1990 Dodge Caravan

Well I guess you can look under the hood when it is running and see if something is leaking. You could have accidently broke or unhooked some thing when doing the spark plugs/wires. That is if it smells gassy in the front.
Gassy at the back well then maybe wires arent hooked up right or spark plug gaps got closed when putting them in.

Give us a shoot back and tell us what you find

thnxs and good luck
Jesse S