Faulty fuel gauge

[Huck]

My 87 325ic fuel gauge will read full when full but slowly drops down to only 1/2 tank and never lower. If the actual tank level drops down low enough the waring light does come on. I swapped out the pass side fuel sending float but now difference in the problem. I've read that there may be two sending units but not on this car. Only access to the tank is on the pass side. Have also read about the grounding of the gauge but I could a faulty ground give me a 1/2 tank reading issue???

[Jean]

Did you install good / known / tested fuel level sender? you can check it with DMM to make sure it drops all the way down and goes all the way up etc...

[scottinAZ]

Also, if you have a 13 button OBC, you can check the level reading by pressing the "1000" and the "1" buttons. If this level (given in liters) changes and goes down, then the gauge itself is faulty. The light is also triggered by the sender, so the problem may be outside the tank.

[Adrian_Visser]

Isn't the light on a separate circuit than the fuel gauge?

[Jean]

ETM shows how it works...it gets trigged by the Fuel Level Sender.

[jlevie]

Since you've tried two fuel level sensors with no change in the behavior of the gage, the cause isn't likely to be the sensor. This car shipped with the early style tank that only used a single level sensor located on the passenger side of the tank. Later cars use two level sensors wired in series. It is possible that someone swapped in a later cluster meant for a car with two sensors. That would produce the behavior you see.

[Huck]

AH HA!! GUYS, YOU ARE GREAT!!! Jean, I did swap the sendors but thought the 87 and 88 325ics were the same basic cars. I did see where the cluster in the car had both VDO and Motor meter components which made me a little crazy. The batteries were crap as were the odo gears. I swapped in a known good sender and a known good speedo/odo and circuit board with good batteries and the last issue to resolve is that fuel tank gauge problem. I kind of thought (WRONG) and the 87 325ic was pretty much the same as the 88-89-90 but that is not the case at all. Apparently the 87 is kind of a crossover car from the 325Es and the 325i's. It has the older fuel tank, the older cooling system (radiator, waterpump, hoses) as well as some other "interesting" stuff! This car has 220,000 miles on it and runs super. If I can work out the minor details, I will invest in a timing belt-water pump replacement too!!
So now I need to get an early fuel sending unit and an early dash cluster to work with it---? ETM---?

[Jean]

You can use either cluster, the fuel level gauge just needs to match your car (your tank really). For example, I have an early car and I use a late model cluster but with an early fuel gauge + original fuel level sender in the tank. I would still double check the sender with a DMM set to Ohms, you can flip / rotate it and listen for the float in it move smoothly, see if it sticks. And while it's moving the Ohms reading should change from about 4ohm to 80ohms (so set the DMM to lower Ohm scale).

ETM = electrical troubleshooting manual, it gives you all the schematics and wire colors/locations you'll ever need and it makes it easy to troubleshoot stuff and see how stuff works. You can google or search for the link on the forum.

[jlevie]

Jean is correct. All you need to do to fix the fuel gage is to swap the late model gage in the cluster to an early model gage. The level sensors are the same for early vs late production. All of the senders I've checked are 0 to 60 ohm sensors (with 0 indicating a full tank).

[Huck]

I picked up a good 87 radiator (mine had a slight leak) an 87 fuel pump with sending unit and an 87 gauge cluster (all out of the same car) so I should be ok---we'll see tomorrow.

[Huck]

Swapped out the cluster and that created more problems but the gauge now works so I went back to the previous cluster but changed the fuel gauge (it was kaka--needle was stuck so that it wouldn't drop more then 1/2 way!). OK then everything seemed to work but now the fuel economy gauge seemed dead----messed with that a while then put it off for a day. Thought about it for a while---read a little---and apparently the guage is rather lax until you drive the vehicle. It reads throttle position but also reads vehicle speed before it changes it's needle position---. Now just about everything works.

Anyone have a source for economical odometer gears? $25. per is crazy especially when I need three!!!!!

[Jean]

Ebay.