Is premature #3 piston failure "normal"?
 

Picture of broken shit to get your attention:

https://www.miataturbo.net/attachmen...ine=1389248544

So here's the deal: We've got this here turbo 1.6 LeMons car. You might have heard of it. If not, here's the short version: Stock B6, pretty much a WRX turbo (with some Mexican Dodge bits mixed in) on a stock exhaust manifold. '99 injectors, BIPES, FMU, coolant reroute. Somewhere between 5 and 9 psi of boost depending on the boost creep gods. Usually 199 at the wheels when we put it on the dynojet at MD Automotive.

Long version is here: Project Frankenmiata (turbo info itself is on the second page and the info is kinda out of date)

With that background out of the way, here's the issue:
Roughly every 160 hours of relentless track flogging, we blow a head gasket. The gasket failure is a side effect of detonation damage in on the head surface.

https://www.miataturbo.net/attachmen...ine=1389248544

The pitting eventually gets severe enough to open up a path between the combustion chamber and coolant passage.

The first time this happened we thought it was funny. We fixed it overnight with JB weld and raced the next day until we threw a rod (which had been damaged when we hydrolocked a cylinder trying to start the car with a blown head gasket)

When it happened a second time, it was just annoying. Of course, we JB welded it faster this time and then raced it for another 10 hours, but still, having the same failure more than once isn't cool.

The failure mode both times is exactly the same. There is some detonation damage in every cylinder, but by far #3 is the worst, and it is only on the intake side of the combustion chamber. The damage to the head stops the party first, but the damage on the intake side of #3 piston is also quite alarming:

https://www.miataturbo.net/attachmen...ine=1389248544

Keep in mind that this piston has 10 hours of track flogging on it AFTER things got bad enough to blow the head gasket, so its a rather extreme example of abuse and neglect.

So here's the point of this post (besides the sharing of broken engine porn): Have anybody else noticed a pattern of #3 running hotter/knocking more? Has anyone else seen this consistent intake-side detonation damage?

We'll be pulling a few degrees of timing and dropping compression a bit for the next engine, but we'd still like to figure out the #3 thing so we can give the other cylinders an equal opportunity to fail.

I dont know if this will help much, but the same thing happened to my B6 when I had an injector fail on me and since it was only functioning at 1/4th the amount it should have it was not pretty.

Number 3 injector is not squirting as much fuel?

Holy detonation, Batman. No, that is not normal.

I agree with the above comments; check your injector/fueling.

I feel like I'm back on the old air-cooled VW listserv, talking about premature wear to the #3 piston... (It was a chronic problem in the pre-1971 engines, due to the layout of the cooling system.)


Foxy 'leet squirrel is correct- this is almost certainly indicative of the injector in the #3 position failing to deliver as much fuel as the other three. If your budget allows, pulling all four injectors and sending them out to sexy nurse racing for a flowtest - clean - flowtest regimen will likely confirm (and cure) the problem.

Dave - are you guys running any sort of coolant re-route? I can't remember, I haven't read the article in a long time.

Usually, without a coolant re-route, cylinder 4 will have premature (more accelerated) wear/detonation because of the temperature variation in the cylinder head (ie cyl 4 runs more hotter).

As others have said, problems with cylinder 3 specifically are not normal.

LOL, massive detonation to just one cylinder is NOT normal. I guess some would say if there was a "normal" cyl to fail, it would be #4 due to the deficiencies in the stock cooling setup, but still that is ridiculous detonation.

Not only do we have a re-route, we have the re-routest re-route ever:

Project Frankenmiata - The Ultimate Miata Coolant Reroute > MotoIQ - Automotive Tech, Project Cars, Performance & Motorsports

For those who think this is a sign of severe detonation, think again. Severe detonation is audible and this is not (though helmets do make it harder to hear things). This seems to be very minor detonation or rough combustion repeated over and over and over relentlessly. Gotta remember, we beat on this car longer and harder than you can possibly imagine.

Maybe your BIPES setup is pulling massive amounts of timing, causing high as hell EGT, and thus a melted piston? I looked again, and actually could agree with you. There isn't any visible det on the rest of the (not melted side) of the piston.

https://www.miataturbo.net/attachmen...ine=1389281712

Ceaseless light detonation is overheating the lean edge of the piston. Flow-test injectors.

Consistently, on one cylinder only, and without harming the exhaust valve?

This is a fuel problem.

Injector was our first thought too, but we actually ghetto-tested the injectors and #3 was right in the middle of the data noise. No sign that it is flowing less than anything else. Different spray pattern perhaps? Impossible to tell with our test, but hard to imagine what could change the pattern without changing the flow rate.

Having all the damage on the intake side is what really baffles me. Exhaust side seems more likely.

Also the damage is not ONLY on #3, it is just very minor on the other cylinders.

I'll try to put the ghetto testing video up soon to explain how we did it...

Intermittent fault in the wiring to the no.3 injector? Unless it's batch fuel and this makes no sense.

Well, how about doing a barrio-test wherein you swap the injectors between the #2 and #3 positions?



Given the amount of power you're making, and the amount of engine management you're using to do it, I can't say that I'm surprised by this.




It's a 1.6, and I'm pretty sure that they didn't sneak a new ECU into the $500 budget, so I'm guessing batch.

The likelihood of an intermittent open-circuit fault occurring within the INJ harness itself, while not completely unimaginable, seems remote.

IIRC, cyl3 is indeed the one that runs hottest once you reroute the car. It's not significant, but it's enough (apparently).

I've only ever destroyed one motor due to detonation damage (likely caused by high IATs), and interestingly enough, it also occurred on cylinder #3. Same thing as you - light damage to all the pistons, heavy damage to one. That's anecdotal to the hilt, but still interesting.

Where the hell did this come from?

Foxyroadster, rleete and secretsquirrel all posted essentially the same thing, thus I virtualized the notion of authorship of the idea down into a single composite abstraction.

And it turned into some weird furry thing.

We will move the #3 injector, just to see what happens, but I don't really want to perform a 2-year test to destruction as my only move.


No, the surprising part is that it takes 160 track hours for it to finally break something...

Are 1.6 ECUs supposed to be batch? When we tested it by spinning the cam angle sensor, it fired sequentially. Does it go batch above a certain rpm?

I have had injector sub-harness failures on other cars before (SE-R rally car) and its a pretty binary failure. That injector fires sometimes, doesn't fire sometimes. When it doesn't fire, your car sounds like a Subaru. We have had occasional high-rpm misfire issues, but they're spark related, since closing the gap up solves the problem. Take one look at the rat's nest we use for a wiring harness and you'll see that there is a high probability of wiring issues. Still, we would feel a misfire..

Didn't cali cars have sequential fuel?