Erratic fuel gauge

[andyfanshawe]

hi all.
i've been hunting down an erratic fuel gauge reading (one day reading 1/4, next 3/4 etc) and have already changed the fuel tank sending unit as part of a fuel tank restoration, but the problem continues.

I have used the NGS tester to command the gauge and this is what I got

10% command and fuel gauge is about right

30% looks close

50% is too high

70% is way too high

80% is over the max

Does anyone know if this is normal?

As a matter of interest here is a website I built for an expert to help at rosedale tech (scannerdanner on youtube - a genius!)

http://andyfanshawe.freewebspace.com/lincolnerraticgauge.html

Heres a summary of the tests so far.

We weren't expecting battery voltage at the sender though.

If anyone's got any comments that may help it would be appreciated.
I am going to monitor the voltage at the message center and the sender while driving to get a direction at least.

Andy.

 

[NoLimit95]

- Fuel Level Sensor harness is open or shorted
- Fuel Level Sensor circuit poor electrical connection
- Faulty Fuel Level Sensor
- Faulty combination meter

Read more: [url]http://engine-codes.com/p0460_ford.html#ixzz1wuGCHGqT[/URL]
​

 

[NoLimit95]

P0460 - Fuel Level Sensor Circuit Malfunction The PCM monitors the fuel level input (FLI) circuit for electrical failure. The test fails when the signal moves outside the minimum or maximum allowable calibrated parameters for a specified fuel fill percentage in the fuel tank. Empty fuel tank
Fuel pump (FP) module stuck open
Incorrectly installed fuel gauge
Damaged instrument cluster
CASE GND circuit open
FLI shorted to VPWR
Damaged PCM
Overfilled fuel tank
Fuel pump (FP) module stuck closed
Damaged fuel gauge
FLI circuit open
FLI circuit shorted to CASE GND or PWR GND
CSE GND shorted to VPWR
Monitor FLI PID and FLI V PID in key ON engine RUNNING. FLI PID at 25% fill (with non matching fuel gauge) and FLI V PID less than 0.90 volts [for FLI PID at 75% fill (with non matching fuel gauge) and FLI V PID greater than 2.45 volts] indicates a hard fault.

 

[andyfanshawe]

Thanks for reply NoLimit95.
Code was generated by myself disconnecting sender wire. Not concerned about that.
So all the meanings of that code are irrelevant.
The FLI V pid and FLI pid seem to match when I test.

yes, gage could be at fault, but it would be nice to be able to understand how the circuit works.

Where is the PCM picking up that pid voltage from?

Do you have further insight into the internal circuitry, and HOW it actually works?

Thanks again.
Andy.

 

[99 Interceptor]

does this help any?

 

[andyfanshawe]

does this help any?

Hi 99interceptor.
Thats the diagram I have drawn in a simpler version above! Thanks anyway.
Since I am in the UK i need to be absolutely 100% sure of the faulty component because 1) of the expense of shipping in a new part, and 2) my Wife would kill me

I need to do some more circuit testing to try to understand how this system works. Most have a 5v reference from the PCM going to the sender unit. The mark 8 hasn't. The sender is "watched" by the PCM and the message center, but I don't know the role of each.

I'm going to monitor the output from the sender to see if it changes when the gauge goes through its erraticness!!

Andy.