Troubleshooting Manifold Pressure MVP

[Safetyo]

Just 1.5 hours out of annual, and in flight I watched the MVP-50 MP fluctuate, then drop to zero/bounce around. Was in cruise flight at time. Everything else stayed normal.

2011, A-1C, 180.

I've been all over the forum and the web seeking ways to "clear the line, etc" if that's what it takes.

So I see that the MP line comes off of the #3 cylinder, while the others have a fuel prime line. Is that correct?

Followed line through the firewall, but I'm having difficulty following it all the way into the back of the MVP or where ever it goes. I'm having a hard time getting up under the instrument panel to do anything effective.

Anyone got a good solution to help ease the troubleshooting further?

For instance "best way to get under the panel?" I really appreciate the advice.

As of yet, I haven't taken anything apart. Just started looking.
Couple of pictures attached.

 

[Snowbirdxx]

Follow that line on Pic #4 it will end up at the MP sensor.

The sensor has cables, which are connected to the main unit. Often the wires come loose where they are connected with the small red cylindric connectors.

There is no way to work convenient under the panel.

I have my glareshild modified, so I can take the whole windhield with the top frontpanels within 10 minutes out. Then working on a topless panel is as usual fun.

 

[Safetyo]

Thank's Thomas...not a lot of room but I'm going to use a hand mirror and a bright light to run the line. It's a tight fit under the panel!

Note the solution of one A&P to work under this panel.

 

[RobertMullins]

I have a 930 but same line. Goes into a bulkhead fitting and a sender on cockpit side. Sender went bad. You can remove the aluminum skin to get to it better. Mine happened at the time of the SB on longeron chaffing. I was familiar from that on what you can get to with the outer skin removed around the cockpit.

 

[Meadowlark]

Try a "see snake"...... Bore scope.....

J/C GTF

 

[Safetyo]

Try a "see snake"...... Bore scope.....

J/C GTF

I do have a Vividia Ablescope VA-400 USB Rigid Borescope that hooks up to my iPad. I might give that a try as well.

 

[Safetyo]

I have a 930 but same line. Goes into a bulkhead fitting and a sender on cockpit side. Sender went bad. You can remove the aluminum skin to get to it better. Mine happened at the time of the SB on longeron chaffing. I was familiar from that on what you can get to with the outer skin removed around the cockpit.

I have to say that thought did occur to me. It's hard leaning in the door.

 

[daryl.west]

You probably have already found your problem but had the same thing several years ago. Turned out to be the fitting on the rubber hose just inside the cowling on right side had worked its way loose. No problems since.

 

[Dipper]

I’ve had 2 transducers fail on me. Part Number PT-30ABS. I read somewhere else that they fail regularly. The best way to get to it is by removing the port side skin just aft of the engine cowling. It’s still tricky to replace the transducer but it’s the only way.

 

[Snowbirdxx]

Sure it failed or is it blocked.what is it indicating?

 

[jimhusky]

A month ago when I took off to return home from getting the GTX345 installed I was amazed to find that in my preflight I had missed an inoperable MVP. The JPI 930 showed 4 inches MP. A few times on prior flights it was indicating too low, then seemed to correct itself. On the flight home it stayed at 4 inches MP for the whole trip. When I took it to the A&P expecting to have to replace the sensor, he simply reached up under the panel on the cockpit side where the hose comes through the firewall and hand tightened the fitting. From outside I could tell he was putting a lot of pressure on the fitting using his hand. We stated the airplane and the MVP worked perfectly. That was 11 flight hours ago and it is still working as expected.

Jim J.
N73GT

 

[Dipper]

I have had another Manifold Pressure Transducer fail! 3rd one in 8 years.
I’ve just received a new one and the instructions for fitting explains that the transducer is susceptible to fuel via capillary action and can damage the diaphragm. It advises to make a hole in the tube that connects the manifold to the transducer. Can anyone advise where and how big the hole should be?

 

[groshel]

I have had another Manifold Pressure Transducer fail! 3rd one in 8 years.
I’ve just received a new one and the instructions for fitting explains that the transducer is susceptible to fuel via capillary action and can damage the diaphragm. It advises to make a hole in the tube that connects the manifold to the transducer. Can anyone advise where and how big the hole should be?

I had done this when I installed my CGR-30P as my old factory VM1000 system MP was way off and had evidence of fuel backing up into the transducer.

Looking at a Vans and I think Mooney forums they mentioned drilling a #70 hole at the fitting for the MP line at the firewall.

I did the same and it reduced but not totally eliminated that backup on my new CGR system.

I think what it is …is when you first start the engine fuel vapor pressurizes the MP line to the transducer. when you shut down that vapor stays there….and it only gets worse as the cycle repeats each time you start.

There is a thread on this issue somewhere here.

Chris

 

[dogday]

I have some information collected on the manifold pressure transmitter problems/repairs relevant to my 2001 Husky with the VM1000. I am not sure if the MTP discussed above is the same, but if it is the following will be helpful. There is a discussion here about gas contamination of the MPT called "How to Avoid the MTP Blues"

https://eaaforums.org/showthread.ph...-EPI-800-How-to-Avoid-the-quot-MPT-Blues-quot

Also if anyone wants to save a lot of money with a bad MPT, consider repairing it. I believe that I can find the part number for the pressure element that was used on the original MPT assembly found in the VM1000 Husky. If I remember correctly it is a Honeywell part that can be purchased from Mouser. It justs takes a little care not to overheat the Honeywell sensor when soldering on the electrical connecting board. The Honeywell part is an exact replacement of the electrical part used on the MPT. Let me know if the part number would be helpful and I will try to find it in my records.

The following is some information that came from a electronics guy that used to repair VM1000 parts after I asked about intermittent incorrect readings:

One or more intermittent connections are the most common problem either at the DPU, at the sensor, or a wiring problem in between (break, fray, kink, short, etc). There should be a MP troubleshooting checklist in the back of your VM1000 manual, if not, let me know and I can send you a copy.

When cleaning the MP sensor, I only use denatured alcohol, it is mild compared to other solvents. I also take care not to get any solvent into the black electronic portion of the sensor, I clean only the port and brass nipple. If fuel residue has migrated into the black electronics portion of the MPT, it's only a matter of time before it fails.

The mfr's spec for the MP indication is within 1% of station pressure. At sea level, station pressure is your altimeter setting. At airports above sea level, the station pressure can be approximated by setting the altimeter to read zero feet. For example, altimeter setting is 29.75 at an airport with an elevation of 1000 feet. You would have to decrease the altimeter setting approx. 1" to 28.75 to read approx. station pressure. The VM1000 should then read within 1% of 28.75 to be considered within tolerance, or a range of 28.5 to 29.0

 

[dogday]

I was able to find the part number that was an exact replacement part for Husky's MPT electronic component used with the VM1000. The digi-key part number was 287-1023-ND. In 2015 it was $102 and a quick google search on mouser with that part # shows the Honeywell part number SCX15AN with a cost of $350.

Dipper I am curious, what does Aviat charge for a MPT these days?

 

[Dipper]

I purchased it from Aircraft Spruce $210 plus $15 for the certificate. EI have modified the casing, it’s now a gold colour and made of metal instead of plastic.

 

[wldwzl01]

Go down to your local National Aeronautics Parts Association (NAPA) store and get a see thru inline fuel filter. Plumb the filter into the line prior to the sensor.