Temp Gauge Problem

Still havent driven the car since swaping the new engine back in april but constantly checking things over to make sure it runs perfect before welding and getting it on the road.

So my temperature gauge wasnt working on the car. I put a new temperature sensor on the engine. Once installed without temperature gauge connected i checked the resistance to GND with a DVM. it was around 80 ohms or so when warm which i know is about right.

With the speedometer disconencted and removed from the car the resistance between TM and GND on the back of the speedo is around 168ohms. i believe this is the coil resistance of the temperature indicator. I re-measured the resistance of the speedometer connector when the engine was running with the speedometer disconnected and was still around 80ohms i so i know the correct resistance is getting to speedometer. However when you connect the speedometer to speedometer connector the pointer does not move. if you measure the resistance between TM and GND with the engine running and temp sensor connected its 0ohm direct connection to GND. what is the problem, i know the sensor is good and the wiring is good but seems to short out when you connect the speedometer to the car.

Knackered gauge?

I was thinking that but don't understand why it shorts the temperature sensor to gnd when the speedometer connector is connected to the speedometer

If someone could measure the resistance between tm and gnd on the back of their speedometer when disconnected that would be great.

Does anyone know what the ECU temperature sensor does, there is two temeprature sensors; one for the gauge (single pin) and one for the ECU (dual pin) but what does the ECU do with this signal.

THanks

If im correct the ecu uses the signal from the sensor to calibrate the fuelling at different temperatures i.e puts more fuel in on a cold startup (automatic choke) then gradually reduces how much fuel as it detects the coolant warming up

As above mate

Dose it have something to do with the dual stage fans also if I remember rightly

johnny gtir wrote:Dose it have something to do with the dual stage fans also if I remember rightly

Ah yes i do believe you are right, forgot about that bit

Does anyone know the coil resistance of the temperature indicator

ecu temp sensor sends signal to ecu which is constantly monitored, then in conjunction with info from other sensors it then alters ignition advance and fuel injected into cylinders to maintain correct afr's,
so in a nutshell all the readings the ecu gets play a part in its decision to adjust or not.
The fans are actually triggered by an earth not by a live wire as most people seem to think.

Easiest way to check either of these sensors is by removing them and use an ohms meter.
Note the reading you get with the sensor being cold then either warm it up in your hand or put in some warm water then the ohms reading you will see change as the sensor gets hotter, if it stays constant from cold to hot or from hot to cold then its no good.
Hope that helps a little

Hi bob. Yer the sensor is good I fitted a new sensor as the old sensor single pin terminal snapped. I measured the resistance directly at ambient and once warm and it ties up with the data sheet.
I traced the yellow/green wire to the dash and the resistance is the same except from an ohm or so which is just cable resistance.
The indicator coil resistance is 160 ohm when open circuit but when you connect the temperatute indicator to the temperate sensor harness it shorts out to ground.
I need to know if the coil resistance is correct to know if the coil in the indicator is part of the reason why it is shorting to gnd.

Today I have spent some time trying to figure out the problem and still have the problem. Here's what I've done

Disconnected temp sensor and grounded wire. I checked the gauge and the pointer went to hot. So gauge appears to be working
I disconnected the gauge from the circuit and with ignition off when engine is warm resistance of sensor is around 50 ohms. However if you turn the engine on the resistance immediately drops to 10 ohms or less. I am leaning to believe there is grounding issue. However I'm not a 100% sure.

Next thing I am going to do is check engine grounds as this may be the issue.
Also I will connect a decade box directly to the gauge and see if I can get it to respond. If I can get it to work then it wiring/gnd related

It's just a strange fault, with engine off the sensor resistance is one value then with engine on resistance is dragged down low