Our cars can't correct for bad or lower octane gas. But some modern performance cars check for knock readings and adjust timing and such accordingly. So yes they can detect bad and good gas but our cars don't.

I'm not sure if this correction would work on a rotary though because by the time it knocks its *usually* to late.

thewird

 

Hey Classic, thx for chiming in.
The apex seals are of an upgraded version. so i am again speculating that the detonation took out the weakest link, that being a side seal?

But like i posted before, i didnt see any signs of detonation when the motor let go and i thought it was due to my high oil temps and high oil pressure. What are your thoughts on this? What would u attribute to losing a side seal too?

 

The problem with the turbo CFM analogy is because (generally speaking) you're comparing 2 turbos at say 15psi. One will heat the air up 10-20F more to achieve 15psi, the other (larger turbo) won't......which is where that analogy differs from the elevation discussion.

Yes, the 02 is the key here. However, more or less oxygen wouldn't matter in regards to fuel cut. I'm unfamiliar with how fuel cut is operated (or which options are provided to operate it) with a PFC, but typically its reading strictly pressure. So if he wasn't hitting it at 15psi one day, and the next day it hit "fuel cut" at the same 15psi then something else has happened (ie. misfire, detonation etc.) presuming the fuel cut was set above 15psi. EDIT: Or there was a boost spike for whatever reason. Its not going to hit fuel cut until the computer sees the preset fuel cut value, it won't know the altitude or care about 02%

 

The PFC will fuel-cut if you go 0.25 kg/cm^3 over the "target" boost level, even if you have an external boost controller. It will also fuel-cut if you go over the rev limit. These are all tuning settings.

thewird

 

Well, depending on the situation there are alot of thigns that would blow a side seal. However, detonation is very low on that list. One of the main reason's I wouldn't figure det. as the culprit of a broken side seal would be their placement on the rotor in regards to the flame front. When the spark plug lights the fuel mixture and that flame front tries to escape, the only items directly in the path of its escape are the face of the rotor, the iron, the trochoid of the housing, and the apex seal. In order for the massive pressure from a misfire/lean condition to hammer into the side seal it would need to hit the rotor, and then squeeze in between the rotor and the iron....for simplification, think of a piston engine and its level of knock resistance. Imagine how fragile the piston engine would be if needed to be sealed directly around the top face of the piston?

However there's alot of factors at play here so don't rule it out as a cause, but I do know that if there was some detonation that your apex seals, upgraded or not, would be the first things take the abuse. Take for example Dave (rxHeven). His tribulations in the NRS thread........a 3mm 1 piece ceramic seal was broken on the dyno with BDC at the helm. A main pulley mismatch caused roughly 10* too much advance...................his side seals were fine.

Regarding the high oil pressure/smoke. I'm not sure how they would be tied to the failure other then the fact that a side seal, while sealing combustion in the chamber, is also thereby keeping it away from the oil control ring. If the side seal chunked, you'd have all kinds of nasty pressure blowing against the respective oil control ring and that could cause a mess of problems....

 

Fuel cut will happen when there is not enough Fuel for the amount of o2 in the engine. So it will cut fuel instead of detonating.

Which in Smitters case makes perfect sense. More o2 in the air in MB, hence whey he never had fuel cut here, because his fuel maps are tuned for the amount of o2 in Calgary. Also like he stated before, 12 PSI felt like 15psi or better, well this would be because probably at 12 PSI he had as much o2 in his Charged air as he did at 15 PSI in Calgary.

I guess his fuel maps maybe should have been a bit more safe, not sure about that im no tuner though.

 

But the fuel cut is not based on oxygen percentage. EDIT: Also, that definition is fairly inaccurate. Fuel cut is designed to prevent detonation yes, but does so by effectively shutting the engine off (by cutting fuel) when you exceed the level of pressure either specified (in the case of the PFC) or preset by the factory.

For the sake of discussion, lets say fuel cut was set at 16psi. According to Marco, you must exceed the preset limit for a given time to set off fuel cut. Therefore, the engine must have seen more then the preset fuel cut amount in PSI (regardless of altitude or air density!) before going off. If its denser, it would be easier to make more boost, but the fact remains that you *must* exceed the limit in order to activate the fuel cut. It won't simply cut fuel at 12psi if its at a lower altitude with denser air because it has no way to judge that.

 

Yea that works. I thought it calculated the air/fuel ratio for fuel cut more then PSI of boost. So there ya go learn something new everyday. So about fuel cut not sure, i guess Smitter may have actually over boosted. That would be a question for him though.

 

Out of curiosity, what did this fuel-cut feel like?

thewird

 

thats how.

 

what does this mean to u guys?

http://www.fd3s.net/fuel_cut_info.html

 

Didn't you feel it on Sunday....first pull?

 

That is for stock ECU.

thewird

 

I should be saying anything as i don't have time to read all 7 pages but this isn't the first car I've heard of exploding due to different altitudes, turbo or NA, now matter who tunes them this still will happen.

Also the factory system has a barometric sensor that allows u to drive at different altitudes. a couple stand alone ECU's don't have this sensor. my haltech does, but i haven't had the time or the need to drive to various cities just to tune the baro map.

 

I've only glanced at the last few pages however here is a blanket statement I think applies. If the motor is built properly, paired with the right fundamentals, if a proper EMS system is utilized, and tuned by someone who knows what they're doing, the idea that altitude changes like those discussed would cause a blown motor is pure nonsense. If you think that altitude change caused catastophic engine failure I'd go head hunting for either the engine builder or the tuner, or go looking at the parts you supported the motor with.

 

You may have "heard" these things and believed the altitude was the problem but the diagnosis is incorrect. Something else was wrong with the car that caused the problem. Using altitude as the scape goat is only covering up for the real problem which was either a mechanical failure or a failure of the tuner/builder. Otherwise we wouldn't be able to drive anywhere with elevation changes. I think TD07 put it as plain as you can.

 

*smiles*

thewird

 

thanx for the help and information in getting my vehicle tuned....

the comrodery is appreciated....

// End Sarcasm....

 

As mentioned before those are the stock figures. Fuel cut is mapped for absolute pressures - which is what your MAP sensor reads. Obviously the stock ECU is mapped to cut fuel at different absolute pressures for different RPM. Absolute pressures are the same - no matter what the altitude is outside the car. I'm not sure but I'm thinking you are having difficulty with the concept of absolute values. Think of it this way. Absolute 0 in temperature is the coldest you can get - it's the absence of all heat. Whereas 0 degrees celcius is +273 degrees higher. Absolute 0 in terms of pressure is a perfect vacuum.

The only reason they make reference to "Sea Level" cut-off is because that is what your boost gauge is referenced to - as they clearly state. Your boost gauge does not reference atmosphere like the MAP sensor does. It is calibrated to read correct at 14.7 psi (sea level).

Here is a good write up on why a MAP sensor works and how using the speed density method altitude is not relevant. Note that the MAP sensor can be used to check barometric pressure but that it has no bearing on the fuel needed in the engine. The barometric pressure sensor in a car/Haltech/etc. isn't used for fuel calculations. Maybe this will help eliminate any doubts you have when we tell you that altitude was not responsible for your problems.

http://en.wikipedia.org/wiki/MAP_sensor


As for your assumption you were hitting fuel cut - it could just as easily been something electrical or something fuel related like bad fuel, injector lock, etc.

 

Just look how much you are learning about EFI systems! You'll be a troubleshooting god after this. Just don't blame altitude for all your problems.

 

Another nice write up on EFI theory by aviation enthusiasts. Who would know more about altitude variations than these guys?

http://www.zafr.com/flymanaged/efi.htm

Note they too say that once started the BARO sensor is no longer need if using a MAP sensor and the Speed Density method.

 

Using the Speed Density method - which most EFI systems use - the base would be the same regardless of what altitude you tuned it at.

As for traction problems, there are many other factors to consider like hotter tires, hotter pavement, etc.

 

Ok, well i believe we can come to a conclusion, that we are all possibly wrong about what happened in Smitters case. Who knows, be it alt difference, tune, or what have you. But what i do know is through this thread there is lots of good info regardless. So Lets call er quits on the arguing, and have a beer.

 

^^uh, who exactly was arguing? i thought it was just a discussion.
Thx for all the info guys, i still dont know what happened to my motor though. i guess its all just speculation at this point

 

^^ maybe too early in the morning to be posting.