General 2008 Fiat Ducato fuel gauge

[angusburke]

Hi there. Today my fuel gauge showed full but as soon as I actually started my van my full drops to empty and the fuel lights starts flashing. The idle is also not good. Does anyone know what may be causing this and what the remedy may be?

 

[Anthony489]

Hi Angus

A bit of a difficult one to diagnose from my armchair !

This could be an electrical problem, and if simultaneous unrelated faults occur you need to find which section of wiring is common to both. This would usually be items like Connectors or Fuses early on in the feed from the battery positive, before it divides to the various components. It also includes earth returns.

On a van of this age, I recommend renewing the braided earth return strap between the engine/gearbox and the Body/chassis if it hasn't already been done. It is low down on the right of the engine compartment (UK passenger side) underneath the air filter canister. These straps corrode internally (may look OK on the outside). This may not cure your problems, but it will at least eliminate it from the list of possibilities.

The fuel gauge sender is connected via 2 wires directly to the body control module under the dashboard, i.e. its wiring isn't shared with any other component. From then on it's all software controlled, with the reading sent to the instrument cluster over a data bus. The sender shares an assembly with the low pressure fuel pump, and is screwed into the top of the fuel tank. It might be worth checking/cleaning the 4 pin connector on this unit. Access is via a small floor panel between the front seats.

Beyond this, fault finding needs a test meter and a methodical approach. One of the more basic tests would be to ensure that electronic assemblies like the Engine Control Unit (ECU) and Body Control Module (BCM) are being properly supplied with full battery voltage. Something as simple as a fuse with corrosion on its blades can cause issues. Sometimes simply pulling a Fuse out and replacing it a few times can clean things up and clear the fault.

There are two sets of Fuses, one in the engine compartment and the other under the dashboard. I particularly recommend checking F31 and F38 in the under-dash fuses.

 

[angusburke]

Thanks very much for in depth reply. I did all the checks in the Earth return as you recommended and then checked all the connector as well. Removed the engine cover only to find that one of the injector connections hadn’t been plugged in properly. Plugged that in and everything started running properly. Even my engine warning light disappeared which was greet.

Today though the van seems to not want to accelerate. When I push down on the accelerator there is a big delay for the power to kick in. Every time I stop, the van idles well for a bit and suddenly just cuts out. Any thoughts on this problem? Thanks again for your previous advice.

 

[Anthony489]

Hi

Regarding the earth strap, these are impossible to test without specialised equipment as their resistance should be only about one thousandth of an ohm. They may look OK, and you can clean the end lugs till they are shiny, but hidden between the crimp and the braid is a layer of corrosion. Replacement is best.

I think your next step would be to get the van scanned for stored error codes. Not all errors result in a dashboard warning light, so there may be some which you would otherwise be unaware of. Error codes remain stored indefinitely until they are cleared. The ideal thing to use is a Fiat specific scanner as used by dealers, or MultiECUscan which is available to amateur mechanics - at a price. However, even a lower cost fault scanner will give some functionality for reading generic codes.

Do you happen to know if the Throttle Body (TB) has ever been changed ? The factory fit for 2008 was a unit made by Wahler, which have proved rather unreliable over time. Better replacements are available e.g. Marelli. The TB sits at the front of the engine with a big curved aluminium pipe leading down onto the inlet manifold. If you take off the large rubber air hose leading into it, you can see the throttle disc (= flap valve). especially if you use a small mirror. Try gently moving the disc with your fingers to check for sticking - it should move smoothly. It is designed to be sprung nearly closed, and the electric actuator solenoid should pull it open it as required. If the flap doesn't open enough, the engine is starved of air and power will be restricted. However, the air flow at idling is fairly small, so it would need to be almost completely closed to cause the engine to cut out. At Idling and low power there is little boost from the turbo, so running the engine with the rubber inlet hose disconnected will not alter conditions much. It's possible to watch the action of the throttle disc. See whether disc movement correlates with the engine cutting out.

Please note that I am advising basic checks, I'm not suggesting you rush out straight away and spend money getting the TB changed and then curse me when it turns out to be something different !