pressure pulses.... one for the scientests

[1jzracing]

while fine tuning my car (1gg) and chasing unstable mixtures and pinging i found the ecu was receiving a very unstable load reading at higher boost, this spikey reading was playing havock with the timing and fuel tables with the timing (and mixtures) jumping up and down causing random pinging and power loss!!

i mostly fixed the problem by reducing the hose size and adding a small accumulator tank in the line from the intake to the ecu (internal map) the tank is very small 2cm diameter and about 6cm long

WHO KNOWS ABOUT THE ACTION OF PRESSURE PULSES ??????

where would be the most affective place for this tank to be, close to the intake or close to the ecu??? the hose is about 1.3m long

would there be any advantage to adding a restriction at one end or the other???? or anywhere else for that matter

i have a rough diagram of the various setups

[Billzilla]

Where are you picking up the inlet pressure from? Directly opposite the inlet trumpets perhaps?
If you are, move it to the end tank.

[1jzracing]

its at the tank end with all the other little vacuume lines, it was on the side on the plenum but thats the first thing i changed

it runs so much smoother and better power as i was able to increase the timing about 4 degrees with no pinging, but the signal is still a little wavey

[oldcorollas]

how fast can you datalog?

small restriction (use mig welding tips so you can slide the hose over easily and clamp if needed), followed by an accumulator/tank, or the other way round with a medium sized restriction before and small one after...

basically, from the plenum, you have a large oscillating pressure function.
you want to reduce the amplitude of oscillation, but not change the average, or slow response too much. but it is not just pressure, it is also the volume of air that can move within the MAP sense line.

by having a restriction in the line from the plenum, you are reducing the volume of air that can be moved with each oscillation. (this will help the signal, but if too small, can reduce response time slightly). ie, it works like a resistor in electrical circuits.

if you have an air space/tank thing after the restriction, that smaller amount of air now must be sucked out of the tank, before it can significantly affect the line pressure after the tank, so the tank is acting like a capacitor..
ie, like a normal electrical RC? filter, where the resistor slows the charging of the cap, and then the cap maintains the voltage as it drains out...

so, use a restrictor to reduce the rate at which air can flow in and out of an air cavity, which acts to cushion the reduced amplitude.

if you can datalog fast enough, try using welding tips from 0.6-1.5mm diameter, and for tank, you can try carby fuel filters... the paper inside also helps a little at damping
at some point, the restrictor will be too small, or mroe correctly, too small for the size of air space... by datalogging and reducing the size of restrictor, you should be able to approach that easily. maybe 2x6cm is not big enough? try it, and compare with an old ryco carby filter witht he same restrictors, and see what different size of restrictor is effective..

the ECU should also have the ability to compensate a little by data averaging, but you don't want to average for too many events, as you could lose a little transient response perhaps...

sorry for the rambling, i jst woke up

[1jzracing]

cheers thats all along the same lines as i have been thinking and i set it up as in my first diagram

tha dattalogging is pretty fast as v4 wolf only logs straight to the laptop and i have reduced the filter target setting on the internal map sensor and its all helped greatly i just wondered if the location if the tank had any major significance, possably a slightly larger tank is needed but as you say i dont want to slow the response down too much if i can help it,

how about the difference in response of biger tank with less restriction vs small tank with smaller restrictor

the difference so far is incredible for power and smoothness when i am at light throttle and lean mixtures

[oldcorollas]

how about the difference in response of biger tank with less restriction vs small tank with smaller restrictor

don't know offhand, would have to think about it
for a given engine condition, and equivalent large vs small setup, the diffrence is minimal.. but when you start changing rpm/amplitudes or transient nature, then there may be some effects
perhaps smaller is less intrusive compared to the actual flow in the throats, but even large should not be significant (in terms of the absolute amount of air going into/out of the tank)

perhaps there is also effect from the ratio of the tank volume to the volume in the line to the MAP sensor..
pressure waves (sound) move fast, but pressure changes can happen slowly....

i suppose it depends if you are filtering out actual physical sound (local variations in amplitude) or filtering out pressure variations (which in a sense is the same thing, but dependent on flow, and a much lower frequency, as such) ... i think reality is a bit of both

i'm sure someone smarter than me in fluid dynamics could model it very easily, by setting orifice and tank sizes (and MAP sense line also), and then varying a sinusoidal pressure fluctuation, and see what happens...

[brett_celicacoupe]

maybe you could place a small filtering circuit in series with the MAP signal wire.


someone with more of a electronics knowledge could design something here

same principal as OC but it uses eletronics rather then fluid flows

[maddog]

have you tried getting the vac. from TWO locations along the plenum? this would eliminated any localized harmonics and average the plenum's internal vacuum reading,i'd venture.........put the tank relativly close to the plenum for a more rapid reading of change.