Where have I expressed any aggression ?
I think you need to grow up or maybe using this is very mature of you

 

You're incorrect on that last one. Alcazar's post is correct, but possibly a little confusingly worded re. this "pre" thing. If you want the techie answer, here tis:

Dumping the air before the meter is exactly the same as venting it to atmosphere so no, this won't work if you want to keep the fuelling "right".

The point of re-injecting bypassed air after the AFM is that it allows the ECU to maintain an accurate understanding of the amount of air in the inlet tract. Under the standard system, when the dumpvalve opens and lets compressed air out of the intercooler and into the recirc pipe, it will, obviously enough, flow back down into the inlet pipe - and most will follow the path of least resistance, which is straight back into the turbo.

Obviously enough, because the turbo is now sucking in a large quantity of recycled air, the amount of fresh charge taken in through the air filter will suddenly drop by an amount equal to the quantity being recycled. This drop in air intake volume can be measured by the MAF and so the ECU will know, on an ongoing basis, how much air is in the system and will calculate the mixture accordingly when you go back on the throttle.

If, on the other hand, you externally vent the dumped air, the turbo is obviously still spinning so all its ongoing requirement will be sucked in through the filter and be measured by the flow meter. The ECU, not knowing you've changed the DV, will think that it has the recirculated air (which has already been measured and accounted for, don't forget) plus the amount measured by the MAF during the throttle lift to deal with.

As a result, on reapplying the throttle, the ECU will be calculating the mixture on the basis of an airflow number that is totally inaccurate (and you'll get far too much fuel injected as a result). And, the inaccuracy will take a few cycles to dissipate while the airflow going into the engine restabilises and the ECU is able to re-establish an accurate measurement.

It is theoretically possible to incorporate code into the ECU that would "work round" an atmospheric DV - calculating the amount of air that had been dumped out of the system and figuring this into the fuelling numbers on the reapplication of throttle. However, that is an unnecessarily complicated way to solve a problem that doesn't exist. As long as you're running a MAF based system, a recirculating bypass valve is the more elegant solution.

Interesting factoid: Don't know for sure about the others, but the MY99-00 MAF can measure reverse flow. I suspect though (atho I don't know for sure, yet) that Subaru didn't program the ECU to react appropriately to a "negative" airflow value - there's no reason why they would have when the code is written with a recirculating DV in mind.

It's also largely a moot point given the speed with which large amounts of reverse pressure will kill the 99-00 sensors.

 

Cheers mate

Oh the joys of bein a noob

 

Look on the bright side. It's not like moving to a small village in Cornwall, walking into the local and hearing the entire place go deathly silent.

Oh, actually...

 

Here?

Or maybe you call everyone you don't know an asshol.e?



Oh, right, I get it: I tell YOU to grow up, you tell ME to grow up.

Ok, I'll sink to your level: NO, YOU grow up

Awaits scintillating comeback with interest

 

Very interesting. At the very least it does create a chunk of turbulent air in the intake pipe even if the sensor doesnt (or is it 'does'?) read negative. Anyway - jerky throttle transitions are the results unless on MAP based ECU or ECU code.

 

lol You need to up the dosage of them tablets youre taking

 

Did I say "scintillating reply"?

You outdid yourself. I bow down to your superior intellect

 

Did I say "scintillating reply"?

You outdid yourself. I bow down to your superior intellect

 

Bad stutter

 

Come on ladies, kiss and make up. There are some making interesting points, amongst all the bitching.

 

Academic at the moment. I've checked the ECU code and unsurprisingly it can't, at least as standard, deal with signed (i.e. negative) airflow numbers.

It's interesting to log it though. Any value less than 1.00 of a volt is reverse flow, and I was seeing the airflow meter drop to less than 0.100 of a volt on liftoff from WOT with the DV deleted. Implies a lot of reverse/turbulent flow.

Aaahhh, did you hear the one about the MY00 Subaru ECU that runs MAFless?