I have an i7 4790K CPU that runs at 4 Ghz,   However, when I run FSX, the speed drops all the way down to between 1.6 and 2.6 Ghz.    It runs at 4Ghz or more for all my other applications.   I can't figure out why I do not get 4 ghz using FSX.    Does anyone else have this problem?   Any help would be greatly appreciated.

 

 

 

 

Do you have Intel SpeedStep enabled in your BIOS? It will automatically adjust the clock rate of the CPU depending on system load. I have mine disabled, and it always runs at 4.5 GHz, regardless of being idle or load. I also have C1E state disabled as well. It's a power saving feature.

I wouldn't turn those off - they're valuable power saving (and heat reducing) measures. What's the CPU utilization? Have you tweaked the Windows power saving features - those can restrict the high/low speeds of the CPU.

 

Cheers!

Luke

Thank you both for responding so quickly.   Yes, I disabled the speed step in the bios.  I have also tweaked the windows power settings for the processor to set for maximum performance.   Yet, I still have the same problem.   I get over 4 ghz consistently with all applications except FSX and other games.   I am getting horrible FPS in FSX with add on payware scenery airports and PMDG aircraft.  I notice the FPS drops as soon as the ghz starts dropping.

 

Please let me know if you have any other ideas I can try.   If it helps, here are my other specs:

 

Nvidia GeForce 750TI wtih 4G

Direct X version 11

16GB DDR3 RAM

 

Thanks

How are you measuring the CPU speed? Are any of the cores maxed out?

 

Cheers!

Are you measuring CPU Core temperatures?

Bert is onto something that may be your issue.  Your dropped clock multiplier could be caused by overheating, which in turn is due to a badly installed or malfunctioning cpu cooler or really bad case airflow (or any such combination).  If you see your temps spike to 90c and above when in FSX you definitely have a cooler issue.

Agree, check temps with RealTemp or CoreTemp. CPU could be throttling back.

 

I doubt it's bad case airflow, given that there's virtually no overclock. CPU fan failed, TIM issues, if an AIO, pump issues, air in system etc. Cooler not mated properly to CPU, CPU cooler jammed up with a truck load of dust, cat hair and sabre tooth tiger fur.

 

 

 

It runs at 4Ghz or more for all my other applications.

Are those "other applications", applications that would put the CPU under significant load? If so, and no issues there, it's not a CPU throttling issue due to temps. Check temps while running FSX or something CPU intensive. Not a synthetic stress test though, because if it is a throttling issue it will just shut down.

 

Might be best to glance inside first, to make sure the CPU fan is actually running, amount of dust clogging the heat sink etc.

I checked the CPU core temp and it is at 99 degrees Celsius when running FSX.  Is that too hot?  When using other programs and browsing the internet the temp is around 55 degrees celsius   I can hear the cpu fan speed up when using FSX and other games.

When I installed the i7 I ensured the fan was secured well in the pins and used thermal paste.  I also opened the case again and double checked that the fan is secured properly and running with no dust.  I used the Intel fan that comes with the CPU.  Is the Intel fan the CPU came with not good enough for cooling?

Good grief yes that's too hot!!! I recall TJ. Max for your CPU is 100 degrees. So yes, you are at the point where the CPU will throttle back to avoid damage. In fact you are only a few degrees away from the CPU shutting down completely.
 
The Intel fan is rubbish, but it still shouldn't be running that hot. So do check that you installed it properly. Proper TIM application, quality TIM and mounted correctly. I'd guess you are 30-40 degrees hotter than you should be with the Intel cooler.
 
 

I ensured the fan was secured well in the pins

 

 

It's the heat sink itself that you need to make sure is mated properly to the CPU IHS.
 
Don't run FSX or anything CPU intensive while you have this issue.
 
Are you sure it's running at 4GHz and that it's not been overclocked?
 
You can set the BIOS to optimised defaults if you aren't sure.

It's pretty easy for that default heatsink/fan to get dislodged or not be seating right and not know it. If you're idling at 55C then that's almost certainly the case.

 

I've had good results with the CoolerMaster Hyper 212 EVO. It's big, but works nicely.

 

Cheers!
 

Luke

Stupid question, but worth verifying: did you remember to remove the backing sticker off the base of the heatsink before installing it?  If it has not been removed the cooler won't work properly.

Problem solved!  Thank you all for your feedback on this.  Ultimately, the problem was the Intel fan that came with the CPU.  I reinstalled the old fan that came with the Desktop that was previously cooling an i5.   The idle cooling temp went down to 30C and now its running at about 65C when fully stressed with FSX.   No more Ghz drop.  That Intel fan is a piece of junk.  

 

Thanks again.   The info and suggestions everyone provided was very helpful.