Tom M'Guinn

Filled up my tank today and the gauge went to 7/8th, as usual... I've mocked up a calibration box and confirmed I can control the gauge from above full to below empty, and turn the low-fuel light on at any point in the process. Thinking about making an installable calibrator (which would mean half my factory gauges are calibrated....)

How common is this issue? Curious to see what everyone else is seeing... I've tried a different gauge and it's the same, so seems like just a reality as these cars age, and resistance builds in the harness, that the gauge won't go all the way to full. And everyone likes a good poll now and then....

Alan 91 C2

Hi Tom,

My car goes to 7/8 also. I put two containers of Techron into the tank, when the full reading was only going to 3/4. I have since added Techron weekly and the gauge is 7/8+ at full.

My 2005 Suburban gauge now only goes to 3/4 at full. I am trying the Techron treatment. The Ethanol is the problem here, with gauge accuracy.

My 1991 911 does not seem to have the gauge issues yet. Will start Techron preventative treatment. The 77 924 gauge reads "0", too late to save that sender.

snb13

http://924.org/techsection/gas_sender.htm

Tom M'Guinn

Thanks for that. In my case, it's not the sender, which gets down to a couple ohms when full. I've been through the whole system (several times) and it's better than it was, but still only 7/8 when full.

From an earlier post I made:

To read full, the gauge needs to see 2.8 ohms from the sender. That's easier said than done when the signal is travelling through 20+ feet of 25 year old wire, into and out of a connector at the sensor, to another connector at the ground point, through the ground point to the chassis, through the 25 year old edge connector at the cluster, through the weird plastic circuit thing wrapped around the back of the cluster, through more connectors inside the cluster, and then to the fuel gauge. If full were 1k ohms, and empty were 10k, then a few extra ohms from that electrical journey would never be noticed -- but since the brain-trust at Porsche decided 2.8 ohms means full, we're left hunting for resistance a quarter of an ohm at a time...

This is really a follow up on an earlier thread really, I just couldn't add a poll so started a new thread:
https://rennlist.com/forums/944-turb...libration.html

mahoney944

I had this issue too, fixed it by moving the gauge needle up a hair and it reads perfect now. Just go get a full tank of gas and pull the cluster out. then plug it back in with the front cover removed. Turn the key on, set the needle at full (also a good time to set any other gauges and replace bulbs) and its good to go

darek_u

I adjusted it as per your calibration thread, it is spot on 4/4 when full now.

Tom M'Guinn

Did you adjust the pot on the gauge itself? I adjusted mine all the way up, and it still isn't enough.

I'd nudge the needle but then it would read a tad high when getting empty, and let's face it I'm looking for an excuse to make a calibrator...

darek_u

Yes, it was trial and error process but I think after third attempt I got it correct. As far as I can remember I had to dial it almost all the way up but still have a little room to go. I have cleaned thoroughly all the contacts beforehand, including sender plug and socket with emery cloth. I also cleaned and tested the sender itself. I did not see any signs of corrosion on the wire and plug, I also inspected the short part of harness running between the tank top and boot floor when I had tank out - it was in perfect condition. That leads me to a conclusion that my signal path is still in fairly good condition and it was enough to crank the resistor a little to get it back accurate.

mahoney944

I found that my gauge was a tad low at empty from use I suppose. Moving it a tad up made it read correct high and low. If the needle is at or on the yellow/ orange indicator light its too low. its suppose to be on or at the bottom of the line above the warning light. If you Google image 944 clusters you'll see these old gauges are all over the place on there starting position. I think they just sag down over time, at least mine did.

Good one
http://forums.pelicanparts.com/uploa...1243437237.jpg

Bad one
http://germancarsforsaleblog.com/wp-.../12/8222_3.jpg

User 52121

Mine always went to 7/8 too.

Then I pulled the cluster and cleaned the "footballs". Ever since, I get 8/8 full tank now.

mahoney944

Yes that too.