Started this thread over on ttora, thought I might get some of you guys over here that could help as well...
Still tuning, Gadget has helped via email some and I am still planning a tune with him, but I know he has a crazy schedule so I am enlisting help here again :confused: My map is tuned at almost any rpm with vacuum, afr stays at 14.7 or so up until .5lb boost, trims stay usually with in 5% of each other. Then at a slight load or grade once I hit 1/2 lb boost up until about 4.5 lbs the trims go crazy dumping fuel? The afr will drop dramatically to as low as 9.3 and throw the long term off badly if I don't drop out of overdrive or floor it. If I drive in this area for a while the long term is so rich that the truck will barely run at any rpm and I have to reset the ecu. Ok, so I figure lean this area out(.5lbs to 4.5lbs boost in 1000 to 4000 rpm range), do it and under a load I get the afrs to 11.5 to 13, good so I thought, maybe lower it a bit more, right.... then I hit a flat road, no load grade etc... 16.5 afr :eek: at the .5 to 4.5 lbs 2500 rpm area?? What gives. Gadget informed me Toyota has a area in the map that will dump fuel to cool the cats. Is their a way to fool the computer into not doing this? Any insight or help here is much appreciated. Sorry to keep posting on tuning this thing, but I drive it every day and want it right. :o

Steve

 

I have a lot of experience tuning my mustang, but havn't delved into yota tuning, so pardon me if none of what I say applies.

First: Are you 100% sure that your truck is mechanically sound? No vacuum leaks, no bad sensors, etc.? If you're not 100% mechanically, you can tune all day and never run right.

What year is your truck? EFI or carbed? How is your timing set? What size fuel pump/injectors do you have? Any fuel upgrades (oversized lines, fuel rails, etc.)? Lay out what you have to help diagnose.

The ECU on my mustang has two basic sets of governing parameters that you tune: full throttle and anything that is not full throttle. At part throttle the ecu uses reading from various sensor (maf, O2, coolant temp, rpm, etc.) to determine parameters such as engine load, available air, and then calculates the necessary fuel; this is closed loop operation. At full throttle the computer can't keep up with all the sensors so it uses a preset fuel curve and timing curve to supply fuel to the motor and adjust timing; this is open loop operation.

When tuning all we worry about is the open loop parameters, since light driving will not be affected by a power adder. Exactly which parameters are you changing to lean out and richen your truck (MAF transfer, injector slopes, injector pulse width?, etc.)? Did you change the Breakpoint? Have you changed any of the Scalars? Are you changing your timing curves when you change fuel curves? How are you measuring your A/F ratio (wideband 02 I hope).

Most OBD-equipped vehicles do have a feature that adds fuel to cool the cats. The name of this scalar in my mustang ECU is Switch_for_cat_temp_ctl, or cat_temp_sensor_switch, and I set that value to 0 to disable the fuel dump.

Sorry for the long post without saying much, but if you can say exactly what parameters you are changing (or have changed) I can go through my notes and try to help.