Fuse question.

[jmc330i]

A couple questions actually....
1) Fuse 11 for the fuel pump should be 7.5 or 15 amp? I've got two late ('93 & '94) M40 tourings here both with 15 amp fuses fitted. And I've just checked another 325i and that has a 7.5 amp fuse.

2) Fuse 9. Is this used on a manual M40 touring?

Cheers

[jmc330i]

Yeah, I've got that saved as a pic on my phone

That's why I'm asking though, the two tourings I have here both with a 15 amp fuse fitted and I've just had my mate check his touring and that also has a 15 amp fuse

[jmc330i]

I am hoping he sees this

[daimlerman]

Fuel pump fuse should be 7.5a.

Now there is conflicting information about this fuse,the early Haynes says 15a,later Haynes says 7.5a.

Early chromie's handbooks also say 15a,later chromies and all facelift handbooks say 7.5a.

As this is an ign live circuit,the fuel pump runs continuously,I would suggest the lower rated fuse.
However,if a 7.5a blows repeatedly without an obvious reason,it would be worth trying a 10 or 15a....

[jmc330i]

Ah cheers. I thought I'd read about different rated fuses being fitted but I couldn't find any mention after a search. I'll dig out a 7.5a and give it a go


Any idea on fuse 9? It's listed as the autobox selector indicator but again, both manual tourings have a fuse fitted.

[daimlerman]

Most of the E30's that I have bought have had random fuses fitted where they are not needed,so I would yank that one out of 9 and put it in the spares box!

Often find relays fitted 'just because there's a hole for them' as well!

Thinking further about 11,I seem to remember Brain writing that the fuel pump load is quite close to what a 7.5a will tolerate,so a slightly bigger fuse may be needed for an 'aftermarket' pump.

[Brianmoooore]

Some early E30s had two fuel pumps - a 'lift' pump in the tank, and a pressure pump in front of the LH rear wheel. These cars required a 15A fuse, as the starting current drawn by both pumps is likely to fatigue a 7.5A fuse in time.
Most E30s have only one pump, and for these a 7.5A fuse is preferable.
The problem with a 15A fuse is that the stalled current for a fuel pump is sufficient to blow a 7.5A fuse, but not sufficient to blow a 15A one, increasing the likelihood of loom damage.
Of course, if the fuel pump stalls (as worn ones frequently do), the engine will stop shortly afterwards and the fuel pump relay will switch off the current, limiting any damage to the wiring.
If, like me, you run your cars on LPG, the engine will not stop, and real damage can be done to the loom.
In practice, if you buy an E30 and find a 15A fuse fitted, it usually indicates a past history, or a current fuel pump problem.
Fuse 9 is used on auto. gearbox cars, and for the lambda sensor heater on so equipped cars, but also someone could have used it for some accessory.

[jmc330i]

Thanks Brian, these are late tourings so both have lambda sensors so that explains that - the fuse box picture in the wiki only shows fuse 9 for the auto selector indicator.

I've changed fuse 11 to a 7.5a fuse in both cars and there doesn't seem to be an issue (I've just done a 65 mile trip in one touring). I will make sure there's at least one 7.5a fuse spare in each just in case. Is it worth/advisable using a 10a fuse if there is an issue with the 7.5a fuse blowing?

[Brianmoooore]

Is it worth/advisable using a 10a fuse if there is an issue with the 7.5a fuse blowing?

MOST DEFINITELY NOT!!! The answer to a blowing fuse is NOT to fit a larger one!
If a 7.5A fuse blows, then it's laying down its life doing the exact job it was created to do, and the reason needs to be determined and fixed.

[jmc330i]

Not wanting to tempt fate but the usual reason for the fuse blowing would be a worn/tired pump?

[Brianmoooore]

That's the usual thing that blows them.

[jmc330i]

Thanks Brian