More Fuel at Idle?

[Peter 92TSI]

Hey guys, I don't know what I am really asking this question, as the problem will probably be solved with my VPC install, but I want to be sure it is the problem, as i don't want to cover up a problem, and then have to sort it out, using a new system.
Anyway the problem is on my 1G AFC I have my idle set to about 20% on the plus side, and sometimes the car still barely idles, and the o2 on my Jumptronix don't cycle.

Here is my setup.
560 Injectors
1G AFC
Vr-4 Fuel Pump
AT FPR
1G Mas, with lower chamber removed.

After idle, I have all my setting at like -12%, so I am hoping it's the hacked mas.

But I have seen a bunch of other cars, with hacked mas, and they all have the idle setting in the negatives.

Thanks
Peter

[Rdy2race]

it is hard to say with all the factors that will effect idle.

With the car idleing normial what are the RPM's? Are they sold or do them flux a bit? What plugs do you run? Do you have a Fuel Pressure GAUGE on the car to make sure that this AT FPR isn't screwing up? ( this wouldn't be the first time I have seen a bad FPR from a AT car ) The fuel pump, is it hard wired? I don't know off hand how large it is do you know how many LTR/HR it flows? how would the VPC correct this? The idle knob?? ( hehehe ) The VPC can only adjust so much for idle and one of the major problems is the way that it TRIED to correct idle fuel curve ( this is why I have not hoped on to the wagon with this now HKS A/F Controler that is like the AFC. It looks good but limited info keeps me away. Sorry i forgot what it was called. ) with a pocketlogger you can see what the VPC does to correct idle fuel curve. ( not much good IMHO this is why it runs SOO much better with a AFC in line. )

And the simple one is that the MAS is not modded correctly and/or is starting to go bad. this is starting to be more and more common as the cars get up in the years and miles.

BM-

[dyezak]

Why did you add fuel at idle? No matter how many mods you have you should never add fuel at idle. Our cars run inherently rich from the factory (safety), so adding fuel only worsens the situation. You should try to lean your idle, like -20%...just try it, you might be suprized.

[Van]

He's trying to compensate for the unseen air thru the hacked MAS.

Sorry for the slow reply Peter.
But you do have some bigger injectors and the higher fuel pressure. So these two things oughtta cancel out the MAS hacking. I'm thinking you wanna lean her out some at idle for those reasons... With my 2g mas, stock injectors and the walbro 255, I'm not even as high as you are on the plus side at idle.
Given that the ecu will compensate 20% +/- (I think it is) I'd try going straight down to +10%. You wanna see the O2 volts cycling at idle when the O2 sensor is warm enough. (I'm sure you already knew that, so for others...)

On the other hand you state the lower chamber is removed...Hmmm, could be the opposite, if -10% of your setting don't work, try going up +10%. You are definitely out the ECU's range of compensating either way, so it's gonna take a big settings jump in either direction to fix it.

A PocketLogger would show you what your low fuel trims are. ;)

[FastGSXauto]

Peter, I have the same problem. With my Rx-7 550's I have my idle at +30, 2400RPM at 0, then -14, -14, -8. I too have an auto FPR but I doubt that is the problem.

The problem is I don't think you can just do straight math percentages at idle when dealing with a hacked MAS. At other rpm ranges you can maybe, but espcially not at lower rpms because there is not enough air flowing. Air takes the path of least resistance, so when you bypass air, at low airflow a larger ratio of air will be bypassed. At higher rpms when there is more flow, the air will get distributed more evenly. That's my explanation. On my car, It doesnt' start to even up until about 3000 rpm. Hence my super high setting at idle (+30), and a lower setting at 2400 (+0), and a correct ratio above that.

[Peter 92TSI]

Thanks guys.

Sorry for the slow response, I've been out latley. ;)

But anyway, yeah I agree it has to be the hacked mas. My mas is beyond hacked, with the whole entire portion removed, and I suppose at idle like FastGSX said the air takes the path of least resistance, which means at least 80% of the air is going to go through the unmetered portion, and the remaining 20% is not a sufficent amount, even with AFC correction to have a great idle.

It's all good now. ;)

Peter
Running a VPC. :)

[nukefission]

Just FYI, 91+ cars have +/-20% more fuel trim correction lattitude than 90 cars.