engine and drivetrain Required inputs for EFI?

[TKMad]

Inlet air temperature is not absolutely necessary. Air temperature corrections are based on degK (Kelvin) and don't have over 2% correction unless you live in Nome, Alaska. It's one that the purists think is necessary and have their fuel maps off by more than what the air correction is. Put one on if you think you neede it.

I don't know about that. I forgot to plug my AIT sensor back in after some maintenance and it ran noticeably crappy until I figured it out and plugged it back in. Being such a cheap part I would definitely not leave it out.

However, on the subject of not strictly needed parts, you can omit the TPS and the idle control valve if you want. I am running right now without a TPS, using only MAP for accel control, and it is 90% as good as having the TPS.

The idle valve is great to have, but if you don't mind revving it a bit until it's warm you can do without it.

[jimk]

Inlet air temperature is not absolutely necessary. Air temperature corrections are based on degK (Kelvin) and don't have over 2% correction unless you live in Nome, Alaska. It's one that the purists think is necessary and have their fuel maps off by more than what the air correction is. Put one on if you think you neede it.

I don't know about that. I forgot to plug my AIT sensor back in after some maintenance and it ran noticeably crappy until I figured it out and plugged it back in. Being such a cheap part I would definitely not leave it out.

However, on the subject of not strictly needed parts, you can omit the TPS and the idle control valve if you want. I am running right now without a TPS, using only MAP for accel control, and it is 90% as good as having the TPS.

The idle valve is great to have, but if you don't mind revving it a bit until it's warm you can do without it.

What's new? If you unplug a device that you have set your software as on, of course it will come in as a buggy reading. Turn the device of (if your software is sophisticated enough to do so) and you won't miss the air temp sensor.

[TKMad]

What's new? If you unplug a device that you have set your software as on, of course it will come in as a buggy reading. Turn the device of (if your software is sophisticated enough to do so) and you won't miss the air temp sensor.

I routinely see about a 50 degree change in IAT from the time I leave for work to the time I get there. Would be less if I had a dedicated cold air intake, but for arguments sake... That is a 9% change in air density. That makes your 14.7 to 1 ration go to 13.4 to 1. Or if it gets colder it would be 16 to 1.

Sure it will work, it just will only be optimal for one temperature. I guess my reasoning is that if you are going to all the trouble of having EFI you may as well give it power to control the mixture as well as it can. Even without it it would still be better than a carb!

[jimk]

What's new? If you unplug a device that you have set your software as on, of course it will come in as a buggy reading. Turn the device of (if your software is sophisticated enough to do so) and you won't miss the air temp sensor.

I routinely see about a 50 degree change in IAT from the time I leave for work to the time I get there. Would be less if I had a dedicated cold air intake, but for arguments sake... That is a 9% change in air density. That makes your 14.7 to 1 ration go to 13.4 to 1. Or if it gets colder it would be 16 to 1.

Sure it will work, it just will only be optimal for one temperature. I guess my reasoning is that if you are going to all the trouble of having EFI you may as well give it power to control the mixture as well as it can. Even without it it would still be better than a carb!

No O2 Closed loop on your system?

[TKMad]

No O2 Closed loop on your system?

Sure, but it only corrects so much. But hey, for $20 and a couple wires, there is no reason not to do it.

[dlmrun2002]

Can you need Megasquirt without an o2 sensor? Just asking.

dlm

[TKMad]

Yes you can, but it would be really tough to tune without using one at least initially. It's called running open loop.

[jimk]

I agree with your 9% calculated effects of a 50F temp rise, but unless you are compensating for fuel density change on s N/A application, it will reduce the effect of air temp density correction on a warmup situation to about an accepted value of 2-3%. The 2-3% can easily ba absorbed with the O2 correction. This is why the originator of this thread can get along without a air temp sensor. If enrichment tables from several prominent mfrs are reviewed for base maps, the air temp correction is 0 for qite a range and only 1 or 2 percent for the 50F.

Usually one needs to keep hands out of pockets on things like this. Hands in pockets end up getting thins all knotted up and it is painful to get thins untied.

[AustrianVespaGuy]

I agree with JimK's assessment. Once you also factor in the density change of the fuel and also the pressure (aka MAP) change due to the change in air density, inlet air temp only plays a small role and can be absorbed by O2 correction. Having IAT is still better, certainly, but not a necessity.

But getting back to the original question, here's my take on the order of importance of the sensor inputs needed for Megasquirt EFI:

1. (can't run without) - MAP, RPM, and Coolant Temp.

2. (you really want to have these) - Wideband O2, Throttle position.

3. (get it running first then add these if you still want) - Air temp, idle control

Hope this helps!

-Carl