Topic: Leaning out very low throttle in BC

[darthekai]

Driving my car over to Revelstoke for the first time. Altitude is 480m. At very light throttle, car seems to lean out real bad, sputtering and popping all over the place. Tuned in calgary on husky 94, filled up in golden on chevron 94.
Anyone think this is an issue? Should I just increase injector pulse width at the  bottom end of vac?

Is it caused by injectors getting tired and old or just by different gas and/or lower air pressure?

[darthekai]

It also idles a full point high. I have closed loop disabled.

[Rathburn]

Driving my car over to Revelstoke for the first time. Altitude is 480m. At very light throttle, car seems to lean out real bad, sputtering and popping all over the place. Tuned in calgary on husky 94, filled up in golden on chevron 94.
Anyone think this is an issue? Should I just increase injector pulse width at the  bottom end of vac?

Is it caused by injectors getting tired and old or just by different gas and/or lower air pressure?

Wait, altitude there is 480m? Calgary Altitude is 1080m. Should be higher air pressure there, not lower. Either I'm missing something, or you're the shittiest engineer ever.

More air going in because of the denser air, and your injectors were already maxed?

[darthekai]

Higher air pressure is what I meant. Little more resistance to gas getting out the injectors at low fuel pressures?


Uhh if they were maxed at idle/light throttle, id have bigger problems.

Is the denser air enough to cause lean out like that? Used to be around 16 with like max vac without hitting gear overrun fuel cut. Now hanging out around 18..

[RockThePylon]

Are you using a MAF, or SD?

[RedBimmer93]

http://www.westernsubaruclub.com/smf/index.php?topic=49109.msg607553#msg607553

Geoff seemed to have a similar issue when he drove down to Vancouver. I wonder if he knows anything about it.

[darthekai]

Are you using a MAF, or SD?

SD

[darthekai]

http://www.westernsubaruclub.com/smf/index.php?topic=49109.msg607553#msg607553

Geoff seemed to have a similar issue when he drove down to Vancouver. I wonder if he knows anything about it.

Sounds like problems on the opposite end. 

[RockThePylon]

Huh. Generally speed density doesn't give a hoot about altitude (Unless you're hitting cells you've never hit before and never tuned.) It's all absolute pressure.

Could it be temperatures instead? Are you tuning a VE table, and not secretly running alpha-n/TPS fueling?

[lakelouise02bugeye]

Tuned for 94 husky in calgary and i still sit at normal 14.7 here in LL

[darthekai]

Huh. Generally speed density doesn't give a hoot about altitude (Unless you're hitting cells you've never hit before and never tuned.) It's all absolute pressure.

Could it be temperatures instead? Are you tuning a VE table, and not secretly running alpha-n/TPS fueling?

That's why I thought it was strange. Absolute manifold pressure is my only load axis, with iat as an enrichment table.
It's possible that it's just poorly tuned down there.

Tuned for 94 husky in calgary and i still sit at normal 14.7 here in LL

LL is like 600m higher than calgary. I had no idea... Car behaved normally when I was cruising around in golden which is only 200m lower.

Car is lean ish in the vac range here, about 15.5-16. I figured better fuel efficiency and it doesn't knock so who cares.. Maybe I should just widen pulse widths across the board down there.

[RockThePylon]

It's weird that you would have to... Vacuum is vacuum. Something is uckyfay, but I don't know what.

Adjust it to nail your AFRs where you are, and see if it goes all dicky when you're back up here.

[Airboy]

Small exhaust leak, perhaps?

[darthekai]

Small exhaust leak, perhaps?

Definately possible. I replaced the header to head gaskets when I did the turbo but there had been a leak that had eaten a bit of the flange off. I sanded best I could to eliminate the channel.


What mechanism are you suggesting? Fresh air reentering the cylinders or fresh air throwing my Afr gauge off and giving a false reading? (closed loop is disabled)
Car pops and bangs around in that throttle range way more than usual so i tend to believe the gauge

[darthekai]

I have determined through extensive testing that its due to the tune.

due to it being "easier" to create the same low absolute pressure at lower altitudes (something to do with air viscosity and so on), my MAP drops below what i had it set up for at low altitudes.
I noticed this at first on my boost/vac gauge (relative to cabin pressure). coasting at 3k rpm at 0% throttle in calgary (1000m) it drops to -22"Hg and at 400m it can easily get down to -25"Hg. As a result, when im puttering around town getting pulled over by cops at stop signs, my foot's barely on the throttle just to keep rolling resistance low, and the engine is operating at -22/23"Hg and not getting enough fuel and backfiring and spitting all over the place. In "normal" pressure ranges, the car behaves the same as in calgary. Didnt log anything, but im SURE that this operating range is not accessible on sunny's dyno and that I simply continued the table slope in either direction. It works fine in boost I postulate because the components are operating at their normal range, where as at bare idle, everything is unhappy and the fueling table gets a little more wacky down low.
Considering putting a BC/alberta switch in the cabin to pull timing and add fuel when I switch to 91.

[RockThePylon]

Don't get confused by Relative Pressure you see on the gauge. Speed density works because it doesn't matter what altitude you're at, absolute pressure is absolute.

Whether you're at 5psia with the throttle plate closed at sea level, or 5psia at 30,000ft with the the throttle plate wide open.

[darthekai]

Don't get confused by Relative Pressure you see on the gauge. Speed density works because it doesn't matter what altitude you're at, absolute pressure is absolute.

Whether you're at 5psia with the throttle plate closed at sea level, or 5psia at 30,000ft with the the throttle plate wide open.

yes, BUT vacuum pumps can make LOWER ABSOLUTE pressures at low altitudes given the same power input.

I know this from speccing rotary claw blowers at work and it never occurred to me that it applies to car engines.
At low altitudes, the vacuum pump action of your engine (driven by lets say a constant wheel speed) will produce lower absolute pressures than it will at higher altitudes.
therefore at very low throttle, MAP runs off the low side of my fuel table I couldn't get to in calgary.

Related question since im running WG boost: stock WG actuator looks to be gauge pressure (ie the reference side of the diaphragm is exposed to atmospheric). Is this true? That extra 1-1.5psi could be dangerous unless timing is pulled.

[RockThePylon]

If you the wastegate is open to atmosphere, then, ya, duh.

[darthekai]

No I don't get it.

Is the spring helped by the extra pressure? Does the new higher exhaust pressure cancel this out?
I'm just gonna log next time in that low and figure it out for myself. I have a feeling that's a dumb question.

[RockThePylon]

Pressure helps the spring.

I would think that the extra exhaust pressure will, more or less, cancel out the increased atmospheric pressure on the diaphragm. Giving you a rough PSIg limit from spring pressure alone.

Basically, there are no answers in this thread. LoL.

[darthekai]

nooope.

except I'm 1000% sure the lower end vac thing is caused by increased vac pump efficiencies and lower absolute manifold pressure at light throttle applications.

[RockThePylon]

nooope.

except I'm 1000% sure the lower end vac thing is caused by increased vac pump efficiencies and lower absolute manifold pressure at light throttle applications.

I dunno man. Are you sure the rotary claw specs you saw weren't PSIg? PSIa seems irrelephant for an industrial pump. Of course a pump is more efficient at lower altitudes - because density.

[darthekai]

I dunno man. Are you sure the rotary claw specs you saw weren't PSIg? PSIa seems irrelephant for an industrial pump. Of course a pump is more efficient at lower altitudes - because density.

yes. the simple way of splaining it is that the thinner the air is, the harder it is to push around. With the same HP motor on the same blower, lower absolute pressure can be reached at lower altitudes.

[RockThePylon]

yes. the simple way of splaining it is that the thinner the air is, the harder it is to push around. With the same HP motor on the same blower, lower absolute pressure can be reached at lower altitudes.

Thinner air is easier to push around. That's why planes fly at 40,000ft. Real easy to push thin air out of the way.

Moving the same mass of air is harder. But, under a given vacuum, a 2.2L engine should be ingesting the same mass no matter what. At idle, you have a basically closed throttle plate, then an IACV adjusting itself to maintain that specific vacuum.

The air is denser at a lower altitude, yes, but the engine sees the same vacuum (density) regardless. Sure it's harder to move the denser air, but it's also a higher pressure on the turbo side of the throttle.

Really, the fuel management doesn't care what's going on before the throttle plate.

[darthekai]

Thinner air is easier to push around. That's why planes fly at 40,000ft. Real easy to push thin air out of the way.

thinner air is less viscous. Lets imagine the system is "closed". For a given vacuum pump, there are 3 factors: Leakage, backstreaming, and pumping speed. Leakage is just what you think. Backstreaming is the flow of fluid backwards through the pumping device (in this case pistonring/valve leakage, overlap, incomplete evacuation), and pumping speed is the rate at which you are removing fluid (measured in volume/time). You will keep building vacuum as long as (backstreaming + leakage) < pumping speed

Less viscous air increases the ease with which it backstreams and leaks, and for a same given pumping speed and with the same equipment, the level of vacuum achievable decreases.

Moving the same mass of air is harder. But, under a given vacuum, a 2.2L engine should be ingesting the same mass no matter what. At idle, you have a basically closed throttle plate, then an IACV adjusting itself to maintain that specific vacuum.

well, the IACV's target is reported RPMs which is a comlpex subject as it involves engine load. As it maintains 800rpms or whatever you have it set to, the mass of air the 2.2L consumes depends on rotational drag on the crank which is changed by all kids of junk.
Regardless, im not talking about at idle anymore, im talking small amouts of throttle that arnt enough to stop gear overrun.

The air is denser at a lower altitude, yes, but the engine sees the same vacuum (density) regardless. Sure it's harder to move the denser air, but it's also a higher pressure on the turbo side of the throttle.

the engine actually sees LOWER absolute pressure (more vacuum. less density) than it does at higher altitudes. It then falls off the table (not actually, just goes into an area I havent explicitly tuned) and i get fuelling issues.

Really, the fuel management doesn't care what's going on before the throttle plate.

Correct, which is why the tune behaves well pretty much anywhere above 23Kpa