[Formula jg]

George,

'Connect the load wire and ground to the sensor +5 and ground and you should be good to go.'

I probably got this part wrong but heres how I understand this:

The 12v supply is connected to the rheostat red
The blk load wire from the rheo is connected to the sensor 5v in
The blk sensor ground wire is just grounded to the block or firewall
The sensor signal output is connected to the ECM

That's wrong, right?

[george kujanski]

Actually, that sounds correct. The cole-hersee data sheet doesn't really specify which wire is which, but red to +12 sonds correct.

I believe the body of the cole hersee thing must also be grounded, preferably at the same spot that the TPS is grounded. They don't mention this, but I'll bet that's the case.

George

[Formula jg]

My brain hurts from trying to visualize all this.

Here's a pic of the rheo:

[george kujanski]

SO you're saying a pic is worth 1k words?

[LPete]

According to the specs, that's an electronic lamp dimmer. It seems to me that there's a good chance it's a pulse-width modulator, not a rheostat. Just speculating.

(Several late-model cars have electronic dimmer circuits that modulate the pulse width, instead of controlling the voltage of the lamp circuit -- that's why I'm thinking that way).

[Formula jg]

George,

Nice schematic, I like it, that really helps, thanks so much.

I just finished wiring a pot for the rpm signal, had wild readings on the data logger. The pot cleaned it up perfectly. Now I can focus on the TPS.

Pete,

Do you think it will work also?

[george kujanski]

Lpete may be right; it may not work in your application.

If not try the following; it's crude and simple, but just may work for you. You will need to buy some resistors at radio shack.

If you don't get approx 5 volts (should be around 4.8 or so), change the 620 ohm to a 330 ohm, and change the previous 330 ohm resistor to a 180 ohm.

We could have you make a small, accurate, regulator, but it would need a few more parts and a little circuit board to hold it all together. If the C-H part doesn't work try the reisistor thing; is cheap and quick to assemble.

George

[Formula jg]

George, again nice layout.

I'm probably not understanding it fully, but you show both the signal wire and the ground with an arrow to the data logger (ECM). Is that correct?

Also, Radio Shack was sold to Circuit City here and they have really reduced their electronic supplies. When I check their website they don't show a 620ohm. The have 330, 470, 1m and to be honest I really don't know difference ie. is 330 the same as 3.3?

Oh yea, I was curious about the pot I just installed, it gives perfect rpm signal but I'm now wondering if it is actually masking another problem like possibly something with the HEI. The issues I was have was from idle up to 2500rpm the data that the ECM was logging was very wild from 0-50,000rpm. Above 2500rpm it would display perfect rpm readings.

Am I fishing to fix something thats not broken?

[george kujanski]

If the RPM signal is working now, I suspect the logger just couldn't handle the normal HEi TACH signal voltage. If it's working, leave it alone. Without knowing what the input signal parameters SHOULD be, all we can do is make educated guesses from here.

I show the ground that way because when dealing with sensor signals good grounding, and grounding devices at a single point is important. When a sensor is generating signals on the order of a few volts, a volt or two lost thru inadequate ground will confuse a ECM. That's why in a normal TPS to ECM connection, the black ground wire goes from the ECM to the sensor instead of just grounding at the ECM and at the sensor.

A 3.3k is not the same as a 330.

Can you do a favor for me? If you can measure the resistance from the gray to black wire on the TPS sensor, I would appreciate it.

If you can't get parts locally order from www.digikey.com . They have all kinds of stuff and fast service.

George

[george kujanski]

Another thought...if you have the instructions with the logger, does it show a 5 volt connection on it that you can use for the sensor?

George

[Formula jg]

RPM is working great now with the pot.

Unfortunately I will not be able to measure the resistance until this coming weekend at which time I'm hoping to have what I need wire up the TPS.

Thanks for the link.

Regards,

John

[Formula jg]

Just wanted to thank you for holding my hand through this. I did get the TPS working with just a 7805 (no caps).