Help w Fuel Sending Unit & Trip Computer going Crazy

E28 technical advice asked and given! Troubleshooting, modifications and more.
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harrypalmer
Posts: 554
Joined: Jul 25, 2012 12:10 AM
Location: Denver, Colorado

Help w Fuel Sending Unit & Trip Computer going Crazy

Post by harrypalmer »

Hi all,

After doing the in-tank fuel pump modification swap, both, the fuel needle and trip computer are not working as they should any ideas please? Video link shows how needle and trip comp numbers start descending gradually.
https://www.flickr.com/photos/109547372 ... ed-public/

Replaced and exchanged the instrument panel (the one with the Water Temp and Fuel Reading Needle) back to my original and the problem persists. BTW, the Water temp needle is reading good on both instrument panels.
Don't know what's causing this situation and want to learn how to address it and fix it. Thanks in advance!
ahab
Posts: 6095
Joined: Jun 11, 2006 9:12 AM
Location: Chalfont, PA

Re: Help w Fuel Sending Unit & Trip Computer going Crazy

Post by ahab »

Ground problem at the sender. As resistance to ground increases and decreases the needle moves around on the dash. Your ground signal isn't constant and therefore you are getting a fluctuating reading. Take it back apart and shake the sender a bit. I've revived a couple senders by spraying PB Blaster in the tiny hole at the top of the sender. Yours may be as simple as the connector (3pin) isn't seated properly.
harrypalmer
Posts: 554
Joined: Jul 25, 2012 12:10 AM
Location: Denver, Colorado

Re: Help w Fuel Sending Unit & Trip Computer going Crazy

Post by harrypalmer »

ahab wrote: Oct 15, 2020 3:47 PM Ground problem at the sender. As resistance to ground increases and decreases the needle moves around on the dash. Your ground signal isn't constant and therefore you are getting a fluctuating reading. Take it back apart and shake the sender a bit. I've revived a couple senders by spraying PB Blaster in the tiny hole at the top of the sender. Yours may be as simple as the connector (3pin) isn't seated properly.
Ahab,
Upon reading you above, I remembered that I shaked it slightly to get the fuel out (it must be a real fragile thing then).
I'll definitely do as you suggest, so thank you very much for your advice.
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