Zero Reading Fuel Gauge - Montecarlo

[lanciatomcat]

My fuel gauge reads zero even with a full tank.
Have checked out, as best I can, the electrics with no better result.
Anyone had this experience and found a remedy please?
Many thanks
Tom

[davidb]

How ironic Thomas. I addressed this issue last Thursday by
removing my sender from the petrol tank. The float had a
bit of gas in it, maybe 1/5th. Drilled a hole, drained the float,
tiny brass screw in the float [drilled] hole. Unlike a Beta/Beta
sender a Scorp sender has a small black plate one can pry off.
That is the rheostat housing is not entirely glued shut. My two
contact tangs seemed a bit loose, I bent them for better contact.
Low fuel @ the top then fuel level tang against the rheostat ribs.
TMK these senders are NLA, an X 1/9 will not work/fit. All this
said you may, MAY, have an electrical issue: gauge, etc. My fix
worked. Scroll back to find the GM sock previously posted this
morning. Luck & such . . .

[lanciatomcat]

David
Thanks for your comments.
I will do a thorough 'search and find' and see what I come up with and report back.
Regards
Tom

[Will]

Could you elaboarte on "checked out the electrics with no better result", do you mean the gauge works,indicating a sender issue, or does not work?

[lanciatomcat]

Will
I checked over the wiring without removing the tank internals or taking the instrumnet panel out to get to the gauge properly. This is my next stage of play. Have a spare instrument panel so may look at swapping over the gauge from there if no results achieved with what I have.
Regards
Tom

[davidb]

You'll quickly realize Thomas that popping the shift linkage rod
off it's ball joint will give you more room to withdraw the
sending unit. The float rod is not only quite long but is "dog
legged". It comes out @ a weird angle. Obviously exercise
caution w/the linkage bushing so as NOT to damage it. While
the sender was out I swished a magnet on the end of a wire
back & forth on the tank bottom. Not an ideal method of rust
removal but I did withdraw a modest amount of rust chunks.
I thought what the heck, better than nothing.

[Will]

Will
I checked over the wiring without removing the tank internals or taking the instrumnet panel out to get to the gauge properly. This is my next stage of play. Have a spare instrument panel so may look at swapping over the gauge from there if no results achieved with what I have.
Regards
Tom

This doesn't really answer my question- when you jump the sender, does the gauge swing to full? And if so, is the sender reading open circuit? It's easy to determine which side of the sender terminals the fault lies. There is no point in taking both sides apart as likely the fault is singular and lies on one side or the other.

[davidb]

Although I agree w/you Will about circuit open, etc. I still insist
removing the sender is THE place to start. One can't move the
float rod when it's still in the tank to test resistance w/an ohm
meter. Once out one can move the float rod thru it's travel on
the rheostat ribs & test. You won't get zip fuel level read if the
float is full of gas or the fuel level tang isn't making contact. Take
the sender out, measure the resistance by moving the float rod,
adjust as necessary, drain the float if necessary, replace the
sender & hope the needle on the gas level gauge moves to the
left. If it doesn't work then we're into gauge testing. My 2 cents.

[Will]

Although I agree w/you Will about circuit open, etc. I still insist
removing the sender is THE place to start. One can't move the
float rod when it's still in the tank to test resistance w/an ohm
meter. Once out one can move the float rod thru it's travel on
the rheostat ribs & test. You won't get zip fuel level read if the
float is full of gas or the fuel level tang isn't making contact. Take
the sender out, measure the resistance by moving the float rod,
adjust as necessary, drain the float if necessary, replace the
sender & hope the needle on the gas level gauge moves to the
left. If it doesn't work then we're into gauge testing. My 2 cents.

You can easily test the gauge without touching the sender, and easily test the sender to the point of determining if it's the culprit without removing it from the fuel tank (it will read open). This takes mere seconds.

If you were a doctor and a patient came to you with abdominal pain, would you attempt to rule out other causes like kidney stones via non-intrusive methods or begin your diagnosis with an appendectomy and then "go from there"? Do you see the parallel?

[lanciatomcat]

Due to personal things here have not been able to give time to getting this sorted out fully. Comments made by David and Will have been noted.
I had established that if I disconnected each of the 2 wires from the sender in turn and earthed them then I got no response with the [RN] red/black but did with the [AG] light blue/yellow. The gauge reads full then.
Is it a simple thing to run an earth wire from one of the fixings for the sender to a seperate earth?
We have a 'holiday' wweekend in the Uk and I will have family commitments till Tuesday next.
Regards
Tom

[davidb]

After perusing the Scorpion wiring schematic to provide you w/an
answer guess what? Item #91: fuel gauge transmitter, can't find
it on the diagram! W/o out finding the transmitter on the schematic
w/it's assoc. wiring I am NOT offering you an accurate, safe answer
e.g. installing an isolated ground. I'd rather beg off than tell you
something incorrect. Maybe Will, others have a workaround.

[Will]

Due to personal things here have not been able to give time to getting this sorted out fully. Comments made by David and Will have been noted.
I had established that if I disconnected each of the 2 wires from the sender in turn and earthed them then I got no response with the [RN] red/black but did with the [AG] light blue/yellow. The gauge reads full then.
Is it a simple thing to run an earth wire from one of the fixings for the sender to a seperate earth?
We have a 'holiday' wweekend in the Uk and I will have family commitments till Tuesday next.
Regards
Tom

OK, Tom, it sounds like now you have ruled out the gauge as the culprit and can forego tearing into the dash!

One final test before you pull the sender, and that is to take an ohmmeter (or even a continuity tester) and throw it across the sender terminals to see if you have an open circuit. I don't think I would personally resort to using a 12V test light and wiring one side of the sender hot to the battery without a current limiting resistor, only because it is a fuel tank after all.

If you read an open circuit, then yeah, go ahead and pull the sender and follow David's previously posted advice. At least now you have confirmed the problem is in the tank and not in or under the dash.

It might make sense to get min and max resistance values off of the sender and post it to the thread that has sensor values (I think DJ made it sticky) so we can think about sourcing alternative replacements.

[lanciatomcat]

David
I had done some research on the wiring and on the RHD diagram it is item 75 and is shown. Looks very simple. You have 2 wires, one red/black which goes direct to one of the 3 multiple connectors on the instrument panel. The other, light blue/yellow goes to one of the other multiple connectors on the instrument panel. Obviously both connections then disappear into the circuitry on the instrument panel. It is clear the gauge is working when the light blue/yellow wire is earthed.
Thanks for your comments. Will soldier on and advise when solution fopund.
Regards
Tom

[lanciatomcat]

Will
Had not seen your response before I replied to David's comments. Will pursue and advise.
Thanks for your comments
Regards
Tom

[Will]

After perusing the Scorpion wiring schematic to provide you w/an
answer guess what? Item #91: fuel gauge transmitter, can't find
it on the diagram! W/o out finding the transmitter on the schematic
w/it's assoc. wiring I am NOT offering you an accurate, safe answer
e.g. installing an isolated ground. I'd rather beg off than tell you
something incorrect. Maybe Will, others have a workaround.

Good catch, David- I checked the wiring diagram ( the one I reformatted, has a title block that includes my email in upper rt corner) and I found you are absolutely correct, the offending item is labelled #9 instead of #91 and is next to #12 on the lower left. I will make a note to correct that!

Tom, if you ground the AG wire the gauge should swing to full. If you ground the RN wire then the low fuel light should come on (I think). Unfortunately no schematic of the internal wiper configuration is shown, but it appears the other side of the light is connected to "+". Why exactly there appears to be a diode on the low oil pressure light I don't know, it appears something can backfeed something else and make lights glow when they aren't supposed to. There's a big surprise (not!).

PS> the whole sender/tank should be grounded.

PPS> I just checked the ORIGINAL wiring diagram in my Tech Data manual, it has the thing labelled as #9 also, i.e. this wasn't my error, (but of course I'll correct it), I think this is 6 or 7 errors so far in the factory WD as published in the TD manual! Eventually we'll get it right! (thanks again David!)

[Will]

Our posts are crossing each other in real-time. Tom is correct on the RHD wiring diagram it is #75 and labelled correctly except the English description says "fuel gauge switch" which is really a combination of the sender and the low-level switch.

[Will]

Scorpion Wiring Diagram updated: latest revision can be downloaded from topmost link at:
http://www.avs.spot-mate.com/tech.html

or direct file link:
http://www.avs.spot-mate.com/images/tech/newswd.bmp

I keep the file name the same each revision, so if you bookmark it you'll get the latest version when you refer to it.

[davidb]

Thanks for the compliment Will. I had KINKO's copy,en-
large a wiring schematic to 2' x 3', taped to my garage
wall. Also found many diagram mistakes I've written in it.
LOTSA NOTES & ARROWS ON THE ENLARGED COPY!!!!!!
I still say pull the transmitter/sender, whatever the "F"
the # but that's just my sense/solution. At least his gauge
works, that's a MAJOR +. Enough . . .

[Will]

I'd be interested in descriptions of the other errors you've found so I can reconcile them to my WD, David. If you can, thanks.

[davidb]

Will I trashed [threw away] my 1ST enlarged garage wall mounted
2' x 3' corrected wiring schematic. Sorry, forgot to mention that.
50% frustration/50% too many arrows + colored lines for wiring.
All my tiny written annotations [labels] would not have helped
anyone. It looked like gibberish. I'm on a 2ND "clean" 2' x 3'
copy [w/o all that crap] on my garage wall as most wiring issues
I've resolved. I guess others will have to "tuff-it-out" as I did.
Sorry . . .

[JGreenslade]

For what it's worth, my S2 Spyder has a pretty 'quirky' fuel gauge, i.e. it doesn't work. The warning light comes on as expected when you're down to the last gallon-or-so. The needle itself rests fully to the left most of the time, and sometimes flickers randomly from left to right to get some exercise once in a while.

I really ought to have fixed it by now... It doesn't strike me as a sender issue as the light works ok.


Justin

[Will]

It most likely IS a sender issue, Justin- the light is on a switch, not the variable-resistance sender strip (which is a common culprit)

[davidb]

My guess, I'm NOT gonna be Mr. "Know-It-All" this time, is an
electrical contact assoc. w/the fuel level wiring making inter-
mittent contact. If the gauge level needle fluctuates that is.
I agree w/Will it's likely a flacky sender. But what do I know?

[JGreenslade]

I didn't know that, Will. Investigation is needed... Point about contacts taken, David.

Thanks,
Justin