From those of you who have eliminated the MAF when going to Megasquirt where have you put the IAT sensor and which one did you use? Photos of you installation would be great if possible.

 

Location? It depends on your car model/engine/intake design/etc. - you want it somewhere where it can measure the intake air temp without getting heat soaked. I have mine in front of the throttle plate; this happens to be on the plug side of the engine away from hot exhaust parts. The standard GM (109?) sensors are accurate, reliable, available, inexpensive and all MS code easily supports their calibration curve.

 

Thanks, that helps me a lot. Did you just drill and tap for the sensor or did you use one of the weld in bungs? I'm not sure the throttle body would be thick enough at that point just to drill and tap, haven't really looked that hard at that area.

 

Oh, guess I should have mentioned that all polution controls and rats nest mods have been made as this is an autox car only in prepared class. So would it be okay to put it behind the throttle plates or would that cause a problem of incorrect temperature pickup?

 

Mine is between the throttle body and intercooler, very close to the throttle body.

 

Behind the throttle plates is fine - ideally what the fueling equation in the MS (or any ECU, really) relies on is measuring the temp of the air/fuel gas entering the combustion chamber. My first install measured IAT 8" past the throttle plate and I drove that without issue for >25K mile. Some OEMs even measure IAT in front of the radiator; it;s all relative. Once again, heat soak is bad. What gen 7 is this?

-Mike

 

Completely custom intake on mine, I'm afraid I can't advise. It sounds like you're making the correct evaluations and using critical thinking on the best place to put it.

-Mike

 

On S4 NAs, the dynamic chamber has the IAT installed on it. It is easy to enlarge the hole and tap for the GM sensor.

On TIIs, the stock sensor is located on the throttle body inlet. Enlarge and tap.

On S5 NAs, the sensor is on the lower intake at the front of the engine. That's a little more annoying. I don't know if there is enough material there but I bet there is a convenient spot near the VDI or on the upper intake runners.

 

Thanks Aaron Cake mine is an 87 S4 NA so I will be able to enlarge the hole and tap it for the GM Sensor. The guts of the engine right now are original, just have RacingBeat roadrace header, presilencer and dual exhaust to the rear with Cherry Bomb like mufflers and a cold air intake rather than the stock intake for now. Once we are ready for a rebuild we will go with an aggressive street port but for now will stay with what we have.

I have ordered the MSII with 3.0 board assembled, an assembled relay board, the relay board cable, an LM1815 chip, and the wiring bundle. Will be picking up the rest of the parts needed for the added VR sensor circuit Saturday. I would like to replace the injector plugs also, which ones should I get?

I am starting to draw up my wiring diagram and will start getting ready so that I can dig in as soon as everything arrives from DIY.

Is there someplace that I can download base fuel and ignition maps to have a starting point or at least have a table to initially load into tuner studio?

 

I just used the stock sensor in the stock location (right between the intercooler and the throttle body). It heat soaks a bit, but not terribly so.

 

There's no need to enlarge and tap. The stock sensor works fine with the proper bias resistor and calibration.

Ken

 

Accounting for heat-soak is one of the things I'm going to be attacking soon hopefully after I'm done with ms3 stuff.

Ken

 

What's your thoughts on how to compensate for this in software?

-Mike

 

I can tell you that my GM spec sensor from DIY doesn't heatsoak. It is tapped into a welded flat on my intercooler piping, and I can assure you guys that it is a lot more accurate in the hot engine bay than my FC air temp sensor was in the throttle snout.

If there is a mechanical solution go that way (I'm an electronics person myself and i still tend the mechanical way).

 

Yeah, Jobro, I fully agree on that concept. Unfortunately, some people don't have the option or testicular fortitude to reengineer things. I, too, have little problem with heat soak using that same sensor. It seems to acquire realtime IAT very rapidly.

 

True about the stock sensor working of course. I've set up a few using it but always found it a major pain to run EasyTherm every time I update firmware and remember what the bias resistor value is. Now I just use the GM sensors since they are stock on the 'Squirt and available at every auto parts store.

 

I had a couple of ideas that involve having a second sensor and a table to merge the two values into what you end up with close to the intake port. Tuned right it should be accurate all the time. I believe the stock 2nd gen had 2 MAT sensors anyway... one in the AFM and one in the manifold.

Ken

 

Hmm, so measuring, calculating and predicting the deltaT as air ingresses? Interesting idea. Now that I think about it, I imagine the heat soak experience isn't all the sensor but rather a result of hot metal heating air on the way in, especially at low loads, like idle. Thanks!

 

I have a feeling the heat soak problem is also somewhat the metal attached to the engine being VERY hot aka inlet manifold and snout, and the stock air temp sensor has a higher heat conduction value to the metal it is bolted to.

Are you concerned about real heatsoak? Or rather than the sensor reading higher than the air really is (I'm talking about sensor measurement error here due to being bolted to the intake).

If the problem is hot air, get cold air, and get an intercooler, they are great.

 

It's pretty much academic to me - after a hot shutdown and upon subsequent restart I get 5-10 seconds of higher IATs that rapidly dissipate and it's a non-issue. Given that ambient temps here are often 90F/32C+ my inspired air isn't at a very cool level to start with and my tune probably reflects that. I'll soon report on how well AI does at reducing IAT further but now I'm way OT...

 

I get the 'hot air after a recent start' thing too. Less than 1km down the road its back to normal. Unless it causes rough running that you simply can't tune out I wouldn't worry about it, short of ceramic coatings or header wrapping your intake pipe there is not much you can do about it.

 

Not necessarily true. We're going to try to work on heat-soak compensation in the code.

Ken