Over the last few months I've been having a problem with the fuel gauge on my 1991 LS400. While driving with a relatively full tank, the needle will slowly drift to a quarter or so. After a while, I'll notice that it has moved back up to what is probably the correct level. I pulled the connector on the sender at the tank and cleaned the contacts. For a few days, it seemed that that had fixed the problem but, alas, it has returned.

I've read other threads here and elsewhere that talk of changing out the electrolytic capacitors on the instrument panel circuit board. I don't remember seeing what symptom or symptoms the various posters were trying to correct so I don't have any feel for whether or not that might solve my problem. I suppose it could be the sender unit itself. I did read one post that talked about cleaning the variable resistor on the sender but, again, it didn't what symptom was being addressed.

So, based on my description of the fluctuating indicator, any ideas on where the problem might lie?

 

From post #12 onward:
http://us.lexusownersclub.com/forums...e-fixed-94-ls/

So yes, you would be advised to replace the dash cluster caps. This has been a common issue among the other areas of the 1-LS cluster that need repairs. (Would be nice to have a summary of symptoms in the first post so that it is clear. )

 

Capacitor issue is a 93-94 issue. 90-92 cluster issues are more complicated. The problem is likely the fuel needle/motor assembly on that one.

We can repair it if you want to send it in

 

On another forum, someone suggested disconnecting the sending unit and adding a fixed resistor to simulate the sender. There are three terminals on the sender unit and the resistance measured 4.7 ohms between the two closest to each other and about 24K ohms between each of those and the third after having just filled it. Based on information I've read elsewhere, I guessed that the 4.7 ohm pair was probably the variable resistance with the third possibly being a ground.

At any rate, I connected a 10 ohm resistor between the closest terminals on the connector and the gauge now reads almost full. Without the resistor the gauge reads empty. Now, I'll watch for fluctuations as I'm driving around.

 

Good work. We have repaired several of these and customers state the fuel gauge still does not work. This is good information to have.

Are you leaning towards the sender being the issue then?

 

I've just today put the resistor in place. Now, I need to drive it for several days to see if the gauge reading fluctuates as it was doing. If it still does the sender is likely not the problem.

 

I modified my test rig to get more varied data. Now, I have four resistance values from which to choose: 5 ohms (two 10s in parallel), 15 ohms, 33 ohms and 75 ohms. The 5 ohm puts the needle just below Full while the 15 ohm makes it just under 3/4. The 33 ohm puts it just below 1/2 and 75 is at Empty. The attached photo shows how I set it up, taken looking into the trunk from the back of the car.

I've driven it a fair amount in each setting and the fuel gauge stays steady at the selected reading. I've concluded, therefore, that the problem is with the sender. When the tank level gets down to a 1/4 or so I'm going to pull the sender and clean/inspect it. If all else fails, I plan to buy one, p/n 83320-59045 (fits 1990-1993 LS400).

 

The fuel gauge has been solid on all resistance levels leading me to conclude that it is the sender that is the problem. This evening, I removed the sender and examined it. There was nothing obvious on a superficial exam so I opened up the box containing the variable resistor. At first, I thought that the wiper arm wasn't making consistently good contact with the resistor element but then I noticed that the other end of the wiper looked odd. Removing it, I found that two contacts that connect to the disk looked "melted". On closer examination, those contacts were worn almost completely off, having remnants that looked like crumpled foil which was easily torn off with tweezers. The attached photo shows the wiper from the bottom side. The contact at the bottom of the picture makes the connection with the resistor. The other two, at the ends of a semicircle, are the ones that are badly worn.

 

Good info and pictures. Thanks. I wonder if this is a widespread issue with 90-92 LS400's or dependent on different variables.

 

I've fixed this using the wiper from a newer fuel sender. Details and pictures at:
https://www.clublexus.com/forums/ls4...el-sender.html