My 1985 Maxim X starts and runs OK but just after driving off the main fuse blows and everything stops.

this is not clear at all (is 3.4L engine my bet)
the starter is silent or not? if the starter motor spins the enigine crank shaft , fast that that is cranks ok not start engine.
no crank means. the crank shaft never spins
and that as a few causes,
blow fuse test them all?
crank in park and in Neutral too? N can work and P fail on any car.
no power to PCM fuse mean main power is dead main 12vdc power buss is dead. and that is much larger fuse even 100amps.
if you scan the PCM well that action will be dead. lacking PC power
so here is that power feed, battery must be 12.6vdc rested, not 10v
here we go ,2 paths dead, starter motor and PCM dead power.

Fuse link C blow out. GM gray coded,same goes fore Fuse a1/2 blown.
fuse link A, blown GM rust coded make alternator 100%^ dead and now the battery dead too ,lacking working ALT.
next is fuse link Z (GM gray) runs vast things.
I wonder what fuse is this PCM fuse as none are marked that.
there are 100 schematic to see, I am working throught them all to find PCM
are head lamps dead, are brake lamps dead?
head lamps work key off, so is always fix it first if dead.
fuse (Fa1/2 ) PCM/ABS fuse 10amps the a1 side is main power to this fuse. and this also kills dead the transmission range switch PRNDL and starter too dies.
So fuse A1 side is your critical failure point on this car.
so maxi fuse 40amps blew out from a short.
A1 FUSE GOES HOT KEY ON ONLY. (NO IMMO FAILURES IF HAS IT.
IF NOT a ign MAIN 1 FUSE 40AMPS IS BLOW
OR POWER TO MAIN ONE IS GONE.
mIAN1 IS WIRED HARD TO THE BATTERY MAIN
ALL MAXI FUSES ARE, SO IS BLOWN THAT FUSE OR THE KEY SWITCH IS BAD.(IN RUN)

run the fault codes
could be a broken timing belt or chain
could have blown the main power fuse next to the battery ( around 80 amps ) and that would have switched everything off

Is the fuse correct amperage rating. There is to much power going to fuse. If it is the correct fuse you have a short most likely ? wire touching metal. The power lose is because this is main fuse.

is the main fuse over rated for amps before it blows. say a 30 instead of a 10 ??

Yeah pal, you've not gone deep enough yet. You'll find a power wire bare inside the unit, pull it apart and tape that wire up to stop it from grounding out and blowing the fuse.

this is the main fuse from the battery that feeds the fuse box etc , take out the fuse and holder and check for signs of corrosion on the terminals , any worn wires etc as to blow this size fuse must be shorting to earth , when does the fuse blow ? if it is on start up then the starter could be pulling to many amps so would need replacing , if it's when driving i'd have the alternator charge rate checked as well . that gives you a few things to get on with , keep me posted if you wish

check fuse rate on dryer if same rate. check dryer for amps if pulling to many will blow fuse, if dryer is ok check from plug in to fuse.

There is one main fuse by the batterry under the seat and the rest are actually under you indicator lights cover.Hope this helps.

Probably faulty oven element, as it gets hotter, then the insulation resistance is probably breaking down.
Disconnect element, and try it again, if it does not blow, then replace element.
Please rate my solution.
Thanks.