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ok, i tried searching to see if i could find answers. i may not be searching with the correct terms. if that is the case please feel free to point me in the right direction. thanks

i have a 97 E350 cab chassis short bus. 10k gvw auto and 7.3 wit about 300k on the odometer. i was told injectors needed replacing when i bought it but it throws no codes. i do sometimes get a stumble and suspect that is from the injectors, yet it pulls the hills pretty good, no complaints. but, the problem that concerns me and has me scratching my head is as follows

towing up a decent grade on a hot day, over 90, pulling 6000# with a combined weight of about 15k it starts out pulling fair, no complaints. but a few minutes of that and i start to see the IAT reading starting to climb, pretty quick. this is on a scan gauge II. about the time the IAT is reporting 135 or so there is a distinct drop in power regardless of throttle posistion or engine rpm and as vehical speed drops IAT keeps going up and then power drops more. by the time IAT is reading 180 or so i am limping along in second gear(bad shift column bushings, on the list to repair so i can drop into first gear) unable to maintain road speed and have to pull over and wait

this does not happen on cool days, only hot summer days of around 90, on cool day or night runs, it does not happen.

engine temp does not go up significantly when this is happening

if i have enough power to keep rpms up in 2nd gear then boost seams ok around 12 but as rpms start to drop then so does boost. but even with rpms up in second gear temp keeps rising and power drops to were i can not maintain speed and i have to pull over to prevent lugging. this does not happen at night or on cool spring/winter days. with same exact load i can pull in second gear and maintain what ever speed in that gear i feel like reving too

i am stumpped as to why IAT would go up if engine is maintaining normal temps

any suggestion on figuring this out so i can stop living the vampire life and be able to drive in the day during the summer

thanks
 

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First off not familiar with a buss chassis , but will give a stab at it and someone will correct me

The IAT - Intake Air Temperature is a thermistor - basically a temperature affected resistor - 2 wire sensor

Not sure where exactly it is located on your buss, but should be in the intake manifold -- my 6.0 has two(one in the intake, and the other in the air filter housing)
sounds like your sensor is going bad or there is a heat source affecting it
 

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In the OBS trucks the IAT sensor is in the Air Filter box, so maybe the vans have it theirs as well. I would agree with Hydro on the thought of the sensor going bad or a heat source affecting it. If you had access to a cheap way to monitor the intake air separately, maybe see what the intake air temp is that way just to check. Cheers!
 

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Discussion Starter #4
I agree that if the readjng is high. It can only be a bad sensor or an elevated temp. But are you saying if the reading is false the computer will back off on the fuel thus losing significant power? If that is possible, is it safe to unplug the sensor and test drive. Or will an unplugged sensor cause other problems.
Any suggestions on how to test sensor on a cool day. Being on the Oregon coast, i am months away from 90 degree days.

If the sensor is good, seams the only other possibility is it is getting hot. But where could this extra heat be comming from. The engine temp gage comes up slightly but hardly at all. And when i pull over and pop the hood i cant feel any extra heat than i get normally. I would think for the IAT to more than double i would be expecting a fire or something. So any suggestions on what could be causing this potential source of heat?

As far as it being a bus, it is only 20ft long, and from the drivers door forward it is indistinguisable from any other E350

There is 1 IAT sensor in the air box. Unknown if there is another. There is NO intercooler. So i dont know if there is even a need for a second sensor. Sounds like all the second sensors i have heard about are after the inter cooler, which would make sense
 

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IAT should not be much above ambient air temp when operating -- if the sensor is in the air box

We don't know all the voodoo and magic smoke that is in the PCM -- but you mentioned the engine barely gets warm -- possible the disparity of temp that the coolant sensor and air sensor are reporting magnify the readings, so the engine is then de-rated to keep from imaginary damage

A cold engine that is sucking 180 degree air -- I'm sure confuses the PCM

Sounds like time to replace the thermostat and IAT sensor
 

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The IAT in the airbox is the only one on your van. Guys have done tests with intakes and air filters and when moving, the underhood air temps are a few degrees over ambient when moving (as Hydro mentioned). I've attached some info on the IAT sensor. Cheers!
 

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Discussion Starter #7
IAT should not be much above ambient air temp when operating -- if the sensor is in the air box

We don't know all the voodoo and magic smoke that is in the PCM -- but you mentioned the engine barely gets warm -- possible the disparity of temp that the coolant sensor and air sensor are reporting magnify the readings, so the engine is then de-rated to keep from imaginary damage

A cold engine that is sucking 180 degree air -- I'm sure confuses the PCM

Sounds like time to replace the thermostat and IAT sensor
never said the engine does not get warm.i said engine temp does not go up significantly when this problem is happening. in other words the engine maintains normal operating temp but does not show any signs of over heating. that is why i am so confused as to how the iat is showing high reading. i did a crude test the other day. i put a meat thermometer right next to but not touching the iat sensor and directed the out put of my blow dryer on it. the iat reading stayed pretty similar to what the meat thermometer was indicating.

so does any one have any suggestions on where this extra heat might be coming from. where should i be looking. any suggestions on what to test. i just bought a obdII reader and downloaded forscan. just starting to learn but if there is some test or sensor i should be suspicious of let me know

still scratching my head
 

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Worn harness shorting out causing the sensor reading to show as high -- time to inspect for worn spots
 
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