Keep blowing efi fuse

[Intense]

My 4agze ae101 ae86 keeps blowing the efi fuse. On the fuse box it says it's a 15 amp module and that kept blowing. So we chucked a 30 amp in it and it was ok for a bit untill it blew.

I've got a theory. When the fuel is low the fuel pump has to work harder, drawing more current and blowing the fuse. Could this be correct or am I way off? Are there any ways to rectify this problem other than keeping the tank pretty full and driving like a nanny?

Cheers

[-GT-]

Ah, how about go looking for a short?? Who wired it up, and what's the job like?

Replacing blown fuses with bigger ones IS NOT a solution! The fuse is there for a reason...

[skiddz]

what is your fuel pump doing on the efi circuit? put it on a separate circuit

other than that an internet diagnosis isnt going to be great, how bout some more details hmm?

[Intense]

Conversion was done by toyospares a while ago. Sorry I'm not even 100% sure the fuel pump is on the efi circuit. But it's the efi fuse that keeps blowing so maybe just when it blows my injectors stop.

Need to figure out why though. I'm going to have a trawl through some wiring diagrams and see if I can make any sense of it

[oldcorollas]

fuel pump doesn't need to work harder when fuel is low.
fuel pump should be pulling nowhere near 30 amps.. 10, maybe 15 at max

look for shorts.
get an ammeter onto the wires the EFI fuse feeds, and see which one is pulling current.

if you want to chekc fuel pump first, put ammeter on it. if it is shagged, maybe it could pull that much power, but...

anything melted? ever had the smell of electonic smoke escaping?

[Intense]

It always seems to happen when I'm putting large load onto the fuel pump. Happend before when i was going WOT. Then now when the fuel has been low.

[oldcorollas]

maybe pump is not happy and is overheating?

connect up pump direct to battery (with switch?) with ammeter inline and see what current it is pulling.

[gianttomato]

Replace the fuse with a nail. That will solve your problems.

[wilbo666]

Replace the fuse with a nail. That will solve your problems.

Make sure it is at least a 50 Nail

Cheers
Wilbo

[af300e]

Make sure it is at least a 50 Nail

Cheers
Wilbo

Or, use a crowbar.

Mercedes test current draw for bosch 950 pump is around 7 amps. If it draws much more (say 10) it's RS. Naturally, a larger pump (say 044) will draw more, but a 950 is a pretty big pump. From memory the pump fuse for the 950 pump is 20A.

[andrew_mx83]

a .22 round works good too

my hilux had this problem for a while, turned out to be a dead fuel pump that kept shorting out.
i solved it by running on gas and selling the damn thing

[Intense]

I've got a feeling its the fuel pump but how can I tell for sure it's busted? I mean it's still working to some extent.

[af300e]

I've got a feeling its the fuel pump but how can I tell for sure it's busted? I mean it's still working to some extent.

As discussed. Just bridge the fuel pump fuse with your ammeter and see what the current draw is.
Do this:
Remove fuse, use multimeter set on at least 20A, attach each of the leads of the multimeter to the fuse box terminals, start the car, observe readout, report results.

[LeeRoy]

Can't you just test pump resistance and work it out that way since you know its in a 12V application?

[af300e]

Can't you just test pump resistance and work it out that way since you know its in a 12V application?

I assume you mean electrical resistance, fair call, but it won't tell you if the prob is a rough bearing causing mechanical resistance and therefore excess current draw.

I'm not sure what sort of pump the car in question has, but the external bosch types generally get noisy (sort of a heavy hissing) when the bearings are getting tired. They can actually lock up every now and then meaning that no fuel is delivered at all.
I've "fixed" quite a few by giving them a tap with a hammer to unlock them, allowing the poor bugger stuck on the side of the road to continue home.