Air temp Sensor for FI

[cowlum]

Hi Guys

Just a quick question, I am almost ready to bolt on FI setup when a realised I dont have an air temp sensor (what a goose!). Im not sure I got one with my 318i e30 inlet manifold. Can anyone tell me where this sensor is located on a 318 so I can attempt to find mine if I did indeed get one.

Regards

[Mike87]

If you are putting the 318 system in including the air door, the air temp sensor is in the air door housing. It is not replaceable.

[Zenon]

I've been using a second Bosch EFI coolant temp sensor, exactly the same as the one that would come with the 318i intake and looks like this (except for the connector colour, IIRC):

It works but is not optimal because it is very slow responding and is prone to "heat soak". I only used it 'cause I had one handy. It was supposed to be temporary. It would definitely be unsuitable for a forced induction setup.

Ideally, you want one with low thermal inertia - either open element or at least a very thin plastic shell over the thermistor. The most popular with Megasquirters (becasue it is cheap, easy to get, and the response curve for it is the MS firmware default) is a GM unit, whicha looka lika dis:

The GM sensor is 3/8" NPT vs the M12x1.5 straight metric thread on the 318i style but for a non-turbo setup like mine where it is self-threaded into a rubber intake duct that would not matter.

One of these style (left) in Bosch would still be better:

There is also a slick open-element Bosch sensor out there that has the same connector and supposedly the same curve as the other versions. It was used on VW New Beetle 1.8T, IIRC, and has sort of a balde style protrusion with a very fast response thermistor totally exposed to the airflow. Damned if I can find a link for it now, though.

regards,

Zenon

[cowlum]

Thanks mike and Zenon. I am sure now after sifting through my box of junk that I never actually had one. Ill head out to the pick-a-part this weekend and grab one.

Mike im not sure what you mean by 'air door', where is the air door located in the system?

Also, once I have found one I assume I must mount it in the manifold? is this correct? or can I place it in the tubing before the throttle body?

Regards

Callum

[Zenon]

Also, once I have found one I assume I must mount it in the manifold? is this correct? or can I place it in the tubing before the throttle body?

Theoretically anywhere in the intake air stream but the manifold itself is not a great location because you may end up reading more of the engine heat than the actual air temp and "heat soak" of the sensor is more of a problem. A very fast response sensor would minimize that drawback, though. Most factory setups have the charge air temp sensor somewhere between the air filter and TB so that is how I did mine:

I think "air door" refers to the flap-style air flow meter used in the stock E30 318i Motronic setup. It had a built-in temp sensor. You would not need or want that AFM in a Megasquirt system.

regards,

Zenon

[cowlum]

Excellent information again Zenon.

much appreciated.