TPS understanding and substitution

[911st]

How dose the output signal from a 3.2 Air Flow Meter differ from the output from a Throttle Position Sensor?

The AFM on a 3.2 seems to output a voltage range up to something like 4 volts.

I think a TPS is a potentiometer and it outputs resistance values.

Please excuse my lack of knowledge.

Is there a TPS that operates over the same value range as the AFM?

And, if there is, is there also one that has a circuit that has the closed throttle switch?

If there is a TPS like this it would be easy to modify out system to work as a reference style injection system and we could eliminate the AFM.

The benefit would be less restriction on the intake or use of individual throttle bodies with a mostly stock Motronics set up.

One of the biggest cost of ITB's is sourcing a new ECU, replacing and adding sensors, and making a new wiring harness.

The maps in the ecu would have to be programed with values that work with throttle position and RPM instead of AFM position and RPM.

Any input appreciated. This could be a cool project.

Thx.

[ischmitz]

The AFM measures air volume and the TPS measures throttle position. The air volume ingested into the engine is a function of throttle position and engine speed. If you wanted to replace the AFM with a TPS signal you would either have to completely reprogram the Motronic or the car won't run properly.

There are systems that attempt to meter the amount of air simply by throttle position and engine speed but they have proven inferior to the air volume measurement approach. Present-day systems use the air mass measured by a hot-wire filament. It is less restrictive and automatically accounts for ambient pressure variations.

Ingo

[911st]

Thx ingo.

Under stood. MFI is a reference system as I believe the Cup Car motors. They however also have a manifold pressure sensor to.

Agreed, having a method that measures air flow is more effective and self compensating and a better choice for an emissions motor.

Yes, the maps would have to be reprogrammed. In some ways we would not need the WOT map with a TPS. Not my interest but it could be possable to then use that map for a under boost conditions with a turbo conversion.

Do you know anything about if there is a TPS than outputs a signal on a 4 volt scale?

[DW SD]

Did you look at megasquirt ECU? Folks control a variety of engine applications with megasquirt and you can choose various sensor inputs, including TPS, manifold pressure, mass air, Oxygen Sensor and more. I'm certain you can even blend some of the inputs. This system was created as opensource, so the prices are modest.

Doug

[ischmitz]

A generic TPS that uses a potentiometer would be required. You feed GND to one end of the resistor and +5 Volts to the other end. The pickup that rides on the resistor will see a voltage between 0 - 5 volts just like the AFM. The AFM is nothing else but a variable resistor that is actuated by the flapper. The resistor is laser-trimmed to make it more linear. Getting a TPS to work is the least of your problems, though.

Doug has a good point. Read up on the Megasquirt website. MS actually supports a TPS-based fueling scheme as one of its many options.

[911st]

So a normal TPS will take a 4 volt source down to 0?

Dose the stock AFM start at low then go to high voltage with increased air flow and dose the TPs start and progress the same way?

I guess it dose not really mater as long as the cells in the map have the correct value.

Are there any TPS's that have a throttle closed or idle switch built in?

My vision is something that plugs into the stock wiring at the motor with no other mods except a chip change.

I know of one builder that converts the Motec but it is 2K but he gives you the program to burn your own chips.

By the way, the AFM input seems to stall at about 5k rpm so the stock system is mostly a reference style injection system from there to red line.