M44 intake air temp = 131F?
 

Title says it all. Car runs well, good mileage, even idle, 127K miles. recently replaced oxygen sensors (finally) but get an intermittent cat efficiency caused check engine light. Trying to run that down I notice that when I read the OBD data it shows my intake air temp as 131 F, even tho it is oh 60 F ambient. I see no leaks/splits in the air intake system from the side of the radiator through to the filter box where (I think) the intake air temp sensor is mounted. I know enough engine F/A chemistry to think that if the computer thinks the air coming in is lots warmer than it really is then the system will be running lean - hot air is less dense, thus computer thinks less fuel to get to proper F/A mixture but since air is 50F cooler than computer thinks engine is really running quite lean - and thus cat efficiency issue. Anyone ever hear of a failed intake air temp sensor?

RAS

Test the sensor. Look at the data while the car is cold, in the morning, with the engine off and see if the ambient and intake temps are the same.

A lean mixture shouldn't throw a cat efficiency code. And the ambient usually isn't that close to the intake temp. Usually a god bit higher, even while moving.

You shouldn't be seeing more than 20 to 25 degrees higher than ambient when you're moving at anything over about 30 mph. I've got a gauge that allows me to see the intake temps in real time and it only gets as high as you're seeing when the car's not moving in hot weather. Under what conditions did you get that temperature reading? If your engine was hot and it's relatively warm where you are that temperature is entirely possible.

Car was fully warmed up, in driveway in 60 degree weather early this week. I was shocked a bit b/c I own a Cessna with a intake temp guage and even on ground, at idle, rarely see more than 10 degrees above ambient at the end of an intake that is about the same length/turns etc.....I am tempted to create a box holding really cold air using dry ice and put probe into box to see what it reads. Bad idea? Cannot think of a any other good way to test.

RAS

Pretty sure what I mentioned before would work fine for testing.

131 degrees seems normal for that situation.

I would also thing your cessna would be pushing air from the propeller into the intake, much more air moving around it. The ti's intake goes over a 200*F radiator slowly.

OT
I wish Clyde Cessna had the forethought that others (Mooney, Piper) had to buiold an engine air intake that benefitted from ram air effect from the prop - but he did not. The intake plumbing on a C 182 loses ~1 inch of manifold pressure from filtering and other piping restrictions. The prop just makes no difference.

As to the TI, I thought that intake crossover pipe was silly but at least the insulation on it should keep the air cooler than 131. Will test when the engine is cold tomorrow and report back.

RAS

Closing the loop.

Ambient today = 55F. Intake air temp at start = 55 F

That intake system really does not keep air too cool when thee engine is running....but at least I know my intake temp sensor is OK...

RAS

You can always add the snorkel from the M42 engines and get fresh air directly into the air box. I did that mod long before I got the gauge, so I don't have the before and after on that. I suppose I could block the opening from the long snorkel over the radiator and see what impact that has on the temps. Hmmm. Maybe I'll mess with that at some point. Anyway, it's a cheap, easy mod and is described in detail in this link.

http://www.318ti.org/notebook/M44_du...ake/index.html

I checked the temp on mine this morning when I got home. Ambient was about 34 and the intake temp was 70. That's after an hour and a half of highway driving then sitting idling for 2 minutes. You might have a torn hose sucking hot air, or were just idling longer.