87gnblackdemon
Don't Be Redikulas!!
- Joined
- May 24, 2001
- Messages
- 369
Hemmings Muscle Machines Issue#23 August 05
It's My Turn
In the Backfire section of issue #21, reader Rod Heubach wrote to comment on some advice about a throttle position sensor setting specification I supplied to a reader. Mr Heubach is under the impression that on a Buick-produced, 3.8l, turbo v-6 engine, a setting of .50volts may induce an idle instability condition. I respectfully disagree. I haved tuned hundreds of these engines over my career. Let me explain why my advice is indeed sound.
It cannot be forgotten that the TPS setting is a function of the throttle angle as defined by the minimum air rate or amount of opening of the throttle plate by the stop screw. GM spectifications list the minimum air rate at 400 to 450rpm and the TPS to be .40volts. I have found that many enthusiasts like to jump on the throttle and feel the power of the engine in short bursts. This leaves fuel film wetting in the intake manifold and port of the cylinder head and creates an overly rich mixture on rapid throttle closing that may induce a stall.
This is especially true if a smaller, high-stall torque converter is employed. The algorithm the elctronic control module uses for the idle air control decay rate is based on the inertia of the stock, and much heavier converter.
I have found that even with a stock engine and converter setting the minimum air rate to 600rpm to 650 rpm and the TPS to 0.50 volts, less authority is given to the IAC and the engine is happier during harsh throttle closing scenarios. I arrived at this setting by first setting the TPS and minimum air rate to GM values and then opening the throttle plates more.
Thus, to the ECM, the relationship of IAC position, idle speed and TPS all correlate and there is no idle surge or hunting. The engine management system and the owner both enjoy a smoother and better driving little turbo Buick.
In regard to the wide open throttle setting, all GM OBD-I ECM's look at 80 percent of the reference voltage to assume full throttle. Many falsely believe that a little higher TPS voltage at WOT will improve performance, and if that makes you happy than so be it! Actually the mass air flow transfer table has more authority then the TPS in this application and becomes saturated after 15psi of manifold pressure. In a speed-density system the TPS becomes more critical since it is used to model the volumetric efficiency of the engine. Thanks for writing in.
It's My Turn
In the Backfire section of issue #21, reader Rod Heubach wrote to comment on some advice about a throttle position sensor setting specification I supplied to a reader. Mr Heubach is under the impression that on a Buick-produced, 3.8l, turbo v-6 engine, a setting of .50volts may induce an idle instability condition. I respectfully disagree. I haved tuned hundreds of these engines over my career. Let me explain why my advice is indeed sound.
It cannot be forgotten that the TPS setting is a function of the throttle angle as defined by the minimum air rate or amount of opening of the throttle plate by the stop screw. GM spectifications list the minimum air rate at 400 to 450rpm and the TPS to be .40volts. I have found that many enthusiasts like to jump on the throttle and feel the power of the engine in short bursts. This leaves fuel film wetting in the intake manifold and port of the cylinder head and creates an overly rich mixture on rapid throttle closing that may induce a stall.
This is especially true if a smaller, high-stall torque converter is employed. The algorithm the elctronic control module uses for the idle air control decay rate is based on the inertia of the stock, and much heavier converter.
I have found that even with a stock engine and converter setting the minimum air rate to 600rpm to 650 rpm and the TPS to 0.50 volts, less authority is given to the IAC and the engine is happier during harsh throttle closing scenarios. I arrived at this setting by first setting the TPS and minimum air rate to GM values and then opening the throttle plates more.
Thus, to the ECM, the relationship of IAC position, idle speed and TPS all correlate and there is no idle surge or hunting. The engine management system and the owner both enjoy a smoother and better driving little turbo Buick.
In regard to the wide open throttle setting, all GM OBD-I ECM's look at 80 percent of the reference voltage to assume full throttle. Many falsely believe that a little higher TPS voltage at WOT will improve performance, and if that makes you happy than so be it! Actually the mass air flow transfer table has more authority then the TPS in this application and becomes saturated after 15psi of manifold pressure. In a speed-density system the TPS becomes more critical since it is used to model the volumetric efficiency of the engine. Thanks for writing in.
