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Wierd plug readings, toastied #4 piston.

Old 03-30-2007, 01:38 PM
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Default Wierd plug readings, toastied #4 piston.

Yesterday's victim was a sleeved D16Z6 with CSaddict short ram, Crower cam, high-Z RC550cc, Disco-P. Car has a history of toasting #1 and #4 pistons due to some installer error and eGay-equivalent basemap boostage, but the engine was a fresh rebuild from a machinist and a builder that I trust, that had all of a handful of warmup cycles on it as well as a 10 minute 30 mph no-boost granny drive to make sure there were no leaks, etc.


I stepped to the car yesterday morning, have never had a basemap turn out like that. Import Z6 map into P30 code, add all the boost/fuel tools/datalogging features, recurve the injectors, project 120% VE fuel maps, etc. Car started up perfectly and during part throttle tuning was at all times within .5 AFR of target, same for boost up to 8 psi or so.

I made 248 whp @ 12 psi and 7700 rpms on a Mustang after seting AFRs and playing around with ignition, and plugs 1-3 looked like sweet perfection... plug 4 had some silver on the ceramic. Not silver-grey speckles, the usualy round speckles, bright shiny silver laid in tiny flat-against-the-ceramic splatters. There weren't a lot of them, but it was obvious. I added 4% fuel to #4 because it alarmed me, and didn't check them again, which might have been a bad error on my part.

Three pulls later the car is running ~17.5 psi with 11.3:1 to 11.7:1 AFRs... and it starts laboring 7000 to the 8200 rpm revlimit. The power dropped off HUGELY on the dyno graph 7000+. The engine at idle sounded like valve train tick, but the owner said it was piston slap. He's very familiar with that sound in D-series by now, so I defer to him on that until a teardown takes place. Plugs 1-3 still looked like sweet perfection, #4 had been detonated on so it was solid semi-metallic grey, and the top of the #4 piston was black, dry, with light pits in it where 1-3 were still shiny with no carbon formed on them yet.

Anyway, long story short, has anyone seen *shiny* silver on spark plug ceramic before? I'm pretty good at identifying between ignition related, AFR related, knock limit related, and the classic chocolate milk "you just caught the headgasket, stunna" signs of detonation from looking at relatively fresh plugs these days, bu this one is a freaking curveball.
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Old 03-30-2007, 01:58 PM
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Default Re: Wierd plug readings, toastied #4 piston.

is it possible the rings didnt set very good in cyl 4 and the metal shaving from scratching the block go in the cumbustion chamber ?? maybe the det. burnt the rings up a little cause the clearance wanst tight enough ??
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Old 03-30-2007, 02:48 PM
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Default Re: Wierd plug readings, toastied #4 piston.

Well here goes nothing... Something bad on the rail?
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Old 03-30-2007, 03:29 PM
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Default Re: Wierd plug readings, toastied #4 piston.

Maybe, oso, I don't see how else aluminum flies around and adheres to ceramic.

Mike, that would have resulted in traditional detonation of the sort I'm used to seeing. I think the cylinder underwent some friction-related heating and it bound somewhat in the bore causing the drop in power over 7K, and the heating from that at that power level caused the detonation visible after the 17.5 psi pull. Teardown takes place this weekend, unless Rob comes to Pinks with us.
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Old 03-30-2007, 04:48 PM
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Default Re: Wierd plug readings, toastied #4 piston.

#4 injector clogged at the little filter, or just lacking in general?
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Old 03-30-2007, 05:09 PM
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Default Re: Wierd plug readings, toastied #4 piston.

Did he cheap out on oil? All I can think of it starved somehow
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Old 03-30-2007, 10:39 PM
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Default Re: Wierd plug readings, toastied #4 piston.

You don't just starve one bore of oil and the rest of the bores look sweet and clean at what was a 270-280 whp (310+ Dynojet) power level. If one starves, they all go, but not before all four rods lock to the crank and tear holes in the side of the block. I'm pretty sure it was starting to bind in the bore before it REALLY siezed up 7000+; power wasn't increasing a lot as the boost went up. In fact, AFRs were right in line with what they should be while power plummeted. I really need to get the dyno logs and post that run, it was making 270+ but dropping over 100 whp of that figure pushing #4 up and down.

It's been making me sad all day, it was running so well I thought it was one of those magic engines where everything goes so right.
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Old 03-31-2007, 12:31 AM
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Default Re: Wierd plug readings, toastied #4 piston.

Ive yet to see metal on a plug, just the black peppering. Did #4 plug have more white ash on the ground strap then the rest of the plugs? Are you using a stethoscope yet?

That thing was making good power on a Mustang dyno.




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Old 03-31-2007, 01:10 AM
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Default Re: Wierd plug readings, toastied #4 piston.

No white ash (oil) at all on any of the plugs.

No stethoscope.

Like I said... I thought it was a magic car... turns out it was 3/4 of a magic car.
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Old 03-31-2007, 02:46 AM
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Default Re: Wierd plug readings, toastied #4 piston.

Originally Posted by Mista Bone
#4 injector clogged at the little filter, or just lacking in general?

I'm with Bone on this one. Those shiny flakes are basically from the piston from lack of fuel.

Post up the dyno sheet. Any dips or wavyness.


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