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Discussion Starter #1
OK, i think i may have a problem with my intake air temp sensor. Haynes says ref voltage @ 5VDC, it's at 4.7VDC. The book also states resistance when cold (@68 DEG F) should be 37.3 Kohms, and when hot (212 DEG F) should be 2.07 Kohms. When mine is cold, it's reading 13.67 Kohms, which is significantly out of range. I'm letting it warm up right now to check the resistance while warm. If this sensor was bad, what would happen if it was disconnected? would the ecm just use the map sensor info to control mixture? if the sensor was bad, could it lean out the engine enough to cause it to misfire? i've been getting the always running rich code, and i believe that it's really running lean, and stumbling. while it misfires, i think that the unburned fuel is what triggers the always rich condition. what do you think?

update: when warm. iat sensor is 4.47 Kohms, about twice what it should be.
 

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I think you are correct and onto the problem. If it is reading less resistance than it should be, it thinks the incomming air is hotter than it really is. It then puts less fuel to make up for what it thinks is less dense air to try and compensate for a potential rich mixture...resulting in instead a lean mixture
 

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just read your update....if its reading twice what it should when it warms up, then it is starting to dump too much fuel in thinking the air is more dense then it really is..causing the rich mix...

edit: i forgot from your previous thread, have you also checked your coolant temp sensor as well as (if they are equiped) an EGR temp sensor?
 

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Discussion Starter #4
yes, it actually has a new ect sensor on it, and all the egr stuff is good. i guess i'm just not sure as to how much of an impact the iat has on the fuel injection. oh well, 17 bucks at advance, no biggie. i wonder why it didn't throw a code? as for the readings being off, do you think it could be leaning it out when cold, and running it rich when it's warm? i don't have a way to check the map sensor, it seems to be the frequency kind, and i don't have a tach to hook it up to.
 

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try running it with the sensor unhooked. you'll be in fmem "limp in" mode...the ecm will substitute default numbers to keep the engine running in case of a total sensor failure
 

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it wont throw a code because it thinks its working..it doesnt know that its really 68 degrees outside because the IAT is telling it its not.
 

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Also forgot to mention, clear your codes (during the koeo test, when its sending you the codes, just disconnect the MIL connector) also since you've replaced sensors, clear your keep alive memory. This is the adaptive settings you're pcm has learned as you're engine has been running and sensors were wearing out etc. If you were running on a bad sensor, and the PCM was compensating for it, it'll continue trying to compensate for it even if you've replaced the sensor. To clear these, just leave the battery unhooked for at least 15 seconds.
 

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Satyr of the Midwest
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I don't know if this helps at all, but it's worth knowing anyway. The IAT is typically used in the determination of the correct spark mapping. So if yours is malfunctioning (or covered in CRAP like mine was), you could either get some spark knock or miss out on some mileage.

By the resistances given already, it's sounding like it's faulty, but I'd really really like to see an actual temperature and not "warm" or "cold" as the sole descriptors. Also, note that the response of the thermistor (the little doo-hickey on the tip that's varying resistance) is NOT LINEAR. The Ford service CD has a graph and corresponding table with all of the voltage and resistance values, from 50 to 248 degrees Fahrenheit.
 

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Discussion Starter #11
i do have some spark knock up high, above 3000 rpm. that's cool to know, i thought it was used to determine fuel mixture. as far as temp, the ambient air temp today was 73 deg F (brrrrr) and after i warmed up the engine, i have no idea what the temp was, the gauge was between "r" and "m". hmm, so the resaistance is not linear huh? hmm, i'll prolly unplug it and see if it misses. after it's warm, it misses between 1500 and 2000 rpm under load. if it stops, i'll replace it, but maybe i'll pull it out and check it for being fouled like yours was, thanks for more helpful advice sig!
 

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You know, there has always been a two wire plug that was tied off to my air hoses in my engine compartment, and I'm starting to wonder if it should be hooked to an IAT.

I'll have to get a picture of it, and see if anyone can recognize it.
 

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Discussion Starter #13
maybe, the iat is right in front of the d.s. front fuel injector. it's got one of those goofy half circle-triangle plugs. check it for voltage, if it's hooked up to the ecm, it'll show around 5 volts key on/engine off. i have an extra plug that hangs down low under the intake hose, down by the steering box, but it's not long enough to reach anything! maybe i'll ask it in a forum and take a pic.

Pete
 

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Someody got a picture of this IAT?
What year Bronco are you discussing?

Thanks

:thumbup
 

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Does my 1986 FSB 302EFI XLT have an IAT and is it near the Schrader valve on the fuel rail?
Thanks
 

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coastiepete said:
OK, i think i may have a problem with my intake air temp sensor. Haynes says ref voltage @ 5VDC, it's at 4.7VDC. The book also states resistance when cold (@68 DEG F) should be 37.3 Kohms, and when hot (212 DEG F) should be 2.07 Kohms. When mine is cold, it's reading 13.67 Kohms, which is significantly out of range. I'm letting it warm up right now to check the resistance while warm. If this sensor was bad, what would happen if it was disconnected? would the ecm just use the map sensor info to control mixture? if the sensor was bad, could it lean out the engine enough to cause it to misfire? i've been getting the always running rich code, and i believe that it's really running lean, and stumbling. while it misfires, i think that the unburned fuel is what triggers the always rich condition. what do you think?

update: when warm. iat sensor is 4.47 Kohms, about twice what it should be.
I maybe wrong but I would say that reading is correct. I bet it doesn't even get down to 68* at night. The reading is between the hot and cold limits without knowing it's exact temperature. Use some water to get readings at the correct temperatures.
Edit: Oops I may have read that wrong.

Test your ECT which measures the engine temp not the air temp.
 

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Well Jean, yes a 1986 FSB 302 EFI does have an IAT and it should be on the fuel rail near the schrader valve and they run about $17.00 if that answers your question. Wow, thanks Bronco guy I really appreciate the effort!



Your welcome :enforce
 

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JKossarides said:
...it should be on the fuel rail...
Not really. It's screwed into the lower intake on the driver's side NEAR the fuel rail on early models & installed in the air filter box on later ones.

It's also called the ACT.

 

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So this IAT is just below the fuel rail near the schrader valve area in the lower intake manifold?

Thanks


:enforce
 

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Dead Horse
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mines always covered with mud that got in the airbox
i cleaned it a few days ago though
 
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