Hi,

I'm having a little bit of confusion with tuning my fuel map. This is on a piggyback (AEM FIC) on an ECU forced into open loop.


Let's say WOT is tuned correctly for 11.8 AFRs in high boost (6-10 psi)

For example, at X rpm and Y psi, you get 11.8 AFR under WOT. (3rd gear pull)
Hitting the same X rpm and Y psi under part throttle, the AFR is lean. (4th gear)

How do you tune the part throttle fueling if the cells are "shared"? Unless they aren't and I'm missing something.

Thank you.

 

The part throttle aspect wouldn't matter if the manifold air pressure is the same. Does the FIC have gear based fuel trim that you can use to compensate?

 

I don't believe the FIC has gear based fuel trimming, unfortunately. Kpro is my big investment pending for this season.

The issue may be within my "crude" method of tuning the OBD2 ECU. I have it faulted into open loop by disconnecting the primary O2. Research tells me this "system fault open loop" is still separate from "WOT open loop". So even if I tune the FIC fueling perfectly in "system fault open loop", going WOT, the ECU will just reference it's own fuel map. Compensating for that fuel map would make me run lean in the non-WOT map (@ high RPM/boost).

Is this a correct observation? Does open loop tuning in OBD1 Crome work by driving the car off the created fuel map, based on RPM x load, whether WOT or not?

 

I've run into this problem before under different conditions, typically where the turbo is too small for the engine. the bandaid fix was to run the wg hose to the intake manifold instead of the compressor housing.

I would suggest plugging the o2 sensor back in and re-tune. because it will be in closed loop at part throttle, you'll want to have a scanner plugged in, reset the fuel trims, and monitor short term and long term fuel trims while tuning part throttle. and make sure to tune part throttle first and completely, before doing any heavy throttle tuning.
By having the o2 unplugged, you are not just forcing the ecu into open loop, you are also putting the ecu into a limp mode, which reads from different fueling and ignition maps and/or uses secondary compensations on top of the standard maps. more than likely you'll find it resolves the issue. but it will require a full retune

 

The turbo is a .42/.48 on a D17. Does routing the WG hose to the IM help by keeping some "vacuum" on the WG?

I will be reinstalling the O2 and retuning the whole map. You suggest I tune part throttle then WOT?

Thank you for the informative help, by the way. I'd love to learn as much as I can.

 

I'm guessing the turbo is a t25, t28, or smaller t3 if those are the housing a/r's. Which isn't terrible on a d17, but is still a little on the small side. It'll spool quick, but wont make a ton of top end power.
Routing the wg hose to the IM just ensures boost pressure stays steady according to IM pressure instead of charge pipe pressure. When the turbo is too small, it's possible for charge pipe pressure to reach max boost at part throttle simply because the turbo is so small and spools so quick and with such little exhaust pressure. Routing it to the IM will simply operate the wg according to IM pressure instead of charge pipe pressure, it helps stabilise the pressure with such a small turbo. but it is a bandaid fix, it is not the correct way to do it. the wg hose should always be connected to the compressor housing whenever possible.

In your case I don't think it's an issue with the size of the turbo, I'm guessing it's just the ecu stuff. Yes, tune all part throttle first, and make sure fuel trims are staying near zero. as you tune you'll probably need to reset the fuel trims multiple times with a scanner to make the tuning process easier, because the ecu will be making corrections as you tune, and will throw off the tune. after you get part throttle fully tuned and fuel trims stay as close to zero as possible, then proceed to tune WOT.