All,

I'm out of ideas on this one. Briefly, no matter how gently I come off the throttle, as soon as the throttle plates close, the car bucks slightly. An inspection of the PFC/Datalogit logs (attached) reveal that the Injector duty goes to 0% until the fuel cut recover (1300RPM on my car) is hit.

The problem is that when the injectors go to 0%, the car bucks. You can see it in the trace as a slight dip in the RPM, but it is VERY noticable in the car. It's to the point that when I am cornering hard it will unsettle the balance slightly--not something I care for at all.

I've inspected suspect items like the dashpot, but since this happens with quick throttle closings as well as slow ones, I don't think the dashpot is the culprit. I can't find a setting in Datalogit to adjust the idle fuel rate. Even if I could adjust the idle decay so it doesn't go to 0% instantly, I think it would help.

This problem began after significant bolt-on mods including intake, exhaust, intercooler, and such.

Any ideas or theories would be greatly appreciated,

-ch

 

I think I'm getting the same thing you are. AFter letting off the throttle, it's maybe .5 to 1 second after? You can hear it in the exhaust as well. Then just decels like normal.

 

cavellm,

Yes, that's it EXACTLY. Just a little annoying blip about a second after you let up completely on the throttle, and then everything else is normal. When did this start for you--when you added the PFC, or sometime after that?

-ch

 

Trying to remember, cause it was a while ago. I think it was when I got my motor back the 1st time, and had removed the air pump and started running a midpipe.

But at that time I had also upgraded the fuel system, got a ported motor, upgraded turbos, etc, etc...

 

Try disabling the 02 sensor

 

R1,

I've done this in the datalogit screen and it doesn't seem to make a difference. I too have removed the air pump and O2 sensor--I wonder if this is a bug in the PFC code? That when you disable the O2 function, it fails to correct the off-throttle issue?

Anyone out there want to remove their O2 sensor, disable it in the PFC, and see what happens?

-ch

 

Also noticed today... That after I let off the gas, the injector duty cycle drops down to about 7 to 9%, then the buck, and that causes the cycle to drop to 0% finally.

Edit: My o2 sensor is disabled in the PFC, and the wire is just dangling, plugged into nothing.

 

cavellm,

Just to be sure--you're actually saying the buck happens before the 0%? I get them at precisely the same time, i.e. I think the 0% is what causes the buck...

I may be forced to pull my WBo2 and put the OEM O2 back in to see if this is the culprit. But I REALLY don't want to do this.

-ch

 

Yup, was watching it today.

I'm at partial throttle, let off completely, instantly.

Watch duty cycle go from whatever % to around 7 or 9% for a split second, then blip in exhaust note and feeling of not decellerating and then 0% and smooth from there.

 

same problem here. my duty cycle goes to 0% instantly when off the throttle completely.

ive had this problem since the stock ECU was used.

 

Spoke with Steve while we were doing some fine tuning the other day about this.

He said he's seen this on just about every PFC he's tuned, and it has something to do with the fuel cutting on decel. Also said he's never been able to get rid of it completely, and doesn't know anybody that can.

ah well, something to live with