Without knowing AFR, we can still see what TCCS thinks by checking vF [w/V-Ohm meter, DC Volts]. An analog gauge is preferred since the values may be difficult to read on a digital unit.
Vf1 Signal EFI Status Fuel Trim
5.00 V Lean + (11-20) %
3.75 V Slightly Lean + (4-10) %
2.50 V Normal ± (0-3) %
1.25 V Slightly Rich - (4-10) %
0.00 V Rich - (11-20) %
At idle or steady-state closed loop, vF leaning toward one side or the other indicates TCCS believes it must correct to maintain optimum engine running. A stalling engine normally pegs vF to one side or the other.
More TCCS: Using the S-AFC in closed loop is like chasing your tail while accelerating the tail's speed simultaneously. You don't simply correct a 1000rpm bump when you correct in closed loop, you also change the long-term fuel trim [aka learned value] in the process.
Step One, put all S-AFC settings neutral within closed loop operational range or under the low throttle S-AFC setting. IIRC, the accepted hi-low throttle setting of the S-AFC is 70%, but someone who knows more may correct me. Reset ECU.
Step Two, use fuel pressure and/or AFM screw adjustments to adjust closed loop running. Crude, but it works- TCCS really responds. I start all tuning on AFMd 7M-GTEs by setting FP to OEM lower value of 33psi [vac line off], then working on the AFM screw, then back-forth until it runs well. Some engines can be stubborn, but usually due to encountering other issues as progress is made. Also, I've tuned more than one engine that behaved counter-intuitively. EG, smoothing out a lean idle burble by dropping fuel pressure 5psi.
Step Three, recheck vF [0-5V] to determine TCCS' level of correction at the problem point. vF is a great tool for dialing in closed loop- when TCCS is not constantly correcting, the engine runs much better. Heck, a WB AF meter would just get in the way in this particular circumstance...quality closed loop is more of a feel than a number, like tuning carbs, LOL.
Good luck, Larry A
