have already done this for another member, and having repaired the print, which incidently had water damage as well, popped it into my car and proved it now to be working. In that case there is a secondary fault which we are checking out at the moment, but on PM`s.
With regard to the later type of sensor, which should be the one you have, the pt.No. should tell all. also I would not necessarally think the fuel caps have any revelance here, as they might have changed the cap assembly due to other reasons, and not at the same time as the sensor change.
Hope this is of Help

Cheers

John

John,

I am quite comfortable with checking things as you suggest, but would need some instructions from yourself to understand it further. I would be curious to know how you would go about checking it, with just a resistor and Led?
However, your suggestion to try it on your ALP would make more sense, providing that you don't mind?

What I mean't with the different fuel tank, is that the later one has a lower neck to accommodate the neck and adaptor ( the arrangement is longer on the later type), therefore because the sensor is in the same location I assumed that the tube what be shorter.

I can check that tomorrow to confirm, providing I can find a part number on it. I will also check the IPC to see what variants there are.

I would be curious to know how you would go about checking it, with just a resistor and Led?

Jeff. Just one more check before we go any further....Can you confirm that the Black lead on the TSU has continuity to the Battery neg terminal ie:- Earth,... just a detail but if you had checked the voltages directly to the battery neg terminal, and not the black lead. that could be misleading....a long shot...but could happen
With regard to the LED, I have not done this myself, but it is something I would try. Solder one leg of a 500ohm resistor to either of the Led`s legs, ie:- Resistor in series with the LED....touch the LED leg to TSU computer output with the resistor leg to the Black lead, and with ign on, engin does not have to be running, check to see if the LED is flashing... or ON ie:- flashing too fast for you to detect...If the led does not perform...reverse the LED assembly....if it still does not work....take the lead off the Black, and put it on the Red on the TSU....if still nothing...reverse connections again...If nothing after the 4 processes, I would suspect the TSU......But if you dont like the idea of doing all of this, I am more than happy to check the TSU out for you. Let me know and I`ll send you a PM with my address.

John

[BIG_MVS]

Jeff - Have you tried the £17 relay yet that I gave you the part no for?

Please do try it!?

Martin,
Yes I did check it, but if you look at my earlier strings the relay was in a different postion to yours? It seems that Renault put a temporary fix in before they finally wired it in on a more permanant basis. The relay that I have checked is identical to the one on the right of your picture (not the one that you mentioned) and is a timed relay. The wiring from it all relate to the wiring diagram that John sent and it works OK.

You didn't have a TSU left over when you broke up your Alp?

John,
I did check the earth lead for continuity and it was showing to have a good ground to the main battery earth. I haven't checked it by running a seperate earth and it is probably worth a try.
I am still curious with the method for checking the TSU. I am not an electronic expert so do not appreciate the finer requirements. Is there a specific resistor that I would need to use, or will any value do?
What will this tester do that a meter will not read, is it because that it will be more sensitive than an ordinary tester?
I do have access to various equipment in work, so if there is another check that could be carried out it may be worth suggesting it in case that I csn get it checked?
What about the voltage going to the tank sensor, does the .48v seem right? I can understand that from the computer side that the voltages can be low, but wouldn't you expect a higher voltage for an unsophisticated float sensor?

[BIG_MVS]

Yes I did read through your posts, just thought for £17 it was maybe worth trying a brand new one? Also yes I was wrong it's the end one on that row, couldn't remember

I looked for a TSU for Mr Viola and could only find one (which is my spare). I'll have another dig around as there must be one from the titanic we just scrapped.

I did check the earth lead for continuity and it was showing to have a good ground to the main battery earth.

Jeff.
If you have checked that, you need not do any more.
.

Is there a specific resistor that I would need to use, or will any value do?

I did actually state a 500 ohm resistor

What will this tester do that a meter will not read,

The output of the TSU should be a square wave pulse stream. A meter will not recognise that whereas a `scope will. If you use an Analogue meter on AC, you might get an indication, but not a true reading.

What about the voltage going to the tank sensor, does the .48v seem right?

It does seem rather low, but if the TSU is not working, that just might be what it shows
.

but wouldn't you expect a higher voltage for an unsophisticated float sensor?

I cant answer that one, Perhaps it would be easier at this stage to send me the unit for checking. If it is faulty, I can see if it is repairable, but depending what is wrong, I cant promise to be able to repair it as I do not have the cct for it. But if is internal damage, which is more likely, due to vibration, I will have a go. At worst, we will prove if the TSU is faulty or not.
Let me know what you want to do

Cheers

John

Thanks Both,

If you do find one Martin, please let me know.

John, I have just opened the unit and there is nothing obvious. No water damage or damaged board.

If it is OK with you I think that the best option would be to send it to you to try? At least that way we will be able to tell for certain of it is working or not.

If you can let me know your address, I will send it ? If you do not want to post your address on the Forum, please feel free to contact me direct by email; [email protected] or call me on my mobile: 07983620187
Thanks again,

Jeff

Jeff, No Problem, I`ll post my address in a PM to you, but perhaps you or someone else who are computer literate . which I am not, can answer this one. When I clicked on your Email address, I get a popup telling me that "Could not perform this operation because mail client is not properly installed". This also happens when I tried to contact Mr Dell. Suggestions would be appreciated.
John.

[BIG_MVS]

John, when you click the email button on a persons profile it looks like it is associated with an "email client" installed on your pc.In my case outlook express, if you don't have one installed that's when you get the error.

If you just hover your mouse over the email button it reveals the address in the bottom left of the page. Scribble it down and then manually input it onto an email, job done.

Thanks Martin, I have found the address at the bottom of the page, I`ll give it a try .
Cheers

John

TESTING FUEL GAUGE SYSTEM

Just for information, I have created a voltage check list for the fuel gauge systems for the later Alpines fitted with TSU`s. Following this check list will check out the Timer Relay, the TSU, the continuity between the computer and TSU, and the robustness of the TSU Earth. The Sensor`s continuity can be checked by removing the connector from the Sensor and checking that there is between 2 and 90 ohms between the pins of the Sensor depending on the fuel level...... LOW for full tank, and HIGH for low level in the tank.
Hope this is of interest

A message to jon_ viola and clee.

I have just woken up with some thoughts with reference to both your fuel gauge problems, and have checked them against the manual just now, and have come to the conclusion that both your faults could be down to the "Fuel Flow Meter" not producing pulses to the computer, which it should when the fuel is passing through it.

Jon says that.....

The fuel display just flashes constantly with the range.

..... which corresponds with the manuals Flow Meter fault diagnosis. Jon had two faults, one was that water had got into the TSU and damaged the print on the pcb which was repairable, also there was a broken piece of print which I repaired and relacquered the board. I then checked the unit in my Alp and found it now to be working, unfortunately on replacing it in his Alp, the Fuel Gauge still did not work, so perhaps this is also his problem.

With regards to Lees comments.....

It will not read any decrease in level but will reset to a seemingly sensible figure relative to volume when the bat is disconnected ..............

.....this makes sense as clearly the fuel gauge is working, as if it were not, it would not read the "sensible reading" once the battery is dissconnected and reconnected.

My mind went back nearly 20 years to when I was having problems with my flashing display, and I traced the fault to the flow meter and I was lucky enough to be given a couple of faulty ones which I did some work on and got them working. the main faults were due to dry joints on the cct board in the flow meter its self, but the other was due to the poor contacts in the 3 pin connector mounted on the flow meter its self. And if my memory serves me correctly, while I was away on one of my long trips and the fault developed, I did what exactally Lee has described and diss and reconnected the battery to check the fuel level every few hours. Having done 400mls like that, I then proceeded to change the flow meter in the campsite while the wife was cooking my meal and setting up the caravan........nothing chauvinistic about me then you understand
Hope this is of interest.

John