Fuel level sensor reading is off

doublespaces

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Oct 18, 2016
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Couple questions. I've ran out of fuel a while back and am in the process of looking for bad connections.

Does anyone know the resistance readings of the fuel level sensors at different actuation points?

Is there a way to read the measured value from the car's perspective? Couldn't find anything for reading individual sensors.

How to make the car 'reset' the fuel level? I've found that making adjustments doesn't translate into a result immediately in most cases. It makes troubleshooting the problem difficult.
 

matreyia

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Apr 19, 2017
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Couple questions. I've ran out of fuel a while back and am in the process of looking for bad connections.

Does anyone know the resistance readings of the fuel level sensors at different actuation points?

Is there a way to read the measured value from the car's perspective? Couldn't find anything for reading individual sensors.

How to make the car 'reset' the fuel level? I've found that making adjustments doesn't translate into a result immediately in most cases. It makes troubleshooting the problem difficult.

Serendipty...i found out my fuel level is all jacked up and also need to fix it. Thought I had half tank but had less than quarter when opened lpfp to see inside tank. I hear there are multiple places that give fuel readings, not just oaseenger lpfp with level floater on bucket.
 

matreyia

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Apr 19, 2017
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Herr is something I found on e90 forum.

"I believe that I have found the source of this problem as I too have ran into it.

I pulled both floats and checked them and they were both spot on. The position they had in the tank was indeed at 3/4 tank or so when I filled it, even though it would not take any more gas. The tank would also report 1/4 gas but you would "run out" of gas.

Now this may not be what was going on for everyone here, but my tank vent system was clogged.

When you take that nasty little clip off of the vent hose inside the tank that connects to the top mount (the one that steveAZ includes a replacement for in the kit) you have to be very careful that the vent hose doesnt also start to come off the connector. Mine did, and I put it back on and I thought it was on good enough, but it wasnt and fuel leaked into the vent system for the tank.

This made it so that the fuel pump had to work much harder for fuel to get out especially if vent air couldnt get in as it would just such in more fuel, it would also prevent the tank from tanking a full amount of gas as it couldnt vent properly to let the air out as it was filling. If the clog is bad enough the tank might not be empty but you'll stall like you are empty as you just cant pull anything else out of the tank without letting air in easily. (doesnt explain people who then put 17 gallons in though).

I have sense put a hose clamp on the offending part and I think it will solve the problem."

Also, do you have a stage 2 or 3 lpfp rig and did you install yourself?
If so, then did you make sure the supprting 3 vertical metal bars of frame the is a part of the supporting scaffold of which the pumps are attached, are all inside the bucket and not outside? Itis important that the bucket is not mis-shapend and is perfectly round to prevent interference of the float arm articulation.
 

doublespaces

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The problem I had running out of fuel was because my tank was bone dry on the passenger side and it said I had a quarter tank or something around there.

It turned out my fuel pressure regulator was set wrong and there was no waste fuel to drive the venturi which brings fuel from the driver side over the hump.

However at the time and even now I'm still noticing some inconsistencies with my tank fuel level and the reported levels so I'm trying to find any known quirks so I can properly diagnose. Lifting the sensors all the way didn't translate into a full tank, sometimes it acted like nothing happened with various key on/off positions.

It's a stage 3 billet system, I have no issue filling the fuel tank completely full. Does ISTA have a procedure for this?
 

matreyia

Major
Apr 19, 2017
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The problem I had running out of fuel was because my tank was bone dry on the passenger side and it said I had a quarter tank or something around there.

It turned out my fuel pressure regulator was set wrong and there was no waste fuel to drive the venturi which brings fuel from the driver side over the hump.

However at the time and even now I'm still noticing some inconsistencies with my tank fuel level and the reported levels so I'm trying to find any known quirks so I can properly diagnose. Lifting the sensors all the way didn't translate into a full tank, sometimes it acted like nothing happened with various key on/off positions.

It's a stage 3 billet system, I have no issue filling the fuel tank completely full. Does ISTA have a procedure for this?

You have an aftermarket fuel pressure regulator? If not, how do you reset the stock one?
 

doublespaces

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Can you check that both sensors read the same voltage for the same position, I imagine they would use the same sensor?

In my limited testing the sensor can read from 50 to 1000. It doesn't have a power source because it's a resistance reading. As you approach 1000 it basically hits infinity and on my multimeter the reading stops working.

You have an aftermarket fuel pressure regulator? If not, how do you reset the stock one?

Yes, I have a billet driver hat with fpr. That issue has been resolved by adjusting the set screw(it was too tight) . As for the stock fpr I've got no clue how it works.
 

rac

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Nov 14, 2016
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Have you checked the bucket orientation and that the sweep of the sensor does not get obstructed by the tank?
 

iminhell1

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Jun 17, 2018
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Ista,
I know I'd read about the fuel level, but on my car I can't get into the fuel pump driver. So I can't get anything to work.
Give the text search a shot once and see what comes up.
I think there was also something where you could watch the readings live for both sides.
 
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doublespaces

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Have you checked the bucket orientation and that the sweep of the sensor does not get obstructed by the tank?

It really only sits one way with my setup, but I'll double check some of that.

Ista,
I know I'd read about the fuel level, but on my car I can't get into the fuel pump driver. So I can't get anything to work.
Give the text search a shot once and see what comes up.
I think there was also something where you could watch the readings live for both sides.

I would like to see this, that way I could rule out a few things such as wiring/connections. I've got ISTA-D on my laptop somewhere, I'll poke around.
 

PFS

Corporal
Nov 19, 2018
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Tyler, sorry I missed this. Sensors read from 50 Ohms to 1000 Ohms. You can read this from the tophat.

If you need new level sensors I have those too.

Chris
 
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doublespaces

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Tyler, sorry I missed this. Sensors read from 50 Ohms to 1000 Ohms. You can read this from the tophat.

If you need new level sensors I have those too.

Chris

Thank you for confirming this. I think my multimeter told me 51 to 994 or something like that.
 

V8bait

Lieutenant
Nov 2, 2016
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Hmm, maybe something interfering with the float on one side or the other? I have that same regulator and haven't had this issue once I set the pressure, getting it into the tank was a bear though.