Engine stalling- course of action

[E46m3zcp]

Hello,

I completed my subframe reinforcement, which involved removing the tank, filler neck, and charcoal canister.

After reassembly the car started and ran for a few minutes before I turned it off. I then started it again the next day and it ran fine but I noticed a hiccup. Then, the next time I started it the idle started bouncing until it stalled and I can start it now, but it will eventually stall. It’s got no power at all.

I took out ISTA and read the codes. There were many - Im assuming some were already in the memory before the issue started (note that the car is new to me and I don’t know its history). I remember potentiometer 1 and 2 (which I believe to be related to TPS), and fuel pump relay.

In order to troubleshoot, I cleared the error memory to see which code would stay, and the Pot are gone but the fuel pump relay came back.

I replaced the two relays in the trunk area on the passenger side: a green one and a black tall one which I understand to be the fuel pump relay.

I then cleared the codes and put the key to ON (without starting the engine), and the code didn’t immediately come back. When I started the engine, and re-scanned the code was back (fuel pump relay).

I realize it could be a bad pump but Im hesitant at throwing more expensive parts at the car without a proper diagnostic. Especially since the pump does work at least enough for the car to start. I’m looking for a course of action to properly pinpoint the source of the problem.

Did anyone experience a fuel pump relay code while the fuel pump relay was in working order ? I’m also curious about how the DME detects a bad fuel pump relay. Could it be related to fuel pressure or is it a current measurement at the pump? Could I be dealing with a clogged filter or fuel lines? Could it still be my TPS even if the Pot codes don’t come back?

[sapote]

Did anyone experience a fuel pump relay code while the fuel pump relay was in working order ? I’m also curious about how the DME detects a bad fuel pump relay. Could it be related to fuel pressure or is it a current measurement at the pump? Could I be dealing with a clogged filter or fuel lines? Could it still be my TPS even if the Pot codes don’t come back?

It's a semiconductor pump relay, not a typical coil/contact relay, at least for all US cars. This is why the DME has sensing signal to check the relay status. You should double check the relay wiring for shorted or bad connection, especially after the subframe work that might move them around.
Also check fuel pressure, something close to 70psi I think.

[E46m3zcp]

Another thing that could be related and forgot to mention is that whatever goes in the conduit that links the rear right wheel well to the right side of the gas tank wasn’t removed before the welding. I had the Redish V3 plates welded so there was welding close to the conduit. I can’t remember if wires run in this conduit or if its just evap lines, and I’m wondering if it’s worth taking the gas tank out to inspect inside.

In case it’s not clear what I mean when I say “conduit”, Im talking about the same stuff you have to be careful while drilling to rivet the vince bar on the right side.

[bigjae46]

Another thing that could be related and forgot to mention is that whatever goes in the conduit that links the rear right wheel well to the right side of the gas tank wasn’t removed before the welding. I had the Redish V3 plates welded so there was welding close to the conduit. I can’t remember if wires run in this conduit or if its just evap lines, and I’m wondering if it’s worth taking the gas tank out to inspect inside.

In case it’s not clear what I mean when I say “conduit”, Im talking about the same stuff you have to be careful while drilling to rivet the vince bar on the right side.

IIRC, the harness runs over the rear wheel well and down the crevice between the seat and inner skin. You'd have to really be off course to mess up the harness.

Probably an evap line.

BUT...you should have sensitive electronics unplugged (i.e. DME) when welding on the car. The welder is using the chassis as a ground like all things electric in the car. I always remove the battery and unplug the DME when welding on the car.

[sapote]

For welding work, I would remove cables from battery and bolt the two cables terminals together for a short circuit with zero voltage between 12v and ground wires everywhere.

[bigjae46]

For welding work, I would remove cables from battery and bolt the two cables terminals together for a short circuit with zero voltage between 12v and ground wires everywhere.

DO NOT DO THIS!!! There are a bunch of grounds in the car. By connecting the positive and negative cables you give a path to the fuse box, alternator, starter. So you basically complete the circuit and then send current from ground and then the wrong way through a DC circuit. You greatly increase the chances of causing an issue.

[E46m3zcp]

Anyways I already welded without these measures, except disconnecting the negative terminal of the battery. So if any harm was done its already too late. Time to troubleshoot.

So today I measured pump voltage, current and fuel pressure. The fuel pressure is very low at 35 Psi when running. The voltage is fine at over 12V. The amperage is low between 3-4 Amps. This is pointing me towards a restriction. Fuel filter would be a convenient root cause as its cheap, I ordered one

BUT I doubt that’s it because of the Fuel Pump Relay code. I’ll clean up my injectors while Im waiting and change all sparkplugs and coils (PO messed around and there is a mix of cheap aftermarket coils and original BMW coils that are probably 30 years old…..)

While I don’t totally discard the bad pump hypothesis my understanding is a failing pump will consume over 5A.