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BMW 325i Fuel Gauge Problem

Q. Dear Sir, I have the subject car, 1988 BMW 325i, automatic transmission, which is in a very good condition. The only defect it carries is that when I start the engine and have a drive for two or three minutes the fuel gauge shows full in the dial even if the fuel tank is half. Kindly guide me as how to fix the problem as the mechanic available in United Arab Emirates have failed to understand as to why it is showing like that. Your early reply will be highly appreciated.

Best Regards,
Qamaruzzaman

BMW 325i Fuel Gauge Problem

A. The fuel gauge works by variable resistance transmitted from a sending unit in the fuel tank directly to the gauge. If you've ever played with slot cars as a child it's much like the speed controller for them, the more you pull the trigger, the less resistance to the cars on the track, the faster they go.

Your sending unit is much like this, except the trigger is a float connected to a lever inside your fuel tank. As the fuel level rises, the float rises and decreases resistance to the fuel gauge, which makes the needle on the gauge go up.

That being said it sounds like your sending unit float is sticking in your tank at the full point after perhaps hitting a few bumps. A few simple tests need to be performed. First the wires to your sending unit need to be unplugged at the fuel tank.

There should be an access plate under the rear passenger seat to get to the fuel tank sending unit. At this point turn the key on verify that the gauge stays at the empty reading, then connect the wire to ground and verify that the gauge moves to full. If it does, the problem lies with your sending unit in the tank.

If it doesn't then the possibility exists that there is either a short in the wiring from the gauge to the sending unit, or the gauge itself is faulty. Inspect the wiring to the gauge for shorts and if it checks out okay, replace the gauge.

You will then need to remove the sending unit from the tank, reconnect it to the wiring and manually move the float up and verify that it moves freely and the gauge moves proportionally. Check for sticking points in the range of motion. If there is a point where it sticks which can't be easily rectified by bending the lever, then you must replace the sending unit.

There was a TSB issued on this problem also. It is:

Group 62: Instructions

Bulletin Number: 62 12 91 (3421)

Woodcliff Lake, NJ
June 1992
Product Engineering

This Service Information Bulletin replaces (Orange) S.I. 62 12 91 (3421) Dated Nov. 1991. It incorporates additional information and refers to another S.I. concerning a related complaint.

Subject:
Fuel Gauge Displays Inaccurate Fuel Tank Level

Models:
3 Series (E36) - Vehicles Produced Before 8/91

Situation:
Two separate, but related complaints may be encountered:

  1. The fuel gauge displays an incorrect level; for example, the gauge appears to stick at approximately ½.
  2. The fuel gauge does not show maximum level when the tank is filled.

Causes:
Two causes may exist for these complaints:

  1. Left-hand side fuel level sender (P/N 16 14 1 180 517) sticking (causes gauge to appear to stick at approximately ½).
  2. Pump nozzle shuts off prematurely when filling fuel tank, creating the incorrect impression that the fuel tank is full, and the fuel gauge does not show the maximum level.

Correction:
E36 vehicles produced prior to 08/91 and exhibiting complaint "A" as described above should have an improved left-hand side fuel level sender (P/N 16 14 1 180 517) installed. The improved fuel level sender bears a blue date code stamp of "9.91" or later.

Any vehicle exhibiting complaint "A" should be checked for proper alignment of the fuel level senders (refer to sections 16/12-3 and 16/12-4 of the repair manual).

E36 vehicles exhibiting complaint "B" as described above should have the breather line inspected for restriction and position. Refer to Service Information Bulletin 16 01 92 (3553) for this procedure.

BMW 325i Fuel Gauge Problem

Additional Information provided courtesy of ALLDATA

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