Fuel gauge always reading 3/4

kalsingh1

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Hi all

I have just bought a SL55 2004. Fuel always reading 3/4.
My friend has a Chinese knock off Star System.
I followed the star step by step to diagnose.
I diconnected the plug on the fuel sender unit on the petrol tank and put various resistors on the plug socket from 51ohms to 1000 ohms, but the fuel gauge needle did not respond. Star also asked me to check resistance on the plug socket,that was within tolerance. Then Star left me hanging asking to check plug 4 on the rear Sam pin 21 and pin 22 with plug one to the sender unit, no more clues to where these pins and plugs are. I have been trying to trawl the internet for a guide to these pin connections to no success.
The last option on star was that if the pin connections were good then replace rear SAM.

My other question is, should I be looking for a updated SAM unit, if so what part numbers are am I to look for, and will I need to get this coded from a online star system, as my friends is a knock off and is not allowed to connect to internet even for developer mode.

Another question, will mine repair with an new updated software flash ??

Can I ask everyone to stay focused on a practical offer and not go off in a different angle.
I am told Televison on here is an expert.
Many thanks
 

Steve@Avantgarde

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Basically what star is asking you to do is to test the continuity of the wiring from the sam (where the senders have their feed, which then signals to the cluster) to the sender units themselves to test for breakages. In other words, your resistance checks have confirmed the senders to be ok...personally, removing them from the tanks and moving the ball cocks is the best way to go, but that is fiddly on an SL.

If you look at the guided fault finding on STAR it will give you a walk through diagnosis using actual values where you have to confirm values are ok or not. If you follow that process, it will give you the answer, either a wiring or component failure.

Look at the actual values of the fuel tank senders in the rear sam and see if there is a difference to what the car is saying and what the sam is reading, give you a clue as to whether the SAM is failing.
 
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kalsingh1

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Star asked me to place different value resistors onto the plug that goes into the fuel sender unit and watch for movement on the fuel gauge. i.e with different resistor vaues should read full. 3/4, half and zero. The gauage did not respond.
So it asking me now to check pin connectors at the rear sam between sam and wires coming from the fuel sender unit. If that is OK, it says replace SAM.

The only problem before the final conclusion is that I can't find any info reference to the colour of the wires and pin locations at the sam. It just says check connector 1, pin 22 and connector 4, pin 21 etc...
I can't find a diagram anywhere to reference this, you would think that STAR would offer a further link with a diagram.

My other question is, that the rear SAM is, looks dry and clean, could it be that the SAm just needs an software update or reboot ?
 
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Steve@Avantgarde

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Why do you need a further diagram?

Go to the SAM module, undo it and pull it forward and look on the back of it where the connectors are, the module has plug numbers on it, disconnect the said connector and meter on the pins.....it tells you specifics to save you looking at wiring diagrams...its only asking you for a continuity test is it not?

If your mate has access to WIS then put the chassis number in and get the wiring diagram to the rear SAM.

No such thing as a reboot of the SAM, I would think there is no software update available on the age of your vehicle either.
 
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umblecumbuz

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This sounds too simple - but I am a simple man:

I suppose the gauge itself is not stuck? Does it read the same when you remove the ignition key?

Umble
 
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kalsingh1

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UPDATE

Bought a second hand rear Sam from a breakers yard. Tank still reading 3/4 full. Pulling my hair out. The only thing I haven't checked yet is the continuity of the wires from the tank to the Sam, and from the Sam to the instrument cluster, although I did do a gauge movement test on STAR, it made all the instruments go up and down.
Any experts out there with good advice please.
 

LostKiwi

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Sounds very like wiring tank to SAM. Pretty sure SAM to instruments is CANBUS.
 
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Steve@Avantgarde

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UPDATE

Bought a second hand rear Sam from a breakers yard. Tank still reading 3/4 full. Pulling my hair out. The only thing I haven't checked yet is the continuity of the wires from the tank to the Sam, and from the Sam to the instrument cluster, although I did do a gauge movement test on STAR, it made all the instruments go up and down.
Any experts out there with good advice please.

Wasnt that the actual next test to do, to test the wiring?
 
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kalsingh1

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UPDATE
Only three of the four sockets at the lower run are used, the one on the left side as you look at it is spare. So logically when star asks to check the yellow wires on socket one, it is the one on the right hand side. See picture
 

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kalsingh1

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I have now identified what the problem was, and will do a write up later to help other people.
My problem turned out two-fold.
1. Faulty rear SAM unit, as proved above by either putting different value resistors from Maplins or somewhere, max resistor 1000 ohms = Full tank reading, 500 oms = half tank, etc.. On mine the guage was always stuck on 3/4. I also checked the yellow wires for continuity from the petrol tank to the SAM as on picture above, before concluding a faulty SAM

2. Baffle plate in tank completely come away and floating all over the place. Hind sight is a great thing, I would have been better pulling the fuel level sensor out and inspecting the inside of the petrol tank first, as the baffle plate was rubbing and jammed on the fuel level sending unit. I might have spent money on a another rear SAM, when it might have been just the Sender unit stuck on the baffle, but for me I had checked the fuel gauge via the rear SAM using resistors across the plug socket pulled of the fuel level sending unit. So I knew it was a faulty rear SAM. There was no sign of any water, dampness or corrosion in the SAM area, but I found some jump leads in the boot, I can only conclude the guy before jump started the car from the rear battery, which is a NO NO.

I rechecked the new SAM with the same resistors, and the fuel gauage responded perfectly.
 
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kalsingh1

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My next job is to fix the baffle in the tank. I have read lots of forums. If your baffle is still joined on the base and the welds have broken on the top, so is pivoting back and forwards smashing against the petrol tank wall and petrol sending unit, I would temporily fix it using the spring method attached between the sensor level unit and baffle plate, as in many other writeups.
But I have a more serious problem were my baffle's welds have all broken and floating around causing havaoc. Also I wanted a permanent fix, without spending thousands. Also no guaranttee if I bought second hand unit, this would happen again.

I propose to take my tank out, cut the top bit off (like a lid). Reweld the baffle plate with some stronger welds, then weld the top back on.Pressure leak test.

I will do a seperate write up, and put the link here. Just waiting for the petrol to run out.

WATCH THIS SPACE
 
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LostKiwi

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My next job is to fix the baffle in the tank. I have read lots of forums. If your baffle is still joined on the base and the welds have broken on the top, so is pivoting back and forwards smashing against the petrol tank wall and petrol sending unit, I would temporily fix it using the spring method attached between the sensor level unit and baffle plate, as in many other writeups.
But I have a more serious problem were my baffle's welds have all broken and floating around causing havaoc. Also I wanted a permanent fix, without spending thousands. Also no guaranttee if I bought second hand unit, this would happen again.

I propose to take my tank out, cut the top bit off (like a lid). Reweld the baffle plate with some stronger welds, then weld the top back on.Pressure leak test.

I will do a seperate write up, and put the link here. Just waiting for the petrol to run out.

WATCH FOR THE FLASH AND LOUD BOOM!


Fixed that for you!

Well done finding the issues.
 
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kalsingh1

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FUEL GAUGE STUCK -SOLVED

When working with Petrol, its always dangerous, could end up blowing up. Thats why I am waiting for the petrol to run out. Also will leave the tank out for a couple of days for the petrol to evapourate out. I think to be on the safe side I will also fill the tank with water to expell any left over gasses out. lol
 

LostKiwi

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Guy I used to go ralllying with had a leak in his fuel tank on his rally car. He drained the tank flushed it several times with water, filled it full of inert gas and started welding....

The boom was heard 2 miles away and his 10 gallon tank subsequently held 11 gallons! Well maybe not but it definitely bulged on all sides!

He was very lucky. Be careful.
 

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I would have thought that the tank would need to be professionally cleaned and defumed.
 

zedmeister

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Anyway, I did tell you to take the sender out and meter it ;)
 
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