98 sierra spark arch at all cylinders

I have a 98 sierra 5.0 Liter engine and it misfires at idle and also throughout the driving range,especially under a load. It is spark arching right at the plug . I 'm getting about 11 mpg. I've replaced wires; Taylor brand,AC plugs,brand new whole distributor,coil,fuel filter and fuel pump. I had it put on the computer no codes, no misfires everything checked out ok. I tried 3 sets of wires and it is still arching at the plugs,I checked and cleaned up all frame and engine grounds. Sometimes it takes 3 turns of the key to start while clutch is pressed in. It also has a motor knock that is terrible when cold and quiets down when gets warm ,but is still noticable. If anyone could help it would be greatly appreciated.

How do you know its arcing? Can you see it? What are you using to install the wire onto the plug? And what is the spark plug gap you are using?


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I can see it arcing when it is dark out, but it has to be absolutely dark. I just installed spark plug boots on with my fingers. The plugs are gapped at .060, I talked to a local mechanic (relative) he thought the spark was following the dielectric grease. I cleaned the plugs up and the boots and it didn't help. When I bought the truck it looked like the original wires so I bought a set of Autolites,they arched also. I then bought Taylors,but the same thing. It seems like there are some for wires crossed somewhere;not plug wires,but I can't find anything noticeable. Like I said earlier I checked all ground straps and sanded the contact surfaces,It is like it is trying to ground to the heads. If I run the truck pretty hard and when I go back to normal driving the misfire seems to get worse. I asked many mechanics in the area and nobody ever heard of it. Thanks for responding mustang mike.

How did this start? Was it after you changed the plugs and wires? What firing order are you using? The grease will not conduct so you are ok using it. With it arcing and you know for sure the boots and wires are good. The timing could be off causing high cylinder pressure witch would make the spark unable to jump the plug gap and the extra voltage would find the path of least resistance and jump to the head. Check this and let us know what you find. By the way how many miles?

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I bought it with a misfire, I just assumed it needed cap,rotor plugs and wires. It has 150k on it. I have all of the wires on correct. The timing is set and can't be adjusted,unless you have the distributor off a tooth, which I don't. I was thinking the ignition control module was bad or I have a bad battery cable. I will never buy another vehicle with a misfire again and assume that I can fix it.