Hot Air Intake too Hot, no good for MPG! - Fuelly Forums

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Old 12-08-2006, 01:35 PM   #1
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Hot Air Intake too Hot, no good for MPG!

Just did almost a half tank with my aluminum duct hose HAI totally up against the Exhaust Manifold, and judging by the gas gauge, I have gotten poor FE. Maybe like mid thirties, as opposed to my average 41-43mpg. Not having instrumentation sucks, but I just backed the hose up so it is parallel to the em, allowing sufficient cool air. When i moved it, it was really hot! Wish I could monitor the IAT in realtime, rather than all this guesswork.
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Old 12-08-2006, 02:36 PM   #2
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You could just use a multimeter to measure the IAT,
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Old 12-08-2006, 03:00 PM   #3
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Ben, just read thru some threads and came across the resistance to iat graph you posted. You know whether our cars like the same iat? did you find your optimal iat? know of a link that will show me how and where to hook up a wire to monitor my iat while driving? thanks!

edit: just saw your iat mod thread from last year when you still had dpfi, and I saw where the iat sensor is on the im. do i need to splice into one of the wires that go into that plug?
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Old 12-08-2006, 03:19 PM   #4
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I've never fudged around with it much myself, someone else might have some insight.

But, you can find a set of pinouts to figure out which wire to tap, shouldn't be all that hard, I don't have any offhand and I'm outside right now, or else I'd help you out.
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Old 12-08-2006, 04:54 PM   #5
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iat sensor has 2 wires. red-goes to ecu, and green-ground. to determine iat, i need resistance, right? so which wire(s) go to which node(s) on the multimeter?
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Old 12-08-2006, 05:56 PM   #6
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just ran red to neg on meter, and green to pos. reading was zero when i set it at 200 ohms, and 2k ohms. Then i switched the dial and then back again, and it would read approx 1k ohms on the 2k setting and 200 ohms on the 200 ohms setting. It only reads for a second and then switches to zero, so i have to keep switching the dial to get a reading that lasts a second or so. This normal? the 1k ohm reading translates into approx 105 degrees fahrenheit which seems normal for a reading with the intake hose sittting 3 inches away from the em, a couple minutes after a cold start. This would def explain my crap mpg when the tube was against the em, must have been really hot, like 200 degrees even, or more
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Old 12-08-2006, 07:26 PM   #7
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Trial and Error

I've found by trial and error that the 'Teg likes IATs around 80-100. Anything above or below, and the fuel maps start to compensate with more fuel to either warm the emissions system or cool the charge. The hottest actual temp I noted was around 220F with an HAI. It was in the summer, and of course the car had no power and needed premium fuel to prevent detonation -- it required more throttle input and leaned-out the mix to a degree as noted on the long-term fuel trim. After trying cold, warm and hot, I noted on the scangauge that 95F seemed to be what it wanted. I can cruise with decent power at a lower throttle input to achieve a higher FE rating.

YMMV as every ECU is different, but you may have to experiment with real temps first or get your hands on a fuel map with the IAT variable included.

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Old 12-08-2006, 07:43 PM   #8
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Slightly off topic, but why go through all the hassle of reducting your intake tract, instead of just relocating the IAT sensor? Or simply rewiring the IAT circuit so that the ECU always sees the ideal temp regardless of conditions?
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Old 12-08-2006, 08:27 PM   #9
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Quote:
Originally Posted by Red
Slightly off topic, but why go through all the hassle of reducting your intake tract, instead of just relocating the IAT sensor? Or simply rewiring the IAT circuit so that the ECU always sees the ideal temp regardless of conditions?
Because:

1. The IAT occupies a hole on the very aluminum intake manifold of his engine.
2. Lying is mean.

But yeah, just changing the air intake charge is the easiest way. Lying would cause problems with lean air mixtures and o2 compensation, whereas the HAI would be working with the ECU and not against it.
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Old 12-08-2006, 08:41 PM   #10
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Not a liar

I've never been comfortable "lying" about it, which is is why the duct-work was installed -- Saturns seem to really like the IAT mod, and other models: not so much. The concern is that you'll detonate the engine to its demise with an overly-lean situation and not let the ECU do job it was hired to do.

To maintain that ideal temp, I'm considering an installation of 2 ducts: one that draws the ambient outside air, and one closer to the exhaust manifold as I had before (I've used both idependently). The goal is to use the IAT signal to get the actual intake closest to 80-100F using a feedback loop and valves to open and close the flues of each air source. It sounds like a lot of work, but it's the safest response for a Honda engine. The IAT-resistor mod can't compensate for reality: air density, emissions system feedback, etc. which changes in an instant.

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