hi guys,

my 93 ls400 has this issue with the fuel gauge. everytime i refuel, the fuel gauge very very slowly creeps back up to the full mark. but when i shut off the car and start it the next day, even with a full tank, it reads around half a tank of the gauge, but slowly creeps back up to full as i drive. it takes a long time to creep back up to its correct state. anybody have this problem and would you guys know what is the problem?

thanks.

 

The float in the tank is bad or is hanging-up.

 

Do you have any problem with your Tach or Speedometer needles not working sometimes?

 

nope, all the meters all work. it's just the fuel gauge acting up lately.

 

Is the gas tank in the trunk like the LS400 if it is than it's an easy fix.

 

yeah, it's for my 93 ls400. do you know what the solution to the problem is Lexkost?

 

It is not from the gas tank. To be more specific, the problem is not from the fuel sender unit in the gas tank but it was from a fuel gauge circuit in the dash. I already changed the fuel sender on mine - I got a thread on this fuel gauge thing a while back here so you can search and read up. Cheers

 

I had a 94 ls400 with 167k miles I bought 6 weeks ago with fuel gauge problem, even I fill the tank full the gauge only show half tank or sometimes 3/5 tank and sometimes show empty and slowly moved to 3/5 tank. I have removed the fuel sender unit the other day and manually moved the float ball up and down but the fuel gauge still cannot go to full. The sender just a var. resistor with a floating ball and the value change according to the fuel level changed so I knew the sender unit was ok, according to the previous poster say its something wrong in the cluster panel pc boards. So i decide to removed the cluster panel to check out what was wrong. My cluster panel all the other function were works good except the fuel gauge. I have locate the bad componemt its a bad surface mount capacitor on the big pc board. There had two pc boards one big one and one small one on the top. The bad cap. was locate on the big pc boad values was 4.7uf 25v. I have measure the the bad cap. its value have changed from 4.7uf to 2.5uf and sometimes 3.0uf. I don't have the surface mount cap. but I have some titanium cap. with the same value so I used it. After I solder,I put every thing back but I don't know it works or not because my tank was not full. I drive the car to gas station and fill the tank up and the fuel gauge go to full right away. I try few times to on/off with the key and every time the fuel gauge moved to the top right away. So my fuel gauge problem solve.

 

pwgtang, would u happen to have some pics of where the cap is located?

 

The cap. was locate at the big pc board and the number was C142 value was 4.7uf 25v

 

Are you saying that you soldered a pin through hole component capacitor in place of the SMT cap that was there? Did you remove the SMT device or solder parallel to the exisiting component?

Was that SMT cap one of the small ones? like 1/16" X 3/32" If you soldered that PTH component on an SMT board without screwing the board up then you have to be an experienced solderer.

No one can just pick up an iron and do micro mini repair like that.

 

you need to remove the bad cap. and use a weller solder iron with temperature control and the right tip to solder the new part you just need to bent lead to the right lengh,not any solder iron will work. Yes, I am an unempoly electrical engineer with a lot of experience on soldering technic and circuity troible shoot. You need to buy some very small 60/40 tin/lead core solder. And best with a magnify glass lamp.Before I am not working on my car but now I have a lot of time. I have the equipment to measure those componemt's value not just a dvm.

 

Yea, I thought so, that you were a professional.

My point was kinda that replacing this component isn't for the average "Joe Mechanic". This is engineer stuff.

It would be so easy to mess up the board by lifting a pad, making a solder bridge, etc. that I wouldn't recommend the fix to just anyone. Unless you have solder and SMT repair experience no one is going to fix this problem.

GSquicksilver, I'd suggest you ask pwgtang how much he will charge you to replace this component for you.

 

pwgtang,

This is excellent news! My 94 has this same problem & I was pretty convinced that it was not the sender.

Your expertise in diagnosing the problem is very much appreciated , now if I can just find someone in Dallas to do the board level repair I will be in good shape. Now that the problem is known , a competent person with a soldering iron should be capable of the capacitor switch but it will require some skill to not damage the board.

Love this forum, info like this can save major bucks that I can use towards my timing belt change

damon