All,

I'm still trying to solve this nagging problem that makes me want to drive my FD into a telephone pole. For those that remember, I'm experiencing a slight buck about a half-second after I get off the throttle. Drives me nuts.

Anyway, I've datalogged the problem. You can see one of the symptoms of this buck as the timing jumps wildly for a brief second. I've reproduced this issue on a completely stock FD as well, although you can't feel the buck nearly as much, probably due to the factory exhaust system.

(The top red line is RPM, the top blue line is TPS. Timing is the purple line on the bottom, and I've highlighted the timing spike with the datalog cursor. The bottom blue line is vacuum.)

It appears to me that this problem is related to the vacuum that the car pulls, i.e. if the PFC doesn't see enough vacuum it freaks out for a second. I'm going to try to talk to the A'PEXi guys about this, but I'd love to know if anyone else ever sees this timing spike in their logs and, if so, experience this hesitation.

-ch

 

can you send the file in excel format. do you mean it bucks like the stock ecu would at 2800?

Never had that problem with mine. what map did you start out with and did it do it then? What changes have you made to the map since then?
Tim

 

What I notice is that the TPS (voltage?) is also oscillating. Does you car have cruise control? The only way the TPS can do this is if something is pulling on the throttle linkage instead of it staying in the close position.
Maybe your throttle linkage is too tight, your cruise control is engaged and screwy, or you foot it tapping the excelerator.

Now if this same PFC does it on other cars with the same TPS ocillation, then the PFC must be bad.

 

Ah, that's me applying throttle and then releasing to get the car to buck. (The legend across the bottom of the graphs is seconds; I'm on the throttle for 3-4 seconds and then genly release.) The buck coincides with the sharp drop in ignition timing.

I've enclosed the datalog file in its original format. The car does the same thing regardless of what map I use, or even when I swap in another PFC. I have reproduced the issue on another FD (completely stock) but the buck is harder to notice because of the resrictive exhaust and heavier flywheel.

-ch

 

Hyperion,

can you post or PM me your PFC maps? I would like to follow your datalogit graph (point by point) and see where it is in your ignition/fuel maps to see if there is some hole or spike somewhere that is causing this bucking problem?

One thing that I noticed looking at your raw data is that the O2 sensor voltage is all over the place. It seems to be in the 0.8~0.9 range until before the bucking when it drops to 0.12 (makes sense) and then jumps to .93 then back to 0.17 and then jumps to 5, 2.99 and 9.99 (doesn't make sense).

I am experiencing the same bucking problem but I don't have a commander or datalogit to view or record what's going on in my car. I would expect to see the same as you are if I had one. Maybe I'll buy the datalogit SW and try to diagnose my car just like you are doing and share my results.

Thanks for sharing all this information and hopefully you'll be able to get rid of it and let us know how.

BR,

Dennis

 

Hey Chris,

I tried to induce the "bucking" that you are seeing by changing my offset from 3400 down to 3100 and then to 2700, 2200 & 1900.

I didn't really notice the "bucking" that you are seeing. I could be wrong... However, my did run like **** (bad idle & rough) with the vacum readings being artificially lowered.

John

 

Dennis: I've seen this O2 behavior on jpandes' car which doesn't exhibit the bucking problem. However, the problem persists on my car regardless of what map I use--even the full-reset 5.08 map that the PFC defaults to. But I'll post my map anyway. (It's tuned for stock motor/turbos with lots of bolt-on mods.)

John: Thanks for trying that out. I'm surprised to see that it had no effect (besides running poorly). Did you ever notice what your vacuum was off-idle? Did it ever get below about 570 mmhg?

-ch

 

Alright, I am now more convinced than ever that the PowerFC has some kind of bug. Check out the attached datalog--I've highlighted a moment where I'm simply revving the car out of gear. You can see that when I get off the throttle the PFC actually changes the timing to minus 13 degrees!! On the map I'm at N4 between P3 and P4. Both cells are set to 12 degrees of advance on IGL and 4 for IGT. There are absolutely no negative timing cells in my map, and certainly not a -13!

All of these things happen on the default PFC map as well as my modified maps.

Gah!

-ch

 

The negative timing is the pfc trying to help return to idle. I usually see around -10 when the car decels and trys to attain it's target idle speed. I've seen as low as -15 for timing values at idle. I had a stumble on decel that turned out to be a tps that was out of adjustment. Changed it from reading .9v at idle to .59v and stumble is gone.

 

The negative timing is the pfc trying to help return to idle. I usually see around -10 when the car decels and trys to attain it's target idle speed. I've seen as low as -15 for timing values at idle. I had a stumble on decel that turned out to be a tps that was out of adjustment. Changed it from reading .9v at idle to .59v and stumble is gone.

 

Was there any resolution to this problem?

 

anybody home?

Okay, I changed my decelerate recovery to 4000rpm. Wow the bucking dissapear...at the expense of gas mileage...

 

I still have not resolved this problem, and it's killing me. I've been able to mask it by setting the idle higher with the throttle plate adjustment, but this also kills the fuel decel (as does setting it at 4000 RPM). So I'm still at a loss.

-ch

 

I still have not resolved this problem, and it's killing me. I've been able to mask it by setting the idle higher with the throttle plate adjustment, but this also kills the fuel decel (as does setting it at 4000 RPM). So I'm still at a loss.

-ch

 

I still have not resolved this problem, and it's killing me. I've been able to mask it by setting the idle higher with the throttle plate adjustment, but this also kills the fuel decel (as does setting it at 4000 RPM). So I'm still at a loss.

-ch

 

okay..so its killing you three times over huh?
I think the problem stems from having cruise/idle area too lean. When I made those area rich ~12-11AFR. Not so big bucking. When I lean them to around 14-15AFR, they buck big time...
Looks like the PowerFC always behind in getting fuel in. So when you step on pedal, it takes a few milisec for PowerFC to think and deliver fuel.
When I did the decel to 4000rpm, fuel is always there, thus it goes lean a little without making the car buck...
Is that wrong to have such a high decel number?

 

I'm no guru, but... have you checked the timing with a timing light to make sure what the pfc is seeing is what is actually going on in the engine?
Good luck
Bob

 

How can I check the timing is correct while running at 35mph in 2nd or 3rd gear?
That does not make sense.
Anyway, I will just use the decel as band aid solution...

 

I have discovered what I believe is a workaround for this problem. I am doing some extended testing this week. If it pans out, I will write it up. I will also send more hate mail to A'PEXi.

-ch

 

hyperion: do you mind sharing the possible workaround, perhaps I could do testing as well.

Thank you,
Reza

 

I'm going to do a bit more datalogging this evening and if everything looks good I'll post the workaround. I just want to be sure that it works before I suggest this as a solution.

-ch

 

Well what i meant was that you could check the timing at idle with an inductive timing light, just to make sure that the pfc is controlling ignition correctly there. Ya know, look for anomilous advancing or retardation of the ignition while the map is flat in the associated cells. Maybe I should have specified that first, hope that makes more sense now?

Bob

 

Put the stock ecu back in and see if you can duplicate this issue on this car? If you can, then it's a mechanical/electrical issue with some other component. If not, then you're probably right to point the finger at the pfc. Have you also tried a known good pfc from another car, loaded this map and tried it in another car (or swapped the pfcs between cars?).

I took a peek at your settings and don't see anything out of the ordinary - I run similar settings in that area and don't have any of these issues. However, you don't seem to have a wideband - it would be nice if you got one hooked up to see what the true afr is when all this is going on. Under decell you should be in free air, but it's hard to tell what is going on since it appears all you have is the stock o2 sensor. However, when you initially decel and get the bucking, your regular o2 seems to indicate a temp rich condition before jumping way up indicating free air conditions. I wonder if you have an injector that isn't shutting off on decel correctly?

Maybe the crank angle sensor is misbehaving? As previously suggested, have you just checked the timing with while reving the car in neutral?

Lots of troubleshooting left (unless you've already done this and just have not provided all the sordid details). I'm certain it's frustrating.

Bizarre.

Beast

 

the table of TPSV does not match the plot, but the inj duty cycle is the same in both places, and appears to be consistent with the table TPSV values.

The table TPSV starts to drop at initial lift off from around 3V with 20% fuel, but then holds constant at 2.54V for about .6 sec or so at 15% fuel, before switching to zero.

Could be excessive fuel delivered after lift off, due to delayed zero tps value?

 

Delayed TPS value would mean that the dashpot works correctly. You know it slows down the closing of butterfly.