924Board.org

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

I have a problem with my fuel meter.

It reads just under 1/4 of a tank when, in fact, the tank is EMPTY!

I got caught out the other night. Luckily, it was just yards from my home (on the way there, not out!)

I've had a look at the sender and I think it's working correctly. The problem is that when the float hits the fuel light contacts, it can't go down any further, so the meter reading stays stuck at that level.

(Why didn't I see the fuel warning light? Because the contacts were covered with a coating of fine powdery rust. They're clean now, so at least the light comes on.)

I've measured the resistance of the sender with the float at the bottom and got a reading of about 75 ohms, but the meter still reads about 1/4. It seems to me that when the float is at the bottom, you want the meter needle to sit on the red 'R' mark, but I think you'd need over 100 ohms to get this.

OK, so I tried a different sender unit. It was WORSE! The meter reads OVER 1/4 full.

Is there some adjustment at the meter end? Or am I missing something?
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

Paul · Posted: Tue Dec 07, 2004 9:28 am Post subject:

Check both ends of the ground connection for the sender unit, or temporary run a new one to see if it makes a difference.

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

Have exactly the same problem as mike here. Checked the resistance levels as per haynes and the senders i have are within range.

But here's what happens

With the float at the bottom, and the light on. The guage still reads between 1/4 and 1/2 full.

When I invert the the sender (turn it upside down). I can see the light switch off, and the when the guage needle rises with the float to full.

This is same problem with the other 2 senders I have.

I have just cleaned and tested the grounds on the car. took a while.
2 crowns under dash.
1 crown behind fuel gauge
1 point between rear lights.
2 points near headlights

I have run a new ground direct to the sender, and checked the quality with an ohm meter. No difference overall though

I have traced the senders signal to E12 and F12 on the back of the relay panel, and cleaned those connections up. No change.

The senders signal also goes through pin 8 and pin 9 on the dash gauge's connector...so im gonna have a look at the connections to that pin and clean them up and tighten the connectors.

All I can think is that over time the resistance of the sender has changed and now no logner allows the correct amount which would let the fuel gauge needle drop down below the 1/4 mark.

any other ideas guys?
tiny
_________________
*****1981 - 924 - Auto - London, UK******

D Hook · Joined: 02 Nov 2002 Posts: 3158 Location: Omaha, NE

Unplugging and replugging the plug behind the gauge (big round white one) a few times helped all my guages in that cluster. Temp gauge, too.
_________________
'80 924 n/a SOLD

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

^ +1

Didn't completely cure the problem, but it did help.

I've just learned to live with it now.
_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

Tiny · Joined: 10 Apr 2006 Posts: 502 Location: London, UK

Well, I cleaned up all the pins and connections on the multi-round connector behind the dash...and replaced the fuse/relay board just for the heck of it...and on an empty tank..the lowest the needle will go is a 1/4.

looks like i'll have to live with mystery of my fuel level...until the light comes on... too.

i might get another fuel guage, and see what that does.
or perhaps...ill once again.... fix that little gear that slips... in the mileometer so i can calculate my fuel in my head.

thanks guys
tiny
_________________
*****1981 - 924 - Auto - London, UK******

Rich H · Posted: Mon Jul 28, 2008 9:53 pm Post subject:

could the light coming on be interfering with the output of the sender? They use the same earth so a trickle of current through the light might be fooling the meter?
_________________
1994 Lotus Esprit S4 - Work in progress...
1980 Porsche 924 S2 DITC Turbo - Original spec
1978 Homo-Sapiens - Tired spec
1953 Landrover S1 - Pensioner Spec

Mike924 · Joined: 12 Aug 2004 Posts: 2601 Location: IoW UK

Good thinking, Rich, but I don't think that's it.

The needle seems to bottom out at about 1/4 full (or just above the 'R' mark now that I've cleaned the rear contacts), sit there for several miles and then the light comes on...

Ho-hum.

_________________
1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

Vince Ponz · Joined: 02 Nov 2002 Posts: 3581 Location: Florida

The fix for the speedo is easy. The cost of the gear is anywhere from 20 to 30 dollars.

You can try to epoxy it if and when you remove the speedo. I did it and it lasted for a couple of years.

Need help ask me.
_________________
"Never let them see you sweat"
77.5 924 modified track car
79 931 Euro stock
88 924S SE
87 911 Targa stock