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New intank fuel pump sender blowing fuse 1
New intank fuel pump sender blowing fuse 1
ok so 1986 528e stock automatic. I pulled the original intank fuel sender assembly out as i believed to be non-operational. I know it's not really necessary for these cars, as the main external pump does the work, the internal is just for lower fuel levels to ensure fuel gets to the main pump when down around a 1/4 tank or so, I think.
But becasue i like to have things working properly though, i replaced the original with a herko fuel sender assumbly, didn't want to pay for the BMW oem part and heard positive things about this replacement. When going to start and to test it out, immediately blew fuse #1 and car wouldn't turn over. replaced fuse and tried again with same result making sure fuse was not loose, etc. replaced the fuse again and unplugged the intank sender connector and she starts and runs as normal. So clearly there's an electrical issue or something with the sender assembly.
I put a multimeter on the fuel sender connector wire contacts and got ~13v or so across that so tells me i'm getting good voltage via the connector wire. looking at the wiring diagram the sender assembly gets power from the main pump and both are grounded via the same splice (S318) same ground connector (G301) under the read seat. So given that the main fuel pump works correctly when the intank assembly is disconnected, this tells me that the ground is good otherwise the main pump wouldn't work correctly. I don't think fuel relay is at issue since the car starts and runs fine off the main pump.
So my next step is to check the splice connection and also check/clean the ground connector under the rear seat just to ensure the connection is good.
Is there anything else i can check to determine why the #1 fuse is blowing when i reconnect the in-tank fuel sender? I could try a different brand of fuse , but feel that's a longshot since i'm using the same brand in most of other fuse slots with no issues. but worth a try i guess.
But becasue i like to have things working properly though, i replaced the original with a herko fuel sender assumbly, didn't want to pay for the BMW oem part and heard positive things about this replacement. When going to start and to test it out, immediately blew fuse #1 and car wouldn't turn over. replaced fuse and tried again with same result making sure fuse was not loose, etc. replaced the fuse again and unplugged the intank sender connector and she starts and runs as normal. So clearly there's an electrical issue or something with the sender assembly.
I put a multimeter on the fuel sender connector wire contacts and got ~13v or so across that so tells me i'm getting good voltage via the connector wire. looking at the wiring diagram the sender assembly gets power from the main pump and both are grounded via the same splice (S318) same ground connector (G301) under the read seat. So given that the main fuel pump works correctly when the intank assembly is disconnected, this tells me that the ground is good otherwise the main pump wouldn't work correctly. I don't think fuel relay is at issue since the car starts and runs fine off the main pump.
So my next step is to check the splice connection and also check/clean the ground connector under the rear seat just to ensure the connection is good.
Is there anything else i can check to determine why the #1 fuse is blowing when i reconnect the in-tank fuel sender? I could try a different brand of fuse , but feel that's a longshot since i'm using the same brand in most of other fuse slots with no issues. but worth a try i guess.
Re: New intank fuel pump sender blowing fuse 1
Any possibility that the positive and negative have been connected backwards when assembling the new pump???
That or the positive was touching the metal of the pump or the support somewhere
That or the positive was touching the metal of the pump or the support somewhere
Re: New intank fuel pump sender blowing fuse 1
My thoughts too.Aldo525 wrote: Jul 04, 2024 12:20 PM Any possibility that the positive and negative have been connected backwards when assembling the new pump???
That or the positive was touching the metal of the pump or the support somewhere
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Re: New intank fuel pump sender blowing fuse 1
I would double check how members cek and or Davintosh did their own electrical wiring around the inner tank pump stalk. I followed the same and had no problems.
Lucky for you she’s only burning fuses.
A lifetime ago, unknowingly connected the wires that came from my Rallye DVO fuel gauge and took my car to proudly fill her up. 25 ft after leaving the gas station the fuel heated enough that my tank exploded behind me. It was a French Simca 1204 race car and my bucket seat protected me from burning, just another for the unforgettable car mistake experiences.
Yes I was young then, and to this day stupid to a point, so that’s why I double check everything I do. You’d be wise too. Good luck!
Lucky for you she’s only burning fuses.
A lifetime ago, unknowingly connected the wires that came from my Rallye DVO fuel gauge and took my car to proudly fill her up. 25 ft after leaving the gas station the fuel heated enough that my tank exploded behind me. It was a French Simca 1204 race car and my bucket seat protected me from burning, just another for the unforgettable car mistake experiences.
Yes I was young then, and to this day stupid to a point, so that’s why I double check everything I do. You’d be wise too. Good luck!
Re: New intank fuel pump sender blowing fuse 1
On the Herko pump, the positive wire is not routed properly down thru the assembly. This lends to the red wire getting caught and punctured once you snug everything down. Happened to me on my 533, even after I saw the routing issue.
Your car's wiring is likely fine, just like it was before the new pump. The variable is the new pump.
You probably need to pull that pump to check the positive wire for damage, however small. Either that or your new pump has another break/chafing in wiring somewhere.
Good luck, any questions lmk.
Your car's wiring is likely fine, just like it was before the new pump. The variable is the new pump.
You probably need to pull that pump to check the positive wire for damage, however small. Either that or your new pump has another break/chafing in wiring somewhere.
Good luck, any questions lmk.
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Re: New intank fuel pump sender blowing fuse 1
At first I thought so too, but then I thought maybe the anode was broken.Aldo525 wrote: Jul 04, 2024 12:20 PM Any possibility that the positive and negative have been connected backwards when assembling the new pump???
That or the positive was touching the metal of the pump or the support somewhereconnections game
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- Location: Denver, Colorado
Re: New intank fuel pump sender blowing fuse 1
Hello blockerb
Did you ever figure what was causing number 1 fuses to be blown?
Did you ever figure what was causing number 1 fuses to be blown?
Re: New intank fuel pump sender blowing fuse 1
not yet. haven't had a chance to pull the pump and see. too many other issues 

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Re: New intank fuel pump sender blowing fuse 1
Any updates here?
I did the single in-tank fuel pump mod about 1 year ago... Starting today, my Fuse 1 keeps blowing. Its gotten progressively worse.
first 4 blocks, then 3, then 2, then 1, now it can hardly idle without blowing a fuse.
* I plan on pulling the in-tank fuel pump today and inspecting the wiring. If i see nothing wrong, I will replace the in-tank pump again.
Also, I plan on seeing if there's some weird accidental connection happening where the old fuel pump connector is.
I did the single in-tank fuel pump mod about 1 year ago... Starting today, my Fuse 1 keeps blowing. Its gotten progressively worse.
first 4 blocks, then 3, then 2, then 1, now it can hardly idle without blowing a fuse.
* I plan on pulling the in-tank fuel pump today and inspecting the wiring. If i see nothing wrong, I will replace the in-tank pump again.
Also, I plan on seeing if there's some weird accidental connection happening where the old fuel pump connector is.
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- Posts: 690
- Joined: Jul 25, 2012 12:10 AM
- Location: Denver, Colorado
Re: New intank fuel pump sender blowing fuse 1
FWIW
Pertinent to this I was running the OEM two fuel pump setup: One in-tank and one main (underneath pump).
Then later on, did my own version of this well researched and proven, one in-tank fuel pump solution here:
viewtopic.php?t=101410
But as I found out later, due to my error in not knowing to REALLY properly tighten the stainless steel locking ties, even with the provided DEI tool, my pump was slipping sideways from the main pipe. So not figuring out what was going on back then, and scared of ever happening (whatever it was) again, I essentially chickened out and ordered a new in-tank pump, this time from eBay and redid my original double pump setup for lack of confidence in my DYI.
Also learned how to properly tighten stainless steel straps, once I figured out this is what was causing the slipping failure:
https://duckduckgo.com/?q=how+to+tighte ... y5xilp_Rec
My OEM in-tank supporting stalk was donated to my brother's '85 535. So had to re install a new cheap one, and what would you know. It blew the same red 16 AMP fuse 1 four separate occasions when turning the engine on.
Upon inspection, and maybe a month later, I discovered that a minuscule part of the protecting red plastic casing was stripped (from the factory) on the positive wire and this was making contact elsewhere in the tank. I emailed my pictures to the seller, and they sent me a new stalk with a pump attached without me even asking for it: https://www.ebay.com/itm/186200582348
So my point (beside being lucky) is to check your wiring in your setup. Most likely you and blockerb's wiring is what is causing a short circuit somewhere. Good luck guys. And a Happy 4th to you all with this country of ours?
Pertinent to this I was running the OEM two fuel pump setup: One in-tank and one main (underneath pump).
Then later on, did my own version of this well researched and proven, one in-tank fuel pump solution here:
viewtopic.php?t=101410
But as I found out later, due to my error in not knowing to REALLY properly tighten the stainless steel locking ties, even with the provided DEI tool, my pump was slipping sideways from the main pipe. So not figuring out what was going on back then, and scared of ever happening (whatever it was) again, I essentially chickened out and ordered a new in-tank pump, this time from eBay and redid my original double pump setup for lack of confidence in my DYI.
Also learned how to properly tighten stainless steel straps, once I figured out this is what was causing the slipping failure:
https://duckduckgo.com/?q=how+to+tighte ... y5xilp_Rec
My OEM in-tank supporting stalk was donated to my brother's '85 535. So had to re install a new cheap one, and what would you know. It blew the same red 16 AMP fuse 1 four separate occasions when turning the engine on.
Upon inspection, and maybe a month later, I discovered that a minuscule part of the protecting red plastic casing was stripped (from the factory) on the positive wire and this was making contact elsewhere in the tank. I emailed my pictures to the seller, and they sent me a new stalk with a pump attached without me even asking for it: https://www.ebay.com/itm/186200582348
So my point (beside being lucky) is to check your wiring in your setup. Most likely you and blockerb's wiring is what is causing a short circuit somewhere. Good luck guys. And a Happy 4th to you all with this country of ours?