Blowen Fuse

Hi
can any one help me ive got a 1994 cherokee limited that blowes the no.12 fuse in engine compartment . It controls the auto trans
ive replaced it and after about 3 miles it blows again, once it blows i have to drive it manually i.e. at the lights i have to pull it into 1-2 and then manually shift up

any help greatly appreciated
Ewen

Are you certain that you are using the correct amperage rating fuse? Is the blown fuse really black, which would indicate a dead short somewhere, or just open, indicating an overload condition? I don't recall what amperage this one should be, perhaps someone else knows??
Don't go higher than factory spec.

Hi and thanks for your response the fuse is rated at 10 amps so i replaced it with the same which blew within 3 miles (i think when the converter locks) i then tried a 15 a fuse and it blew the same and the plastic body of the fuse is not burnt the fuse wire is just blowen

Ewen

Is there a chance something else is hooked up to that same circuit? Could be perhaps someone connected accessory lights, etc which is causing an overload? I once saw a vehicle that had a short in the back-up lights, blew the fuse each time you put it into reverse.
I can't imagine the transmission controller itself blowing a 15 amp fuse, unless the input voltage is excessively high. If the system voltage goes very high, there are MOV's (varistors, transient voltage absorbers) in the TCU which will short out, thereby protecting the TCU itself. But the voltage would have to go above 18 volts or more, which is unlikely. Check your alternator voltage anyway to be sure.
I would suspect something unrelated is causing the short.
By the way, on my '90 XJ the transmission fuse is below the dashboard just behind the glove box, not under the hood.

Yeh your right mine also has a fuse under the dash and this is ok

The workshop manual i have has virtually nothing on the 4 speed auto. Does any one have a wiring dia. for the under hood fuse/relay block again the manual i have is limited in this area.
on the weekend i might have to try and manually follow the wires from the fuse and see were they go
Failing that i will have to take it to a dealer and i hate to do that

and thanks again for your input

Ewen
Australia

The only diagrams I have are for a '90 XJ, but might be similar. There is a TCU fuse (7.5 Amp) and a TCU in-line fuse 15 Amp, I think the latter is behind the glovebox.
Besides the TCU, the 7.5 A fuse also feeds, you guessed it... the backup lights! Check for a bad socket/bulb and perhaps that nasty NSS/back-up switch on the transmission, although this switch is not likely to cause a short. Perhaps someone with a newer set of diagrams could confirm this for your '94 model year?
Good Luck.

Thanks
that nasty switch on the trans was playing up prior to this problem and i striped it out and cleaned the contacts and refitted it - i wonder if i got it right or if i got a crimped wire in the loom up to the firewall. i'll check it out

Ewen
Australia

i posted this prob ages ago and i thought an update might be in order.

the problem was a broken engine mount allowing to much engine movement which in turn chafed thru the loom to the tranny causing the fuse to blow, i drove it like a manual for a year before puting it in to a mechanic to repair.

However i suspect that when the head was done some time earlier that the mechanic may have routed the loom out of the original position and that caused the problem

anyway 320,000 kilometers and still going strong

Regards Ewen
Australia