Accu-Sim Cessna C172 for P3D - no vacuum

[Dave210]

I've had a couple of instances in P3D v4.5 where, on starting the engine at the beginning of a new flight, the Accu-Sim C172 (latest version 19.12.27.0) does not have any vacuum which causes the attitude indicator to fail and the vacuum malfunction light to come on. I have tried doing a complete overhaul in the maintenance hanger, even though no problem was indicated, and also resetting the C172 to new condition. If I recall correctly, the first time this happened a few weeks ago I ran "Delete Generated Files" to fix the problem and the second time, yesterday, I rebooted the computer (Win. 10 Pro). I searched the forum and on-line but didn't find anything about this exact problem although I may have missed something. Any ideas as to how to avoid this problem in the future would be appreciated.
In addition to the Accu-Sim Cessna C172 for P3D, I also have the A2A C172 for FSX:SE (with the latest updates for Steam and the A2A C172 installed). I found posts on this forum which recommended deleting the files in both the ..\Documents\A2A\FSX\Cessna172 and ..\Documents\A2A\P3D\Cessna172 folders to try to solve various other problems. In my case, even though I am running both versions of the A2A C172, only the ..\Documents\A2A\FSX\Cessna172 folder contains any files ( C172RLog.dat.f, dme & v2_C172RLog.dat) which I deleted while trying to solve the vacuum problem but that didn't help. I'm wondering if this is the expected behavior since it seems that the FSX:SE and P3D versions of the C172 should each be writing to their own folders. I haven't had any problems with the FSX:SE version of the A2A C172 but I very seldom use it, so.
I may have missed a previous post about this problem and I apologize in advance if that's the case.

[Nick - A2A]

Hi Dave - welcome to the A2A forums.

Firstly it's normal that both FSX and P3D version of the 172 share the same log.dat file in "Documents\A2A\FSX\Cessna172". This is to allow the same persistent aircraft to be used across both platforms, and for those upgrading from FSX to P3D, it means they can keep 'their' aircraft without having to rearrange any files.

As regards the behaviour which you describe with the low vacuum pressure, is this just a momentary issue and does increasing engine RPM cause the suction gauge to respond and the annunciator lights go out? If so, it could just be that spark plug fouling is causing the engine to run a little rough, in which case the engine-driven vacuum pump may not be spinning fast enough.

If it's a persistent issue even at higher RPM, and you've checked for a broken vacuum pump in the hangar, the issue may be caused by a corrupt flight load. One possible cause of this is using a complex add-on such as the 172 for your default flight. Can I just check which aircraft currently loads in your default scenario in P3Dv4?

Thanks,
Nick

[Dave210]

Thanks for clarifying my question about the two sets of folders and which one is intended to be used by both FSX:SE and P3D.
My default aircraft is the Carenado C172N (I had an earlier problem using the Accu-Sim C172 as the default after it gradually wiped out my P3D resolution setting and the instrument panel turned solid gray). The vacuum problem doesn't go away if I increase engine RPM, or if I install new spark plugs or do a complete overhaul in the maintenance hanger (and no vacuum pump problem was indicated). In fact, the engine appears to run rough which would probably happen in reality with a loss of vacuum and trying to fly results in crashing. I don't know if your C172 is modeled to have two vacuum pumps and I didn't think to look at the annunciator lights to see if both L & R vacuum pumps failed or only one of them failed. I have all P3D Failures set off. If the your C172 has it's own Failure settings, I haven't found them.

[Nick - A2A]

Okay Dave - thanks for the info. There's a couple of things you can try for starters.

First of all, try reverting back to P3Dv4's original default flight and see if this resolves the issue. To do this either reselect the flight in the P3D menu, or the fool-proof method is to back up and then delete all files in the "Documents\Prepar3D v4 Files" folder.

The second thing you can do is delete the contents of the "Documents\A2A\FSX\Cessna172" folder. This will completely reset the persistent state of the 172.

Cheers,
Nick

[CaptDan]

Just a thanks to Nick. I had this problem with the Comanche. After I loaded a default flight and then changed to the Comanche, I had suction again (and the attitude indicator started working). This solution seems to solve many issues in a variety of complex aircraft.

Initially, I loaded the Comanche after a flight in a T-prop. I'm guessing this was why the problem started. Thanks again!