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Fuel pressures and AFRs all over the place


Dash Rendar

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Charlie is right it will make it read leaner as the oxygen content of the H20 is released

 

Just going by my experience's with WI, my old S14 used to show slightly richer AFRs with WI turned on, yet the Supra shows no change in AFR even with WI turned up full, runs crap though;)

WI seems to have very Little affect on AFRs in general, but i guess if it was coming from the turbo, (have to be pretty fooked to allow water through, and it would be burning plenty of oil to)

then it would have a more marked affect.

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Just thinking about this from another angle.... I'm sure you've not done this recently, but lets say you get it fully warmed up (i.e. seeing lean condition on the AFR gauge) and took it out for a drive, set the BC to off (1 bar) and go for a WOT run in 4th. Do you get a det warning flash up? If it doesn't detect det, what is the afr reading at the max load point (about 5.3krpm)

 

It's slightly risky to try this as it means you're relying on the knock sensors to tell you to back off...

 

Try again at 1.2 and then 1.4 bar provided there are no det warnings.

 

The reason for suggesting this is to ascertain if you're seeing an afr reading that would *certainly* cause det, but no knock is being found by the sensors.

 

Risky approach though!

 

At full boost at 1.0 / 1.2 bar, the AFRs sometimes show 10 (as Ryan had mapped it to), but sometimes seem to only go down to about 12.5, during the lean condition.

 

The knock sensors do flash occasionally at full load, but it's a bit random. I think this is because we never completed the mapping under boost, so it still needs some tweaking.

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Sorry if this is a silly question, but how? I'm presuming exhaust gases dont make an electrolytic environment, and I'm pretty sure exhaust gases dont get hot enough to cause fission! (It's been nearly 10 years since my biochemistry days, and I have a memory like a sieve!)

 

Ok need to reword my post, unless i have just found a way to split the hydrogen and oxygen in H20 through the exhaust system. :)

 

Basically the wideband oxygen sensor reads the oxygen levels in its environment. If water is entering the exhaust system at the top of the downpipe system which is alot hotter than 100c then the water turns into vapour. When it turns into vapour it is still H20 but IIRC the oxygen sensor cant read the hydrogen but picks up the oxygen. But a sensor will not last for long in the this sitution and water in the exhaust system is one of the main reasons for Oxy sensors failing.

 

Just to add also on a supra with decent coil packs i have had the mixture as lean as 17:1 with no missing on cruise but over that and the engine will definatly spark to miss, so if it is going off the scale lean which is 20:1 on the aem and still running alright then something is 100% compromising the AFR reading.

 

Ryan

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At full boost at 1.0 / 1.2 bar, the AFRs sometimes show 10 (as Ryan had mapped it to), but sometimes seem to only go down to about 12.5, during the lean condition.

 

The knock sensors do flash occasionally at full load, but it's a bit random. I think this is because we never completed the mapping under boost, so it still needs some tweaking.

 

Damn right i mapped it that rich when i saw the fuel pressure dropping like it was on the gauge as thats enough to worry any mapper but Could i ask that you dont bring the car on full boost as i said when we met as although the knock sensor warning works well you could be doing damage.

 

Again though, im not sure why the knock sensors will be flashing up knock as i pulled around 7 degrees on load. Could be ghost knock.... or the AFR's are going lean which i why i said when i first left the car not to bring on boost until an issue has been found as IMO something is still changing the fueling when it is overwelmed by heat.

 

Ryan

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Just going by my experience's with WI, my old S14 used to show slightly richer AFRs with WI turned on, yet the Supra shows no change in AFR even with WI turned up full, runs crap though;)

WI seems to have very Little affect on AFRs in general, but i guess if it was coming from the turbo, (have to be pretty fooked to allow water through, and it would be burning plenty of oil to)

then it would have a more marked affect.

 

All depends on the Jet size used as Meth is a fuel so burns and will make the AFR read richer but most kits these days will not affect the average wideband as the water content with the meth adds o2 to make it equal again.

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Damn right i mapped it that rich when i saw the fuel pressure dropping like it was on the gauge as thats enough to worry any mapper but Could i ask that you dont bring the car on full boost as i said when we met as although the knock sensor warning works well you could be doing damage.

 

Again though, im not sure why the knock sensors will be flashing up knock as i pulled around 7 degrees on load. Could be ghost knock.... or the AFR's are going lean which i why i said when i first left the car not to bring on boost until an issue has been found as IMO something is still changing the fueling when it is overwelmed by heat.

 

Ryan

 

Dont worry. I haven't (since you advised me not to) routinely been boosting the car. I have occasionally (and rarely) given it short bursts of boost merely for the purposes of diagnosing the symptoms and informing you guys how it behaves. :)

 

It's a shame to have a 550bhp car and not be able to drive it on boost. :(

 

BTW, I think my AEM goes off the scale >18, rather than 20. Even so, would you expect the car to be misfiring with these kind of AFRs, as it drives fine in the lean condition?

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  • 1 month later...

SORTED!!

 

Well, this seems to have been one of the longest threads in history, so I thought you'd all like to know that the car appears to be fixed.

 

It's hard to see at exactly what point the problem was resolved. So many parts have been changed, and with the first three of four major components that were swapped, I had Ryan remap the car after each. But I did feel I was taking the mick with the amount of time I needed from Ryan, so after a while, I started getting work done without having subsequent remaps.

 

Recently I had a few more parts changed, which included two short plastic hoses above the fuel tank which attach to the fuel line. (There was one on the feed line and one on the return line.) Mark changed them at Pheonix and was under the impression that a previous diesel fill-up and damaged these hoses. He reckons that filling up with diesel caused more long-term ongoing problems than anyone could have anticipated, and that this was just another symptom.

 

Anyway, since changing the hoses and subsequently having the car remapped, it's running like a dream!

 

Well, it wasn't, but that's 'cause the XS Power gaskets on the turbo and the oil return line had fallen apart, and most of the boost was getting vented into the engine bay! Darryl... ehem, helped me replace the gaskets... Well, to be more accurate, he swapped them, while I adopted a supervisory role. ;)

 

It's like a whole new car now and goes like poo off a shovel. Just in time for the summer. :)

 

So thanks all for sticking with me in this, and for all your help and advice. It's been a learning curve!

 

P.S. Big thanks to Ryan, Darryl, Matt Harwood, Terry and Mark Curnow, who have all personally devoted a lot of time and attention looking at the car.

 

P.P.S. And the RLTC is fixed now too! Plus, I have a lot more gauges!

Edited by Dash Rendar (see edit history)
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