1997 C1500 Silverado , 5.7L

biscaynekid · March 20, 2020

180,000 miles on engine, runs great.

Most forums jumped immediately to the spider assembly as the culprit.....I didn't want to believe .....hoped it wasn't the problem.

For about a year I will get a CEL come on. Auto-zone would tell me the code indicated : Cylinder 1 misfire. I would clear CEL. The problem would not re-occur for a few months, then CEL would come on again. Lived with this, as I say, for about a year.

Now it's happening daily and CEL stays on....truck drives Ok, but the miss bugs me to no end.

Finally decided to take it serious.

Bought a code reader for myself (Autel)...nothing fancy. Code indicated Cylinder 1 miss-fire.

Since most forums pointed to the spider I did a fuel pressure check on it. I connected a pressure gauge to the fuel line schrader valve. Started the motor. gauge read about 50 PSI.

I turned engine off and watched the pressure gauge. The gauge held the pressure for 6 minutes with only about 5 PSI drop. That meant the spider was not leaking fuel. I eliminated the spider for now.

I have 100,000 miles on the ac/delco plugs (irridium), wires, distributor cap and rotor..

Hooked a timing light to each plug wire and checked firing...all fired fine....checked several times.

It's time for a tune-up anyway, so I started with replacing the distributor cap and rotor, (They showed some corrosion on terminals. )

Still had miss and CEL.

Next, I decided to check my plugs. Since the Code reader indicated Cylinder 1 misfire, I started with cylinder 1 plug. The idea was to inspect it and if it looked OK I would swap it to another cylinder and see if the problem followed the plug.

Well, the plugged appeared to be OK. The gap was still correct after all those miles. I wire brushed the plug.

I was installing the plug when I noticed something on the electrode. That something was the ceramic electrode isolator of the plug ! The isolator was sliding up and down the electrode.

In all these years I had never seen that. As the isolator slid out to the end it caused the plug to fire inside the thread area of the plug instead of out at the electrode, thus causing the misfire, CEL, and engine stumble.

The fact that the plug was still firing, although sometimes to ground, fooled me because my timing light indicated the cylinder was firing fine.

I replaced the plug and all is well. Truck motor runs smooth.

Thought this might be of help to someone and maybe save them from jumping on the spider too quickly.

ChevroletTough · March 20, 2020

WOW! I've never seen that either. Nice find. I have those year long diagnosis steps. Been there. Tracked a cam position sensor for a year and finally found that was it.

Glad to hear you found the problem and resolved it!

What brand plug was it?