JPI 930 Install Costs?

[Don Ostergard]

But seriously, folks......

I have a windowless, unheated hangar. If I'm in the hangar and the engine is stone cold, and compare the OAT readout on my JPI probe with the readout on my "meat thermometer" probe, the temperature values shown will be identical. If I am parked outside, with the same sun shining on both probes at the same time (both probes being situated on the same pilot's side of the plane) again with the engine stone cold, the temperature readouts will once again be identical.

But if I start the engine, warm it up and go flying, the JPI (which has its probe just an inch behind the firewall) will show an OAT reading that is 2 degrees C warmer than my "meat thermometer" OAT thermometer which is mounted in the lower front corner of the pilot's window. There's nothing wrong with the JPI reading. It is giving a perfectly accurate reading of the ambient temperature where it happens to be situated. In other words, the engine is throwing off a lot of heat. I should have known better than to have mounted it right behind the engine compartment (and in my case, about 3 inches behind the big single muffler) of my 250.

I like Dave Gitelman's idea of mounting the probe in the wheel well. In fact, I wish I had mounted it almost anywhere else. One of these years, I'm going to paint the plane and when I do I'm going to move it.

Don Ostergard

[James Turner]

Hi All,

Sorry to dredge up an old post but I am one week into my new panel install and all seems to be going well.

We are at the stage of installing the OAT probe and I recall the discussions in this thread confirmed to me that it was not a good idea to mount it behind the firewall.

One option that makes sense is to mount it in the right side (single muffler at the moment) main gear well. I'd really appreciate some thoughts on this location from those with a lot more Comanche experience than me...

Thanks again,

James.

P.S. The attached picture is what I am hoping to achieve and where I'm at to date...

[N3322G]

Posting the after and before photos is pretty funny - thanks for the giggle

[Jason Brown]

[Don Ostergard]

Hi, James-
I'm the one who lamented having mounted the OAT probe right behind the firewall and the inaccurate temp readings that resulted from doing so. My plane is in the paint shop as we speak; I had them remove the probe and fill in the hole. (and tape up the wires for now). In the coming weeks we'll be gutting the interior and reupholstering it. At that time I plan to reroute the OAT probe to a main gear well. I'd be interested to learn from your experience in doing so. And, if it turns out that we get the task accomplished first, we'll share our findings as well.

Don Ostergard ICS 3263
Drumheller AB Canada
c-flhv@magtech.ca

[James Turner]

Hi Don,

Yes your comments were at the forefront of my thinking to carefully consider where I place the OAT probe...

I emailed JPI and they said they do not have a preferred location but indicated that the gear well would be a better option than behind the firewall. As an aside I have seen mention of mounting the probe just in front of the lower right corner of the wind shield. Not sure if this would still have heat issues or not??

I'm at the unenviable stage of having to remove the internal liners and floor boards to replace the fuel sender wires. Any advice would be appreciated as at the moment I can't see any obvious way of getting the side liners off... I'm assuming you don't have to pull the (glued in) carpet out first??

I'm away for a couple of weeks now so won't have the chance to get back into the refit until I return but I will certainly let you know how I get on.

Cheers,

James.

[Don Ostergard]

Previously in this thread I lamented the erroneous OAT readings on the JPI 830 that we installed in our '59 250 a couple of years ago. We had installed the OAT probe immediately behind the firewall without having given any thought to the amount of heat thrown off the engine, with the result that our OAT readings in flight were consistently 2C high.

We recently had the Sturdy Bird repainted and reupholstered (I'll be turning 70 in a couple of months and I want to start the second half of my life with a nice airplane) which gave us the opportunity to relocate the OAT probe. We now have in mounted in the left wheel well - out of sight, out of drag and away from any heat source. Our OAT readings are now accurate.

I am indebted to Dave Gitelman for making this suggestion.

I will try to attach a photo of the new installation. The photo is looking toward the front of the plane.

Don Ostergard ICS 3263

[James Turner]

[N3322G]

James, I run a different fuel pressure gauge however the symptoms may point to a similar resolution. When we have fuel pressure fluctuation in the Shadin, it means, either an electrical problem or an air leak somewhere in the fuel system.

Have you been able to track the fluctuation and any actual corresponding change in engine perfroamcne via the JPI download? We do this by noting the time of the fluctuation and then look for it in the download.

[N3322G]

Let me add another tip we've used to locate problems in the past. By logging when the fluctuations occur and the altitude, we found electrical ones were random and happened at any altitude, air leaks happened predominantly at higher altitudes. Hope one of the ideas helps you find the problem.

[James Turner]

Hi Pat,

Thanks for your reply.

I did manage to download the flight data yesterday and the FP (the green line) is actually quite stable but it sits at between 5.2-6.5 psi (5.0 psi is the red line and I think 6.0 psi is when the warning is flagged). Anecdotally, the warnings happen at any time; on the ground, during climb, in cruise, and on descent. I should also say having the electric fuel pump on or off makes no difference.

At JPI's recommendation I have placed an in-line pressure snubber immediately before the sensor; no change. At the Avionics shops recommendation I have re-pinned all the connectors on the JPI wiring loom; no change (although I'm not getting GPS COMM fails now...). I have asked JPI for another FP sensor to trouble shoot but they weren't able to do that.

Yesterday in the hanger I switched the electric fuel pump on and left it on for 5 mins to see if the FP indications would spike but they were rock steady at ~4.6psi.

My feeling is that the engine driven fuel pump is to all intents and purposes working fine but producing slightly higher pressure than the nominal 0.5-5.0 psi. The problem is that the JPI warning is very distracting and given that it is a primary value there appears to be no way to adjust the warning trigger level or to cancel the warning for the whole flight...

I'm talking with JPI so hopefully they can come up with something to help...

Regards,

James.

[Mark Anderson]

James,

I am having the same problem on my 930 after having the electic pump replaced. FP spikes over 5 and get the warning. I was told by someone that there may be an adjustment on the FF transducer that may help? I am stumped. Let me know what you find?

Thanks,

Mark

[James Turner]

Hi Mark,

I have been in discussions with JPI about the problem. Looking at my engine data it appears that my engine driven pump is functioning correctly albeit at the high end of the nominal range. JPI agree and are sending me a new key card with the Fuel Pressure alarm set to 8psi; albeit at a cost of $100. This will solve the problem for me.

Regarding an adjustment on the Fuel FLOW (?) transducer; I think the person who told you this may have been thinking Fuel Flow rather than Fuel Pressure (I've done it myself a number of times...). There is certainly an adjustment to the Fuel Flow transducer (K factor) but no adjustment to the Fuel Pressure sensor that I know of...

Maybe take a look at your engine data and give JPI a call. I spoke with Ken Friedland on (714) 557-3805. He (and JPI) have been very helpful.

Best of luck.

James.

[Mark Anderson]

James,

Thanks for the info. I will contact them and do the same. I feel sure that my pump is fine. Did they change your red line to 8psi or just change it so the alarm does not flash until 8 psi?

Thanks again,

Mark

[James Turner]

Hi Mark,

I haven't received the new key card yet but I would be pretty sure they will have kept the limits as per the POH (5.5psi) and just adjusted the alarm limit. What I hope they have done is increase the scale of the gauge to show up to 8psi. I'll let you know.

James.