Odd temp sensor behaviour with DL1 and Lexus V8 sender unit

[andref]

Hi Folks

I wonder if anyone can assist me here. I have a DL1 and DASH2 installed in my Lexus V8 powered race car. All engine sensors are connected to the analogue inputs of the DL1 which then feeds the DASH via the serial connection.

I am having some strange issues with the temp output. It was appearing to over read and on investigation (using Monitor to log the actual voltage outputs from the sensor) I see that as soon as the engine is started the sensor output voltage drops by around 0.5 volts from its value with just the ignition on. This equates to close on 15 degC when the engine is warm. The sensor is using a 1k pull-up and is powered off the 5v ref from the DL (which is stable as I logged that on the DL as well just check).

The standard Lexus sensor is a single wire unit so I assumed an earth problem between the DL and the engine block. The battery neg is tied to the block which is then tied to the chassis. The DL gets it's earth from the chassis. However, if I tie the earth of the DL directly to the block there is no change in the behaviour.

The only thing that I can see changing here is the battery voltage due to the alternator charging. What am I missing here? The easy fix is to fit one of the RT two wire sensors, but I would rather like to keep the engine parts standard, besides this should work fine.

Many thanks
Andre

[Support]

Sounds like a grounding issue to me. Try running a piece of wire from the negative of the battery and touch it on to the outside of the GPS antenna connector. If this makes the voltage move up and down as you take it on and off then it is a grounding issue.

K

[andref]

Thanks for the reply. I did try connecting a wire from the block (which is connected to the neg of the battery) directly to the GND input on the DL1 and it made no difference, but will try directly from the battery to the logger this evening just be be 100% sure.

I'm also wondering if there could be a "resistance" issue where the sensor screws into the block. I know some folks use PTFE tape when they mount their sensors. I guess there could also be some corrosion as the engine stood for some time prior to me fitting it.

Glad you agree its likely a grounding issue, thought I was going mad for a while there.