What are your AFR’s

[Jinks]

Hey guys,

I’m curious what your boosted motors run at throttle lift here. My car runs rich as it is tuned that way so I’m not too concerned about that nor do I want to mess with it, but I just wanted to check what you guys here run after lifting throttle. Mine goes to about 16 afr. Idle for mine is a dead on 14.4 stoich. The car seems to be running great on this current tune after having some other issues not related to WOT corrected.
TIA.

 

[jwmelvin]

Throttle lift? Fuel cut, i.e., 21:1 (the limit of my gauge).

 

[Jinks]

Throttle lift? Fuel cut, i.e., 21:1 (the limit of my gauge).

Yes fuel cut/letting off accelerator. Does your car hit around 16/17 afr when doing so?

 

[jwmelvin]

Yes fuel cut/letting off accelerator. Does your car hit around 16/17 afr when doing so?

To my memory it goes to 21:1. Will be a couple weeks until I get the steering rack back in and drive again. It definitely goes higher that 16/17:1.

 

[Old Guy]

Something to consider. The swing in the AFR can depend on the driving style and the driving conditions in addition to the fuel cut settings. If you do a throttle lift at lower engine speed and vehicle speed the RPM drops fairly quickly. The ECU will resume fuel delivery at an RPM above idle so that the engine does not stall. If the engine RPM hits that resume RPM fairly quickly the duration of the fuel cut may be so short that its impact on exhaust O2 is not significant, particularly if the controller for your O2 sensor has a more vigorous filtering algorithm (all controllers provide some degree of filtering - some of them are adjustable). If (on a track of course) you take your 1991 up to 220 kph or so in 5th gear and then lift the throttle and let the car coast down in gear you may get a better sense of what your AFRs can go to on fuel cut.

On an aftermarket ECU like your AEM, the fuel cut will likely have a bunch of settings which will include the RPM at which fuel is resumed and may include a % of fuel cut (fuel cut may not be complete). I have another car with an aftermarket ECU on which I experimented with very aggressive (trying to maximize) fuel cut. Aggressive fuel cut can make for very jerky driving, particularly in stop and go traffic if you are triggering fuel cut and resuming fuel as you slow down and speed up. I now have much less aggressive fuel cut. If I lift the throttle on the highway I can still swing the AFR up into the 19 + range.

Your fuel cut AFR values may have been a function of the way you were driving the car at the time you checked or maybe your tuner decided to play it safe with fuel cut so that they didn't have a cranky customer complaining about a car that was a pain in the ass to drive in traffic.