15 ft/lbs is max. I get them all snug, then wiggle the im and tighten down the bolts. I like to start in the middle, but there isn't a prescribed order.

The o-rings are at every terminus of the fuel pipes. There are only two sizes. You will see a white horseshoe clip at each one. Push the horseshoe inward then pull the connector out. Lots of people pull the clip and break it. Be gentle and push it inward while you wiggle the pipe out.

There are lots of threads here indicating the size of the o-rings.

Replace the return lines (cloth covered grey or black rubber hose). Note that there is a plug in the return line closest to the firewall. Do not, do not, do not use a utility knife to remove the old return line from the injector nipple. A slight score on the nipple could cause a leak.

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2009 E320 Bluetec 117,000
1995 E300D 306,000 Sold
1996 Ford Taurus LX 130,000 Sold
1985 300TD Still 225,000 Sold
2016 Ford Fusion 24,900