Throttle Pot query

[TVRPierre]

Hi
I had my 1997 Chim 500 serviced last week.

They hooked it up to Roverguage and said that the throttle was showing at a constant 87%. The car drove ok though.

The throttle pot was change and all seemed good readings.

I have now got RoverGuage (thanks for the lead Mark) and connected up to find that the throttle is now showing a constant 90%.

I have disconnected the plug and tested across the 3 little spade connectors.
Blue to brown 4.86K ohms - no changed when throttle moved.
Blue to Green 0.00 ohms
Brown to green 5.03k ohms - varies through to 0.78K ohms as the throttle is turned from fully off to fully on.

This seemed reasonable to me so I tried to prove the wires back to the ECU. The yellow was ok to pin 3 but I can't prove the other 2 which are supposed to be going to 20 (red) and 25 (red/black) although to be honest at the throttle end they both look red.
I did try all other points on the ECU but could not find the connection.

So should the red go straight to the ECU or does it go through any connectors?

The red/black should also go to fuel temp sensor and coolant temp sensor and AFM. I should have tested these back to the ECU / between each other but I didn't think of it at the time plus I don't know where the fuel and coolant sensors are.
So is it likely that the red/black to the throttle pot is at the end of the line so if it is broken somewhere all the others would be ok.

If the red and red/black wires are broken somewhere is the permanent 87% to be expected.

Any help would be very much appreciated.

Cheers Pete

[TVRPierre]

I have still been tinkering around and I have obviously got an intermittent open circuit on the red wire.

However whilst looking at the throttle pot I noticed that immediately underneath there is a metal tube coming out of the plenum with no hose on it. the hose is underneath and not connected. the hose goes off to the engine between the coolant temp sensor and the 1st injector.

I don't think it has been connected for a while looking at the colour of the metal tube - what does this tube do and what will it be causing please?

Pete

[blitzracing]

The plate with the pipes is the preheat plate for the plenum- the idea is hot water from the engine keeps the plenum warm in sub zero climates. Its not used on the TVR as they have not sold a lot in Iceland, and heating the intake air hotter than needs be reduces its density and the available oxygen, so reduces power. I doubt you could measure this however.

As for the throttle pot- 3 connections. 1) ECU earth 2) Throttle pot input to ECU 3) 5 volt supply for sensors from ECU

The throttle pot itself is about 5 k ohms, so you should see a shifting resistance sweeping about 5 k ohms between the "wiper" (green wire) and either of the other connectors, just the direction will be reversed between the connections. This is with the unit unplugged-

With the unit connected and ignition on:

Voltage measured between the red wire (+ve ) and green (wiper)
Throttle closed .085 - .545 volts

Throttle wide open 4.2- 4.9 volts

Make sure you run any RoverGauge tests with the ignition on- as the display freezes with the last readings if it stops getting updates from the ECU as the ignition goes off.

[TVRPierre]

Thanks Mark

Should the hose be connected to it though as it is just flapping about under the plenum?

Pete

[blitzracing]

You can connect them if you want- TVR just blanked them off from memory with small bolts.

[TVRPierre]

Thanks again Mark.

I have checked the throttle pot again and it's ohm readings are pretty much as you have described.

I will have a play, hopefully tomorrow or Wednesday, with checking the voltages.

[TVRPierre]

Just an update - well done BlitzRacing spot on with the bolt in the end of the hose.

Secondly I had the connectors changed on between the throttle pot and the loom wiring. All good for the best part of 60 miles.
I went for a bit of a spin today with Roverguage running on the laptop on the passenger seat.
Then after about 25 minutes the throttle was showing as 93% - it remained about this figure all the way home.
I disconnected the ECU and tested the throttle pot wiring from the ECU plug. Yellow and red both ok but nothing from the red/black.
The red/black also goes to the AFM, water temp sensor and fuel temp sensor. I proved each of these back to the ECU plug and checked the throttle pot again (still no go).
I could just put another wire between one of the other units and the throttle pot but does anyone know where they are likely to be joined together.
I am guessing they will have a single branching point as there is only one wire at each of the connectors.
Does anyone know where this is likely to be?
Cheers
Pete

[blitzracing]

Bit odd- the red black is the common 5 volt rail to the sensors, so if you loose this the throttle pot voltage would drop to zero, not 93% that you are seeing. To see 93% it would imply that earth wire to the throttle pot had gone open circuit. They are prone to breaking inside the wire covering where the wire enters the pot itself.

[TVRPierre]

Thanks again - it's a new pot and the plug (male and female) has been changed.
I am gonig to check again tomorrow, weather permitting.

[TVRPierre]

Good and bad news on this today.
Good news is I tracked down the high resistance/open circuit on the red/black wire from the throttle pot to the ECU. My multi-meter was flashing all over the place when I was moving the wiring loom by the ECU. I traced back up the loom and found this blue plug.



It is about 6 inches up the loom from the ECU plug.

I found that loads of the connectors inside were rather crusty so I assume it must have got damp/wet in the past. There are bars in there that basically bridge wires together.

All cleaned up and throttle pot tests ok through to the ECU on all 3 wires.

I also found that the fuse/relay board by the battery was not fixed to anything even though there was a bolt there.
I re-attached this and tightened up - much better.

The bad news - when I put the key in the ignition, turn it to test the throttle on Roverguage, and I get absolute nothing on the turn of the key.

Door buttons, headlight etc. work fine but nothing through the key.

Any ideas on what should actually operate from the turn of the key or what else could be wrong please?

Cheers