Alan

You have a quite different problem - fuse bodies don't melt before they blow for overcurrent - the metal fuse element just blows. Fuses melt because the contact with the fuse holder is poor e.g. the ends of the fuse are getting hot due to the build up of resistance due to corrosion/oxidation. This causes a voltage drop and power consumption across that contact resistance - this will get very hot and the fuse body will melt from the ends - not from the middle.

You need to do 3 things:

1) Replace all plastic bodied fuses with ceramic fuses of a quality brand (check the values are all correct as you do this)

2) Gently clean and as needed tighten the fuse holder end clips - they should be clean metal and a firm fit

3) Use an electrical contact cleaner/promoter/protector on the fuse holders and on the fuse ends to prevent future degradation (De-oxit/Stabilant etc.)

From time to time rotating the fuses and reapplying the De-oxit/Stabilant can keep thing in good order. If the degradation was as a result of an apparent water leak - you need to solve that problem - most likely a leaf build-up in the blower motor cowl area, or a seal issue around the blower motor

Alan

LeonLewis

Thats excellent info thank you. Yes i confirm the fuse has been melting from the top. With the metal element intact. I was not aware that ceramic ones existed! I will see if I can get hold of some. I did replace them all around 8 years ago. It seems weird that this is happening now after the car was left out in freezing temperatures, which is the first time I have done this. It doesn't get freezing much here as I am in the south of France. Perhaps the filter got a bit blocked with ice. The pump was drawing more amps and the fuse was not sitting well and melted? So many possibilities! i Confirm however the area was not humid and no sign or evidence of any leaks.

I would like to test the fuel pump however. To rule that out. Maybe ice got in there and messed it up? It was changed around 3 years ago and since then I have bearly used the car. So if its failed it seems logical its because of an ice related issue.


Thanks again,

LeonLewis

So just to give an update on this to close the discussion. After replacing the fuel and changing the fuel filter. The issue seems to have stopped. Alan rightly pointed out that I have poor quality fuses which was causing the plastic on the fuse to melt instead of blowing the metal element of the fuse. However the cause of the heat melting the plastic seemed to be fuel pump working on overtime due to water in the fuel and or damaged/blocked filter due to ice build up after leaving it out in freezing temperatures.

Note for myself for future and to any other interested parties, don't leave the 928 out in freezing temperatures especially with an empty tank. Maybe that's obvious to other people. But not too me. I still have a lot to learn it seems! I will change the fuses to ceramic ones as i currently have plastic ones in there.

Mrmerlin

great that you have this figured out
I suggest to use Deoxit 100 on any electrical connections you touch

LeonLewis

Yes thanks will have alook for that. I have never heard of it, will see if i can get it here in france

Mrmerlin

amazon sells it not sure if you have that in FR.

Alan

Everybody thinks this first part: "The pump was drawing more amps" - however it was certainly not true here. For the fuse to be getting hot the pump was actually drawing less current than normal - because its voltage was lower than normal since some voltage was being dropped over the resistance build up at the fuse holder terminal contact. This seems totally unintuitive I know - but it is ALWAYS true in such cases. It is therefore also likely the pump was not working at its best at the reduced voltage

I would venture that almost everyone who sees a melted fuse instantly thinks "Current too high" - But it is entirely the wrong thing to think. Worry about the condition of the fuse(s*), fuse holder(s*) and wiring directly attached to them and solving the conditions that allowed contact degradation in the first place and NOT the terminal equipment loads.

*NB - this means all of them - not just the one that has already shown symptoms - they likely all experienced similar conditions.

Thinking a single load was the source of an issue not only leads you down the wrong (possibly expensive) path for that solution, it also stops you thinking about the systemic issues that perhaps already affect the rest of your electrical system.

Alan

jpitman2

Read this thread of mine......https://rennlist.com/forums/928-foru...e-sockets.html
jp 83 Euro S AT 57k

LeonLewis

FYI I purchased some proper ceramic fuses and no more problem! Thanks for the excellent tip!

SwayBar

Did you also clean all the contacts per #2 above?

That is the root of your problem - not the fuses.

LeonLewis

no i didn’t clean the contracts. No visible oxidation present. Also I noticed the plastic fuses I had in there were slightly bigger than the ceramic factory spec ones. Which probably created a bad contact. Agreed cleaning of contacts should be done aswell

LeonLewis

Great info, this actually seems to have been totally true in this case.

having replaced the fuel, fuel pump and filter. At first I thought it had solved the issue. But no after a whilst the problem still persisted. I then changed the fuse to a ceramic one, and problem seems to be now solved. FYI the plastic fuse was slightly oversized and didn’t sit in the contacts as well as the ceramic one, which it seems would contribute to the problem, or perhaps even be the sole source of the problem.

What had slightly blowen my mind is that all of this started after I left the car outside during freezing conditions with a near empty tank. Which let me to believe it was a condensation related issue. Perhaps initially the issue was the frozen water, then after changing the fuse to another plastic one, the contacts decided they didn’t like larger plastic ones anymore? God knows

Alan

As I said the problem wasn't the terminal equipment (in this case the fuel pump) but the connections to the fuse. Now there is a risk that the connections are still actually not great - but the ceramic fuses will not melt - they might still get very hot but you don't see the tell tale melting. This is still important because the insulation on the CE wires (back of the panel) could still melt due to heat. The fuel pump would also still not be getting full voltage in this case. I'd verify that the fuse connections are really now sufficiently good - several options:

1) Verify by touch that after running for a while that the fuse ends are not hot.

2) Verify the voltage at the top & bottom of the fuse are the same within a few millivolts.

3) Verify the voltage across the fuse is close to 0v - a few millivolts is OK

If any of these show issues follow the cleaning routine described earlier.

Alan

LeonLewis

Thanks for the info! I will get onto that,