Pulsing peak boost with PFC
 

Hey guys, I need some advice with the boost performance of the PFC installed on my FD. What is happening is that the boost pressure is not steady when it peaks – it fluctuates/pulses between about 10 and 11.5 psi either on the primary or secondary turbo. This is using a PFC that came with the car, and its original tune except that I had a shop adjust the ignition coil dwell to optimize for AEM coils.

When I use a Pettit Unlimited chipped ECU or the stock ECU, the peak boost is rock solid – really the only reason I want to move to the PFC is that the Pettit ECU boosts to about 13-14psi and I am a little uneasy running that much boost on the stock turbos and the 91 octane gas that is available here. Otherwise the Pettit has fantastic driveability. I should add that my car is running stock turbos, stock airbox with paper filter, larger SMIC, JDM downpipe and OEM main catalyst.

The PFC tune seems good otherwise; I have a good idle, good cold start, and good overall drivability – but it has the boost pulsation issue (and, the AC compressor only seems to work on fan speed 1 but that is a topic for another day).

I am hoping someone here has knowledge about this condition, if it requires a tweak to a duty cycle map or something like that I can pick up a Datalogit somewhere and make the change.

Thanks in advance!

The PFC boost controller is shit. Never used it since getting my PFC in 1999!

Have your tried adjusting the values to see what happens? Maybe the boost is set too low compared to the duty cycle values.

You only need a Commander to adjust the boost values.

Thanks for the the reply, I should add that my setup uses the OEM wastegate controls - I don't have the Apexi boost controller.

Do you have any suggestions about the boost or duty cycle values? Clearly something is wacky since the OEM ECU's have rock solid boost, and only the PFC has the pulsing boost issue...

If boost goes over .25 over the set value you get fuel cut. If you are on the edge, you may get oscillations. Maybe the WG actuator control hose has a split and it is oscillating burping pressure. You could remove the WG solenoid connector and plug in a mechanical bleed pressure control to see what happens.

It looks like I have a couple of threads on this topic in this section now that the mods moved my other thread from the FD-specific section so I will stick with this one...anyway...

I downloaded a copy of the PFC user guide and I see that you can adjust the boost pressure and duty cycle values. The settings now in my PFC are a little off from what is in the user guide, presumably adjusted by the previous owner or tuner:

Setting 1:

PR boost 0.65, duty 56%
Sc boost 0.65, duty 64%


Setting 2:

Pr boost 0.65, duty 63%
Sc boost 0.65, duty 70%

So it looks like the boost values have been adjusted/lowered from the user guide values, and the duty values were left alone, assuming that this is what is actually set in the PFC from Apexi originally. I thought that boost pressure was determined by the duty cycle % so it's not clear what the interaction is between the boost setting and duty setting. I don't really want to raise boost, as it is already at 10-11psi so I guess I could try lowering the duty % and see what this does...Any thoughts on this would be appreciated!

I am sure that all this is commonly known info for most, but this is my first time with a PFC so I am learning this from the beginning point...

After doing some research, probably the issue is that the duty settings are too high for the boost pressure level, as suggested by cewrx7r1 and this site:

Apexi PowerFC FAQ

So I will dial back the duty cycle a bit this weekend and see what comes of it. It would be great to get this one remaining issue resolved...

Okay, so I have been progressively lowering the duty cycle of Pr and Sc, but the issue still exists. It seems to only affect the primary turbo though, the secondary boost is solid. I guess the next thing to try is to maybe raise the boost set point slightly?

Since the boost stability is excellent with the OEM and Petit ECU’s it has to be a PFC setting issue, but why the same settings that work okay for others don’t work for me is a mystery.

Then maybe there is a problem with the transition and holding the 2nd turbo in operation.

There are two control systems for going from seq to non-seq operations.
The vacuum and pressure control. Maybe the non-seq(both turbos working) has a problem that fluctuates.

Go single and never look back!

Thanks, since the problem only seems to affect the primary turbo when it hits peak boost (~10psi, well before the transition), and the issue is only present with the PFC (not with the Pettit or OEM ECU), it seems like a tuning issue. But OTOH, there could very well be some mechanical issue that only manifests with the PFC. I guess I can either just re-install the Pettit ECU (and regain AC compressor operation on all fan speeds), or schedule some time with a tuner and pay some $$$ to see if this can be calibrated out.

Thanks again for the feedback!