All you need is an Allen wrench and a screwdriver. The hardest part is getting the lever type plug through the hole in the firewall. I decided it was easier to run the individual wires through the hole from the back. It took less than an hour. Lay the new one out over the old one. It's really easy. The injector wires are numbered.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles