Fuel pressure, running hot?

[JayMatt]

Quick Update. The Fuel pressure gauge is bad. Sender or receiver I don't know but we put a manual valve on it and ran it, the analog gauge went up and down with RPM and different weird stuff and the Manual inline gauge stayed at a perfect 22psi. So that solves that question and I'll get that fixed. 

Then there is the heat, I sealed everything off so that the air would flow more correctly over the engine, there were a few spots that could use improvement. The most important thing was that the probe for CHT's was also likely bad as the connection was very loose. Who knows, after 10 hours of flying I guess that's not a crazy thing to happen so I'll be looking for a new probe. If anyone know they best place to get one I appreciate the advice. 

Add an edit here: I've read a few spots on mooneyspace where guys modified the sheet metal baffle on the right side intake and cut it down about a half inch to improve cooling. Anyone have opinions or experience with that? 

Edited August 2, 2023 by JayMatt

[PT20J]

3 hours ago, JayMatt said:

Quick Update. The Fuel pressure gauge is bad. Sender or receiver I don't know but we put a manual valve on it and ran it, the analog gauge went up and down with RPM and different weird stuff and the Manual inline gauge stayed at a perfect 22psi. So that solves that question and I'll get that fixed. 

Then there is the heat, I sealed everything off so that the air would flow more correctly over the engine, there were a few spots that could use improvement. The most important thing was that the probe for CHT's was also likely bad as the connection was very loose. Who knows, after 10 hours of flying I guess that's not a crazy thing to happen so I'll be looking for a new probe. If anyone know they best place to get one I appreciate the advice. 

Add an edit here: I've read a few spots on mooneyspace where guys modified the sheet metal baffle on the right side intake and cut it down about a half inch to improve cooling. Anyone have opinions or experience with that? 

I’m always suspicious of instrumentation and personally would not modify anything until I knew the instrumentation was accurate. In my case, when I put in the rebuilt engine in my M20J, I had the EDM 700 calibrated by the factory and installed all new JPI CHT probes. (Cylinder number 3 got a ring probe under the factory bayonet probe replacing the spark plug probe). Cylinder #2 ran 20 deg F hotter than the 1 and 4. Cyl 3 was lowest, but I expected that since the piggyback probe runs cooler. The baffle seals were new and all leaks had been plugged.

When I replaced the EDM with a G3X/EIS, with the same CHT probes and wiring (except #3 which was replaced with a JPI bayonet), #2 fell in line with the others and is usually slightly cooler.

To determine whether the fuel pressure problem is the gauge or the transducer, I would take the back-shell off the CPC connector which will allow you to get DVM probes on the wire end of the contacts with every thing connected. You can check the excitation voltage from the gauge ( (pins 1,2) which should be steady around 10 Vdc and the voltage from the transducer (pins 3,4) which should change depending on whether the boost pump is on or off and should be steady. If the excitation is missing, the gauge is bad. If the output voltage is missing, varies or is not different when the boost pump is on/off then the transducer is bad. Otherwise, it is a problem with the gauge.

Of course, it’s always a good idea to check the wiring and especially the connectors. There is a CPC connector at the transducer, a cannon plug at the firewall, and a connector on the back of the instrument module. 

If the problem is the gauge, Sigma-Tek still repairs them.

Skip

[JayMatt]

2 hours ago, PT20J said:

To determine whether the fuel pressure problem is the gauge or the transducer, I would take the back-shell off the CPC connector which will allow you to get DVM probes on the wire end of the contacts with every thing connected. You can check the excitation voltage from the gauge ( (pins 1,2) which should be steady around 10 Vdc and the voltage from the transducer (pins 3,4) which should change depending on whether the boost pump is on or off and should be steady. If the excitation is missing, the gauge is bad. If the output voltage is missing, varies or is not different when the boost pump is on/off then the transducer is bad. Otherwise, it is a problem with the gauge.

Of course, it’s always a good idea to check the wiring and especially the connectors. There is a CPC connector at the transducer, a cannon plug at the firewall, and a connector on the back of the instrument module. 

If the problem is the gauge, Sigma-Tek still repairs them.

Skip

I'm just going to have to save this comment and wrap my head around it when I go back down there. 

[JayMatt]

I'm going to revive this thread with an update.

I messed with some baffling and test flew the plane. The OAT was 97F when we went up and the first flight was interesting. I was so worried about watching the temperatures I forgot to put the gear up...lol. So as I thought I was having issues and the temperature was climbing again, I circled back to land. That's when I realized my gear was down. So I did a touch and go instead and took off again. Next take-off was better, stayed cooler longer. Not as perfect as I would have liked and it did take some tweaking to keep it just right. including having the cowl flaps cracked open. 

So the Temperature is still slightly higher than I would like it to be and so is the oil temperature. Not nearly as much as originally but not where I want it to be if it can be helped. Tonight I plan on messing with it some more. Check the top baffling that I've seen can be an issue with Mooney's. Previously I just sealed all the gaps and didn't check how well the baffling sealed against the top cowl. That's could be the whole issue but I want to ask a few things and get some opinions.

What's the best way to test the vernatherm? How much cooler would the oil cooler run than the oil temp maybe? I don't want to pull and test it just yet but that could be part of the issue. Would a faulty vernatherm cause higher CHT's? If I'm not getting the proper cooling out of my oil cooler that could be a significant part of the issue. I'll get a laser Thermometer tonight and run the plane for a good bit and then test all the cylinders and see if I detect much difference

Another thing that may be in my head, maybe not, it seems like the EGT's jump pretty quickly when I start leaning. I never paid attention to all of this stuff as closely as I am now but either way, fast rising EGT while leaning is a possible indication of something else? Keep in mind, absolutely nothing has changed since running great to getting a hot run on a long trip. 

[JayMatt]

And I'm going to close this out. Went out yesterday and checked on the baffling and found the issue. When I originally checked the baffling with my AI, the cowl was off. He noted all the small gaps and holes all over the place that could be sealed up. I didn't think they were serious but research on here and elsewhere made it seem like every pin hole needed filling so I went to work. That did help with cooling and I could manage 400f but not at full power. 

Anyway long story short, I looked though the oil door with lights and cameras and found out my baffling doesn't seal against the cowl anywhere. there is a good half inch gap in a lot of places and about a quarter inch gap everywhere. So you live and learn and with proper research you figure it out. So this post is for the next guy that comes along years down the road and wants to know why their plane can't take the hot summer days very well.