Take it to a trained professional.
I believe that the gapping is .044" on this engine.
Not sure what you mean by change the ignition on a diesel, diesel engines don't have spark plugs, spark plus wires, coil, etc.... If you are asking about the ignition switch, it is mounted on top of the steering column on most pre 2000, after that they are located in the steering column.
Each spark plug has its own coil located on the top of each plug
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Could be a number of things... bad air filter, fouled spark plugs, weak fuel pump...
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Have you checked your spark plugs, spark plug wires, destributor cap and rotor, do you have dirty fuel injectors. It could be any one of these seperatly or a combination of any or all of these. Then it could be your magnetic pickup in the distributor or your engine control module. You need to test all these components to know that they are the problem. If you just start changing parts it can get expensive.