Blending fuel - snake oil or reasonable

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Iowa999
I don't mean to argue and what I say depends on the condition of the other pistons, but I've seen a partially-clogged injector do exactly that to a 4G63. The gas, in that case, was fine.

And, as I said, all of the injectors were sent away, tested, and cleaned. Results were that everything was a-okay before cleaning.

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EricW
I am 100% confident of bad gas. Car was PERFECT at RWV - all ECU logs showed no issues. If it was knocking at RWV, it would have melted down there - especially considering it was a two day event with huge elevation changes, lots of wide open throttle, and pegged boost.

Ring gap and everything was fine on teardown. No major blowby issues (catch cans were catching some mild fuel and oil mix depending on which can, but it was nothing dramatic. No increase or decrease in blowby after engine build and through RWV).

It is absolutely possible to finish with bad gas... but not if you're wide open throttle and you're keeping it out of the boost.

Since everyone is curious for for photos of the damage:

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The heads sustained NO damage. Just engine block and melted piston.

It's what makes a subaru, a subaru.

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Grant Hughes

Not trying to be argumentative, just wanting you to get to the bottom of this. I went through this once and found the 'smoking gun' problem which gave a positive indicator of what happened and what to fix.

Yeah, that looks pretty 'melty'....! Could be detonation but it does not look like a clear cut case of such; looks more like severe heating for some reason; could be detonation induced, could be other. No pitting anywhere that can accompany detonation. I like this discussion from a piston Mfr: http://www.kb-silvolite.com/features.php?action=read&F_id=46 Did you see any other similar damage or impending damage to the other pistons? How abou tthe plugs? All look the same or not? Some telltale dark spots on the pistons top side edges above the top grooves would probably (but not necessarily) have shown up if they were doing the same thing, which likely would be the case if it was the gas octane or contamination. If they are very different looking with no signs of any issues, I would wonder elsewhere than about the gas.

As mentioned above by another, I have seen this type of damage from a large ignition advance. Can it be the gas? Yes, but it could also be other problems.

Is this a standard O2 type sensor or what? If the AFR sensor got buggered and gave the wrong readings, the ECU would 'think' it was adjusting to the right AFR reading per the buggered sensor and would record perfectly good looking readings....but the real AFR would be wrong. And AFR being off due problems in one cylinder from some reason like a erratic injector or injector connector would throw the sensor off a bit and provide a partial adjustment to the problem but not enough to one correct cylinder that went way off. After this incident, I would certainly replace the sensor and that injector and check the connections reeeelly good.

And BTW more humidity at RWV might be of help in a marginal case presuming it acted to lower combustion temps and combustion speed: afterall, H20 injection IS used for smoothing the burn and giving the effect of octane boost. The cooler air temp and lower elevation at BRS would give more air density and more O2 and leaner burn if the ECU did not adjust for that, but a proper working AFR sensor SHOULD help to compensate for that, as well as the temp sensor to the ECU. IS the ECU working with a temp sensor? The higher air density is probably not an issue.... just thinkin'....

ECU runs in open loop mode. The O2 sensor is simply for logging/tuning feedback. It does not affect the actual normal running operations.

All other pistons looked fine.

O2 sensor is a wideband unit and not a typical narrowband unit.

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EricW


The heads sustained NO damage. Just engine block and melted piston.

Heh. That looks familiar.

Essentially everything in the crankcase covered in aluminium "splatter", I bet....

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Grants "it's what makes a Subaru a Subaru" comment made me recall a similar situation here in Colorado. Owner melted two motors during PPIHC week in very similar fashion. Turned out to be a bad fuel distribution block which was causing one cylinder to not get enough fuel. In his case injectors would've tested good.

I think I remember another subaru with issues related to the wiring harness under the intake manifold grounding out on something. Can't remember if it was misfire or boost related problems on that car though.

Dave

Quote
EricW

Knock did not cause this failure. Knock would have cracked the piston into pieces. You'd have broken ring lands, and there would be signs of detonation on the piston surface. All as someone else already mentioned.

To melt a forged (i'm guessing) piston like this, something fundamentally is wrong.

I do not believe the blame should be put on bad gas for this one, because if it was bad, all pistons would show signs (likely indication of detonation).

When you say "AFR's were fine", please give us numbers.

Are you sure that AFR's are ok at all running conditions? Is it ok at part throttle? "tip in"? high load/low rpm cells?

What fuel rails are you using? OEM? OEM rails in series (oem fuel line routing)? OEM Rails in parallel?

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Chris



Edited 2 time(s). Last edit at 01/16/2013 02:04PM by Do It Sidewayz.

Usually a single oxygen sensor is located in a position where it picks up an average AFR reading for all the cylinders, so presumably this means that if there is a problem with just one cylinder for whatever reason, be it a valve, injector, spark plug, inlet manifold air leak etc, then could it not be masked to a significant extent by the good cylinders? Especially when there was obviously still some kind of combustion going on in the duff cylinder.
If none of the other pistons are showing any visible signs of anything untoward it must be isolated to that particular cylinder.

Not on Subarus but I've seen a few brake servo pipe connections fail on inlet manifold runners in the past resulting in the cylinder that particular runner fed running lean.

I also spend an extra few seconds making sure the wrist pin circlips have the gap at either the top or the bottom. Maybe that is only something to bother with in a 10,000rpm engine though.

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Disappointingly not yet a Jackass



Edited 1 time(s). Last edit at 01/16/2013 01:16PM by danster.

Quote
EricW
ECU runs in open loop mode. The O2 sensor is simply for logging/tuning feedback. It does not affect the actual normal running operations.

All other pistons looked fine.

O2 sensor is a wideband unit and not a typical narrowband unit.

OK, tnx for patience with info. O2 sensor per se not the issue. Air temp sensor becomes critical for air density adjustments with the temp and humidty change of the RWV vs BRS case. MAP should take care of pressure altitude changes.

Going from 40F dry from 80 F humid changes oxygen content by around 4-5% for unpressurized. I am not sure how this effects octane needed; shouldn't if proper fuel corrections are made for temp unless there is some off threshold effect of the final compressed air temp going on. Will do some reading as it is an interesting question. (to me)

Temp sensor located where? Tested OK? Mapped into the ECU program for temp variations? Margins for more oxygen when cool and dry? Yeah, proably dumb questions, and probably already thought of by you long ago and in the programming; just checkin'.

Quote
DaveK
Grants "it's what makes a Subaru a Subaru" comment made me recall a similar situation here in Colorado. Owner melted two motors during PPIHC week in very similar fashion. Turned out to be a bad fuel distribution block which was causing one cylinder to not get enough fuel. In his case injectors would've tested good.

Wow, I bet that was not easy to find.

Just ran across a graph of octane versus temp and relative humidiy to avoid detonation in "standard auto engines". The engine at 80F/80%RH needed < ON85. The same engine at 60F and 20% RH needed > ON88. (The ON change was approx another point bigger for 40F and low RH but the octane changes at lower temps get small.) Seems like a big ON change.

Not sure if this does anything for your situation, Eric, except to make sure there is margin in the ECU mapping to account for low temp, low humidty situations; otherwise the same xyz octane gas will be OK at a warm, humid RWV or STPR or NEFR, but will not be OK at cool, dry BRS or LSPR.

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The heads sustained NO damage. Just engine block and melted piston.

Heavenly god! How the hell is that even possible without Aliens acid for blood?

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Kirk Coughlin
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darkknight9

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The heads sustained NO damage. Just engine block and melted piston.

Heavenly god! How the hell is that even possible without Aliens acid for blood?

Pretty easy...I have a set that looks more or less like that...
2 heat ranges too hot on the plugs, bad fuel feed and fuel rail set up because of the bizarre engine being half here and the other half somewhere way over there...pretty easy...

But, being forged pistons they didn't shatter into 100 pieces so the crank and block is salvageable if somebody chose to salvage it...

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John Vanlandingham
Sleezattle, WA, USA

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Interesting thread, and I'm sorry that I'm seeing positive discourse from your unfortunate event!

Starion887 mentioned timing being too far advanced which took me back to high school. I was into Type 1 Beetles back then, swapping the OEM distributer with a Bosch 050 on a built motor was common place. Of course so was trying to get as much power as possible by advancing the timing. When the timing was advanced too far, the #3 piston suffered a meltdown. Now I can't rmember the reason but "seem" to remember that #3 was more affected than the others because it was the furthest away from the oil pump.

I know zilch, zip, nadda, about Subie engines (yeah ok I used engine and motor for the same reference in one singular post, my bad) other than them being pancakes. That said, my high school failure in the Type 1 got me thinking about why the one particular piston in your case melted. Why that one and not the one beside it?

Could lubrication (lack of) or cooling play a part in it's failure?

Later in life (but still years ago) I raced stand up jet skis and organized events. Including one in Mr. Bottles backyard... on Spencer Spit on Lopez Island. The event was with the permission of Washington State Parks, which was difficult to obtain from a Canadian Company doing the event in the US. Launching from Anacortes with chase boats (graciously donated by ABC Yacht Charters in Anacortes) a large group of Jet Skiers crossed through Thatcher Pass to arrive for the event at Spencer Spit. Seems like eons ago... 1989! (But fuck was it fun!)

Steve "Cosmic" Miller (The Man, The Myth, The Legend - as Splash jet ski magazine coined him in an article) had a Jet Ski performance shop just off the I-5 in Everett. He lived on Lake Stevens and tested all his builds there. I had 2, a Kawasaki X2 and a Kawasaki 650 SX. Standard bolt on mods, hi comp head, SS impellers, 44mm Mukini's, etc were common place.

I got a little off topic, remeniscing (sorry about that!). Anyways Steve knew his shit, and there was no one North of California with his knowledge.

Okay here's the point... When I had an engine failure and didn't have time to trailer my ski down to Everett I went to a local Kawasaki shop that did the rebuild. They messed up the air/fuel mixture and I melted a piston the first time out. Granted it's a 2 stroke and nothing like a fancy Subie, but is it remotely possible that air/fuel ratios could be a play in your failure? Presumably the ECU, the tune, etc have fail safes (again I know very little about these topics), but is it possible that there's somthing the system isn't able to diagnose?

Sorry for going off topic slightly...



Edited 1 time(s). Last edit at 01/17/2013 10:34AM by RWD4ME.

Blending:

Has anyone mixed Xylene with pump gas in order to increase the octane?

I seem to remember reading that adding 30% Xylene to 92 Octane, yields 99.5 Octane.

Is this true? (I mean does anyone have real life experience)