Merc 496 GURU Question
 

The intake manifold air temperature (IAT) via the PCM555 ECU I have observed seems to track engine temperature and to be almost non responsive to the intake air temperature to include the fact that the IAT continues to rise to its steady state soak temperature regardless if the engine is idleing or running at WOT. I am told that this is not the case with IAT from outer intake manifold systems which typically show a significant drop in IAT when running at WOT versus at idle because of the higher cooler air volume and velocity moving through the intake manifold at WOT versus at idle.

Is this typical of the 496 PCM555 IAT system?

Re: Merc 496 GURU Question
 

Rage,
I suppose it will depend on the installation, but after looking at some recorded files for 496's, there seems to always be a drop in MAT as the engine is throttled up to WOT or even cruise. Typical drop seems to be about 10 degrees and somtimes more.

Dave

Re: Merc 496 GURU Question
 

Interesting data Dave. It looks like the MAT worked up to 129*F during maybe an extended period of idleing or other and then your data shows the motor was accellerated to ~50% throttle then ~full throttle which cooled it down to 113*F. My data is different in that at idle for a moderate period of time the MAT settles in at ~95F. Then upon repeated accelleration runs of WOT it increases until it eventually reaches a max of ~107.6*F. Upon throttle reduction it cools back down to ~105*F after a short period. Additional WOT causes it to return to 107.6*F. Ambient air was in the 60's and the water temperature was darn cold. My main interest is the very slow 496 MAT temperature response to change in engine RPM versus MAT of other intake manifold systems. I have been told that other MAT system sensors display a very close response in temperature change to the change in engine RPM and therfore the velocity at which cold air is sucked through the manifold i.e. the higher the rpm's the cooler the MAT. The 496HO seems to be more a temperature reading of the intake manifold metal than the air inside it based on its very slow response. Any insight on this?

Also the MAT readings always appear to change in stair steps as your data displays and those temperture step valves seem to always be the same valve in a temperature range. I believe the other MAT systems show a uniform temperature curve change and not this stairstep. I do not know what that means , just an obsevation. Any information on this?

Re: Merc 496 GURU Question
 

Dave do you have any more MAT data under different operating conditions?

Bill

Re: Merc 496 GURU Question
 

Bill,
I have a bunch of other files, most are kind of similar because I typically record them on a test run consisting of idle/cruise/wot, and some of them record some kind of failure. If you have Diacom I could email you some files to look at.

Dave

Re: Merc 496 GURU Question
 

Sent PM to you with Email address.