E30 Fuel Tank Return - Blocked

[tdf]

I've been struggling to find a cause of my engine running excessively rich. Installed a gauge on the return side of the pressure regulator and got a pressure gauge pegged out. I couldn't understand why this would be the case. Blew air through the lines (disconnected at both ends).

Finally, I took the car to a BMW specialist, and they discovered that the fuel return line was blocked. Blocked within the fuel tank itself. The car had sat with the engine removed for years and only recently had I gotten back to working on it.

Looking to see if anyone else has seen this issue.

[Jcrunk]

I may indeed have this issue, my E30 has been sitting for 14 years man, im just going through it all now, have been for a lot of months now lol

Do you know how that fuel return line got blocked? What was it blocked with? Have you been able to unblock it?

[tdf]

I may indeed have this issue, my E30 has been sitting for 14 years man, im just going through it all now, have been for a lot of months now lol

Do you know how that fuel return line got blocked? What was it blocked with? Have you been able to unblock it?

There is little access to get inside the tank. I have no idea what internal bends and angles may be involved inside the tank.

I can only assume that while the car was sitting idle some dirt or insect critter got into the fuel line hoses in the engine compartment and that debris was forced further downstream after the engine was re-installed and started. I have no proof of that and no debris to examine. There should be little or no pressure in the fuel return line and there is very high pressure there due to the obstruction (whatever the cause).

[Mikealwa]

There is a YouTube video where a guy cuts open an E30 tank you should be able to find easily. Theres not a lot going on in there at all. I believe the fuel return enters the tank via a nipple that's only .5 inches long on the driver's side lower half of the tank. You could almost disconnect the return line that attaches to it and poke an implement in there to see if it's clogged someone how, but idk how that clog would occur. There's lines that run on top of the tank but I think those are all supply from the pump and some venting 🤔.

[Mikealwa]

In my case the nipple on the tank where the fuel return hooked up to was so rusted out I couldnt remove the hose without breaking off the nipple. I have replaced my tank since then. It's possible that it's so rusted up as well it collapsed in on itself...you should be able to inspect this fairly easily.

- - - Updated - - -

https://youtu.be/GG1f9xc2L-M

sorry to respond in bits, but as you see the nipple is actually connected to a siphon tube in the tank, so heavy rust in your tank could be blocking this as well. You may be able to clear this with compressed air on the nipple or with a coat hanger or something.

[tdf]

In my case the nipple on the tank where the fuel return hooked up to was so rusted out I couldnt remove the hose without breaking off the nipple. I have replaced my tank since then. It's possible that it's so rusted up as well it collapsed in on itself...you should be able to inspect this fairly easily.

- - - Updated - - -

https://youtu.be/GG1f9xc2L-M

sorry to respond in bits, but as you see the nipple is actually connected to a siphon tube in the tank, so heavy rust in your tank could be blocking this as well. You may be able to clear this with compressed air on the nipple or with a coat hanger or something.

I have removed my tank from the car. Not too difficult except for getting all the top venting lines disconnected. I will be inspecting what I can see. No apparent rust. My E30 has very little rust.

The video is very much appreciated! It helps me in knowing how the fuel return works and the internal tube layout. Thank you!

I will most likely be buying a new tank.

[tdf]

The return tube is blocked inside the tank. I can only force air through to the driver's side well where there is only a small break in the tubing intentionally there to affect the siphon function. . No air gets to the pump well on the passenger side. No way to access that internal tube.

New tank ordered.