Jump to content

IGNORED

1977 280z "Fuel" warning light always on


Recommended Posts

Read in this forum that many suffer the ID10-T of the warning "FUEL" light not lid up.  My is opposite.  It always on even though the fuel gauge is half fuel.

Mind you that I haven't drove the car to gas station to get a fill up as I haven't register/insurance yet.  I made a few trip when convenience with a gas can of shy of 2 gallons.  I must have done that at least 5 times.  During my diagnose to fix other problems and driving around the neighborhood to test out brake, lights ... I put in 6 miles on the odometer.  I trust the fuel gauge  to be in working order and reports correctly.  So give or take, at least 7-10 gallons still in the tank given the tank's capacity is about 17 gallons full.  So the gauge says half full, the warning light is on.

Pull the darn thing out but didn't know what to do with it.  How do you diagnose, test to see if the "thermistor" is working/faulty?

 

regards

 

 

 

Link to post
Share on other sites

Disconnect the fuel sending unit. Check resistance on both sides of the connector from yellow/blue to black. (Note: the wire color could be different on the sending unit. Check the pin that goes to the yellow/blue wire in the body harness.)

Report your results here.

Link to post
Share on other sites

So now measure resistance from the yellow/blue to the black on the wiring harness side of the connector. 

After we rule out a short In the wiring harness, you'll take some voltage readings.

Link to post
Share on other sites

Well, it looks like you don't have a short to ground between the fuel light and the sending unit, otherwise you would have gotten the fuel light with the sending unit unplugged.

You seem to have good resistance at the thermistor (1kOhm between the yellow/blue and black wires).

You could pull the sending unit and see if the thermistor was covered with gas. It seems like it is not immersed in fuel with the meter readings you got.

 

Link to post
Share on other sites

Not sure if I understand you.  

4 hours ago, SteveJ said:

Well, it looks like you don't have a short to ground between the fuel light and the sending unit, otherwise you would have gotten the fuel light with the sending unit unplugged.

You mean the sending unit does not have a ground properly? Connect chassis to the black wire ?

Link to post
Share on other sites

No, that's not what I said. A short would be a bad thing. You ruled that out. That's why I gave you another test to run. Pull the sending unit and see if there is gas on the thermistor can.

Link to post
Share on other sites

there has been a lot of discussion on fuel sending lights. when everything electrically checks out I would suggest you pull the sending unit and look to see if its all crudded up with deposits.

the theory of operation is the gasoline cools the thermistor inside the thermistor housing. IF that housing is plugged the fuel will not get to it to cool off and the light goes on. A simple test would be to remove the sender, immerse the housing in a cup of gasoline (not water use real gas for this test) and look to see bubble come out, then remove it and look for a good amount of fuel to pour out of the holes in the housing (not just drip off the sides but actually dribble out of the housing holes. The housing has a filter element that is a fine mesh. this can be clogged. IF its clogged try immersing in a cup of vinegar overnight. swirl around now and then to see if you can dislodge the particles clogging, blow out the crud thru the various hole in the can. Try the gas cup test again. If its still clogged you may need to disassemble the housing. This is some delicate work that requires some soldering and is likely to destroy the existing thermistor. However if its not working you don't have a lot to lose. A possible replacement thermistor has been identified. I would suggest you rebuild the existing housing with that replacement thermistor. That housing was better designed that the replacement housings out there.

Oh and make sure the light in the indicator is NOT an LED. The car was not designed for LED lights, so things like the sending unit and the dimmer will not work with them. The instrument lights were always dim, that is what folks were used to back in the 1970's. Bright instrument lights also are not good for night vison when driving in darkness.

 

Edited by Dave WM
  • Thanks 1
Link to post
Share on other sites

Hi all

 

pulled the sending unit out of the tank.

measure the length from the cap to end of the thermistor with a long stick as shown in the pictures.  Mark the stick and dip it inside the tank to make sure when the sending unit installed, it needs to submerge under the gas and it did almost twice the length of the thermistor.  That can be crossed off the todo list.

dip the thermistor into a left over plastic cup of last weekend son’s birthday. I know, glass, metal or approved plastic... all I had at my disposal at the moment.

dip it in the gas cup and see bubble rushing.  Pour gas out of the thermistor and observe gas was pouring out vs dripping.  Stir, not shake, just like Bond likes his martini, moderately not to spill gas outside of the cup. Observe stir motion had lot of bubbles and no dirt. Gas looked clean.

Measure current temperature both gas in tank and in cup.  Connect wires while the thermistor is outside.  Light on. No surprise there.  Submerge the thermistor to the gas cup. Light still on.

Been tracing wire diagrams and it lead to many places like relay under passenger seat, cigarette lighter, floor temperature, voltage regulator, condenser at voltage regulator... clean all connections.

Seem like we all agreed on the prognosis there is a problem somewhere but where exactly is the question.

Reread @Dave WM twice didn’t see anything wrong.  The third time caught my eyes

“ Oh and make sure the light in the indicator is NOT an LED. The car was not designed for LED lights, so things like“

being anal as I am that I need uniformity... I replaced everywhere possible with LED as I like it a bit brighter.  And being a hoarder like I am, keep junks until project is done many months or years before throw them away with great pain in the guts still.  Dig through the used bin and pull out a bulb.  Swap back.  Light gradually brighter while the thermistor is outside.  Submerge it to the gas cup and smoke is coming out of the thermistor.  Scary my friend.  We’re talking about highly flammable here.  Light went off. 
 

Ladies and gentlemen, I haven’t had breakfast yet and the moment I see light went off, the feeling as if I just had an all you can eat and now is sipping a piña colada somewhere in the Caribbean ?

I repeated the experience multiple times and works as expected.

boy, what a fun chasing this problem.  The old saying is truly applicable here.  If it ain’t broke, leave it alone or something along that line.

thank you everyone for the help and support.

 

regards

 

 

 

 

A34E18EA-C62B-4087-916B-71D5E43DD090.jpeg

9BED037B-075E-4D07-AB8E-B1C90447C6C3.jpeg

35BB83A4-AB85-4D89-98CA-D34E7AD125B4.jpeg

BC5428B5-BFAF-4303-B18E-BC64B3299639.jpeg

29D5B67E-01E5-47F6-87C6-AC04395CAA0F.jpeg

1BAD9105-13C7-44B2-B79F-FF87FB77AB79.jpeg

113BF5DD-529C-47A8-A507-93584A26A6CD.jpeg

59663090-5CD5-4934-948A-A28258A2A7E4.jpeg

  • Like 2
Link to post
Share on other sites

You aren't the first to use an LED where the incandescent bulb is needed. I doubt you'll be the last. I'm glad @Dave WM thought to mention that.

Here is another old-school application where incandescent lights are needed. In the past to synchronize an AC generator to a live system, you had two lights that are connected in series and to the same bus phase on each side of the breaker. When the sources were 180 degrees out of phase, the bulbs burned bright. The closer the generator was to being in phase with the bus, the dimmer the lights would get. When the lights were extremely dim or out, it was safe to close the breaker...if you were quick enough.

Some people still want this antiquated functionality on new equipment, but they also want LED light bulbs. I submitted a design package to a consultant complete with my parts list that had LED bulbs and the incandescent bulbs for the synchronization panel. The consultant wrote back that his specification called for LED lights. I replied that the incandescent lights were for the synchronization panel that he also specified. That was the end of that conversation.

Yes, the life of an electrical engineer can be so exciting...just like arguing on the internet.

  • Thanks 1
  • Haha 1
Link to post
Share on other sites
3 minutes ago, SteveJ said:

I submitted a design package to a consultant complete with my parts list that had LED bulbs and the incandescent bulbs for the synchronization panel. The consultant wrote back that his specification called for LED lights. I replied that the incandescent lights were for the synchronization panel that he also specified. That was the end of that conversation.

Yes, the life of an electrical engineer can be so exciting...just like arguing on the internet.

You made the mistake of calling them incandescent light bulbs, instead of variable luminosity hot filament synchronization components.

  • Like 1
  • Haha 3
Link to post
Share on other sites
10 hours ago, 240zadmire said:

Ladies and gentlemen, I haven’t had breakfast yet and the moment I see light went off, the feeling as if I just had an all you can eat and now is sipping a piña colada somewhere in the Caribbean ?

Haha!! Very nice!   :beer:

I'm glad the solution was a simple bulb change. 

Link to post
Share on other sites

@Captain Obvious

 

when you work alone all by yourself... the car is simple but there are just so many little things.  It’s overwhelming and overlooked stuff.  Part ignorance, part just rushing through and omit stuff.   As you’ve notice on the brake issue, I’m so bless having such folk with a wealth of knowledge.  A second pair of eyes/ears/hands definitely a good thing.

 

regards

 

Link to post
Share on other sites
  • 2 weeks later...

Thought to share the fuel light on when fuel is near empty.  It works beautifully. I’ve been chasing the running rich/powder/sooty on first 3 cylinder and kept an eye on th fuel light to see if it works inside the fuel tank. As the gauge dropped a bit to the left of near empty, light gradually brighten.  So cool.  Rushed to gas station to get another 2 gallons and fuel light is off. So nice when things work the way you expected.  Wonder how many gallons/mileages when the light is on?

reminded me of a scene of Kramer and Jerry in one of the episodes where they test drive a car. It keeps running and running for hours even though the warning light is on. ? Only if it was true in real life !!

E9C7508E-CF58-4B04-B21E-D7759A09752F.jpeg

  • Like 1
Link to post
Share on other sites
  • 11 months later...
6 hours ago, DramaZed said:

If you haven’t changed the light, why would it light up on a full tank?

Failed thermistor 

Link to post
Share on other sites

geez this keeps coming up.

I would recommend you pull the unit out of the tank and bench test it with a 12v source and the light used in the car. could be you just have the wrong light, pulling too much current causing the thermistor to run away.

Link to post
Share on other sites
27 minutes ago, DramaZed said:

Brand new sending unit. Hate to see it. Will just deal with it till I get this car running right. 

The full story helps. Bench test per @Dave WM's instructions.

Could a previous owner have changed the bulb?

Link to post
Share on other sites
Posted (edited)
3 hours ago, DramaZed said:

It was working the last 2 months. Started acting funny yesterday when I filled up the tank. 

ok so its brand new, two months old, works perfect, as in it would come on when tank was nearly empty. I mean I rarely see mine come on as I rarely get down that low on fuel. so approx how many times did it work? off and on at low fuel?

describe the way it came on, suddenly or slowly when it was working.

Edited by Dave WM
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
×
×
  • Create New...

Important Information

By using this site, you agree to our Privacy Policy and Guidelines. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.