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Dynon wrong MAP reading

KayS

Well Known Member
Hi All,

my dynon skyview MAP indication worked well, until today. it was showing 21,5" disregarding of throttle setting. i have the Vans steam gauge as back up which indicated correctly. i did not change anything.

any ideas would be appreciated.

Cheers
Kay
 
Transducer?

Disconnect the MAP transducer and see what happens.

From what you've described, I'd put my money on the transducer failing.
 
MAP

Have seen a little oil get into the MAP line and cause similar symptoms. Can’t hurt to disconnect all the lines and blow them out to troubleshoot. I’ve reworked several RVs so that the MAP fitting on the cyl head points up instead of down to mitigate this issue. Do not apply any air pressure to the transducer or your backup gauge.

Don Broussard
RV9 Rebuild in Progress
57 Pacer
 
I have the same setup and have seen my MP fluctuate in flight up to unrealistic values and then back down. This isn't a new thing. I replaced my MP sensor and it's happening again as recently as Tuesday this week. Went from 27" to 33" and back down in less than a second. No engine fluctuations or any other abnormalities. A buddy mentioned the possibility of the restrictor fitting being clogged. I think this is a prime candidate for causing these problems and I hate to admit that I've never cleaned it since new. It's going on the CI checklist immediately. I didn't have time to clean it after landing but it's next on the list of stuff to do.
 
Another common culprit in these situations is if the insulation around the wire between sensor and EMS gets chaffed and intermittently grounding out. The best way to check for this is to just replace the wire and see if the problem goes away. This applies to many different sensors connected to modern EFIS systems.

:cool:
 
Went from 27" to 33" and back down in less than a second. .

That's a pretty good indication of a wiring problem or possibly a failing MAP sensor. 33" implies positive pressure on the MAP sensor vs the standard vacuum. Highly improbable without backfiring or broken intake valve. A plugged restrictor can't create pressures at the sensor that are above ambient pressures at seal level.

The MAP sensor is really a transducer that sends a variable voltage based upon the pressure/vacuum it is seeing. At 30" (it's max reading), it sends 4.7 volts. So, if you have a wiring issue of failing transducer that is putting 12 volts (the voltage provided on the power feed of the transducer) on the return wire, you will go to the max reading, as defined by your instrument. I would expect most EMS provides to have a max of 32 or 33" on this reading.

Larry
 
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That's a pretty good indication of a wiring problem or possibly a failing MAP sensor. 33" implies positive pressure on the MAP sensor vs the standard vacuum. Highly improbable without backfiring or broken intake valve. A plugged restrictor can't create pressures at the sensor that are above ambient pressures at seal level.

The MAP sensor is really a transducer that sends a variable voltage based upon the pressure/vacuum it is seeing. At 30" (it's max reading), it sends 4.7 volts. So, if you have a wiring issue of failing transducer that is putting 12 volts (the voltage provided on the power feed of the transducer) on the return wire, you will go to the max reading, as defined by your instrument. I would expect most EMS provides to have a max of 32 or 33" on this reading.

Larry

Since I've replaced the sensor once for the same issue, I'm thinking it's the wiring and/or the restrictor fitting. The latter needs to be cleaned up anyway since that's not been done. Those wires on that plug are not very robust. I will also add some strain relief
 
Mark, interesting that your problem is recurring.
Ross at SDS advised me to always mount the MAP sensors vertically, & higher than the intake vac source, and have the vac hose sag a bit before entering the unit. This keeps contaminants from entering or draining into the sensor, the cause of most sensor failures, besides wiring.
Just another thing to check.
 
Mark, interesting that your problem is recurring.
Ross at SDS advised me to always mount the MAP sensors vertically, & higher than the intake vac source, and have the vac hose sag a bit before entering the unit. This keeps contaminants from entering or draining into the sensor, the cause of most sensor failures, besides wiring.
Just another thing to check.

The sensor is mounted vertically on my firewall and it's definitely above the cylinder fitting, and it does sag before going uphill so I think I'm ok there but the wiring connection to the sensor has always seems a little fragile to me so I'm thinking and hoping that reworking that will help
 
thanks for the input guys. i am pretty sure that it's not the hose or restrictor fitting. the MAP sensor unit is way above the the cylinder and the independent sensor for the vans steam gauge is very close to the dynon sensor. so that leads me to the conclusion that it must be a sensor problem.

but i have the good old Vans MAP gauge that indicates correctly... so no show stopper so far.
 
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