AFM "trick" in reverse.... my idea

[DeftAnesthetik]

so anyways i have to work next weekend but have gotten today off. I have been thinking about this whole situation ive gotten myself into and am comming up with more and more ideas to keep this going..... i digress. back to the task at hand.

When running quads on stock management (4age) the system is just dumping fuel into the cylinders like crazy, my guess for this is that the air velocity created by the quads is keeping the AFM flap fully open and as such the ECU thinks it needs to dump fuel.

I've seen it come up every now and then those who do the little "trick" to their AFM by opening up the sealed unit and turning it back a few clicks to make the ecu think its getting MORE air than it really is..... now is there any reason why this could not be done in reverse thus making the ECU think its getting LESS air than it really is. I will go one further and ask can this mod be done WITHOUT opening up the AFM? just by using a variable resistor in line? this would be much simpler than taking the damn think apart, plus it would give you the ability to tune it on the fly (if need would arise).

well like i said day off and all. I will be going at it seeing if it is at all possible to do this. posting before i get started so maybe i will have some responses when and if i get stuck.

thanks in advance for your input.

[Ben Wilson]

Couldn't you just hook up a second valve in your airbox to allow air to bleed in past the AFM?

[Duk]

Taking an AFM appart isn't that hard to do .
You could try a variable resistor (trim pot) but thats pretty crude. Also, the AFM goes from 5 volts down to just over 0 volts so you would have to wire in a trim pot between the 5 volt supply and the AFM signal output to pull the voltage higher.
A Jaycar Digital Fuel Adjuster would be my preferred cheep way out.

[Duk]

Couldn't you just hook up a second valve in your airbox to allow air to bleed in past the AFM?

I tried this a while ago and it doesn't work with flap type AFM's. The spring tension is too tight and so the air just bypass's the AFM at low loads. I couldn't get my car to free rev even after loosening off the flap spring tension.

[thechuckster]

wouldn't it be safer (in the long run) to run an aftermarket ECU that uses a MAP signal or (if you do a lot of WoT driving) the TPS only?

Or use an ECU that will run off a combination of both input sources?

[IN 05 NT]

if its a flap type, wont the flap just close under vacuum?

[Hen]

Can you point me at any background to this problem. I'd be suprised if the quads would interfere with the function of the AFM, if it was mounted on the inlet of a airbox covering the quads.

I assume this has been an ongoing problem and you've already checked the basic things like wiring/correct injectors/fault codes/fuel pressure etc...

Hen

[oldeskewltoy]

I'd try to swap the guts of your current AFM into a larger shell. From memory, the MA6 Supras used an AFM, swap in your electronics and you are running a larger door.


BTW... the AFM and clicks is a Pat Braden* myth.... It never really works... and in the three cases I've seen it used... ALL three dumped the AFM within 6 months!!!

[Mos]

Yeah, more info needed, because, like for Hen, it doesn't make sense to me.

AFM metering does not require the ECU knowing the volumetric efficiency of the engine, so you can change something that changes VE (eg cams) and the AFM will correctly meter the change whereas a Map sensored engine wouldn't.

To answer your original question, you can both inrich and lean out an engine by adjusting the tension of the spring. But I still think you're barking up the wrong tree.

Mos.

[oldcorollas]

if it was MAP sensored, it would be understandable, with a lower vacuum signal making ECU think it needs more fuel.. but with AFM, seems odd...

are you using the same injectors as the ECU requires? or changed to the quads injectors? are the injectors the correct type (HI/LO-Z) for the ECU?

[allencr]

my guess for this is that the air velocity created by the quads is keeping the AFM flap fully open and as such the ECU thinks it needs to dump fuel.

My guess is that the same intake ports & cams & pistons & exhaust ports and system are going to draw in exactly the same amount of air as before, below 5,500rpm, and even above that if the previous setup wasn't too restrictive.

[DeftAnesthetik]

what i am trying to do is to lean out the mixture of air/fuel i am getting in the cylinders.... I know the fuel mix is calculated on a few factors. I am thinking if i can fool the system into thinking less air is getting in then it will toss in less fuel.

I know I can fix this by upgrading to aftermarket, and i just so happen to have one, i just wanted to wait to install it until i get the system turbo'd. Tuning costs $150/hr, I am not confident enough to tackle tuning myself (especially on a $3000 ecu). Plus $100 tow charge from my house to the tuner (about 100km away) plus the car is my daily driver.

To reply to some responses here..... I will work in reverse order.

allencr: if what your saying is correct why has my fuel use gone up.... DRAMATICALLY I currently have only 1/4 of a tank left of fuel and have driven 139km, I can normallly be at about twice that.

oldcorollas: stock ecu, stock injectors(blue topped, single nozzle). i removed t-vis plate,intake pleneum, and single throttle. replaced with a stripped and expoxied tvis plate, quad adapter, quads, plenium.

arrgh, just noticed the time i gotta get to work, back after.

[dencio1976]

what about output on afms or map going to ecu? when it reads more air how is the voltage output affected?

[DeftAnesthetik]

quick thoughts at lunch here......

a few electrical things changed..... no longer running vsv for tvis, i just disconnected and then zip tied the wire so its not all over the place.
I figured i should use the TPS from the silvertop quads, this is the only change in electrical, everything else was a deletion. should i have used the original TPS? i think they rotate in different directions but i should be able to fix that with some clever wiring. I never checked if it would fit but easily could.

dencio1976: i was trying to figure that out last night..... for some reason though what i have for wiring diagrams does not quite match up to what i would expect (it seems #7 and #5 are switched) so i am unsure if im checking on the right leads but as the AFM opens voltage drops..... again im not 100% that i am testing it right. i will be comparing to some other diagrams i have later.

[dencio1976]

on a silvertop 4AGE that would be pin 6. ok so it's voltage going down as the flap opens. ok thanks. very useful info.

is this true with map too?

i do feel that the afm needs tricking out too. i feel that it runs lean on sudden open throttle on lower rpms.