360 Fuel Gauge reading empty

Hi,

My fuel gauge on my 360 F1 is reading empty even though it is half full.

I did the obvious and replaced the sender unit inside the tank following RayJohns Excellent write up http://www.ferrarichat.com/forum/360-430-sponsored-yellow-compass-group/118530-360-fuel-sending-unit-replacement-2.html

But this hasn't fixed the issue. I compared the old and new resistance readings while I was doing the swap out and found them to be pretty much the same I wasn't expecting it to fix it. And when turning on the ignition there were still no bars.

I have tried to see if there are any fuses or relays involved in this circuit but haven't found any yet.

Any clues in where to look next will be greatly appreciated. I have read that the sender feeds the ECU which in turn feeds the display so hopefully its not the ECU.

Many thanks


Andy

 

Well, taking a voltage reading to earth at the connector (unplugged) on top of the fuel tank I have 10v on 1 pin and 5v on the other which I wasn't expecting. Thought it would be 12v and 0v with a variable potential difference across the pins when the connector was plugged in.

Reading in workshop manual, the SD2 can diagnose faults on the Instrument panel ECU which controls the fuel gauge.

So maybe will have to take it into the shop to have it looked at.

 

You know the sender is going to be good. Then I'd turn the key to accessory position and wiggle the wire connector atop the plastic housing. Does the fuel level change? Are the grounds on the engine bay clean? Then, the connectors go to the two bottom connectors in the compartment behind the drivers seat. 22h and 23h. I'd probably disconnect these and then reconnect them. Just to renew any connection. Doing a continuity test probably isn't a bad idea either....

 

I filled mine up over the weekend, drove out of the station and the gauge was already down 2 bars. Parked on the slightest of inclines in my driveway and it showed full. I think the gauge is just horribly inaccurate but to be off by 1/2 tank seems beyond Ferrari levels of lunacy.

 

Often find that the fuel tanks are getting sucked down by bad emissions check valves. The side of the tank will rub against the sender arm causes wrong reading. Solution, fix the vacuum issue and replace tank........or tanks..........

 

Fuel tanks look fine and no sign of imploding. Float was floating just fine and free to move.
This isn't a case of reading incorrectly. It doesn't read anything. Zero bars, not even flashing last bar and refuel warning sign constantly showing.

 

Do we really trust the new part? Just a thought. Seems to be a power/ground issue.

 

Any new work under the dash? New radio or parts installed?

 

I think so. I compared the old to the new and the resistance swing was about the same. 3-350 ish Ohms seemed to be the sweep. Agreed, I need to get into the other connectors mentioned behind the seat. Will probably have to wait until weekend to continue.

 

None very recently but I did replace the radio head unit about 12 months ago. Replaced the cassette unit for a Becker CD unit.

 

Andy, to me the question that needs to be answered...Can you confirm no modification has effected the working fuel level gauge and the vehicle is as Ferrari fabricated the car? And no correlation between your radio installation and the fuel level going INOP?

 

Well as I say. The replacement head unit was an original Ferrari unit from a 599 I think and just dropped straight in without any wiring modifications. But I do need to get into that area to trace connection up to the dash and instrument panel anyway so will check. I can easily slot the old unit back in.

 

Replacing the sender may not be enough unfortunately.... You may have to change the whole fuel pump. Check to see if the plastic connection holding the sender isn't cracked. If it is, you need to replace the complete pump. Had this same problem in my 360 three years ago.

 

Sender clipped in nicely and was very firm so not an issue I don't think.

 

Had another shot at this over the weekend.

Studied the 360 workshop wiring manual and tried tracing a few things. Main place was around the connectors behind the seat. Connectors 23H and 22H seema good place to work and I managed to continuity test between these two connectors so basically one pin, through loom, through the sender back to pin on other connector. Got a reading about 89 Ohms which is about right as sweep of sender was 3-300ish ohms.

22H/10H eventually goes to Instrument ECU and with ECU connected power on I get 10v at this connector. Disconnected ECU I see 0v so is signal originating from here?

23H/11H goes to an S156H which the manual describes as an Internal cable Multiplexing "Thing". So my question is what is S156H and where might it be. I think, need to go back and recheck as I am now doubting myself, I had 10v at 23H as well, which would point to open circuit after this point. But I need to check and will probably have to wait till Saturday again.
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Okay, having typed down what I have found so far I realised i should just look at where S156H goes to after. And it eventually returns to 6E plugging into the back of the instrument panel. so signal starts and finishes here. Makes sense.
So I will check 6E Pin8 to Pin11 continuity and that will give me complete through circuit check.

If that is okay then it looks like a problem with the instrument cluster itself.

 

Where can you get just the sender and not the whole fuel pump?

 

Got mine from eurospares. It is a genuine Ferrari part 194140. It's a £20 part so not expensive

 

So as I said the S156H thing in the wiring diagram was bugging me and I had totally ignored the fact there were 3 wires that came into this point.
Secondly, I had, before running out of time on Sunday, seen 10V at connector 23H which for all intense and purposes was the dead side of the circuit.

So, what was this 3rd wire and where did that go? Would you believe it, it goes back into the engine bay and bolts onto one of the cylinder heads just underneath the L/H cam seals.

So had a closer look and look what I find. First pic.

So I give it a small tug and it breaks off in my hand.

Anyway, cut back the sleeving and trimmed the broken ends. Joined the two with an in-line crimp, bit of black heat-shrink sheathing and bolted back in place.

Turn on the ignition and I now have over half a tank :-D

Now, a previous poster asked about any electrical work under the dash that had taken place recently and don't know how I forgot this, suppose because it wasn't under the dash, but I had the Oil Pressure sensor replaced at last service and it pretty much didn't work since then. Look how close the two are. Not saying the Ferrari Tech broke it but how did he not see that? 8-|

So yes, I will be dropping them a line.
Just happy its fixed but have pulled half the car apart. replaced the sender unit, for what was a simple fix in the end.
I'm also puzzled as to why the earth goes all the way back into the engine bay and earths on the engine block when it would be easier to terminate the earth in the cockpit?
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I'm also puzzled as to why the earth goes all the way back into the engine bay and earths on the engine block when it would be easier to terminate the earth in the cockpit?

IT'S A FERRARI

 

Good find.

The problem with the engine bay wiring is that it gets very brittle with heat, made even worse by aftermarket sports exhausts, headers and sports cats without appropriate heat shielding (most of them). The earths in the engine bay can cause all sorts of gremlins so well worth checking them all.

-T

 

Its a Delphi harness. Engineering is not a word in their vocabulary.

 

Lol...

 

Turning on the car and seeing the gas gauge read correctly, is nearly as exciting as taking delivery of the car in the first place

Nice job on the repair.

Ray

 

Back from the grave!

Filled up my FARARA with 9 gallons of VPower juice and the gauge barely moved.
I looked behind me from flames or a trail of gas but nothing. Stopped, filled another 5/7 gallons to full full and still barely made over the half.
Will be checking that wire next!

For now, the old trip from the tachometer will do...