Last try before I bring the car to a mechanic: fuel delivery problem

[E46m3zcp]

Hello,

I am a bit out of ideas for troubleshooting what seems to be a fuel problem. I am trying to ascertain that I need to change my fuel pump. First the symptoms.

- Currently crank/no start but was starting, rough idle and would stall. The problem was somewhat intermittent as it would rarely start idling smoothly.
- The pump buzzes when the ignition is put to ON. Measured 12.7 volts at the pump and between 1.25 and 4A when it's running.
- Error code for fuel pump relay (DME error 1)
- Fuel pressure won't go past 25 PSI (reading with a gauge at the Schrader valve in front of the fuel pressure regulator)
- When pressing the gauge's purge button after building pressure what comes out is a spray, not a continuous flow - there's a lot of air in it (is this normal??)
- I noticed that the small hose that connects the fuel pressure regulator to the air-rail comes off easily.

What I did to troubleshoot:
- Swapped the fuel pump relay with the one in my working E46 M3. No luck
- Changed coil packs and spark plugs - no luck
- Disconnect the MAF - no luck, although one time when the car was running rough, it did stabilize the idle.
- Pinched the fuel regulator and attempted to start, fuel pressure is still at 25 PSI and won't budge.

If that's not enough, here is some context: The car was running fine. I did my subframe reinforcement myself and dropped the fuel tank, charcoal canister, fuel filler, etc. The car sat for a few months. When I put it back together it ran fine for about 5 minutes. A day or so later I started it and it had a rough idle and would stall. I did all the steps mentioned above to troubleshoot and now it won't start anymore.

Any hints are welcome. Or if you are convinced that I need to change the fuel pump let me know.
Many thanks!

[eacmen]

Have you removed the fuel pump to make sure the main pump and scavenge pump are installed correctly? If there is a lot of air there might be a break in the pickup tube and the pump is trying to pump air?

Stupid question is fuel tank empty?

When you did subframe reinforcement did you take proper precautions to protect the electronics from the welder?

[E46m3zcp]

Have you removed the fuel pump to make sure the main pump and scavenge pump are installed correctly? If there is a lot of air there might be a break in the pickup tube and the pump is trying to pump air?

Stupid question is fuel tank empty?

When you did subframe reinforcement did you take proper precautions to protect the electronics from the welder?

Thanks for the reply. Answers to your questions:

1- I've not removed it yet. The pickup tube break theory crossed my mind, yeah, it would make sense. Do you think the fuel pump relay code would come up?
2- Sometimes it's worth asking these questions . Unfortunately, there's fuel: the fuel tank is at about 1/3 (one large jerry can of gas).
3- The only precaution was to disconnect the negative terminal. How bad is the outlook?

[eacmen]

Thanks for the reply. Answers to your questions:

1- I've not removed it yet. The pickup tube break theory crossed my mind, yeah, it would make sense. Do you think the fuel pump relay code would come up?
2- Sometimes it's worth asking these questions . Unfortunately, there's fuel: the fuel tank is at about 1/3.
3- The only precaution was to disconnect the negative terminal. How bad is the outlook?

1. Not sure how drivable the car is but the lazy approach might be to top off the fuel to see if the problem gets better? I was mistaken on how the sucking jet pump works, it's not actually attached to the main fuel pump. BUT if the sucking jet pump has failed all the fuel might be on the drivers side. Using hidden OBC menu you can see left/right fuel levels. Google it.

2. See above

3. That should be enough.

[E46m3zcp]

The car won't start, but I could use jerry cans to fill it up. The car ran for 5-10 minutes, I'm wondering how the entire passenger side lobe would have emptied, but I'll certainly double-check.

[eacmen]

The car won't start, but I could use jerry cans to fill it up. The car ran for 5-10 minutes, I'm wondering how the entire passenger side lobe would have emptied, but I'll certainly double-check.

Try the hidden OBC menu first only takes a few minutes.

https://www.bmw-driver.net/threads/diy-e46-hidden-obc-functions.31204/

Or if u have a scan tool that should be able to read the values as well.

[sapote]

I'm wondering how the entire passenger side lobe would have emptied, but I'll certainly double-check..

During running, the the jet pump, based on the returning fuel, transfer the left to the right tank. So using the hidden menu to see each tank volume: if left is more than right tank then the pump is running weak.
As about crank but not start, maybe it's flooded with gas and lost compression. Add a spoon of oil into the spark plug holes, but you need to fix the low fuel pressure first.
Why low pressure? either bad pump or leaking intake hose when there is 12v or higher at the pump.

[E46m3zcp]

I see it, but I can't explain it. The car ran for 5 minutes.

[eacmen]

I believethat 6.0 value of 188001 means 18.8L in left tank and 00.1L in right tank.

[E46m3zcp]

I do see that, but what is really going on? I'm not exaggerating when I say the car ran for under 10 minutes at idle, so it's not possible that the right side of the tank would have emptied from the fuel being consumed by the engine. When filling the tank, the gas goes to the right (passenger) side of the tank. Is the jet pump stealing all the gas from the right side? I could benefit from someone explaining how that works.

[eacmen]

The sucking jet pump moves fuel from the left side to the right side of the fuel tank. It is powered by a venturi effect driven by the fuel that is pumped through the fuel system and returned to the fuel tank. So when the sucking jet pump is disconnected the car effectively pumps all the fuel from the right side to the left side and runs the right side dry.

You need to dig into the left side fuel tank lid and reconnect or replace the sucking jet pump. You will also need to siphon fuel from the left side and add it to the right side so then pump has something to pump through the fuel system.

[E46m3zcp]

That is a lot of progress today!! Thank you so much for the hint and I will keep you posted on the progress. I still don't fully understand how that works but I'll look into it.

[eacmen]

That is a lot of progress today!! Thank you so much for the hint and I will keep you posted of the progress.

Just edited above as I had right and left mixed up in one part of the explanation. So re-read it please 😂. It's a pretty simple concept but putting it into words can be challenging.

[E46m3zcp]

The sucking jet pump moves fuel from the left side to the right side of the fuel tank. It is powered by a venturi effect driven by the fuel that is pumped through the fuel system and returned to the fuel tank. So when the sucking jet pump is disconnected the car effectively pumps all the fuel from the right side to the left side and runs the right side dry.

You need to dig into the left side fuel tank lid and reconnect or replace the sucking jet pump. You will also need to siphon fuel from the left side and add it to the right side so then pump has something to pump through the fuel system.

I get that a venturi effect transfers gas from left to right, replenishing the right side as fuel is consumed. What then transfers gas from right to left? That's the part I'm missing. Is there a motor that does that?

When you fill the tank, some of the gas goes to the right side, correct? I don't explain yet how the gas I put in there made it to the left side. The car didn't run long enough for the right side to go dry by just consuming gas... So something drew the gas out of the right side of the tank, and into the left side of the tank. Is there an electric pump that does this, and a venturi-powered system that does the opposite?

[eacmen]

If I understand it correctly - when the main fuel pump pumps fuel from the right side some of it gets consumed by the engine and the fuel rail but most of it gets pumped back to the tank on the left side via a fuel return line from the fuel rail. So Without the sucking jet pump the fuel pump will effectively just run the right side dry even if the engine isnt using that much fuel.