How do I change the rear 3 spark plugs on a '94 Grand Caravan?

Tensioner badly adjusted or pulleys are misaligned.

Take it back to the shop and ask them to fix the tension under the repair warranty.

There should be enough tension that the belt can't jump the pulleys. There is a small chance is is misrouted.

https://www.2carpros.com/diagrams/dodge/grand-caravan/1994

https://www.google.com/search?q=94+dodge+grand+caravan+serpentine+belt+diagram

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Try these links;

Spark plug wire firing order for 2003 dodge grand caravan Google Search

dodge grand caravan 3 3l engine

3 3 liter V6 Chrysler firing order Ricks Free Auto Repair Advice Ricks...

bingo transfer smoked

Check the vacuum switch that controls it mostlikely to be in the dashboard

I understand the coolant temperature sensor on a 2003 caravan is located just under the coil.
There are two sensors located in that position, it's the one toward the passenger side of the car.
I'm changing mine in the morning so I will know for sure and if it's not there I will return and correct this post.

Replacing spark plugs (2003 caravan); can be done from the top, reach around the engine (not over) from the transmission side to get to the rear spark plugs, I have done this twice.

Sounds like the cv joint on one of the axleshafts. I would also try rotating the tires, front to rear, rear to front.

No! It is just very difficult to change rear plugs in a V6 front wheel drive

The upper part of your intake manifold needs to be removed.I think Chilton lists spark plug replacement on your Caravan at something like 3 hours.

unfortuneately......there's no easy way around this. You need to have 3/8 drive extensions and wobblies so you can navigate around the right bank to get those plugs in...it's a bad design.....but the only way it can be done in a timely manner is by the topside....sorry to tell ya that....hope i could help!!!

Your likelihood that it was your coil in the first place was slim. First thing to check is your fuel pressure. Not enough fuel pressure, your ECM won't let your coil fire.