Last year I did a complete shade tree tune-up on my son's 87 SC with a 2.5 and the DIS ignition. I did the whole 9 yards - wires, BOSH PLATINUM plugs, air filter, fuel filter, etc.
Well, the car ran fine for about a month and then started bucking and missing under load - like when you come out of a curve.
I spent many, many hours trying to find the problem - putting on new coils, spark module and all. I even changed the wires, again. But did not change the plugs. Finally, I put in a fresh set of BOSCH PLATINUM plugs. The engine ran fine - for about a month. Then the problem returned. This time I tossed the BOSCH plugs and dropped in a set of regular old ACs. The car ran great, and continued to do so.
OK. Here is my theory. The DIS uses a waste spark that fires one plug from the center electrode out to the shell, and the other plug from the outer shell to the center electrode. Upon close examination of the BOSCH plugs, TWO of them had the center electrode burnt off up inside the porcelain insulator! The other two were OK. If you have ever looked at a BOSCH PLATINUM plug you will note that the center electrode is flush with the insulator anyway. The plugs that fire from the shell to the center electrode burn off VERY quickly.
My conclusion - Don't use BOSCH PLATINUM plugs in your DIS ignition Fiero (87 & 88).
From: Randy T. Agee
Take the deck lid OFF. It is really very easy to remove and makes the job much easier. Mark the hinge outline with a scribe, unplug the electrical connectors for the lid release, Ajar switch and ground strap (if you have them). Remove ONLY the four 13MM bolts on the sides of the hinges (Yes, it takes two people). DO NOT remove the "funny" center bolt as the hinge torque arms are attached here. Set the lid aside and access to the front (rear?) plugs is easier.
From: Randy T. Agee
Actually, I've never really had a problem with these. I use a standard 3/8" drive spark plug socket with a flex handle (Not a ratchet) and slide a 3 foot piece of rigid copper plumbing pipe over the handle to use as a breaker bar. The copper is rigid enough to apply sufficent torque, but will bend before you break anything. Once the plug is loose, I turn it out by hand. Obviously, I do this with the motor cool.
From: Hal Spalter