Injector o-ring question, 3800

I just replaced the lower intake manifold gaskets and upper plenum in my '98 Olds Intrigue (with help from the people in here). Car now ran good and has good power, but after driving a short time,
I noticed the car has a vibration, at idle only, it kind of lopes, and I opened the hood and could see the engine visibly rocking. I recall when I was re-assembling the engine, and upon opening the Dorman UIM set, I noticed two different sets of o-rings, 6 apiece. One set looked like every other GM injector o-rings I've ever seen... while the other six looked slightly larger diameter, and thinner. Since the injectors are a smaller diameter on top than bottom, I used the larger diameter but thinner ones for the bottom of the injectors. They didn't seem to fit that tight, but I found the other ones to be such a tight fit I could not really get them on, without being afraid I was going to break the injector tip while putting on the o-ring. Besides, what would the other set of 6 been for? When finishing up and plugging the wiring harness onto the injectors, I noticed the injectors would rotate in their bores quite easily, even though the rail and everything was torqued down. I thought that was kind of strange, and I remembered that the o-ring issue didn't set quite right with me, but continued on. Anyway, the car runs as described as above. No MIL, and I put my vacuum gauge on the fitting that goes to the power brake booster, and drove it around with the gauge taped to the windshield, and the needle behaves exactly as it should at various loads, etc, it reads right in the green, and steady at idle. I did this to see if it would point to a possible vacuum issue causing the rocking at idle, but it was inconclusive. Also, and this probably is unrelated, but I notice the cooling system doesn't have the pressure I would expect at operating temperature, the upper hose isn't very hard. It doesn't drink or leak any coolant. I have not yet checked the radiator cap, although I would have presumed the cap held good pressure since this whole situation began with the engine hydro-locking as it sat overnight -- so presumably the cap would likely have been holding at pressure when the gasket failed and flooded the LIM with coolant. But maybe not, I guess.
My questions are: 1). Since many of you have likely replaced the UIM with the Dorman unit, I presume you know of the second, larger set of 6 o-rings included in the kit... if they aren't for the larger, bottom part of the injector, what are they for?
2). If the fatter o-rings do indeed go onto the bottom of the injector, is there a special tool for installing them, or are they just surprisingly difficult to install and you really have to wrestle them onto the injector? I don't know what the bottom of the injector is made of, but I was under the impression it was breakable if you put a lot of pressure on it.
Any advice appreciated, TIA. I love this forum and you guys are very knowledgeable and helpful
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On Mon, 9 Aug 2010 20:20:35 -0700, snipped-for-privacy@msn.com (blowout preventer) wrote:

You don't need a tool to get the o-rings on. Apply a little clean oil to them. It's been a year since I did this with my son, who did most of the assembly work. This was a '95 Bonneville, but it's the same injector, My recollection is that the o-rings in the Dorman UIM kit were useless. Since I got the LIM gasket at the dealer I might have picked up o-rings at that time too. Seem to remember that. But maybe we used the old rings. With the Bonneville rail/injector setup I felt like I was going to bend the fuel rail when I went to put one side on, so I let my son handle it. His car. He popped them right in, But he breaks more stuff than me. They seemed a tight fit to me. Sorry I didn't remember that and warn you. But until my son confirms that I won't swear to that. He'll remember for sure. He'll call me sometime tomorrow, and I'll let you know.
--Vic
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On Mon, 09 Aug 2010 23:26:25 -0500, Vic Smith

He said the Dorman o-rings were all wrong size and useless and we went to O'Reilly's and got all new. Said they go on easy enough with a little lube. And the injectors shouldn't turn "quite easily" as you said. They have a good grip and require some twisting force to turn them. I suggest you get new o-rings and put them on. That's the safe course. You might be getting enough air past them to lope the engine while not affecting the vac gage. I'm assuming the engine has "relearned" idle and that isn't causing the rough idle. Maybe not an issue with the 3800. As for the coolant pressure by feeling the hose, the engine has to be hot and the coolant at operating pressure, but you probably know that. If the temp is normal you should have no problem, Good to hear the hydo-lock did no damage.
--Vic
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