Carrera Motronics: Cyl Head Temp Sensor
 

Further to my recent post regarding low idle, I decided to measure the resistance on my Cylinder Head Temp sensor.

Can you guys please confirm that the TOP wire on the metal bracket to the left of the engine bay is actually the CHT sensor wire? There are three wires going into this bracket.

I take it the wire running to the right actually goes down to the head and the wire on the left runs to the DME ECU, correct?

Anyway, the connector on the right has a 3 pin connector on mine :confused: I measured the resistance across the two top pins and I get a reading of ~124 ohms (and slowly dropping). If I measure between any of the two top pins to the bottom pin, it's open circuit, so I assume the 3rd pin isn't going anywhere.

Questions:

Have you guys seen a CHT sensor with a 3 pin plug like mine?

Isn't the reading above WAY lower than what it should be?

A good sensor should read in the 2K-3K ohm range, right?

Can someone please confirm asap.

EDIT: The current outside temp is 23DegC. My understanding of these Thermistor type sensors is that they are in the Kohm reading when cold and this reading drops as the sensor/engine heats up to operating temps???

Hmmm, looks like my ex-wrench mounted the bracket upside down, or the wires the wrong way round. The CHT sensor wire (white) was actually on the bottom of this bracket, NOT the top like any normal Carrera :mad:

I measured the 3rd "single wire/pin" connector to a ground point in the engine bay and it read ~2.8K ohms, which I believe is good working order, even though it's a single wire unit :confused:

I guess it now comes down to finding a vacuum leak which is causing my low & rough idle :(

For !@#$ sake, this is really p!ssing me off now :mad:

How 'bout looking after hard-to-see vacuum leaks.... ?

Here's an interesting one by Jim Smolka.... http://forums.pelicanparts.com/showthread.php?s=&threadid=156474&highlight=vacuum +hose+Carrera

Happy hunting....

- Wil

Thanks Wil. Yeh I'm probing around for leaks at the moment.

Quick question, should I replace the single wire CHT sensor with a dual wire unit, even though the single wire one measures OK @ ~2.8Kohms?

Or is it a case of, if it aint broke, leave it alone?

if the sensor is within spec leave it.Have you gone throught the factory DME test plan for drivability problems? l`ve got a couple copies of the factory update folders,very systematic troubleshooting for stuff like this. What happens when you unplug the MAF while the car idles? lf no change then it`s the MAF...probably.l`d use a carb cleaner to check for vacuum leaks as WD-40 won`t always change the idle.However a vacuum leak will almost always result in a raised idle,not a lowered one.

Soooo, what would result in a LOW idle? Exhaust leak? Batter/alternator power output? Fuel pressure?

I'm at a loss :(

The CHT vlaue is diffeetn based on temperature...

here's one of many posts.... your values look OK for near ambient...

http://forums.pelicanparts.com/showthread.php?s=&threadid=215319&highlight=CHT+sp ec

- Wil