[yogi_123rd]

It's unlikely the grade of gas caused this.
You should download the fault codes stored in the computer and work from there.

Chysler computer codes (80-95 Chysler's):

Chysler faults codes are stored in the computer for up to 50 ignition starts. Each code is two digits. Beware that some problems can generate multiple faults codes. The code's meaning (i.e. faulty sensor) can be found by doing a web search using keywords "Chryler computer codes".

To obtain codes: Turning the ignition key on-off-on
three times (don't start the engine) will put the
computer into diagnostic mode. Watch the "check engine" light. Count the flashes for each digit which is followed by a pause between digits. Two digits to a code with the end of the list being code 55.

To reset the codes, turn the ignition key on-off-on
50-55 times (don't start the engine).