What'd I break?
 

I've got about 1500 miles on my built motor, I'd gradually bumped the power up to where it was making around 300whp. Last weekend after about an hour drive, I got into it and could hear it detonating really bad. I drove around a minute and it seemed fine. I rolled into the throttle as I watched the wideband, as it came into boost it'd go to 15:1 and start to hear knock again. I babied the car back home; swapped the fuel filter, checked fuel pressure (good), and swapped the plugs.

These are what I pulled out:

Left to right: 4, 3, 2, 1:
https://www.miataturbo.net/attachmen...ine=1393028966

Left to right: 4, 3, 2, 1:
https://www.miataturbo.net/attachmen...ine=1393028966




After putting the new plugs in I pulled 5 degrees of timing from my timing map (that had previously been fine). Let the car warm up, and started to make a pull. It knocked exactly the same so I let out of it and brought it back home.

I'd been considering swapping to E85 so I drove 12 miles to the nearest station, topped off, and added fuel to the tune. The car was reading rich, so again I attempted to roll into the throttle with the same result, horrible detonation. I drove back home and pulled the plugs to find

Top to bottom: 4, 3, 2, 1: cylinder 4 smells of well cooked oil
https://www.miataturbo.net/attachmen...ine=1393028966






So I pulled the head

Cylinder 4 (No holes, yay!)
https://www.miataturbo.net/attachmen...ine=1393028966

https://www.miataturbo.net/attachmen...ine=1393028966

https://www.miataturbo.net/attachmen...ine=1393028966




Head

4:
https://www.miataturbo.net/attachmen...ine=1393028966

3:
https://www.miataturbo.net/attachmen...ine=1393028966

2:
https://www.miataturbo.net/attachmen...ine=1393028966

1:
https://www.miataturbo.net/attachmen...ine=1393028966


So given those results, what is the prognosis? Anything you see here that you'd say is definitely the source of the oil? Greatly appreciate any suggestions.

Running out of fuel under power ?

weird, it looks like 1st time around 1 and 4 were lean and possibly detonating, then 2nd time around 2 and 3 were lean
also 4 kinda looks like it had a bunch of blowby
possibly 1 as well

I should have plenty of fuel and it seemed fine before, but I'm definitely going to pull the injectors out of the rail and look them over.

Ehh, now that you mention blowby, I did blow the dipstick out last week. It only happened once, so I was hoping it just wasn't pushed in all the way to start with, but probably not a good sign.

What is your ignition setup like? Cops? Coils? Tell me more...

I failed to look at your sig...I was seeing 1&4 looking different than 2&3 so I assumed that if 1&4 fire at the same time perhaps weak spark on that side? But you have cops that fire which cylinder when?

I've got Toyota COPs on an otherwise stock ignition. 1/4 & 2/3 are paired so they fire at the same time. I suspected I had an issue with the wiring on them. I pulled the wiring all apart after my last drive and it looked solid to me. That's when I pulled the plugs again and saw the oil on cylinder 4.

I've definitely got some underlying cause that suddenly made the car run poorly, but my main concern at this point is identifying the hole between where oil is supposed to be and where oil is not supposed to be.

When were the valve seals last replaced? Oil doesn't ignite well.

Valve seals were done when the motor was assembled, about 1500 miles ago. There's not any way to check them without at least pulling the cams is there? It'd be awesome if that was the problem.

Nope. In fact I'm pretty sure you could take them out and look at a used one that was sealing well and a used one that was leaking and have no idea which is which.

Looks like lots of oil in #4. Rings or valve seals?

Did you compression test it?

I didn't compression test it, probably should have I guess. I just felt like that much oil in the cylinder is going to distort numbers a lot.

I've got no experience at all in this stuff, but I keep looking at that top right oil passage hoping it had somehow found it's way into the cylinder.

https://www.miataturbo.net/attachmen...ine=1393028966

Oil will cause detonation like a champ. You obviously have oil in cylinder 4 did you check the head gasket to see if it has a hairline crack on that cylinder or possibly a void going to the oil passage?

purely speculative based on the fact that where oil is burned, it tends to look whitish/tanish on my spark plugs (and online pics/reading)...I would think the top left valve seal is a likely culprit.

if you puke oily substance out of your tail pipe after letting the car sit, its probably a valve (seems more likely to happen with exhaust valves too). I noticed that hard running, then letting the car cool off, then starting it up, my car will "puke" some blackish substance. Initially I was thinking carbon build-up + condensation, but I am more convinced its oil sitting inside my valve and getting shot out on startup especially since it still happens after getting a new cat.

Mostly speculation on my side and a lot of reading online, but...If one spark plug has the "oil burn" build-up on one side, its usually the side closest to the valve that is leaking. If its pretty uniform, its usually not from the valves (I suppose it could be all the valves...), but piston/rings/maybe gasket??

I wish you would have at least done a leakdown test like i recommended in your thread. That can really help diagnose things before you tear them apart like this. It's really hard to tell from the looks of it but I'd have the head checked first since its off anyways at this point.

Yeah, with that much oil I figured the results would be skewed, plus I was really expecting to see a hole in the piston anyway.

A friend suggested pouring oil in the cylinders and seeing if one leaks through quicker than the others, I'm gonna try that tonight. If that checks out I'm going to clean it up and slap it back together. I bought a cometic headgasket, apparently they're reusable so I'll give that a shot and see what happens.

Yeah, the oil really would have skewed a compression test - but a leakdown test at ~100psi should push past the rings even with oil helping to seal them. It would also clearly tell you if you have a valve issue going on or not.