TPS sensor plug question

[Richard Wood]

I have disconnected all engine and transmission wires as part of a conversion to electric but planning on keeping components that can be translated for use in the new form.
With the key in and turned I get the instrument panel lighting up, so all good there.

Looking at the Throttle Position Sensor plug:
If I then connect a multimeter to negative on the battery and positive on each of the three bits of the TPS plug on the harness I get 0V, 1V, and 0.1V
Does that make sense to anyone? Shouldn't I be seeing 5V on one of those? Or does the ECU only deliver that 5V when it senses some other conditions are valid, such as the engine going or something?

Cheers
Richard

[bazar01]

Can you connect the plug to the TPS and back probe the plug?

[Richard Wood]

Will have a go. Not sure how to access the pins in that case but maybe can open up the TPS or pull back the wire covers.
I guess the idea is that once connected the ECU might then deliver voltage, although I thought it always delivers its 5 Volts to sensors if key is turned.

[xxxJohnBoyxxx]

TPS works on a 0V-5V scale to let the DME know how wide the throttle is open.

[Richard Wood]

Yep. Understand that, which is why I am looking to see the 5V on one of the wires coming from the DME to the TPS, and then will look for a range coming back on another wire, depending on position of throttle.

[Richard Wood]

Facepalm! I have a second 318ti in operational order. So I put the multimeter on that TPS plug and it showed 0, 5.somethingV, 4.somethingV. So those are the values I should be looking for.

I'm going to print out the electrical diagrams and try to see if there is something I need to do with one of the unplugged plugs to ensure the voltages appear. I tried plugging 4 engine-related sensor plugs back in but the rest have nowhere left to plug into as I have pulled things out of the car.

Another interesting behaviour I noticed incidentally while checking all the various plugs for voltages. After a minute or two of the key being on there were 5 beeps (not the ones for an open door). Then a little later there was another five beeps and the instrument panel went off. I turned the key off and on and it stayed off. I left it a little longer and tried again and it turned on again. Anyone seen that behaviour before?

Cheers
Richard

[Richard Wood]

Further to this thread, I've checked the TPS again and it is in working order, and I've done continuity tests from the DME plug to the TPS (pins 59 (5V reference), 12 (TPS signal) and 43 (Sensor ground). The wires all checked out fine.
Plugged the battery back in and switched the key on, but not getting the 5V through the TPS plug as I do in my other 318ti. Which means it's not coming out of the DME.
Of course I have a lot of other wires disconnected, so am wondering if under certain conditions the DME switches off the 5 volts for the TPS. For example the Transmission warning light is of course showing at the moment as the transmission is temporarily out of the car. Has anyone heard of anything like that? If it is the case then I need to ensure or simulate the right conditions to get the TPS to operate.

For background, I'm checking all this so that I can have the TPS input from the DME's DKV into the Transmission Control Module. If anyone knows what role this input plays in gear selection please let me know. In some conversions people just put a 5K pot over a TCM's TPS and leave it in a tuned fixed position. Another option would be to feed the TCM's TPS input directly - does anyone know if the TPS could bypass the DME and be connected directly to it?

In terms of managing all the DME to TCM connections. I've identified there are 6 wires. There are four outputs from DME: 1 Fuel Pump Control, 11 DKV, 17 Fuel Consumption, 48 A/C Compressor Control. There are 2 inputs to the DME: 64 Ignition Timing Interrupt, 65 Drive Range Pin.

The inputs I understand are to slow engine during gear change and (i'm guessing) to limit engine if in Park or Neutral. I can figure a way to use these directly without the ECU.

For outputs there is the DKV which I know is the TPS input into the TCM and there is the A/C status, which is also an input to the TCM to account for added load (I'm guessing that can be done without).

But for the other two, why would fuel consumption be relevant to the TCM? And what is the relevance of the fuel pump relay control to the TCM?
Are these outputs from the TCM to other components, or inputs into it?

A good reason for me to keep the DME is that it also feeds the speedo and tacho. I’m keen to keep it in place for the features I need so long as lack of inputs on other engine sensors don’t prevent other things working.

Looking for assistance in understanding all this.
Cheers
Richard