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Erratic Gas Guage

2K views 5 replies 4 participants last post by  DJProfessor 
#1 ·
My 89 325i cabrio gas guage stayed stuck on full, so i changed the batteries on the SI board, it still remained on full. I then took the fuel guage off the cluster and re-did the three contact points, the guage then went to half full and stayed there. is this common, can anyone suggest which way to go next i'm tired of gas guessing....
 
#2 ·
well you need to figure out whether or not it's your sending unit or your cluster. you can disconnect the sending unit and using a wiring diagram you can make it read full or empty. if it doesn't read at all one way or another, then your cluster is to blame. if she reads like she should then the sending unit is probably the cluprit....but i like to pull the sending unit after having tested the cluster and slowly sweep it just to double check.
 
#4 ·
To be honest Ervin, that whole concept is based on how confident you are with electronics and wiring. Take that into consideration when going into wiring diagrams as DJ has professed. I agree with that Ohio vinyl spining freaque more often than not, and his observations are sound and based on a LOT of hands on experience. My first suggestion would be to have a shop do the work if you are not 100% confident in your own skills, but if you are 80% confident, give it a try and use this board to get you out of any bind you might find yourself in!

Hope this helps you decide!

Josh W.
 
#5 ·
misterervin said:
Thanks for the heads up DJ, is that sender unit something I can do myself or should i consider sending it to a shop....
The sending unit in your car is located under the rear passenger seat, pasenger side. Remove seat and you will find a inspection plate, remove the plate and you will see the elecrical connector and fuel hoses. Disconnect electrical connector and then the hoses (expect to lose some fuel, I use two vise gripts to clamp off the hoses before I disconnect them). There should be three or four screws or nuts for the sending unit, remove them and the sending unit pulls straight out (have a bucket or pan at hand to catch residual fuel). Replacement is the reverse of removal.In my experience, the funky fuel gauge is generally a bad sending unit.
 
#6 · (Edited)
Bear said:
The sending unit in your car is located under the rear passenger seat, pasenger side. Remove seat and you will find a inspection plate, remove the plate and you will see the elecrical connector and fuel hoses. Disconnect electrical connector and then the hoses (expect to lose some fuel, I use two vise gripts to clamp off the hoses before I disconnect them). There should be three or four screws or nuts for the sending unit, remove them and the sending unit pulls straight out (have a bucket or pan at hand to catch residual fuel). Replacement is the reverse of removal.In my experience, the funky fuel gauge is generally a bad sending unit.
Bear is only half right....i recommend removing the electrical connector for the sending unit, and with the help of a trusty wiring diagram you can make the guage read full or empty. no sense just ripping out the sending unit, removing and replacing a part you haven't tested to see if it is good or not. if you bypass the sending unit and the guage reads nothing or doesn't act like it should then you have yourself a bad guage and didn't remove the sending unit for nothing....now if you test the guage and it tests good, then you can rip away at the fuel sending unit to your heart's content.....(AND HAVE A FIRE EXTINGUISHER CLOSE BY, FUEL IS NOTHING TO FUNK WITH)

need to get in the habit of testing parts not just blindly replacing them. if a part is known to go bad 99% of the time you still should test. no sense going out buying a new one and then going thru all the trouble of replacing it and then finding out that that is not your problem. when you could have simply tested it in the first place and save yourself all the trouble. diag. is the most important thing in car repair. it saves yourself time, money, and headaches........blindly hanging parts is a job for Midas.

oh and thanks for the props Josh.....
 
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