Spark plug diagnostics

Chenn2389

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C78C42B9-D837-431B-B396-EE4CE02209B4.jpeg I got my engine broke in and changed out the break in oil. Started to rev it higher and give it some throttle. I’m starting to get vibrations 3k rpms plus. The exhaust smells really rich. I pulled the #4 spark plug, it looks pretty bad. The gap on these Motorcraft AGSP32C plugs is .050 +\- a few thousands. Let me know what you think about the plug I’ll post a picture. Typically what does it feel like if you blow out the spark? I’m gonna get some autolite 3924s and close the gap to .032-.035. I have a screaming demon coil and distributor I don’t think it’s the ignition.

engine: 331 stroker, efi, edelbrock aluminum heads, truck flow intake. Comp ratio 10.3:1
 

skidoo

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Not a lot of information here, can you give more details?
When you say you broke the engine in, does that mean it's a complete rebuild? New pistons and machined the crank, bored the block? Was the engine balanced? Original crank. Flywheel and harmonic balancer? Did you check all the plugs and header pipes for temperature with an infrared gun? What is the ecu tune? How much timing, initial and total? Have you driven it?

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Chenn2389

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Not a lot of information here, can you give more details?
When you say you broke the engine in, does that mean it's a complete rebuild? New pistons and machined the crank, bored the block? Was the engine balanced? Original crank. Flywheel and harmonic balancer? Did you check all the plugs and header pipes for temperature with an infrared gun? What is the ecu tune? How much timing, initial and total? Have you driven it?

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I was just asking about the plug.
 

skidoo

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I was just asking about the plug.
Doesn't look like it caused a vibration. A little rich but really to read a plug you have to do a run with new clean plugs and kill the engine then look deep down at the porcelain with a strong light and maybe a magnifying glass. Some racers will cut the metal threads off to further examine the porcelain. Nobody can really truly tell from that picture. Also look at all 8

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Chenn2389

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I pulled all 8. The gaps were between .044-.052. They all looked "orange" I looked it up and its from the fuel additives in octane boost so that seems normal. I switched to autolite plugs and gapped them to .035. No change.
 

ttocs

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I was wondering about that myself. I was told to gap my plugs at .35 when I installed the supercharger but but I thought .54 was where they were supposed to be.
 

Chenn2389

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If you are n/a, stock plug gap in .054" What heat range of a plug?
Autolite 3924. Not sure the range I called Autolite and told them my set up and that was their recommendation. They came out of the box gapped at .035". Hanes manual says .052" stock. I have 331 stroker and the edelbrock heads have been milled down and comp ratio is 10.3:1 compared to the stock 9.0:1. I called up my engine builder and he said to gap them down to .035-.040" and if/when I run boost to gap down to .025-.030".
 

Wmac

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Autolite 3924 is the correct plug for Eddy heads. They are cheap, so why not pick-up another set, try a gap of 052-054. See how it runs.

Most plugs do not come pre-gapped and should always be checked prior to installation.
 

Chenn2389

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Autolite 3924 is the correct plug for Eddy heads. They are cheap, so why not pick-up another set, try a gap of 052-054. See how it runs.

Most plugs do not come pre-gapped and should always be checked prior to installation.
I measured all of the autolite ones prior to install, they were all at exactly .035". The motorcraft equivalents I used were anywhere from .044"-.052" with a mean value of .047" so I already tried plugs up there around the stock .052". I didn't measure them until after I pulled them. From what I been told is there is nothing to be gained running a larger gap than .040" on a modified engine with the comp ratio bumped up, but who knows. I'm thinking I'm having a sensor issue not an ignition issue. I pulled the wires with engine running one at a time and I was getting a massive arc.
 

Chenn2389

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I was mostly concerned about the orange coloration on the plugs. I didn't know the additives in octane boost did that but after reading some information on the web it seems like that is normal.
 

ttocs

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I measured all of the autolite ones prior to install, they were all at exactly .035". The motorcraft equivalents I used were anywhere from .044"-.052" with a mean value of .047" so I already tried plugs up there around the stock .052". I didn't measure them until after I pulled them. From what I been told is there is nothing to be gained running a larger gap than .040" on a modified engine with the comp ratio bumped up, but who knows. I'm thinking I'm having a sensor issue not an ignition issue. I pulled the wires with engine running one at a time and I was getting a massive arc.

Massive arc?
 

Chenn2389

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Each plug wire on the distributor one at a time at idle. The one 1,3,8 were arcing to the upper intake the rest started grounding to my hand so I didn't make it around all 8.
 

ttocs

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so you have a bad set of plug wires then. Do you hear a clicking/ticking sometimes? That is the arcing of the wires.
 

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