Brandontwalker Posted July 7, 2016 Report Posted July 7, 2016 (edited) I had a JPI 900 installed just over a month ago and have had a couple of slight glitches on initial start up here and there. I called JPI and they recommended I verify that the 900 is grounded to the engine block. Sounded crazy to me, but I checked this afternoon and the shop grounded it to the airframe behind the panel. Kind of pisses me off considering how much money I just paid them. Nonetheless, I would appreciate any guidance from the Mooneyspace pros as to where the engine block ground is on an IO-360 (M20J). Edited July 7, 2016 by Brandontwalker Quote
carusoam Posted July 7, 2016 Report Posted July 7, 2016 There are a few that attach various parts like the engine to the airframe and the panel to the airframe. Since the EGTs and CHTs are measured in tiny numbers, the grounds are going to be important. The electronics shop should be able to point out the grounding straps for you. If they are missing, they should get replaced... PP thoughts only. Best regards, -a- Quote
N201MKTurbo Posted July 7, 2016 Report Posted July 7, 2016 I have always used one of the mounting studs of the prop governor. There isn't a dedicated ground on the engine. When I bought this plane it didn't have a ground strap. Adding one fixed a lot of issues like poor starting! Quote
Yetti Posted July 10, 2016 Report Posted July 10, 2016 My 75F which is almost a J in design has a grounding strap from the engine to the airframe on the starboard side. I think it attaches at the foot well. Have to look. Given that the alternator needs one to charge the battery, I would think all planes would have one. Possible it go left off. Quote
RLCarter Posted July 10, 2016 Report Posted July 10, 2016 There should be ground somewhere from the Engine back to the air frame, mine is located next to the lower right hand rubber engine mount and ties into the firewall Quote
LANCECASPER Posted July 10, 2016 Report Posted July 10, 2016 On 7/6/2016 at 10:17 PM, Brandontwalker said: I had a JPI 900 installed just over a month ago and have had a couple of slight glitches on initial start up here and there. I called JPI and they recommended I verify that the 900 is grounded to the engine block. Sounded crazy to me, but I checked this afternoon and the shop grounded it to the airframe behind the panel. Kind of pisses me off considering how much money I just paid them. Nonetheless, I would appreciate any guidance from the Mooneyspace pros as to where the engine block ground is on an IO-360 (M20J). I would take it back to the avionics shop and insist that they do it, even if it costs an hour of labor. If there are any problems down the road they may try to blame it on the last person that worked on grounding it. Quote
Marauder Posted July 10, 2016 Report Posted July 10, 2016 I would go even one step further than Lance. I would make them correct the grounding at their cost. The 900 is considered a primary for your gauges and it should have been installed correctly. Sent from my iPad using Tapatalk 1 Quote
N601RX Posted July 10, 2016 Report Posted July 10, 2016 I used a 1/4 tapped hole that was already present in the top part of the case. It was on the top side back close to the rear of the engine just inside the baffling. I think it was on the copilot side. Quote
Brandontwalker Posted July 12, 2016 Author Report Posted July 12, 2016 On 7/10/2016 at 10:52 AM, LANCECASPER said: I would take it back to the avionics shop and insist that they do it, even if it costs an hour of labor. If there are any problems down the road they may try to blame it on the last person that worked on grounding it. I had the same thought. They are "researching" the issue and will hopefully reach the same conclusion as I. They simply did not follow the bold letter instructions in the installation manual. Quote
cnoe Posted July 13, 2016 Report Posted July 13, 2016 JPI makes this VERY clear in the installation instructions. I vote for making the original installer correct it. But FYI my engine ground runs from a prop governor bolt to the firewall box. I tied into that connection when installing my JPI. In fact my IA insisted that I add another ground strap from there to the actual airframe to forgo any other ground issues. Sent from my iPad using Tapatalk 2 Quote
DXB Posted July 13, 2016 Report Posted July 13, 2016 I'm curious what kind of starting glitches you have...I've had a couple too. Also I wouldn't know where to find the ground on my 900... Quote
Brandontwalker Posted July 13, 2016 Author Report Posted July 13, 2016 I'm curious what kind of starting glitches you have...I've had a couple too. Also I wouldn't know where to find the ground on my 900... The JPI scans through all probes and scrolls messages: "BAD EGT1 PROBE, BAD EGT 2 PROBE, BAD EGT 3 PROBE, BAD EGT 4 PROBE, BAD CHT 1 PROBE..." I can pull the breaker and power cycle the unit and it is resolved. However, it concerns me since this is primary. Sent from my iPhone using Tapatalk Quote
carusoam Posted July 14, 2016 Report Posted July 14, 2016 A couple of questions come to mind... 1) It works perfectly normal after the off/on recycle? 2) When does the JPI get turned on, before start? best regards, -a- Quote
OR75 Posted July 14, 2016 Report Posted July 14, 2016 the JPI getting power from the main bus or the avionics bus ? Quote
N601RX Posted July 14, 2016 Report Posted July 14, 2016 10 minutes ago, N601RX said: The voltage difference on the ground is what is causing the problem. When the starter is engaged under the higher current flow a small voltage difference on the ground between the airframe and engine will develope. This is why jpi wants the ground on the engine. The thermocouples only produce a few millivolts when heated. The instrumentation amplifiers inside the jpi takes this small signal and amplifies it. This small signal is expected to be referenced to ground, otherwise it is riding on the voltage differential between the engine and airframe and is outside the range the jpi can measure causing the jpi to think the probe is bad. Don't ground it at the firewall, connect it to the engine Quote
DXB Posted July 14, 2016 Report Posted July 14, 2016 On 7/13/2016 at 8:19 AM, Brandontwalker said: The JPI scans through all probes and scrolls messages: "BAD EGT1 PROBE, BAD EGT 2 PROBE, BAD EGT 3 PROBE, BAD EGT 4 PROBE, BAD CHT 1 PROBE..." I can pull the breaker and power cycle the unit and it is resolved. However, it concerns me since this is primary. Sent from my iPhone using Tapatalk Never had that one - once I had my EGTs read off scale upon startup (but with no warning alarm) - resetting the breaker fixed it. I also had it stop reading any MP, RPM, or CHT/EGT in flight once. It self rebooted just as I was about to pull the breaker. Still, as primary, I'd rather not see this stuff happen. Quote
N601RX Posted July 14, 2016 Report Posted July 14, 2016 I installed both my 830 and later 900 exactly by the manual with IA's blessing and in 200 hrs have not once saw it lock up, reboot, or give an error. It's beyond me how some of these so called avionics shops will install something with even reading the manual. The jpi manual is one of the easiest to follow that I have seen. There have also been a lot of these installed with the star washers under the nut instead on between the ring terminals like they should be. 2 Quote
Brandontwalker Posted August 24, 2016 Author Report Posted August 24, 2016 UPDATE: The ground location was moved to the engine block per the install manual. All erratic behavior of the 900 is now resolved. Sent from my iPhone using Tapatalk 1 Quote
carusoam Posted August 24, 2016 Report Posted August 24, 2016 Great follow-up Brandon! Best regards, -a- Quote
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