melted no 5 piston

[mellonman]

Hi

i was at my monthly karting and a guy there said he had a supra so we got chatting and he said that he had melted no5 piston when doing a 185mph run because he lifted off the throttle completly and said this was a common fault with the supra due to once you lift off there is no longer a 12v feed to the pump or something like that,

Is that true ?

he had a bpu tt auto jspec non vvti

[cje001]

I`d like to hope not!?

[Tricky-Ricky]

The injectors are shut off when the throttle is completely closed, but in any case if there is no fuel then there is no combustion, so i can't see it, sounds more like detonation has caused it to me.

[hodge]

Where the feck was he doing 185mph.

[Wez]

[Nic]

he had a bpu tt auto jspec non vvti

 

Where the feck was he doing 185mph.

 

.........down a very long hill with a tail wind

[Animal]

He wasn't re-enacting the movie Speed, was he?

 

"Sorry officer, I can't slow down or my engine will blow up..."

[Ian C]

The injectors are shut off when the throttle is completely closed, but in any case if there is no fuel then there is no combustion, so i can't see it, sounds more like detonation has caused it to me.

 

This

[mellonman]

The injectors are shut off when the throttle is completely closed, but in any case if there is no fuel then there is no combustion, so i can't see it, sounds more like detonation has caused it to me.

 

I think thats what he was trying to say , because there was no fuel the piston got hot as it was slowing down with high rpm and no fuel to cool it.

 

Where the feck was he doing 185mph.

 

he said the m2 (i does have a nice long hill )

[Ian C]

I think thats what he was trying to say that because there was no fuel the piston got hot as it was slowing down with high rpm and no fuel.

 

It sounds to me like he was saying it ran lean because the fuel pump voltage dropped, which is wrong, as the injectors would be off anyway. It melting due to no fuel or spark at all is even more ludicrous, what exactly would cause the damage with nothing to burn and nothing to ignite it? If we are going for 'friction' I'm leaving now before I swear

[Soopra]

Hi

i was at my monthly karting and a guy there said he had a supra so we got chatting and he said that he had melted no5 piston when doing a 185kph

 

edited for accuracy

[skippyboyo1]

sounds a load of rubbish to me

[mellonman]

If we are going for 'friction' I'm leaving now before I swear

 

i do think thats what he was trying to say,

but it would be more to leaning out at top end with standard injectors right?

he also said he found out it was a common fault with the supra 5 & 6 running lean?

i have heard the running lean on 5 & 6

 

now i had some work done and they said this to me so they said they would plum in my fuel rail with 6 & 5 being first fead from the fuel filter, but after some thought im thinking this would be worse due to the fuel flow fighting g's (pull of the car where you get pushed back in the seat )

so if it was plumbed 1-6 it is helped by the pull or g.

does that make sence or am i talking out my bum

or does it not matter as the pump will be man enough to push it

[bignum]

Why do the uk/euro spec`s have the air scoop on the bonnet;)

[little num]

I know im going to get slated for this BUT when we do the Nurburgring laps at the very end when you go under the gantery the EGT'S go sky high when you let off totally.

Its soon comes back down when the clutch pushed in and revving it slightly to get fuel in pistons.

So maybe if it was weak anyways then it might of not helped.

[mellonman]

I know im going to get slated for this BUT when we do the Nurburgring laps at the very end when you go under the gantery the EGT'S go sky high when you let off totally.

Its soon comes back down when the clutch pushed in and revving it slightly to get fuel in pistons.

So maybe if it was weak anyways then it might of not helped.

 

intresting !

so there is some trueth in what he said then, he did seem to know abit about tuning but you just never know

[Tricky-Ricky]

i do think thats what he was trying to say,

but it would be more to leaning out at top end with standard injectors right?

he also said he found out it was a common fault with the supra 5 & 6 running lean?

i have heard the running lean on 5 & 6

 

now i had some work done and they said this to me so they said they would plum in my fuel rail with 6 & 5 being first fead from the fuel filter, but after some thought im thinking this would be worse due to the fuel flow fighting g's (pull of the car where you get pushed back in the seat )

so if it was plumbed 1-6 it is helped by the pull or g.

does that make sence or am i talking out my bum

or does it not matter as the pump will be man enough to push it

 

 

I know im going to get slated for this BUT when we do the Nurburgring laps at the very end when you go under the gantery the EGT'S go sky high when you let off totally.

Its soon comes back down when the clutch pushed in and revving it slightly to get fuel in pistons.

So maybe if it was weak anyways then it might of not helped.

 

 

First off on a BPU supra you shouldn't be seeing weak AFRs unless there is a problem, as they will run over rich as std, IE its not unusual to see AFRs in the 9s and more usually 10s.

As Ian and i where saying, its not possible to melt a piston when there is no combustion, the pistons and valves would have to be more than red hot, and once combustion has ceased IE no fuel, the engine is still pumping air which will instantly cool it.

 

Little num where was your EGT thermocouple? in the exhaust manifold runner, or the turbo? as you will see higher EGTs when lifting off from a high speed/power run as the turbo heat is transfered to the rest of the system, and this Will be hotter than the in cylinder temps.

Edited May 16, 2011 by Tricky-Ricky (see edit history)

[mellonman]

haha i love the added for me talking out my bum

[bignum]

I know im going to get slated for this BUT when we do the Nurburgring laps at the very end when you go under the gantery the EGT'S go sky high when you let off totally.

Its soon comes back down when the clutch pushed in and revving it slightly to get fuel in pistons.

So maybe if it was weak anyways then it might of not helped.

Oh yeh i`d forgot about that, noticable increase in egt`s on liftoff, probe mounted in runner 1 just to confirm.

[Ian C]

Anyway, forget about "melting", it's a misleading phrase. Your exhaust system can withstand 1000degC, so your pistons bloody well can stand a lot more than that. The "melted" effect is detonation, which is actually more of an arc-welder sputtering erosion of metal. Nothing is going to withstand that. Temperatures too high in the combustion chamber (high EGTs) or a weak mix (high AFRs) can cause hotspots or an explosion fuel/air mix or both, and that explosion rather than a controlled burn causes the erosion of metal off the pistons.

 

Once you stop combustion there is no physical way at all to come even close to 1000degC inside the chambers, and that's a temperature it can withstand anyway. And with no fuel and spark, you can't get detonation either, it too is physically impossible. That cylinder 5 died due to hotspotting or a weak mix and blokey lifted off straight away because he felt a sudden and dramatic loss of power - the damage was already done.

 

As for the EGTs rocketing up when you lift off, here's my thoughts. After a high boost run, suddenly you have practically no exhaust gas flow velocity because the throttle plate is shut and the engine is pulling a vacuum. All the gas now hangs around for ages between the combustion chamber and the (restrictive) turbo. Heat more readily conducts into the temperature probe, so the reading rapidly goes up. A blip of the throttle with the clutch in, and therefore off-boost, pumps a cooling draft of air and gas through, vacating the old hot exhaust, and cools it back down again

[mellonman]

bloke lifted off straight away because he felt a sudden and dramatic loss of power - the damage was already done

 

This is propably true

 

as is the rest of your statment !!

does make complete sence but thought i would see what people here said as he did say it was a common fault and said about a 12v feed in the boot for a pump mod which i have herd before some where for something

 

i will point him in the clubs direction for some correct knowledge

[stevie_b]

said about a 12v feed in the boot for a pump mod which i have herd before some where for something

 

This? --> http://www.mkivsupra.net/vbb/showthread.php?240328-fuel-pump-12v-mod-2jzgte-jdm-supra

 

It doesn't come highly recommended. Did he say he'd done it, hasn't done it, should do it, shouldn't do it?

[mellonman]

This? --> http://www.mkivsupra.net/vbb/showthread.php?240328-fuel-pump-12v-mod-2jzgte-jdm-supra

 

It doesn't come highly recommended. Did he say he'd done it, hasn't done it, should do it, shouldn't do it?

 

i think he must be on about the same thing, he was saying once he has rebuilt the engine he will do it, but as in this thread i think he is thinking of a fault that couldnt happen and trying to over come it he was saying something like the voltage drops from 12v to 4v once you lift off all the way.

sorry i cant really explain much as its not my car

[Nic]

As for the EGTs rocketing up when you lift off, here's my thoughts. After a high boost run, suddenly you have practically no exhaust gas flow velocity because the throttle plate is shut and the engine is pulling a vacuum. All the gas now hangs around for ages between the combustion chamber and the (restrictive) turbo. Heat more readily conducts into the temperature probe, so the reading rapidly goes up. A blip of the throttle with the clutch in, and therefore off-boost, pumps a cooling draft of air and gas through, vacating the old hot exhaust, and cools it back down again

 

Could it be the fuel igniting in the manifold on overrun causing the rise in EGT's?

[Tricky-Ricky]

Could it be the fuel igniting in the manifold on overrun causing the rise in EGT's?

 

No! as the throttle is shut = no fuels at the injectors, after a full throttle run its going to be heat soak causing the rise in temp, don't forget that the manifold and turbos comprise of quite a large chunk of extremal hot metal thats likely still gaining heat at shut off point.

 

i think he must be on about the same thing, he was saying once he has rebuilt the engine he will do it, but as in this thread i think he is thinking of a fault that couldn't happen and trying to over come it he was saying something like the voltage drops from 12v to 4v once you lift off all the way.

sorry i cant really explain much as its not my car

 

 

I think this is being looked at in the wrong way, the guy is trying to look at it as an underlying fault with the Supra, whereas in reality its most likely to be something as simple as a dirty injector restricting fuel at full throttle causing detonation, a stuck oil ring allowing oil past and causing a hot spot, the list is long.

 

Saying its due to a fault with Supras, is just an excuse, as is likely here-say, in any case if the pump voltage had dropped during the full throttle run, and in turn dropping fuel pressure, it wouldn't be just no 5 piston melted, the pump voltage does drop when the throttle is closed, but as already said the injectors are not firing anyway, so it still makes no difference.

Edited May 18, 2011 by Tricky-Ricky (see edit history)