4AGE AE86 EFI main fuse keeps dying!

**70XIN** · 20-10-2009, 05:47 PM

Good afternoon ladies and gentlemen,

Car - AE86

Motor - 4AGE/7AGE.

Problem - Car keeps blowing the 'EFI Main' Fuse in the engine bay fuse box. The car can sit and be revved at idle, but as soon as it's put under load being driven, the fuse dies within seconds.

Possible problems?

**CrUZida** · 20-10-2009, 06:02 PM

Factory wiring, or something you've changed?

If its something you've changed then look over the diagrams, normally there are 2 fuses that supply the engine/ecu/components.

The EFI fuse does one lot, and the AM2 fuse does another lot.
You've possibly wired the whole engine up to the EFI fuse, and the injectors/ignitors/coils are blowing the fuse (they are generally powered from elsewhere, such as the AM2 fuse via the circuit opening relay).

**70XIN** · 20-10-2009, 06:05 PM

No wiring has changed (all stock ae86 stuff) .. and the car has done a couple of thousand k's since the conversion without this hiccup

And as far as we can see so far, nothing appears to be shorting out, and no exposed wires

JP · 20-10-2009, 06:14 PM

had to fix a similar problem on an ae92, turned out to be a dodgey turbo timer install with part of the ignition harness shorting out on the dash support.

**river** · 20-10-2009, 07:25 PM

Hi,

I fixed your title. Please put in engine/vehicle info in the title.

seeyuzz
river

**70XIN** · 20-10-2009, 11:59 PM

^ Cheers

So we've been told a wire could be grounding (especially after today's hot track day, anything could've melted), that the fuel pump or filter is clogged or screwed, and that there could be a problem with the alternator or grounding wires

Will be a fun day of diagnosing tommorrow i guess, unless someone has some bright idea

Oh yeah and i guess i should stress again: the car idles fine for as long as you want, you can even rev it without any dramas, it just can't be put in a gear and move anywhere without the fuse dying shortly after

**CrUZida** · 21-10-2009, 01:12 AM

Disconnect the alternator (tape up the wire) and try again. That will isolate that.
Very unlikely its the fuel pump or filter.

Put a 20A fuse in there (I'm assuming the stocko is 15A), if its pops at the same time, most likely a dead short (due to earth somewhere, or melted insulation). Had similar problem on a mates car, kept blowing fuses. Put a higher rated fuse in there to test, and suddenly smoke started coming out from the manifold. Turns out a wire had come loose that wasn't affecting anything, but was sitting on the manifold and shorting the fuse out. It smoked for just long enough to find the fault. Not ideal method, but it worked.

I'm presuming manual, in which case auto wiring is not a cause.

Try changing the EFI relay with a good spare, unlikely but an easy test.

Also, to save from blowing all these fuses, rig up a circuit breaker of the same amperage. Every time it trips you just reset it.

**racsov500** · 21-10-2009, 07:15 PM

we have used up to a 30 amp fuse and it still blows after about 10 seconds of driving

**CrUZida** · 21-10-2009, 08:23 PM

Most likely a dead short.
Time to pull things apart and look for a bare wire near metal.

**Robo86** · 25-10-2009, 10:53 PM

Hey guys

its my car.

Had a play tonight, oil cooler line was touching the oil pressure sender, do you think this could have been the cause?
I have put the car back together (also using 15A fuse in the EFI slot) and i have done a solid 20 minutes driving (both heavy load and lots of revs) and it's all good now.

thanks

**allencr** · 26-10-2009, 08:59 AM

Originally Posted by Robo86

...oil cooler line was touching the oil pressure sender, ...could have been the cause?

No, not a chance. An unsheathed cooler line won't conduct elec. , at least low voltage, and the wire going to the sender can be direct to ground & it will only peg the gauge - that's how It's tested.