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E30 (1982 - 1993)
God's Chariot. The E30 was produced primarily from 1982 through 1991. The cabriolet was the one exception which was produced through 1993.

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  #1  
Old 07-04-2013, 12:58 PM
LocoMex LocoMex is offline
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E30 Fuel System Question

First question on this forum. I have 1990 325ic. with several issues, but the one that troubles me most is the fuel system. It leaks badly if I fill up. If I run it down to near empty, I can put 10 U.S. gal. in it without leaking. From reading, I find that this type of leak is probably corrosion/rust where the filler neck attaches to the tank. Can I access this area without first removing the gas tank? Guidance here would be really helpful.

Also, my fuel gage is having issues. It seems to function well showing fuel level at the top end. But, when level gets below 1/2 tank, it fluctuates a lot. The gage needle will go from a little under 1/2 to near Empty. A few miles later, it show a full 1/4 tank, etc, etc. It seems the system has two senders. One sender is isolated, and the other is incorporated into the fuel pump. Question, does one side read on the high end and the other on the low end? If so, which side reads the low end and visa-versa. Thanks for any help.
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  #2  
Old 07-04-2013, 06:51 PM
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downhiller downhiller is offline
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pop the bottom rear seat cushion out, youll have 2 covers that are bolted down. the pass side has you fuel pump, driver is the other sender. technically the tank is split or has 2 low sides. the leak could also be from one of those seals. you can barely see the filler as it attaches to the tank but its enough to get an idea.
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  #3  
Old 07-05-2013, 10:10 AM
LocoMex LocoMex is offline
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Thanks. I'll see what I can see.
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Old 07-11-2013, 06:14 PM
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Re: E30 Fuel System Question

Locomex
Raise the rear of your car and secure it on jack stands. You will also need to remove the right rear tire for your inspections.
1. Inspect the tank for stains/discoloured areas from leaking fuel.
2. Inspect the rubber hose which connects to the gas tank fuel filler inlet. It is located at the front of the right, rear control arm.
3. Inspect the fuel hard line that connects both sides of the tank. It is located at the lower portion at the rear of the fuel tank.

***You will need a multimeter for this portion of your troubleshooting. Remember, your fault can be caused by either a faulty guage or sending unit***

4. Remove the rear seat and two access panels. Your car has two fuel level sensor. Each measures the level of fuel in their portion of the tank and the resistance is averaged.
5. Remove the wire and use a multimeter to test the resistance of each sending unit. They should have the same resistance. The unit should have a resistance of 8-12 ohms for empty and 245-255 for full.
6. If the resistance is different, remove both units and visually inspect the fuel levels in both sides of the tank. Differences in tank levels could indicate a faulty/clogged hard line (item 3).
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Last edited by BigBoy740il; 07-11-2013 at 06:16 PM.
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  #5  
Old 07-11-2013, 09:16 PM
LocoMex LocoMex is offline
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Thanks for the Post BigBoy740il . I'll give it a try tomorrow and post back results. Thanks again.
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  #6  
Old 07-12-2013, 09:21 PM
LocoMex LocoMex is offline
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Follow up. I jacked up the rear of the car on passenger side and removed the wheel. This vehicle has been spay painted on the underside with a black anti-corrosive type of coating. It did not appear to have any evidence of a fuel leak. Lowered car back to floor and decided to pour fuel into the filler very slowly until I could detect a leak and then try and find its source. When the fuel started streaming onto the floor, I used a mirror and flashlight and found a massive amount of wet fuel on the drivers side of the tank and apparently coming from the topside. The right hand underside of the tank appeared to have a very large indentation; i.e. it looked as though someone had tried to jack up the car right using the underside of the fuel tank, or perhaps the car bottomed out big time on a large bolder pushing the bottom side of the tank up at that location. I pulled the back seat and unscrewed the 2 inspection plates so I could check resistance on the two sending units. When I unscrewed the passengers side plate, it was dry as a bone. When I removed the drivers side plate, it was covered with fuel all over that side of the tank. It seems clear the underside of the tank was bent so far up that it pushed up on the sending unit such that the o-ring seal was ineffective. I removed the sending unit, cleaned it up and then tried to put it back into the tank. I will not seat itself onto the top of the tank and it will not engage the retainer built into the fuel tank.

My plan is to take a 1 X 1 or 2 X 2 piece of wood, and see if I can hammer out the "upward" damage by pushing it back down. With any luck, I will then be able to re-seat the sending unit with a new o-ring and stop the top side leak. My description of the damage is confusing. Picture this: you have a fuel tank on the ground with the top side facing down. Then you get a medium side sledge hammer and smash it down onto the drivers side, thus caving it in a inch or two. Then you turn the tank over so the top side is on top and try to put the sending unit in. The sending unit will not fit because it is bottoming out on the bottom of the tank itself.

If anyone can make heads or tails out of my description, please let me know if you think this is a good approach, and if not, what do you suggest as an alternative other than pulling the entire tank out. Thanks very much for the help so far, and I hope you stick with me on this project.
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Old 07-12-2013, 10:02 PM
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Re: E30 Fuel System Question

I fully understand your description. Your plan is sound and should work, just ensure that you place a supporting flat panel below the tank to prevent over stretching the metal while pushing the metal downward.
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Old 07-13-2013, 01:00 PM
LocoMex LocoMex is offline
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OK, following your suggestion BigBoy, I have been able to take enough of the dent out to allow the sender to seat itself using the old 0-ring. I've ordered a new o-ring, and hopefully, it will solve the fuel leak problem.

As for the other issue, I checked resistance after getting the sender back in place, and these are the readings:

Passenger Side: 1.7 ohms
Drivers Side: 24.7 ohms This is the side with the damage.

Using your ohm range, it appears the sender/fuel pump on the passenger side is bad. When I get a new o-ring and finish the drivers side, I'll do another slow leak check like I did before, and if it has indeed stopped leaking, I'll go ahead and fill up and then re=check ohms.

Question, can I replace only the sender or do I have to replace the entire unit which includes the fuel pump?

Thanks again for your help Big Boy.
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  #9  
Old 07-13-2013, 03:26 PM
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Re: E30 Fuel System Question

You can replace the sending units individually. The one on the passenger side is installed with the fuel pump assembly. Simply remove the four 8mm nuts and the sending unit pulls out.
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Last edited by BigBoy740il; 07-13-2013 at 03:40 PM.
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  #10  
Old 07-13-2013, 05:35 PM
LocoMex LocoMex is offline
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Both me and my 1990 325ic really appreciate you staying with us and helping out.
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  #11  
Old 07-15-2013, 09:04 PM
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Re: E30 Fuel System Question

LocoMex
I stand corrected. With your full tank and a resistance reading of 1.7 ohms, your passenger side (PS) sending unit is ok. The bad unit is your driver's side(DS) sensor. After more research, I found that the correct test resistance are 0 for full and 50k full. You can also test the guage by unplugging the DS cable and connecting a wire between the brown and brown/green wire. See attached wiring diagram.
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Old 07-16-2013, 10:54 AM
LocoMex LocoMex is offline
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Thanks Big. Question, your resistance test shows full and full.
"correct test resistance are 0 for full and 50k full".

Is this a typo or does DS gage read different than the PS gage? Before you indicated resistance should be the same for each gage?

Also, on the gage test, the brown appears to be "ground distribution". Both gages have a brown/green, which appears to be the business end of the voltage so to speak. When doing this test (wire between the two), do I apply voltage, or am I measuring resistance? Looks like I can connect a wire between a brown and a brown/green for each sender. If I test each sender vis a vis the gage, how should I interpret the reaction on the gage itself?

Thanks again for your help.
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  #13  
Old 07-16-2013, 05:57 PM
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Re: E30 Fuel System Question

Using multimeter, your resistance test should be 0 for full and 50k empty on the sending units.
To test the fuel guage:
Disconnect the plug on the DS sending unit and use a piece of wire to ground the green/brown wire of the two wire connector and the guage should read full.
Q: "Also, on the gage test, the brown appears to be "ground distribution". Both gages have a brown/green, which appears to be the business end of the voltage so to speak. When doing this test (wire between the two), do I apply voltage, or am I measuring resistance?"
A: DON'T apply power to the circuit. This is a "ground based" resistance circuit. The guage has 12v applied directly to one side and by increasing the ground's resistance, your guage will vary from full to empty.
Q: Looks like I can connect a wire between a brown and a brown/green for each sender. If I test each sender vis a vis the gage, how should I interpret the reaction on the guage?
A: start with a predetermined fuel level, preferably half full. With the PS sending unit installed and connected, disconnect the DS sending unit and by pass it using a piece of wire between the two terminals of the connector. Your guage should register halfway. Repeating the same test on the other side will pin point your bad sending unit.
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Last edited by BigBoy740il; 07-16-2013 at 07:41 PM.
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  #14  
Old 07-16-2013, 09:10 PM
LocoMex LocoMex is offline
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Got it Big Boyz. Really appreciate your patience with me. I'll post back results. Thanks.
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Old 07-31-2013, 06:26 PM
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Re: E30 Fuel System Question

Locomex,
Did you ever get a chance to work on this?
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Old 08-02-2013, 08:46 AM
LocoMex LocoMex is offline
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I'm sorry Big. SW Oregon is burning up and I've been up in the mountains at a fire camp for a couple of weeks. Probably get a chance to test it out next week. I'll let you know. Again, sorry for the delay, but duty calls. Thanks again for the info.
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Old 08-02-2013, 11:14 AM
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Re: E30 Fuel System Question

No problem. Good luck with your training and be safe.
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Old 08-03-2013, 11:49 AM
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Old 09-20-2013, 01:24 PM
LocoMex LocoMex is offline
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Bigboy, sorry about not getting back. After Oregon, I went to rim fire in Calif. Although I've been busy, the season is over for me until next summer. Since I got back I remeasured the fuel sensors as per your post, and the Pass Side sensor showed -0- ohms. Replaced it and all is good. Thanks again for all your help, and I apologize again for my hit and miss posts.
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