JPI 900 Manifold Pressure Problem

[PR474]

I have a 1992 M20J and did a panel update late last year that included updating from a JPI 830 to a JPI 900 engine monitor. Since the install the manifold pressure has been constantly fluctuating as much as a full point either way making it impossible to accurately set power. JPI sent a loaner unit that did the same thing while they did a software update to mine. New unit came back with same problem. Next, JPI sent a new sensor that did not resolve the problem. Went back to installer and they moved the sensor from the #1 cylinder to the back of the engine baffling with no change. Plane just came out of annual, and we replaced seals and gaskets on all 4 intake tubes with no changes. Wiring has been checked twice by installer and my mechanic. Any thoughts or suggestions?

Edited May 24, 2022 by PR474
Misspell

[anthonydesmet]

Did you say this started after last annual or since you installed the 900?  Obviously if after last annual or sometime other than install may isolate what’s changed.  I’ve found changing wires and sensors but still getting same results means the engine is telling me something. What’s are causes of fluctuating MP other than gauge/sensor error?

[LANCECASPER]

8 hours ago, PR474 said:

I have a 1992 M20J and did a panel update late last year that included updating from a JPI 850 to a JPI 900 engine monitor. Since the install the manifold pressure has been constantly fluctuating as much as a full point either way making it impossible to accurately set power. JPI sent a loaner unit that did the same thing while they did a software update to mine. New unit came back with same problem. Next, JPI sent a new sensor that did not resolve the problem. Went back to installer and they moved the sensor from the #1 cylinder to the back of the engine baffling with no change. Plane just came out of annual, and we replaced seals and gaskets on all 4 intake tubes with no changes. Wiring has been checked twice by installer and my mechanic. Any thoughts or suggestions?

It may need a snubber. You might talk to JPI.

 

 

[Ragsf15e]

Search online for a snubber.  Mine is from Omega (which jpi recommended).  1/8” npt which means you’ll probably need an adapter to 37 degree flare on both sides.  Mine was like yours, now it’s +\-0.1 inches.

[PR474]

13 hours ago, anthonydesmet said:

Did you say this started after last annual or since you installed the 900?  Obviously if after last annual or sometime other than install may isolate what’s changed.  I’ve found changing wires and sensors but still getting same results means the engine is telling me something. What’s are causes of fluctuating MP other than gauge/sensor error?

The problem started after the new install. Zephyr did major overhaul of the engine in September 2019. When the airplane went in for the new panel upgrade it had a JPI 830 and a Electronic International digital MP gauge with no problems.

[PR474]

9 hours ago, Ragsf15e said:

Search online for a snubber.  Mine is from Omega (which jpi recommended).  1/8” npt which means you’ll probably need an adapter to 37 degree flare on both sides.  Mine was like yours, now it’s +\-0.1 inches.

Thanks for your reply. I have read about the snubber before, but JPI's current tech support says the problem was fixed with the newer units. After a conversation with the tech support I found him lacking in personality and willingness to help. My installer had told me earlier that was their opinion as well. That being said I think I will try to find a snubber and hope that works.

[LANCECASPER]

4 hours ago, PR474 said:

Thanks for your reply. I have read about the snubber before, but JPI's current tech support says the problem was fixed with the newer units. After a conversation with the tech support I found him lacking in personality and willingness to help. My installer had told me earlier that was their opinion as well. That being said I think I will try to find a snubber and hope that works.

JPI was saying that they didn’t need a snubber long before “the problem was fixed it’s the newer units”, so it wouldn’t surprise me if the snubber fixed your issue.

[Ragsf15e]

8 hours ago, PR474 said:

Thanks for your reply. I have read about the snubber before, but JPI's current tech support says the problem was fixed with the newer units. After a conversation with the tech support I found him lacking in personality and willingness to help. My installer had told me earlier that was their opinion as well. That being said I think I will try to find a snubber and hope that works.

I definitely agree with your assessment about their “service”.  I was told that it was mostly fixed with the updated firmware, so I sent mine in for the update first.  Then they had me do a field update to the newest software version.  Then they said to try the snubber.  It’s always the last thing…

[PR474]

The snubbber worked. I used a .004 from McMaster-Carr. Omega had a 9 week delivery time. Like you said "Ragsf15e", it is always the last thing....  Thanks and this will be the final post.

[Ragsf15e]

1 hour ago, PR474 said:

The snubbber worked. I used a .004 from McMaster-Carr. Omega had a 9 week delivery time. Like you said "Ragsf15e", it is always the last thing....  Thanks and this will be the final post.

Excellent!  Glad it worked.  I also ended up with a snubbed on my oil pressure sender.  Not sure if the snubber fixed that too or messing around with the connection to install the snubber did it, but that one is also stable now.

[carusoam]

Check to see if the snubber that worked… disappeared…. Or went with the old engine…

when measuring things like air pressure and fluid pressure…and volts…

It is common to have many rhythmic noises in the line… as pump vanes go by, or intake valves open and close, or electric motors turn on and off….

These added noises should be easy to filter out and or deaden….

Our old analog gauges used to do this internally to the gauge on some things…. Some got external snubbers…

Our old mechanical MP gauges also have a calibrated weep hole… the gauge’s face is calibrated with the weep hole in the line… constantly leaking small amounts of air into the system…

JPI is known for their quirky style of customer service…

Their competitor, EI, is familiar as well…. 
 

We get great support around here from the EI guy…

Best regards,

-a-