Check engine light on when towing

Every time I tow a trailer, tent trailer or small cargo, the check engine light comes on and starts to flash. Then the black smoke, no power, high fuel usage happens. Its as if the van is complaining about towing???
Is there an instruction in the computer that says if the weight is too high, I'm going to complain?
Is it a carbon build up problem?
Could it be plugs and wires?
Should I use higher octane gas?

I will try to get to a mechanic today to get the codes read.

Suggestions wecome!

2001 Safari, 216,000 km, rwd.

Thanks

Get the codes read first. Then report back.

The check engine light went out today half way through my journey??? The van drives okay now.

This is driving me crazy!!! Will the light go on when I tow again?

Any ideas anyone?

Crystal ball is broken.... As mentioned, get the codes and post them here. You'll probably find a P0300 series DTC in memory. If that's the case, likely causes are plugs, wires, cap and rotor will need replacement.

Me again!

Van ran okay for a few months...then engine light and flashing engine light...stranded away from home, however found a good mechanic with a good local name. He checked the codes and reported something very strange (or at least I thought it was strange) one of the cylinders had over 500k misfires and another one had around 300k, since the last diagnosis?
He changed the distributor cap, rotor and one of the O2 sensors.
It was finally fixed, or at least we thought it was...today the light goes on again! But it went out after running a few errands (several engines stops and starts)
The common link to the problem seems to be the outside temperature. I can always tell when the light is about to go on...its usually when idling, the engine vibrates or rolls, and its hot, humid and muggy out. A friend is convinced its the coolant temperature sensor? Could he be right??? How easy is this part to change...is it an expensive part? Everything has been changed over the last year or so except this and the wires/plugs.

Thanks