Fuel level indication in 951

[arnebret]

In my search to kill all the annoying things that have come up over the last couple of years i'm in the search of the problem that causes my fuel level indicator to give a too low reading.

When the fuel indicator is telling me there is only a quarter left, the tank is actually half full. I took out the complete send unit and floater. Cleaned it up and measured the resistance. Everything was right up to spec. I then hooked the sender online and tested what the gauge would do. When the floater is all the way at the top (about 3 ohm), my gauge displays just over 3/4 full. When i go to the bottom (about 63 ohm) the gauge already shows reserve way before the floater reaches the bottom.

Conclusion: somewhere along the way form the send to the gauge the reading has to go wrong. But where?? Is there an gournd that's rusted up or something?

Any experience is welcome!

[swimmingly]

I have this same problem and it's very annoying. Most of the time, I only know that I'm somewhere between 3/4 and 1/4 of the tank full because as you said, the gauge only goes up to 3/4 (even on a full tank) and the last time I filled it with the gauge reading 1/4 I only put in 6 gallons and the gas station pump stopped.

Sorry that I can't answer any of the questions but just wanted to let you know that it's probably a common problem since I have it too. If you ever find out what's wrong with it, post what it is.

[arnebret]

Another interesting flaw that the good old p-guys allowed in their brilliant design? Don't get me wrong, these cars are built to last and hell they do. But some minor things really do seem to go wrong in time, maybe they tested it for 5 years and none of this came up. After more than 15 years we are complaining about little things, bless those Porsche/Bosch guys!

Anybody got the solution?

[ronin]

I'm not sure if this is the problem as I don't know the composition of the float. However, on many cars the floats will get fuel-logged over the years and lose some of their buoyancy. This will cause the float to not, well, 'float' as well as it used to and dip below the waterline. Also, it could be a resistance problem in the sending unit, I suppose.

[arnebret]

I checked the sender unit, all up to specs. The floater doesn't seem to lose buoyancy. Besides that, i tested the floater on the car. All the way up (3 ohms) should give me a FULL reading, but it stops at 3/4. So the sender unit is fine, something is wrong between the sender and the gauge. See my initial post.

The resistance somehow gets too high for the gauge, so the lines aren't 100% clean somewhere a long the way...

[ronin]

Originally posted by arnebret

The resistance somehow gets too high for the gauge, so the lines aren't 100% clean somewhere a long the way...

sorry, should have read your post a bit more thoroughly. if everything at the tank checks out o.k. then I definitely agree that it's in the lines somewhere. also, I'm trying to think if there is something in the gauge itself that could cause this.

[arnebret]

at clarks garage there is a short article about this. it's all very clear, and it has some things you can check.

A ground point is mentioned inside the firewall on the drivers side. Which one is that??? On the inside or in the engine bay?

[ronin]

hmmm, probably under the carpet in the footwell or somewhere close by. I'll probably be checking the same thing shortly because I did notice that my gauge is starting to slack of just a tiny bit. it doesn't get quite as 'full' as it used to.

[arnebret]

well i have the garage manual, i'll check the grounds scheme

[arnebret]

ok, have it here... It's either MPII or MPIII. MPII = Inside firewall, electronics chassis, MPIII = Inside Firewall cable to ground. They are both located at position 7cP which is roughly in front of the relay box, but just slightly to the middle of the car. I'll check right now and disconnect a ground, see what happens to the fuel gauge...

[ronin]

lemme know exactly where that ground is when you find it. speaking of relay box, my climate control relay keeps ticking, gotta address that.

[arnebret]

yeah, got some spare time now, just fixing all the small things.

But erm, i can't find the BLOODY ground point. There's only one, but that seems to be for the abs or something. Damn it, anybody there with a pic of MPII and MPIII?

[ronin]

C'mon So Cal, whip out that CD!

[1.2gees]

Cleaning the contacts/bridges behind the cluster should help, and cleaning the grounds also may do the trick.

I had my odometer apart (broke for the 3rd time, so I ended up fixing it for good this time around, binding gears), anyway I went ahead and did the cleaning. The oil pressure and fuel level gauges read higher now, and seem to be a bit less effected by accessories coming on. Oil press. is also more steady.

Could be worth a shot, please keep us updated.
Ahmet

[arnebret]

Ok, could you be more specific in where the ground is for the fuel gauge? And are you suggesting to take the whole panel out to clean the cluster? As I want to replace some broking lights there, this might come in handy to do right away.

[1.2gees]

Pulling the gauge cluster isn't hard, I would recommend doing so. There's a very good write up on pelican, I'll find a link for you if you can't get a hold of it (but it's getting late, and I have a lot of school work to do right now). I would suggest upgrading the bulbs that provide regular gauge lighting also, while the cluster is out.

I'm not positive where the ground is for the fuel gauge (but I assume it's common with at least a few other things). I'm going to look into this, but I don't think it'd be too far from the firewall. I'll let you know when I get around to it if you like. I cleaned the connectors/bridges behind the panel. The pelican write up I mentioned has instructions for this, I seem to recall a similar write up at clarks garage that also covers it.

Anyway, let me know if there's anything I can help with, if you can't find the links also let me know and I'll post them tomorrow.
Ahmet

[arnebret]

Yeah, found it. I'll try that in the near future, thanks! Oh, and clarks garage has some nice pics with it as well.

Maybe some of you guys can help me with yet another question i have: which lights should come on after you turn the key right before you start. In my case: handbrake, low oil, abs, brake fluid come on. Should anyhing else come on, if so i can replace the bulbs rightaway.

Oh, 1.2Gees, what did you mean by 'upgrading the bulbs'?

[1.2gees]

On your car, I would think the oil level light as well as pressure, and maybe the SRS lights should come on? The bulbs are cheap, I would replace all (and did). This is kind of like replacing the water pump when doing a timing belt, except on a much smaller scale.

The factory bulbs are 2 watts. I recoated the light tunnels (clarks garage mentions this I believe), and replaced the two outer bulbs with 3 watt bulbs. This is plenty of light for me, as I don't like anything bright inside the car at night. Some people have tried up to 5 watt bulbs. Don't do this, it'll melt the sockets. The highest I would go is around 3.5 watts. 3 should be no problem if you're paranoid.
Ahmet

[arnebret]

Little update: i took the instrument cluster out, and cleaned all the contact points etc. I then sprayed them with a little 2-26 Electro to keep the dirt off. I only reconnected the three plugs and already noticed the fuel gauge is giving me a higher reading then before. Tomorrow, i'll get me some new bulbs and replace them all. It's not a hard job and actually worth to clean once every 4-5 years or something.

[ronin]

Hey Ahmet, just checked your profile. Man, I just never get tired of looking at this car from the rear 2/3 angle. (image 3, parking space) from your pictures I can also really appreciate how great this car looks in silver.