87 sierra backfires and will not start

Chilton manuals are junk IMHO. Also, the computer cannot be "confused" by the parts you replaced. Are you sure you have the number one wire in the right spot? Number one cylinder will be at the top twice during the cycle, and because the distributor turns at half the crank speed, you could be 180 degrees out with your number one position. Also, verify the rotation of the distributor.

By the backfiring, it sounds like it is off time, which can be the result of incorrect indexing of the distributor, incorrect wiring of the distributor with respect to spark plug cables, or a slipped timing belt or chain.

Remember there are two TDC occasions..one between the compression and power strokes, and one between exhaust and intake. Be sure you are on the right one.

What firing order did you use? GM used two entirely different V-6s in that chassis and their firing order is different also. Try 1-2-3-4-5-6 clockwise around the distributor. #s 1-3-5 are on the _PASSENGER_ side of the engine #1 being the front most. #s 2-4-6 are on the _DRIVERS_ side #2 being the front most.

No, it's confused because you put the parts on wrong.

It's got nothing to do with the brand.

Timing, IMHO, is not just the advance that you are speaking about.

It takes into account everything needed to get the spark to the right cylinder at the right time. And that includes the wiring of the distributor spark cables. If you got them wrong, then you would get the symptoms you have described.

Assuming you followed wiring diagram correctly, simply move wires at dist to exactly backwards from where you put them--start w/#1. Assuming fir. order is 1 6 5 4 3 2, swap 1 with 4, 6 with 3, 5 with 2. Get the system? This should be sufficient to start, & then you can time it 'finely'. May be a chance you will need to walk the wires one step(move each wire one place forward or one step backward): that's most u should be off(if any) to reach the fine tune marks. HTH, sdlomi2