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Fuel level reads full all the time (1993 945 turbo)

PNW760

PNW760

Member
Joined
Jul 8, 2015
Location
St. Louis, MO
I'll be quick and to the point. Installed a new in tank fuel pump in my 93 940 turbo wagon and now my fuel level reads full all the time. What did I do wrong?

Are there any diagrams/cutaways that show the sender unit from the side to get a better idea of how it's supposed to be installed if i did it wrong?

Thanks ahead of time
 
Possibly(?) unrelated but I put a brand new fuel sender in my 245 a few years ago. A cheap one from eBay. I did replace the pump and wiring and hoses, but did NOT disturb or alter the fuel gauge sender wiring. And it was wired wrong, and reading backward as well. I discovered this after installing it, pulled it back out of the tank, messed around with it, discovered it was backward, then moved a couple of wires around in the pump multiplug and it works properly.
 
Do you know which of the wiring exactly is the one that leads to the sender? I could take a look and see if something didn't get installed properly.
 
240 and 940 pump/senders aren't the same at all, but this was back at the tank - there was a short harness from the sender to the car body harness.

Just saying - brand new fuel senders can be wrong.
 
I guess I forgot to mention it but I never replaced my sender. Just the pump and sock. Is it even possible to source a new sender? Or am I looking for a junkyard one if I do need a new one?
 
Can you take it back out and measure the resistance in the full and empty position? Then you can match it up to the expected reading and see if it is the sender or the wiring in between it and the gauge.

This thread has a picture of what the expected values should be.

http://forums.turbobricks.com/showthread.php?t=346974

Maybe the ground is bad causing infinite resistance, which would measure full on the gauge?
 
Did you verify that the sender unit float(? the white plastic thingy) moved freely when reinstalled? I had some problems with getting it to move freely when I installed an AEM pump, it wanted to get stuck in the upper position. Fits nicely in the tank that way, but I guess it would cause problems when the fuel level drops.
 
I have a feeling you knocked the float tube loose when you reinstalled the sending unit. It snaps in place to the rest of the sending unit housing and is easy to knock apart when trying to reinstall the sending unit in the cramped location Volvo gives you to work in. The float can't move when this happens. Take it back out and see if this is the problem.
 
I’ve gone back and re-installed the whole sender. I verified that float tube moves freely and the pump was installed correctly. I didn’t touch any of the wiring but now that it’s reinstalled, it’s reading completely empty... what could it possibly be? I’m at my wits end
 
PNW760 said:
I?ve gone back and re-installed the whole sender. I verified that float tube moves freely and the pump was installed correctly. I didn?t touch any of the wiring but now that it?s reinstalled, it?s reading completely empty... what could it possibly be? I?m at my wits end
Click to expand...

Perhaps you fixed the problem and the tank is truly empty?
Simple explanations first.

You didn't check to see if moving the arm moved the gauge when you had it out? bummer.
 
Tank had plenty of gas in it. And no, I took of the negative cable on the battery, just to make sure I’m not taking any unnecessary risks when working around a large tank of flammable liquid
 
PNW760 said:
I?ve gone back and re-installed the whole sender. I verified that float tube moves freely and the pump was installed correctly. I didn?t touch any of the wiring but now that it?s reinstalled, it?s reading completely empty... what could it possibly be? I?m at my wits end
Click to expand...

There is a strip of metal that slides up and down the two rods that are wrapped with wire creating really long resistors. That piece of sheet metal may have worn through, creating a sharp edge that catches on the wire wrap. I had this happen on a Bertone many years ago. When it catches on the wire wrap, the float can't move. You might try banging on the bottom of the gas tank with a rubber mallet and see if you start to get a reading from the gage. Also, before going any further, you may want to re-flow the solder joints on your instrument cluster. You may have more than one problem going on. Have you put an ohmmeter across the sending unit connector pins to see what the resistance reading is?
 
PNW760 said:
I?ve gone back and re-installed the whole sender. I verified that float tube moves freely and the pump was installed correctly. I didn?t touch any of the wiring but now that it?s reinstalled, it?s reading completely empty... what could it possibly be? I?m at my wits end
Click to expand...

You need a voltmeter and the circuit for the fuel sender. I considered a new sender assy. for my 92 Sedan and there were several on eBay for near $100, NOS. When all else fails, renew to zero miles and likely your issue is gone.

If you want the thrill of analysis, get the fuel circuit drawing and your meter..... the system is fairly simple. As 2manyturbos said, the design is a PITA, and you have to clock it in order to insert in position properly. There is an excellent tutorial on HOW TO in the famed 700/900 Maint. pages...... give it a read.
 
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