Does anyone know what the purpose of the Air Charged Temperature Sensor is? Just curious. I suspect it measures the temperature of the air passing through the intake tube but not sure.

Thanks,

Anthony

 

Its other name is Intake Air Temperature sensor (IAT).

 

This sensor monitors the air temp into the engine for among other purposes altering the ignition timing and fueling.
For example at cool air temps the air density is higher and the engine needs more average fuel to compensate, less at hi temps.
Granted the OX senors adjust the running mix but general compensation is done ahead at the same time.
In addition the IAT has some influence on inital cold start fueling.
Some older engines, this sensor is in an intake runner and becomes sensitive to both engine heat as well as intake air temp for the same purposes.
The engine coolant temp does much of the same but has wider control over fuel.
These sensors also can detect overtemps and this alters the running program for engine protection by doing things like retarding timeing, increasing fuel to cool cylinders, dropping cylinder etc.

 

Thanks Bluegrass! I can always count on you to give me a complete answer.

One more question about this - is it possible for it to fail and not throw a code? The reason why I ask is because I've been dealing, or should I say living with a horrible shaking/vibration at idle after my truck has warmed up. It seems as though the vibration is most evident when the outside air temp is warm. It annoys the heck out of me at times. This one really has me stumped.

BTW - my truck is a 2001 Expy with the 4.6 V8.

Any feedback would be great!

Thanks,

Anthony

 

IAT would normally not cause rough idle.
It would deal with rich/lean table calibrations and changes in timing for all cylinders rather than individual cylinder roughness.
AIr leaks, ignition, fuel faults all can cause roughness.

 

Thanks Bluegrass. That makes sense.

I've checked all hoses for air leaks - none found.
I've replaced all plugs and coils so it can't be an ignition problem.

I did initially suspect a fuel problem but am stumped over which specific portion of the fuel system it could be. By saying 'fuel faults', what do you mean? Do you mean things like fuel pressure or injectors? I've checked the fuel pressure regulator with a pressure guage. Pressure was within specs. Can you elaborate a bit on this?



Thanks again.

Anthony

 

A dangerous assumption. Just because a part is new doesn't necessarily mean it's good. I've burned by that before.....

It would be beneficial if you could look at your live data. You would probably see a parameter that is being reported incorrectly, but not so much that the PCM would set a fault code.

 

The pressure regulator is mechanical, so it's not affected by any sensor.



The injectors themselves also aren't affected, but the EEC will change how long it holds them open based on the sensors.

 

We can only tell you the things that normally contribute to rough running by 'remote' if you will.
Anything you miss is at issue.
As with any procedure, you have to keep getting deeper into the
testing to uncover the reasons.
Consider a vacuum gage test and see if it suggest what might be going on.
Reading vacuum gage is an art/science unto it'self because various faults causes the gage to react in specific ways. That becomes the art of reading it's value in suggesting a fault.
For example an easy one to understand is the needle deflects downward everytime a faulty cylinder attempts to fire (for whatever reason), then just how the needle reacts can suggest poor valve seal, ring seal, sticking valve stem, bad spark plug/wire etc. So you can see where the 'art' is in this.
General low vacuum can be late timing, intake leak etc.
Water in the fuel can play games with overall running.
An EGR that leaks exhaust gas at any other time than when it is supposed to will wreck idle cause hard stating, ping etc..
Assumption about anything in this situation has low value and can cause you to chase a long way before you arrive back at the a place that was assumed to be good.
One thing I can relate to you for instance is if you sub a vacuum gage at the EGR and cold start the engine, you most likely will see some small amount of vacuum and change as the PCM plays with the system, then as it warms up the action stops. Any vacuum comanded enough to open the EGR with large amount of vacuum in the 3 to 5 inch range will certainly cause rough idle.
If you do decide to use a vacuum gage and it shows anything but a steady reading in the 18 to 20 inch range, get to info on what the gage actions mean for interptation. There are quite a few to see. For any action, list all the items that could cause that action and address them one at a time.
This is the way I have to work on issues in the absence of high cost testing scanners and being able to put 'addressing message requests' to the PCM for all the actions in question and looking at the results.

 

Ok, thanks Bluegrass. I'll grab a vacuum guage tomorrow and give it a shot. Will repost my findings.

projectSHO89 - I don't think the plugs or coils are bad because the vehicle was scanned at the dealer for miss (or bucking) that was occurring at cruise speeds. At that time, I knew it was a coil pack (COP) because I've had one go bad before. It did not throw a code however. Dealer was able to find the bad one though.

Thanks again for the input guys.

Anthony

 

I have a 97 f150 4.6 that does the same thing once it gets warmed up. Plus going down the road it will get rough so I let up on the Gas pedal and a few seconds later it smooths out. I as well thought it would be the IAT.
When going down the road at about 70 mph it is as its flooding out and when I let up on the gas it smooths right on out. I am only averaging about 17-18 miles a gallon. I used to get about 20-22. I did a full tune up on it.

Any thoughts?
Thanks,
David

 

David,

Unfortunately, I have no idea. I've been dealing with this issue for years now and have pretty much wrote it off as this is the way the truck runs. Tired of throwing money at it. I've repalced numerous parts while checking/testing countless others. Everything seems to be in line. Everything but the shaking.

If yo figure something out, please share it with the rest of us.

Anthony

 

Now your giving something to chew on!
I would be looking at the possibility the EGR is not being operated correctly by allowing to much EGR back into the intake. Once you find out what happens when EGR is called, you can see where there could be faulty operation.
When EGR is called, the ignition timing is advanced, the fuel is cut back to match the intended mixture conditions. If any part of this operation goes out of limits you can experience immediate drivability issues.
On top of this; if the plugs are poor, a coil has low output, the required coil voltage goes up because the mixture is the hardest to fire under these conditions.
Next, the mass air tranfer curve may be to lean under fully warmed conditions.
I believe there is a TSB on this from back in your year range.
Bottom line is a good tech with a scanner has to look at all these areas same as a doctor sometimes has to do testing to find what course of corrective action to take.
There comes a time when you need to enlist the services of a well informed tech. He normally has the ability to look and note the limits for each item and can see an out of limit condition that can contribute to the issue.
There are many parameters to look at from total EGR system operation, mass air meter output vs throttle application and on & on.
If not, you live with the situation as you chose.
Good luck.

 

I unplugged my IAT and it seems to make a difference. Of course the check engine light came on, but it seems to run better. So I just might have to change that.

 

Without at least looking at the Live Data from something like a Scangauge II you're just taking stabs in the dark.