Crankshaft Pulley Fell Off. Ugh.

So over this van. The crankshaft pulley fell off, I didn't even know it could fall off. Just the outer part, it has a very thin rubber lining on the inside. It came off when I started the engine and I immediately shut it down. Wth do I do?! Maybe I'm not even looking for the right part, but I don't see any crankshaft pulleys on my local auto parts websites.

Rockauto.com has them. Look up harmonic balancer.

I am going to hazzard a guess and say its either a 3.1 or a 3400?

What year is the van?

A few years ago, our 3.8L 95 van had a terrible vibration that ramped up sporadically from idle. I had not time to work on it, and Firestone said it was the water pump. I told them it was not the pump, as I replaced it a few months prior for leaking and age. They replaced the water pump with no success.
The harmonic balancer was found to be torn. Van had around 120K miles at the time....merry Christmas guys

I am going to hazzard a guess and say its either a 3.1 or a 3400?

What year is the van?

Sorry, It's a '98 with the 3400.

A few years ago, our 3.8L 95 van had a terrible vibration that ramped up sporadically from idle. I had not time to work on it, and Firestone said it was the water pump. I told them it was not the pump, as I replaced it a few months prior for leaking and age. They replaced the water pump with no success.
The harmonic balancer was found to be torn. Van had around 120K miles at the time....merry Christmas guys

It has a terrible vibration too, for about 15 seconds from a cold start, throwing a code that says misfire in the #1 cylinder. So trying the hit or miss tactic, I replaced the spark plugs, which I hope to never have to do again on a Trans Sport. This pulley fell off as soon as I started the engine back up after the spark plug job.

Like GMTech1 said, it's called the harmonic balancer......this had to have a bad vibration for some time......they don't just come apart right away...

Like GMTech1 said, it's called the harmonic balancer......this had to have a bad vibration for some time......they don't just come apart right away...

Well the 15 or so seconds of "misfiring" at cold start ups has been happening for about a month now. And with the engine code pointing to cylinder 1, I was advised to change the plugs and/or injectors. Then the belt started slipping and tearing. So now knowing that pulley is a "balancer", the misfiring feeling makes more sense. Thanks!

But now what is involved in replacing that? I see a repair sleeve here (http://www.autozone.com/autozone/parts/1998-Pontiac-Trans-Sport/Repair-Sleeve-Harmonic-Balancer/_/N-jad59Z8znnf?filterByKeyWord=harmonic+balancer&fromString=search), or do I have to replace the whole balancer?

Well the 15 or so seconds of "misfiring" at cold start ups has been happening for about a month now. And with the engine code pointing to cylinder 1, I was advised to change the plugs and/or injectors. Then the belt started slipping and tearing. So now knowing that pulley is a "balancer", the misfiring feeling makes more sense. Thanks!

But now what is involved in replacing that? I see a repair sleeve here (http://www.autozone.com/autozone/parts/1998-Pontiac-Trans-Sport/Repair-Sleeve-Harmonic-Balancer/_/N-jad59Z8znnf?filterByKeyWord=harmonic+balancer&fromString=search), or do I have to replace the whole balancer?
You'll have to rent a crankshaft pulley puller and pull it off and replace it with a new one. Without an impact wrench, the bolt that holds it on can be difficult to remove. You can put a wrench on it and lay it strategically across a frame member and bump the starter with the key for a split-second to get it off.

Yes--the whole balancer.
A few pictures from a 3.8. Probably quite similar qith the 3.4
www.avigex.ca/xport/ckpphoto.jpg
www.avigex.ca/xport/cksphoto.jpg

Thanks for the help everyone. I did rent a puller and did the job, but upon completion, the engine ran worse than before, as if the balancer coming off had messed up the timing. That was the last straw, and the next day I sold the van on Craigslist as a mechanic's special. This van had given me more problems than any other vehicle I'd ever owned, and I only had it for just over a year.