EDM830 - New Install / Erratic RPM

[Skates97]

Many of you have read my other thread about the high RPM after take off. I was hoping the 830 would give me some hard data to use. The shop put a strobe on it and the tach reads about 90 rpm high. They checked everything out and couldn't find anything wrong. They also installed an EDM 830 and today I got out to the airport and checked the plane over and played around with the 830 a bit before taking it for a couple turns around the patch.

First take off the 830 was reading 2,630 rpm and the tach was showing just over 2,700 which is consistent with the readings that the shop was showing (tach reading about 90 rpm high). The second time I took off the 830 started jumping around showing 4,000, 8,000, back down in the 2,000's etc. I checked the tach and it was at 2,800 which would be 2,700 given the error the shop measured. Obviously something wrong with the rpm's on the 830 given there were no great fluctuations on the tach and engine sound did not sound odd/fast. (Not sure why it would make higher rpm the second time around, I have read on some other forums that fluctuations in the tach could be due to issues with the tach cable?).

Did my best to ignore the bright red warnings on the 830 in the corner of my vision and concentrate on the tach on the right side of the panel. Landed and while taxiing back at 1,100 rpm the 830 started jumping all over the place again. Stopped and just watched the instruments for a minute, no change to throttle or MP, no change in the sound of the engine, and yet the rpm's on the 830 were all over the place. I took a picture of it showing 4,840 and the tach showing 1,100... I'll give the shop a call on Monday, they have installed a lot of 830's but appears there is something wrong here.

Here is about a 3 minute span why sitting with the tach idle at 1,100 and rpm jumping all over the place on the 830.

[Piloto]

Nothing like good old fashion gauges, reliable and easy to read.

[Marauder]

Many of you have read my other thread about the high RPM after take off. I was hoping the 830 would give me some hard data to use. The shop put a strobe on it and the tach reads about 90 rpm high. They checked everything out and couldn't find anything wrong. They also installed an EDM 830 and today I got out to the airport and checked the plane over and played around with the 830 a bit before taking it for a couple turns around the patch.
First take off the 830 was reading 2,630 rpm and the tach was showing just over 2,700 which is consistent with the readings that the shop was showing (tach reading about 90 rpm high). The second time I took off the 830 started jumping around showing 4,000, 8,000, back down in the 2,000's etc. I checked the tach and it was at 2,800 which would be 2,700 given the error the shop measured. Obviously something wrong with the rpm's on the 830 given there were no great fluctuations on the tach and engine sound did not sound odd/fast. (Not sure why it would make higher rpm the second time around, I have read on some other forums that fluctuations in the tach could be due to issues with the tach cable?).
Did my best to ignore the bright red warnings on the 830 in the corner of my vision and concentrate on the tach on the right side of the panel. Landed and while taxiing back at 1,100 rpm the 830 started jumping all over the place again. Stopped and just watched the instruments for a minute, no change to throttle or MP, no change in the sound of the engine, and yet the rpm's on the 830 were all over the place. I took a picture of it showing 4,840 and the tach showing 1,100... I'll give the shop a call on Monday, they have installed a lot of 830's but appears there is something wrong here.

Here is about a 3 minute span why sitting with the tach idle at 1,100 and rpm jumping all over the place on the 830.

Sounds like a bad connection. The RPM may be wired to the mag or the ignition switch (can’t recall which). The JPI connectors have screws to hold them together. I have had issues with the screws loosing up on EGT sensors and it would give erratic readings.


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[carusoam]

The whole idea of the modern gauge is to do away with the tach cable that wears and goes bonkers.

The electronic sensor needs some understanding... find out what it is using, and where it is, why it’s not working...

My C’s tach wore the cable, the tach's response was to become inaccurate and bounce around.  One day the bounces got so large the needle popped off...  it is hard to set power levels without a tach...

At the back of the mechanical tach, find the oil cup.  See if the cup is getting any lubrication....

PP thoughts only, not a mechanic...

Best regards,

-a-

[Skates97]

45 minutes ago, Marauder said:

 

Sounds like a bad connection. The RPM may be wired to the mag or the ignition switch (can’t recall which). The JPI connectors have screws to hold them together. I have had issues with the screws loosing up on EGT sensors and it would give erratic readings.


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It is wired to the mag. It could very well be a bad/loose connector. That would explain the erratic behavior. If it was picking up interference from an ignition wire which is one of the things they list as a possible problem on the JPI website I would think it would have shown constant interference. Is there a ground involved that would effect just the rpm sensor? Just thinking out loud.

With the number of these that they've done I'm guessing they've seen it before. I'll see what they say Monday morning. 

[kortopates]

It is a loose or bad connection. Unlikely that the sensor would be bad or damaged in the installation. These wires aren't usually prone to interference (like the thermo couple sensors) from ignition leads or high current, but you wouldn't want them bundled with them for any length either. The shop will be find it and fix it for you.

Edited November 19, 2017 by kortopates

[bradp]

There’s also a number of pulses setting in the 830s setup.  It’s to help determine whether it is counting pulses from a 4 or 6 cylinder engine. 

This sounds like a bad connection or a bad probe.  

Connection is most obvious. 

Make sure that the ground for the 830 and the ground for the engine to airframe are intact and clean of oil.  

Then examine the connection from the rpm sensor to the rest of the JPI harness.  It should be that the two ring terminals are separated by a washer, and the nut goes directly onto the second ring terminal.  It’s not screw head -> ring terminal -> ring terminal -> washer -> nut.  Although counter intuitive this can result in erratic measurements and is one of the more common problems with JPI installations during checkout.   

[Skates97]

Update - Appears to be solved.

They got to it earlier this week and found that the pin in the connector coming from the rpm sensor was loose. They re-pinned it and said it should be good to go. I was able to get out to the airport this afternoon and take it for a few trips around the pattern and there were no fluctuations.

The tach looks to read fairly accurate at low rpms (idle) but once up above about 1,600 it starts to read too high. At 2,600 on the 830 it is near 2,700 on the tach and at 2,700 on the 830 it is above 2,800 on the tach. Seems that the higher the rpms go the further off the tach is.

Next up will be to replace the old original tach with an electronic one instead of one that runs off a tach cable.

[DXB]

I  had a heart attack when this first happened to me  on my EDM-900  - I thought the engine was over-speeding but calmed down when I realized there was no change in engine sound. Assuming you have the JPI rpm sensor that goes into the vent plug of a Bendix mag, your issue is likely identical - see my thread below.  And if my experience is any guide, your problem will recur.  The design of the connector from the sensor is inadequate for the job - re-securing the pin contacts on mine only helped temporarily. At that point, JPI tech support was worse than useless - recommending I overhaul my mag because "your magnets must be getting weak."   Ultimately the company CEO gave me a free new sensor, but the sensor itself turned out not to be the problem - it recurred with the replacement after a couple months.  Jumping to the punchline, just drench both ends of the connection with this $60 bottle of pixie dust (Stabilant 22)  https://www.amazon.com/Stabilant-5ml-Kit-Makes-30ml/dp/B001E50GQS/ref=sr_1_1?s=electronics&ie=UTF8&qid=1511624193&sr=1-1&keywords=stabilant+22.  When mine had issues again a while after the first application, I just applied more liberally, and problem solved. It also might be amusing to call JPI tech support just so you can hear them insist that it is not a problem anyone else has ever had with their sensor. Two  exasperated pilots who fly something other than a Mooney have found my prior thread and contacted me for guidance after talking to JPI first.  I am happy to provide JPI's tech support for this specific issue going forward .

 

[jlunseth]

This may have nothing to do with your failure, but I learned that with the EGT probes there is a very specific order of assembly for the JPIs and it is counterintuitive.  Its been a very long time, so i don't remember the details, just something about a small star washer that had to be mounted in the right sequence and was not on a couple of my probes.  Simple fix.  The "problem" arises when they have the new guy, or the part time guy, who is not really familiar with the sequencing, doing "that easy job."  At any rate, your connection might be loose, or it might have been assembled wrong, have them make sure they check the order of assembly against the manual.

[thinwing]

On 11/25/2017 at 9:20 AM, jlunseth said:

This may have nothing to do with your failure, but I learned that with the EGT probes there is a very specific order of assembly for the JPIs and it is counterintuitive.  Its been a very long time, so i don't remember the details, just something about a small star washer that had to be mounted in the right sequence and was not on a couple of my probes.  Simple fix.  The "problem" arises when they have the new guy, or the part time guy, who is not really familiar with the sequencing, doing "that easy job."  At any rate, your connection might be loose, or it might have been assembled wrong, have them make sure they check the order of assembly against the manual.

The star washer is placed between the two eyes than screwed together...intuition tells you to place under screw head