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Need help with VM1000 Manifold Pressure issue

brucespears

brucespears

Member
Hi Everyone! I hope that you are all doing well!

My name is Bruce Spears and I have an RV-8A.

On a recent flight I noticed that my Manifold Pressure was pegged at 33+ and throttle/prop changes didn't reflect in the MP readings on the VM1000. RPM, fuel flow, etc. were reading normally.

When the airplane is on the ground and I provide power to the VM1000, the MP still reads very high, with the engine not running. My understanding is that when the engine is not running, the MP should be close to the barometric pressure at the time. (at least I think I remember that being the case in the past.)

I am in the process of trying to troubleshoot the problem, but confess that I'm a little over my head on this. I've found the troubleshooting information and plan to make the appropriate electrical checks this week.

Any advice on what could be happening would be greatly appreciated. Also, if I find through testing that the MP Transducer is indeed bad, do you have any idea of where I can find a replacement?

Thank you very much for your time and consideration! Have a great day!

__________________
Best regards,

Bruce Spears
RV8-A - N922ES
Houston, Texas (KIWS)
"Home of the permanent RV grin!"
 
I had one of the VMS MP sensor go bad. They can get contaminated with fuel/vapor over time and that likely contributes to the failure. I sent mine to a fellow named Reggie who used to repair the VMS displays, CPU's, and sensors. Unfortunately I believe he is no longer doing any of that. The sensor is likely mounted to the firewall (follow the MP sensor line to the firewall). The little circuit card and sensor should be on the cold side of the firewall. If you look at the sensor and it looks crummy with blue staining from fuel I a would suspect that the sensor has gone bad. You can probably pull a part number off the sensor component on the circuit card. If you are very lucky maybe the part can be sourced from somewhere like Digi-Key or Mouser. If so you could try repairing the circuit board with a new component. Also Electronics International who purchased VMS a long time ago may be able to help with a suitable replacement and possibly some troubleshooting info.

Good luck. Let us know what you find.

Bill
 
I had one of the VMS MP sensor go bad. They can get contaminated with fuel/vapor over time and that likely contributes to the failure. I sent mine to a fellow named Reggie who used to repair the VMS displays, CPU's, and sensors. Unfortunately I believe he is no longer doing any of that. The sensor is likely mounted to the firewall (follow the MP sensor line to the firewall). The little circuit card and sensor should be on the cold side of the firewall. If you look at the sensor and it looks crummy with blue staining from fuel I a would suspect that the sensor has gone bad. You can probably pull a part number off the sensor part on the circuit card. If you are very lucky maybe the part can be sourced from somewhere like Digi-Key or Mouser. If so you could try repairing the circuit board with a new component. Also Electronics International who purchased VMS a long time ago may be able to help with a suitable replacement and possibly some troubleshooting info.

Good luck. Let us know what you find.

Bill
 
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