Anyone Know What Vacs (variable Airflow Control System) Is?

[judasentinel]

I have a 1995 R33 GTR, which came with a little box inside the cabin, connected by wires to the ECU. It is called VACS - Variable Airflow Control Systrem, and I am wondering how it works, and what it truly does. I have been trying to set my idle properly, and cleaned up the AACV/IACV, after which the car hunts and the revs are very hard to stabilize. Even if I am able to stabilize them, once I give throttle, they jump and then the car tries to stall.

I am wondering that the seller of the car has added another variable for me to mess around with, and this has got me stumped. It also also says on the VACS box that it is for racing purposes only. But it is turned on. It has two control knobs - one is titled Control Point, which you can turn from 1-10, and the other is called Main Volume, which also runs from 1 to 10. There is no change when I turn the control point knob, but turning the main volume knob changes the idle and the rougness of the idle.

Does anyone havce any ideas as to what this could be, barring the obvious answer that it controls the airflow? What I would appreciate knowing is why it is connected to the ECU and what it is actually manipulating/changing to control the airflow. Does it mess with the MAF signal or the TPS or the AACV/IACV or the idle switch on the ECU? Or does it change the fuel flow and the airflow?

Lastly, if anyone has ever seen anything that like before and knows how to set it up properly, and what the control point means, it would be a great help.

Thank you.

[Guilt-Toy]

what pins does it go to the ecu?

[GTSBoy]

It's a piggy back signal bending "tuning tool". By "tuning tool", I really mean it is probably almost completely useless in the modern age and should be replaced with something less likely to cause a major f**kup. Like a tuneable ECU.

[judasentinel]

Thank you for your inputs.

What is this signal bending tool tuning, to be exact? One of the knobs (Master Volume) causes the revs to go up and down a bit when I turn it, but the other (Control Point) doesn't do anything. My feeling is that it plays with the Air-Fuel mixture, but higher revs mean that the mixture is getting leaner, I take it?

I wish there was some way of knowing what each knob does, so I can either use it to my advantage until I can muster up the dough to go standalone or just chuck it out without any issues to the ECU/car. Does anyone know how to tune this thing or point me to any online resource for it?

I have also noticed that since cleaning up the AACV the day before, the idle has become somewhat erratic, in that it starts off as stable, but as the car warms up and the revs drop to around 1000 rpm, if I give it gas or drive it and then come to a stop, the car wants to stall and the revs start hunting, going up and down. Upon restrart though, the revs go back to being stable and normal. This has only started top happen after I cleaned up the AACV and reinstalled it. I didnt clamp the hoses though, since they are sitting snug fit onto the metal tubes on both ends. Could air be escaping into or out of the hose connecting the AACV to the plenum?

Do I need to reset the TPS at all since I cleaned up the AACV?

Thanks.

[scotty nm35]

One knob melts the pistons and the other snaps the rods.

It needs to be setup on a dyno preferably now you played with the knobs, or road tuned with a wideband fitted. Playing with the AFM signal isn't a great way to tune a car at all...

[judasentinel]

Funny guy

On a serious note, can someone please just tell me what each knob does, as I need to road tune it, or should I just disconnect it? A straight answer about the functionality of this box will really help me. Saying that it deals with AFM doesnt tell me which part it deals with - the fuel or the airflow.

Thank you.

[GTSBoy]

Funny guy

On a serious note, can someone please just tell me what each knob does, as I need to road tune it, or should I just disconnect it? A straight answer about the functionality of this box will really help me. Saying that it deals with AFM doesnt tell me which part it deals with - the fuel or the airflow.

Thank you.

What I said and what Scotty said are both 100% accurate. The "control point" will be (say) 10 arbitrary AFM voltage levels and the "main volume" will be how much the voltage is adjusted at each of those points. This is a rude, crude and shitful way to do things. You would be better to tear it out, pour petrol on it and set it on fire than try to waste time dealing with it. If that meant parking the car riding a pushbike until you can afford to Nistune the ECU or buy something else, then so be it.

[iruvyouskyrine]

Saying that it deals with AFM doesnt tell me which part it deals with - the fuel or the airflow.

Thank you.

Both. It changes the airflow reading which in turn changes the delivered fuel amount.

[paulr33]

yep sounds like an apexi SAFC, bend the afm signal as required

[Scott Black]

What mods does the car have, if it's got stock afm and stock injectors mostly stock turbos then rip the box out and drive with stock ecu, if it's got non stock afm or injectors then rip the box out and go nistune or adaptronic

[Blackkers]

What mods does the car have, if it's got stock afm and stock injectors mostly stock turbos then rip the box out and drive with stock ecu, if it's got non stock afm or injectors then rip the box out and go nistune or adaptronic

Op follow this advice.

Both options involve removing the piggy back thing.

There was a time when these used to serve a purpose.. That time is long gone

[judasentinel]

I am reviving the thread, as I recently changed my engine after frying cylinder 5 (zero compression). Now that the new-ish engine is in, I decided to disconnect this VACS.The VACS has 5 wires - two go to each of the pics for the two AFMs (MAFs), one goes to 12V power, and the other two go further back into the ECU and are soldered into god knows what.

Since I could not just cut the wires out, I unplugged these wires from the VACS box itself and the car started running stupid rich - 10.2-10.6 afr, even under idle. Now this has got me stumped. If the stupid box is not connected anymore to the ECU, why would the car be running so rich on the R33 ECU? I have stock AFMs and stock injectors, so there is no reason it would be so. Does anyone have any ideas about it?

As a test, I decided to swap out the ECU and used an R32 GTR ECU to run the car and with that, it runs crazy lean - 17.5-18 afr.

Now I am stuck between a rock and a hard place - R33 GTR ECU runs it stupid rich and the R32 GTR ECU is running it crazy lean. Please help me here if someone can, with any ideas. The four wires coming out of the ECU and going into the VACS are still soldered into the ECU but they are no longer connected to anything on the other side, they shouldn't be causing any issues - basic electronics, right?