Quarter gas in tank causing misfire???

[Slideways]

Theres a metal rod on the jet pump; does that need to be oriented any specific way? Or does it just attach to the sending unit and sits in the tank?

I'm not sure on what part that is as the jet pump just clips to the sending unit. Also, the gasket seal for the level sender to tank should be replaced.

[michaeljchn]

Theres a metal rod on the jet pump; does that need to be oriented any specific way? Or does it just attach to the sending unit and sits in the tank?

[Slideways]

Yeah, almost always that lever sender unit tab and not the jet pump itself.

[Casa de Mesa]

Glad you got that figured out!

[michaeljchn]

This ^^^

The driver's side sending unit has a small clip that secures the sucking jet pump which extends from the driver's side of the tank to the passenger side. After that tab fatigues, the jet pump can fall off the driver's side sending unit and fuel will get stuck on that side. It is easy enough to check if you want to troubleshoot before buying the sending unit.

Well, you were right on the money.

I took out the sending unit and the tab holding the sucking jet pump was fatigued to the point where I could touch it and it finally gave out. Check out the photos.

[George Hill]

Fuel is transferred from the LH side of the tank via siphoning. After the fuel returns from the FPR it enters the LH side of the tank, creates a low pressure siphon that draws fuel from the LH side of the tank to the RH. If that hose is disconnected (as many people mentioned above) then the siphon doesn't work. SO you will use all of the RH side (where the fuel pump is) and half(ish) of the LH side because it will slosh over to the RH side.

If you use the hidden menu fuel level display you'll like see 12L or so of fuel in the LH side when this situation occurs. IF you are able to whip the car back and forth you could likely slosh fuel back to the RH side and the car will then run proper as a test. But it's an easy fix/diag, just pop the cover off the LH tank cover and give it a look.

[sapote]

but when i fill up during this whole debacle, i get 13.9 gallons. Wouldnt that indicate my sending unit is reading correctly? If the fuel tank is 16 gallons its sending the right signal to the gauge?

The total volume seems to be correct, but a tired weak pump is not fast enough to transfer fuel from left tank to right tank when gauge shows total 1/4 or less. A good pump should has zero left and all the fuel in the right tank at this moment. This is why I suggested below:

"Use hidden dash display to show fuel volume in left and right tanks when it got down to 1/4 on the gauge. If the left has more than the right tank then it is not good."

It seems this hasn't been done.

[Mayan-Viking]

This ^^^

The driver's side sending unit has a small clip that secures the sucking jet pump which extends from the driver's side of the tank to the passenger side. After that tab fatigues, the jet pump can fall off the driver's side sending unit and fuel will get stuck on that side. It is easy enough to check if you want to troubleshoot before buying the sending unit.

This is exactly what happened to me. That clip broke and the fuel hose was resting (because of the way it's constructed) at the same height as the fuel when at 1/4 tank. Once fuel went below the 1/4 mark there was nothing left for the hose to suck and the car would act as you would expect.

I wasn't sure what the exact cause of my issue was. So I ordered both the pump and sending unit and planned to install both figuring one of the two were the culprit. Once I pulled the sending unit I realized immediately what the issue was.

[Arith2]

The line for the sucking jet pump is possibly clogged or cracked. It would still send fuel but not enough. Not a common failure but it's plastic that's been constantly submerged in fuel for almost 20 years.

[Shonky]

Check the two readings on the hidden display as mentioned when the tank is low and make sure they're even. Free and easy to do before throwing parts at it.

[geee428]

Try a new sending unit. If you’re on a budget then get a VDO brand. If it still acts up then try the sucking jet pump. Even though the jet pump is supposed to suck fuel from the left side of the tank it could still be slowly failing.

Try the sending unit first since it’s a cheaper option vs the sucking jet pump.

Good luck.

[Slideways]

Bad sending unit is what I'm thinking. Have a friend who had his sending unit fail and it was showing 1/4 tank of fuel but was actually empty.

Mayan-Viking

This ^^^

The driver's side sending unit has a small clip that secures the sucking jet pump which extends from the driver's side of the tank to the passenger side. After that tab fatigues, the jet pump can fall off the driver's side sending unit and fuel will get stuck on that side. It is easy enough to check if you want to troubleshoot before buying the sending unit.

[michaeljchn]

You need a new main pump.
once the fuel level gets to 1/4 tank, the pump is too weak to force the fuel up and out of the tank against gravity.

I hope not. My main fuel pump is no more than 2 months old. And its oem bmw

[FBloggs]

Imo You need a new main pump.
once the fuel level gets to 1/4 tank, the pump is too weak to force the fuel up and out of the tank against gravity.

[michaeljchn]

It could be the sucking jet pump.

Is that something you can reach from under the back seat? Or do you have to go under the car?