Sensor Temperature And Resistance Values

[peterc.lewis@blueyonder.co.uk]

Still having issues with my car running rough and not revving till warmed up and was hoping for some info' about resistance checks for the temperature related sensors.

Does anyone know what the resistance value is for the Inlet Air Temperature sensor at various temperatures from about -10 degrees up ?

Cheers,

Pete.

It's a 1.8 GS 1998 Avensis I , 7 AFE engine.

[Gooli]

The water and air inlet sensors should both be about 3K ohm at +10C

and about 2K ohm at +20C.

[peterc.lewis@blueyonder.co.uk]

So would it be fair to assume the following values.

If I did would putting a resisitor of that value across the sensor connector fool the ecu in to thinking the sensor is sending that temperature and simulate correct fuelling ?

At £60+ for a new sensor I want to be sure .

I calculate values as :

Temp in celsius Ohms kilo ohms

-10 0.00600 6.00

-9 0.00590 5.90

-8 0.00580 5.80

-7 0.00570 5.70

-6 0.00560 5.60

-5 0.00550 5.50

-4 0.00540 5.40

-3 0.00530 5.30

-2 0.00520 5.20

-1 0.00510 5.10

0 0.00500 5.00

1 0.00490 4.90

2 0.00480 4.80

3 0.00470 4.70

4 0.00460 4.60

5 0.00450 4.50

6 0.00440 4.40

7 0.00430 4.30

8 0.00420 4.20

9 0.00410 4.10

10 0.00400 4.00

11 0.00390 3.90

12 0.00380 3.80

13 0.00370 3.70

14 0.00360 3.60

15 0.00350 3.50

16 0.00340 3.40

17 0.00330 3.30

18 0.00320 3.20

19 0.00310 3.10

20 0.00300 3.00

21 0.00290 2.90

22 0.00280 2.80

23 0.00270 2.70

24 0.00260 2.60

25 0.00250 2.50

26 0.00240 2.40

27 0.00230 2.30

28 0.00220 2.20

29 0.00210 2.10

30 0.00200 2.00

Of course this does assume a linear increase.

[MW0ELC]

Peter,

Can I refer you to this website http://www.boosterplug.com/?id=Basic_Resistor_Tuning&menu=3

This is something that someone has developed for motorcycles, people were putting resistors on the inlet air sensor to fool the ecu into thinking ambient air was cooler that it actually was, thereby enriching the mixture. It may give you an insight as to what I think you are trying to achieve and may give you some ideas.

Les

[Gooli]

Yes, i guess you could fool the ecu in that way.

Have you measured the sensors? Did one of them give the wrong values?

Here are some diagrams of the right values at specified temperatures:

Water temp sensor:

Air intake temp sensor:

[peterc.lewis@blueyonder.co.uk]

The engine coolant temp sensor was definately checked by the mechanic.

What I am getting is hard starts when really cold and a tick over of 1200 on start dropping to 800. This is normal (or the car has always done that).

The problem is that until the car is up to temp it will not allow revving , as the temperature increases the revs it allows increase till it is up to normal temp then it runs normally.

I measured the inlet air temp sensor this morning with 20 C showing on the dash and it as near 2 kilo ohms. I though it should have been nearer 3 . My theory is that the ECU is getting the message that the ambient temperature is actually 10 degrees or so warmer than it actually is so is not providing cold start choke.

Of course I have jumped to a whole raft of conclusions so far but just want to put then resistor that corresponds to , say , 20 degrees in and see what happens.

Unplugging the sensor makes no difference.

I've checked voltage at the connector and I am getting near 5 volts so the wiring seems ok.

I greatly appreciate people taking the time and effort to answer and offer advise, thank you very much.

Pete.

[Jamesbelfast]

Air temperature inside the inlet system is always likely to be higher than outside ambient so it ain't good to make measurements based on these values. Inlet air temperature can vary at all times even when the engine is hot - imagine climbing through the alps for instance so unless performance when hot is poor I would think the inklet air temp sensor is OK. Disconnecting either sensors is not a good test as in many cases this forces the ECU into default mode whereby it assumes standard figures.

I suggest you check the resistance values of the coolant sensor both when cold and then when hot - not in a bowl of water but still in the engine. When hot its resistance should drop dramatically. I don't have the exact figures at hand but some ball-park figures should be roughly as shown below and I have used these figures for test purposes only and have found them good enough to detect numerous coolant temp sensors. You'll notice a vast drop between 20 and 80 degress C

20 degrees C = 3550 ohms + or - 500 ohms

80 degrees C = 335 ohms + or - 35 ohms

90 degrees C = 240 ohms + or - 30 ohms

Obviously if there is a fault in the wiring or connections the ECU will get entirely bum readings so check that aspect out as well.:)