Hello,

I am need of some assistance. Any help would be greatly appreciated.

First some info on the engine:

2.0L, Crane 16s, ported head, 10.5:1 comp pistons, new plugs, coil is good, wires are good, MAP sensor is good, coolant sensor is good, IAT is good, new EGR valve and stock engine management system.

For a while now (2-3 years) I have been fighting a rich condition on my car. Gas mileage is horrible and I am constantly getting a P0172 CEL code.

So, thanks to some fellow 2gnt'ers I recently purchased a Bluetooth OBD2 scanner which allowed me to view engine live data.

Almost every parameter I looked at seemed normal but these two: short term and long term fuel trim.

At idle (after warm up) my LTFT was sitting at -25% while my STFT was bouncing around between -4% and -15%. The O2 voltage pretty much bounce between .2V and .9V.

At normal cruising speed (2500-3500rpm) my LTFT was at -25% and my STFT was sitting around -7% and 0% (It seems like it got better). ONce again, the O2 voltage was bouncing around just as if it was at idle.

At WOT,or upon engine breaking (High vacuum), both STFT and LTFT parameters would go to zero percent.

I need some assistance interpreting this data. I can see that the ECU is trying to take fuel away (lean it out) at idle and at cruise, but I don't see why the LTFT doesn't fix itself once I am cruising around. What am I not understanding?

Also, I have theory: I believe that part of my problem at idle is because of the cams that I have; this is based on some research that I've done on neons.org. I am thinking that the ECU is thinking that there is more air in the engine than what there really is (this being due to the higher overlap because of the cams) or maybe there is not enough air in there and it can't pull anymore fuel? Would this be possible?

Any theories would be greatly appreciated. Right now my next course of action is going to be the installation of my SAFC2, attempt to lean out the idle, and some low rpm settings based off of my fuel trims. WOuld the SAFC be able to remove enough fuel and help with this issue?

Thank you all for your help,


Oscar

Bump.

The SAFC is only going to act as a 'band-aid' to the issue as it will simulate voltage to trick the ECU into leaning it out. Once the ECU plays catchup to this , you'll be back to exactly where you were.

I had an SAFC in my car prior to MS2 and that's my take from using it. You can still use it but it's not going to be as effective.

The car will only run as good as its limiting factor. In this case, it is the ECU. You need full control, in other words Megasquirt or another form of fuel control or at the very least an AFX ECU if you can find one of those still.

Otherwise just deal with it or put the stock cams back in.

Thanks for the reply, Cas!

I understand what you're saying, but if that is the case, then that means that the SAFC is not useful for every car? or does this just hold true with our cars? The reason why I am asking is because I know people have used the SAFC with turbo applications to lean out the idle once they get bigger injectors. Does the ECU eventually take over again in their case as well?

Once again, thanks for the reply!!!

Originally posted by barza21
Thanks for the reply, Cas! I understand what you're saying, but if that is the case, then that means that the SAFC is not useful for every car? or does this just hold true with our cars? The reason why I am asking is because I know people have used the SAFC with turbo applications to lean out the idle once they get bigger injectors. Does the ECU eventually take over again in their case as well? Once again, thanks for the reply!!!

It's just not that useful on our cars due to the MAP sensor...in other words the way the stock EFI system simulates its readings based on manifold pressure.

I like to look at it this way...SAFC stands for 'Super air flow converter'. Right there is a dead giveaway that it is more oriented for vehicles that utilize a MAF or air-flow sensor vs. a manifold pressure sensor.

Yes, it does work "good enough" for controlling idle situations as you stated above since it's only dealing with a sort of 'static' state if you will. There are better options out there obviously, but it always comes at a cost.