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The BMW E46 ///M3 is the M version E46 and puts out an amazing 333 HP and 262 lb-ft of torque at stock specs! There are an amazing amount of modifications for both the coupe and convertible models so read up and get started modifying your cars today!

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Old 05-11-2019, 05:42 PM   #1
DrunkUncas
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Fuel pump won't turn on. Car won't run with fuel pump jumped.

Halfway through 3rd gear at WOT yesterday, car immediately died. When attempting to start, it fires, then immediately dies, just like video I've seen of a dead fuel pump.

Pump doesn't start with key. In the tall black relay harness, if I jump the constant 12v to the positive pump wire, the pump runs, and flows a gallon a minute, but the car won't start. It fires, and immediately dies, exactly as if the pump wasn't running at all.

I bench tested the green relay, and it clicks. I can feel the black relay clicking in my hand when the key gets turned.

I did check the coil wire ground on the passenger side of the motor, and the 20a fuse.

Ideas?

Solved: Check your MAP

Last edited by DrunkUncas; 05-17-2019 at 09:49 PM.
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Old 05-11-2019, 06:01 PM   #2
Luke_palma
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Bench testing relays isn't 100%. They can click but still not make full contact or have a damaged secondary or primary winding. First thing is check ground power and signals from relays. If that's all good check wires from relay to pump. Follow a schematic. Worst case scenario could be a bad dme but unlikely. Probably a relay or could be failing pump. Not sure with this car exactly but a lot of manufactures will kill the pump if it sees too much electrical resistance (worn pump) but jumping it would still let it run. If you have a good scan tool you can run a dme self test and it will test the relays. In my case my car wouldn't start occasionally. No codes, when I ran the self test pump ran perfect but primary relay( the one with more than 4 contacts) failed test. Replaced it $100 on ecs and car starts no problem.

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Old 05-11-2019, 06:02 PM   #3
Luke_palma
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You can also try jumping the relays but be careful. Follow a schematic jumping it wrong can cause a lot of damage. Also use a fused jumper just incase.( Put fuse on ground side, protect dme)

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Old 05-11-2019, 06:15 PM   #4
DrunkUncas
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Thanks, Luke.

I'm leaning towards a worn pump. I've got a 120k on what appears to be the original. The fairly thick, uninsulated jumper wire gets too hot to touch within 15 seconds.

If it's not the pump, I'll consider it preventive, and move to the next most likely fault, which is the $21 green relay.

Unless someone has any better ideas.
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Old 05-12-2019, 02:24 PM   #5
Luke_palma
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No problem. Hope it goes well. A lot of people drive their cars on empty and are overheating the pump because it's cooled by the gas in the tank.

Back to the relay, you could check continuity in the Normally closed position and normally open, then activate it with a small battery and recheck. You could also check resistance but I have yet to find any specs on BMW relays anywhere. Without specs all you can really check for is shorts and opens.

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Old 05-12-2019, 02:52 PM   #6
DrunkUncas
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Quote:
Originally Posted by Luke_palma View Post
No problem. Hope it goes well. A lot of people drive their cars on empty and are overheating the pump because it's cooled by the gas in the tank.

Back to the relay, you could check continuity in the Normally closed position and normally open, then activate it with a small battery and recheck. You could also check resistance but I have yet to find any specs on BMW relays anywhere. Without specs all you can really check for is shorts and opens.

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After sleeping on it, the pump plug is getting the correct power, at the correct time, so replacing the pump is a no brainer.
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