Indicated MAP on D120 is low - Help Tech Support!

[DavidRose]

Hi All,

Help needed! On our first flight the MAP was under reading on the D120. We have a woodcomp sr 3000 2 blade VP prop and Rotax 912ULS.

On the ground it reads 21 inches with engine switched off, I looked in a Cessna 182 beside our aircraft in the hangar and it's MAP gauge read 29 inches. When airborne at full power only about 19 ½ inches, throttled back at about 5000rpm it reads 17 inches.

It’s set up on sensor 1 at the moment which doesn’t seem to have any scope for adjustment. I noticed in sensor 2 that there are two settings that you can vary AUXSF and AUXOFF.  What are these settings for? Can I use sensor 2 ?

Can you tell me how I can use AUXSF and AUXOFF to get the indicated MAP to be correct for my D120. I'm able to get an accurate QNH and QFE as there is an Airport close by and I know the exact height of my hangar.

Really want to get this fixed so we can carry out the test schedule asap

Thanks Guys

David

 

[dynonsupport]

Re: Indicated MAP on D120 is low - Help Tech Suppo

You cannot adjust our sender, but you should never need to. The sender type 2 is for a sender that is totally uncalibrated at the factory, which is why we need those numbers.

First off, what altitude is your field at?

The next thing to check is that all 3 wires are connected well. You should have 5V between the black and white/red wires when the D120 is on. If you have this, then when the green/red wire is shorted to the black, you should see around 0" MAP, and when you short the green/red wire to the white/red, you should see around 60" MAP.

If it doesn't behave that way, I'd guess you have a wiring issue somewhere.

 

[DavidRose]

Re: Indicated MAP on D120 is low - Help Tech Suppo

Hi,

My field is at 590 feet.

The QFE today was 1016mb which is 30.03 inches which ties in with what the Cessna was showing.

The D120 indications behaved in the correct sense in that they reduced when the engine was running, were higher at higher power setting and lower at lower settings.

Could you tell me what AUXSF and AUXOFF mean. Are you saying that I cannot use them to manually set the D120 indicated MAP with the engine off to what I have calculated from the local QFE?

I'll check the wiring also.

 

[dynonsupport]

Re: Indicated MAP on D120 is low - Help Tech Suppo

You cannot use the AUXSF and AUXOFF. They are for a totally different sender.

 

[DavidRose]

Re: Indicated MAP on D120 is low - Help Tech Suppo

Okay I've checked the wires as you recommended and these are the results:

Black & red/white gave 5 volts with the D120 on

Green/red shorted to black gave 2.5"

Green/red shorted to white/red gave 61.4"

engine off gives 21.1"

all of the indications are fluctuating markedly.

 

[dynonsupport]

Re: Indicated MAP on D120 is low - Help Tech Suppo

It could be one more thing. A while ago, we had a few incorrect MAP sensors that got delivered to us incorrectly (and therefore, to you). They are identifiable by the label on the sensor itself:

* Correct Sensor: marked with p/n: 12247571
* Wrong Sensor: marked with p/n: 12223861

If you have the wrong one, call tech support at 425-402-0433 to set up a RMA to get it swapped for the right one.

 

[DavidRose]

Re: Indicated MAP on D120 is low - Help Tech Suppo

Thanks, I'll check the serial number.

Would placing a resistor in one of the wires be an option to get the correct value indicated?

It's under reading by 9.0" so what value of resistor would compensate for this and which wire would it go in?

 

[dynonsupport]

Re: Indicated MAP on D120 is low - Help Tech Suppo

No, a resistor cannot correct this problem. The MAP is not a resistive sender.

Given what you are seeing, chances are really high that you have the wrong sender. If you're really anxious to get it fixed ASAP, you can buy one at a local auto parts store (the MAP sender is off GM cars).

 

[DavidRose]

Re: Indicated MAP on D120 is low - Help Tech Suppo

You were right it was the wrong sender. FortunatelyI live 30 minutes from the UK Dynon agent so I have fitted the correct one and it is reading fine.

Thanks for your help.