i recently switched from a 350 tbi to 454. With the throttle at idle, the tps % is 10 percent. as i slowly give it throttle, it the tps goes Down to 0 then shoots to 22% tps every time. and it will stay at 22% if at half, 3/4, or wot

My 454 tbi came with two adapters, and i used one for the iac, but the connectors for the tps would not interchange. currently my stock plug is plugged directly into the throttle body. Am i missing an adapter, or do i need to repin something?

 

Sounds like it needs to be re-pinned. The wires from the ECM are: +5V, TPS signal to ECM, and ground.

The TPS is a potentiometer (variable resistor). The +5 V goes to one end, ground to the other end, and the signal is from the wiper.

If you have a DVM can do this: disconnect the TPS connector, hold or prop open the throttle about half way.

Then with the DVM on the ohms scale measure between sets of two pins. There are three sets of two pins, find the set with the highest reading. These will be the resistor end pins.

The remaining pin will be the wiper. That pin goes to the ECM as the TPS signal (pin C13 at the ECM).

To find out which of the end pins is which: close the throttle, measure between the wiper pin and one of the end pins. Then between the wiper and the other end pin. The end pin with the lowest reading is the ground pin. The other end pin gets the +5 volts.

RBob.


{edit: I wanted to add to this. To verify that you have the end pins, measure there resistance while moving the throttle. It shouldn't change. If it does then one of the pins is the wiper.}

 

I will try that tomorow. thanks for the advice!

 

I am still having no luck. When i measure the sets in ohm, i stick a pencil in the throttle, and can find the two with the highest (7.5) . Then I close the throttle, and take the two sets of two-with the wiper being tested both times- and find the set that is low. that is the ground. Everything is normal there. but when ever i test the ground and +, i alter the throttle and the ohm's do change.

What is the chance the tps is bad?

 

it was a bad tps. 454 tps and 350 tps are same part number, when switched tps and went back to stock wiring it worked fine. thanks for the help though

 

One pair of the pins should never change in resistance as the throttle moves. These are the end pins. They are usually the outer two pins in the connector.

It may be that you are not getting good contact on the TPS pins with the probes. And the moving around is also affecting the connection of the probes to the pins.

RBob.

 

Even with the new tps from my fathers truck, i could not get one pair of pins to not change at different throttle. I cut the tps sensor wires about 1 inch from the connector, stripped them, and plugged the tps connector back in to check the ohms. i am pretty sure all three sets of the pin pairs changed. But i will retest when i get the tps off my old throttle body and post results.

regardless, thanks for the help

 

retested again. the ohm values do change with all 3 sets. the tps works fine, but should this be something to worry about?

 

If the scan tool shows the correct readings while connected to the ECM, then all is good. Which style connector does the TPS have? The small round one or the flat in-line one?

RBob.

 

It has the round connector

 

Surprisingly I found one with a round connector for a TBI. All the others I have around have the in line connector. I think this one came off a 4.3l Astro van.

Anyway, the two pins that are adjacent to each other are the resistor ends. With the odd pin out being the wiper.

I did find something interesting about the in line connector style TPS sensors.

Of the in line style all but one have non-slotted, non-adjustable, round mounting holes. Of these the two outer most pins (the pin on each end) are the ends of the resistor. With the center pin being the wiper (signal to the ECM).

The one in line connector style TPS sensor has slotted holes to be adjustable. On this sensor the two resistor ends are adjacent pins (an end pin and the center pin). With the wiper being the other outer most pin. Not sure where this TPS sensor came from.

But if it was swapped in for a standard round mounting hole TPS, it would require re-pinning the harness connector.

RBob.

 

Of the three round style I have seen, 2 of the three were non adjustable. one being about 7 months from being new, and the other off of the non working 454 unit. the tps i use now(most likely stock 91 full size sbc) is adjustable with slotted holes.

the round styles to me look like a T adjusted left 90 deg. every time i would test, the bottom, and far right would be the resistor pins

You may want to change "The one inline connector style..." to the round style. I think that is what you meant to say