JPI 900 Manifold Pressure Problem

[jrwilson]

Just had a JPI 900 installed in a 63 C; pretty cool EXCEPT...The manifold pressure is jumping around +- 1 inch, pretty quickly.  The gauge was rock solid before the install.  I read on mooneyspace about a snuffer valve to fix it and called JPI about it.  JPI said the sensor is super sensitive and they sent the snuffer free.  Mechanic just installed it and now MAP is stuck at 27.5" and wont move...

 

So now JPI says they're going to send another sensor, less sensitive, different manufacterer...  Anyone else had this issue?  JPI sending it for free but their first solution didn't work.  Is maybe something else going on?  Install error?  Thoughts?

[Marauder]

Can the valve be installed backwards?

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[jrwilson]

I don't know, I would hope the mechanic would be able to figure it out. I think it can just go one way .

[Marauder]

I would hope there was a flow direction on it. Possible he mistook the vacuum as pressure and put it in that way.

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[Lood]

My EDM 900 does EXACTLY the same. According to the shop that installed it, the installation manual did not call for a restricted AN fitting, so a standard one was used. Apparently, a restricted one is indeed needed. We played with the though of taking a standard fitting, fill it with either lead or epoxy and then drill a smaller diameter hole in order to "restrict" it, but I quote JPI:

 

">>Please send me a data download from the unit so we can assess the MAP issue.  If the data shows no inductive noise on the MAP line, we can send you a snubber valve.  There is no small hole.  It looks like a porous material with no orifice..."

 

My problem is rather unique though in the sense that I am thousands of miles from the US and sending anything to the US and back, will set me back R4k in our money! I can't help but think, a certified instrument in this price range should not have issues like these...

[jrwilson]

Well the data dump can be emailed. They said the same thing to me about not sending until I sent the data. I threw a fit and they sent it. It was free and tiny so shipping shouldn't be too bad .

[jrwilson]

I would hope there was a flow direction on it. Possible he mistook the vacuum as pressure and put it in that way. Sent from my iPad using Tapatalk

I checked and there is a flow arrow on it. Good suggestion though

[Marauder]

I checked and there is a flow arrow on it. Good suggestion though

Now for an even bigger question. Which way was the flow arrow pointed? My guess is it should be pointed towards the source of the vacuum -- the engine. It's not pointed towards the gauge is it? Sent from my iPad using Tapatalk

[jlunseth]

It sounds to me as though you are on the right track.  I just want to add (have a 930) that you cannot simply assume that the factory gauge was "rock solid" and giving you good readings.  One thing you will find with the JPI is that all of the readings will be much more sensitive and quicker to react than the old factory strip gauge set up, and they may show you things that were going on with the engine that you were not aware of.  So your engine RPM may in fact be jumping around, your factory gauge just reacted slowly, averaged it out, and never told you. 

[jrwilson]

So marauder was right, snubber in backwards. In mechanics defense jpi tech said put it that way and it required adapters to make it go the right way... But still, annoying.

I guess you can trust "some guy on the internet"

[Marauder]

So marauder was right, snubber in backwards. In mechanics defense jpi tech said put it that way and it required adapters to make it go the right way... But still, annoying.

I guess you can trust "some guy on the internet"

Glad it worked out.

I credit all to the fact that I slept at a Holiday Inn Express the night before

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[Bob_Belville]

Well, wish I had been sitting here on MS instead of chopping onions and garlic for a batch of All Around Spicy Italian Sauce. I could have been the hero instead of B26. We received the snubber, w/o instruction, put it in (in the center of pic) and solved the annoying fluctuation. (As my old Latin teacher used to tell us "intuitively obvious to the most casual observer".   

[Marauder]

Well, wish I had been sitting here on MS instead of chopping onions and garlic for a batch of All Around Spicy Italian Sauce. I could have been the hero instead of B26. We received the snubber, w/o instruction, put it in (in the center of pic) and solved the annoying fluctuation. (As my old Latin teacher used to tell us "intuitively obvious to the most casual observer".

Normally I would use the phrase "You snooze, you lose". But in your case "You chop, you stink" and by the way, you still lose

I have been busy making zucchini chips using my dehydrator. That particular vegetable has quite a bit of flexibility to it.

Finished another batch of dehydrated chives last week. Harvesting scallions and leeks soon. Yummy.

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[Bob_Belville]

I came home after a week plus to 3# cukes and 5# zucchini. ;-( I also picked 50# of tomatoes, hence the sauce. No kidding about the stink. 

[Marauder]

My tomatoes are still green. You must be a couple of weeks ahead of me in the growing season.

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[Marauder]

I'm reviving this thread because I was editing some of my videos with the new JPI 900 I installed and noticed I too have a manifold pressure fluctuation that I did not have with the JPI 830. Can one of you point me to the correct snubber? Is this something I need to get from JPI?

[Lood]

I just stumbled upon this thread again and as a result of the lack of any help from JPI, I found my own solution to this particular issue:

 

I got hold of a spare AN fitting and filled it up with epoxy. After the epoxy had dried, I put it in my lathe and drilled a 1.5mm hole through it. I then re-fitted it and took my F for a flight. The fluctuation was still very much present, but definitely less - about half an inch. So, I took the original AN fitting which I removed, filled it with epoxy once again, but this time, I took a 0.5mm steel wire, dipped it in oil and pushed it through the epoxy filled AN fitting.

After the epoxy had set, I pulled the steel wire out (the oil kept the epoxy from sticking to it) and a very nice 0.5mm hole was the result. I then re-fitted this AN fitting and voila!! - my MP indication on the EDM900 is rock solid ever since.

[Ratherbflying]

I'm reviving this thread because I was editing some of my videos with the new JPI 900 I installed and noticed I too have a manifold pressure fluctuation that I did not have with the JPI 830. Can one of you point me to the correct snubber? Is this something I need to get from JPI?

In June I contacted JPI about this issue and expected them to send me a snubber. No, they said, you need to return the unit. It seems they figured out how to smooth this in the software and don't send snubbers any more.

And they did... MAP is rock steady now. The process is a pain in the ass but it worked.

[Marauder]

In June I contacted JPI about this issue and expected them to send me a snubber. No, they said, you need to return the unit. It seems they figured out how to smooth this in the software and don't send snubbers any more.

And they did... MAP is rock steady now. The process is a pain in the ass but it worked.

How old is your unit? Mine was built in February. Wonder when they applied the firmware.

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[N601RX]

The software can be updated in the field on the 900's. They emailed me both new software, new config file, and directions last year to install it. What is the current version of firmware?

If you search mcmaster you can find orfices of any ID you want down to .010.

[carusoam]

Chris,

You didn't swap out the MAP sensor when you went to the 900, right?

FP and MAP must be the noisiest signals to measure...

The JPI's job is to duplicate the reading of the old style gauge.

The old style gauge included things like a calibrated hole in the line to the MAP gauge.

The dimensions of the calibrated hole doesn't even get on the drawings of all the older models that have it.

Snubbers are a typical method of smoothing out readings on industrial gauges. Some gauges have internal or integral snubbers...

You would think JPI could handle smoothing out the data electronically.

Maybe they need a really good statistician with an aviation/Rocket background?

Best regards,

-a-

[Bob_Belville]

In August '13 JPI's solution was to send us a snubber. (Free) They told us at the time that they'd seen the problem in a "few" installations. The electronic version of my engine logs in my computer does not list part numbers or specs. 

[Marauder]

Chris,

You didn't swap out the MAP sensor when you went to the 900, right?

FP and MAP must be the noisiest signals to measure...

The JPI's job is to duplicate the reading of the old style gauge.

The old style gauge included things like a calibrated hole in the line to the MAP gauge.

The dimensions of the calibrated hole doesn't even get on the drawings of all the older models that have it.

Snubbers are a typical method of smoothing out readings on industrial gauges. Some gauges have internal or integral snubbers...

You would think JPI could handle smoothing out the data electronically.

Maybe they need a really good statistician with an aviation/Rocket background?

Best regards,

-a-

I think the MP sensor was updated to a new one with the 900. Will need to check my old posts to see what I sold with the 830.

[Marauder]

The software can be updated in the field on the 900's. They emailed me both new software, new config file, and directions last year to install it. What is the current version of firmware?

If you search mcmaster you can find orfices of any ID you want down to .010.

Thanks. I will contact them in Monday.

[Marauder]

The software can be updated in the field on the 900's. They emailed me both new software, new config file, and directions last year to install it. What is the current version of firmware?

If you search mcmaster you can find orfices of any ID you want down to .010.

I will check the firmware tomorrow.