Mark Cline Posted April 1, 2022 Report Posted April 1, 2022 Based on recommendations from past posts within this forum, I purchased GAMI injectors for my 1998 M20M. At the same time I also installed fine wire spark plugs. I did this because my fuel flows had never approached the POH values – they are around 20 to 25% higher. After I had the GAMI injectors and fine wire plugs installed I found only a slight decrease in fuel flow and thus only a slight decrease in fuel cost savings. I performed the GAMI Lean Test per GAMI’s instructions, and sent those data to GAMI. They sent me some replacement injectors that I swapped out on four of the cylinders. The new injectors did not make any difference in fuel flow. I preformed another GAMI Lean Test and send those data to GAMI. GAMI replied that the GAMI Spread was not very good at around 1.6 GPH. My #5 peaks early, and #3 is late. GAMI says they have made my #5 as rich as they can, and my #3 as lean as possible. Basically they imply that there is nothing else that they can do. Per the recommendation of GAMI (and others) the following test have been performed: - The CHT and EGT probes have been confirmed to be reading the correct cylinder. Before I start the engine, they all read the same temperature. - The fuel flow meter has been replaced and replumbed. - Individual FF to each cylinder has been checked. The FF to each cylinder are 1) 7.25 oz, 2) 6.75 oz, 3) 7.00 oz, 4) 6.75 oz, 5) 6.5 oz, and 6) 7.0 oz within 2 minutes and 30 seconds. - Intakes checked for leaks. None noted. All exhaust gaskets were replaced due to 3 of them leaking. The engine is around 1200 hours since overhaul at Western Skyways. The overhaul was performed in 2008. I purchased the airplane in 2018. Since 2018 I have replaced the turbocharger and prop governor. The engine has really not given me any trouble at all other than burring much more fuel than the book values. The Garmin EIS was installed in 2018 with all new probes. No excessive oil burn. Oil changed very 25 hours. When I am just out flying for fun (which has been 95% of my flying since COVID) I usually poke around at 27 inches 2300 RPM leaned to 1600 to 1640 TIT with around 16 to 17 GPH fuel flow and 150 knots at 8,000 feet. The engine seems happy at those settings. So more than anything, I am curious why I can’t get a better GAMI spread on this engine. Per GAMI, they have had much success on other Bravos. I do not have any STCs applied to the engine. It’s a stock Lycoming engine. I would be grateful if a knowledge Mooney mechanic has any insight on my situation.
rbp Posted April 1, 2022 Report Posted April 1, 2022 42 minutes ago, Mark Cline said: I usually poke around at 27 inches 2300 RPM leaned to 1600 to 1640 TIT with around 16 to 17 GPH fuel flow and 150 knots at 8,000 feet. for reference, i fly 30/2400 (78% power) at 1550F TIT and 18.6 GPH 1
LANCECASPER Posted April 1, 2022 Report Posted April 1, 2022 4 hours ago, Mark Cline said: Based on recommendations from past posts within this forum, I purchased GAMI injectors for my 1998 M20M. At the same time I also installed fine wire spark plugs. I did this because my fuel flows had never approached the POH values – they are around 20 to 25% higher. After I had the GAMI injectors and fine wire plugs installed I found only a slight decrease in fuel flow and thus only a slight decrease in fuel cost savings. I performed the GAMI Lean Test per GAMI’s instructions, and sent those data to GAMI. They sent me some replacement injectors that I swapped out on four of the cylinders. The new injectors did not make any difference in fuel flow. I preformed another GAMI Lean Test and send those data to GAMI. GAMI replied that the GAMI Spread was not very good at around 1.6 GPH. My #5 peaks early, and #3 is late. GAMI says they have made my #5 as rich as they can, and my #3 as lean as possible. Basically they imply that there is nothing else that they can do. Per the recommendation of GAMI (and others) the following test have been performed: - The CHT and EGT probes have been confirmed to be reading the correct cylinder. Before I start the engine, they all read the same temperature. - The fuel flow meter has been replaced and replumbed. - Individual FF to each cylinder has been checked. The FF to each cylinder are 1) 7.25 oz, 2) 6.75 oz, 3) 7.00 oz, 4) 6.75 oz, 5) 6.5 oz, and 6) 7.0 oz within 2 minutes and 30 seconds. - Intakes checked for leaks. None noted. All exhaust gaskets were replaced due to 3 of them leaking. The engine is around 1200 hours since overhaul at Western Skyways. The overhaul was performed in 2008. I purchased the airplane in 2018. Since 2018 I have replaced the turbocharger and prop governor. The engine has really not given me any trouble at all other than burring much more fuel than the book values. The Garmin EIS was installed in 2018 with all new probes. No excessive oil burn. Oil changed very 25 hours. When I am just out flying for fun (which has been 95% of my flying since COVID) I usually poke around at 27 inches 2300 RPM leaned to 1600 to 1640 TIT with around 16 to 17 GPH fuel flow and 150 knots at 8,000 feet. The engine seems happy at those settings. So more than anything, I am curious why I can’t get a better GAMI spread on this engine. Per GAMI, they have had much success on other Bravos. I do not have any STCs applied to the engine. It’s a stock Lycoming engine. I would be grateful if a knowledge Mooney mechanic has any insight on my situation. I wouldn’t go up to 1640 TIT for sure. In the three Bravos I owned 1600 was max for me and I never changed a turbo or a cylinder. You stand a very low chance of ever being able to run lean of peak with this engine, only a few ever have had a TIO-540-AF1B that would do it. But having cleaned up the spread as much as you have it should be running smoother. If you want it smoother yet I would get the prop dynamically balanced. I had my last Bravo running as smoothly as any Lycoming piston I’ve ever flown behind. The first thing I would do is look through the logs and see when the TIT probe was changed last. If the TIT has been run hot by the previous owner or you, it is burned up and reading low, meaning you think you are running 1600 - 1640, but it’s considerably higher than that. That will throw off what you think your fuel flows should be and will burn up your exhaust valves and guides and exhaust system. The probe is not terribly expensive and it’s a good benchmark to start with a new one and see what the numbers really are. Give a good tug on the tailpipe every time you preflight and really look closely at the exhaust every time you have the cowling off. When the exhaust or turbo clamps fail it send a 1600+ degree blow torch through the firewall into the cabin, incinerating the pilot and passengers. It has happened a few times with Bravos. I don’t say this to add drama but to validate that your airplane is extremely capable but must be maintained by someone that has a good Bravo-specific knowledge and a healthy respect for your life. 4
Mark Cline Posted April 1, 2022 Author Report Posted April 1, 2022 5 hours ago, StevenL757 said: Mark, PM sent. Thank you
Mark Cline Posted April 1, 2022 Author Report Posted April 1, 2022 1 hour ago, LANCECASPER said: I wouldn’t go up to 1640 TIT for sure. In the three Bravos I owned 1600 was max for me and I never changed a turbo or a cylinder. You stand a very low chance of ever being able to run lean of peak with this engine, only a few ever have had a TIO-540-AF1B that would do it. But having cleaned up the spread as much as you have it should be running smoother. If you want it smoother yet I would get the prop dynamically balanced. I had my last Bravo running as smoothly as any Lycoming piston I’ve ever flown behind. The first thing I would do is look through the logs and see when the TIT probe was changed last. If the TIT has been run hot by the previous owner or you, it is burned up and reading low, meaning you think you are running 1600 - 1640, but it’s considerably higher than that. That will throw off what you think your fuel flows should be and will burn up your exhaust valves and guides and exhaust system. The probe is not terribly expensive and it’s a good benchmark to start with a new one and see what the numbers really are. Give a good tug on the tailpipe every time you preflight and really look closely at the exhaust every time you have the cowling off. When the exhaust or turbo clamps fail it send a 1600+ degree blow torch through the firewall into the cabin, incinerating the pilot and passengers. It has happened a few times with Bravos. I don’t say this to add drama but to validate that your airplane is extremely capable but must be maintained by someone that has a good Bravo-specific knowledge and a healthy respect for your life. Thank you. I replaced all of the engine probes about 300 hours ago when I installed the EIS as part of a G3Xtouch. I have never taken the TIT above 1650 since that time, not even transiently. I gave up on trying to run lean of peak soon after starting to fly the airplane when I first got it -- just too hot, and after considering all of the perspectives from this forum. All work has been performed at a very solid Mooney Service Center that I fully trust, and it took me a while to find one I trusted. I check the exhaust, waste gate, and turbo every 25 hours at oil changes as if my life depends on it (because it does). 2 1
carusoam Posted April 2, 2022 Report Posted April 2, 2022 Bravos are challenging… 1) They have the old style log system for air intake… 2) The log system doesn’t naturally deliver the same airflow to each cylinder like expected… 3) Compare that to the curvy tube systems found on other engines… Lycoming has curvy tubes in other applications… 4) Getting Gamis balanced with different openings is the best that can be achieved to match the FF to the airflow… of each cylinder… 5) Now… compare to other Bravos… 6) The best way to see how your engine compares to other Bravos… is to do the Gami Spread test…. And compare to other Bravos…. 7) A place called Savvy does this for a living… 8) If your plane is doing something different than all of the other Bravos… Savvy has the data to help identify what is going on…. 9) For a finely balanced IO550… a Gami spread close to zero is quite possible… lean until rough doesn’t exist…. It is lean until no power is being produced…. The engine just shuts off around 90+°F LOP…. At 5k’ 10) Savvy supplies really good details about how to run the procedures as well… in case your technique or sensors need some help…. 11) Your Gami selection is probably done using data at one power settings typical of cruise…. What power setting do you use for this? 12) Unfortunately with the log intake system… it can only be tuned to a relatively narrow power setting…. If you tuned it at one setting, but fly it at another…. That would be less than optimal… When discussing Savvy details I always invite @kortopates to the conversation…. Paul is highly technical and knows all the usual things about pilots and engines…. And some unusual things as well… Go Bravo! Best regards, -a- 1
Pinecone Posted May 24, 2022 Report Posted May 24, 2022 You say #5 is as rich as possible and #3 is as lean as possible. BUT, your actual fuel flows are opposite - "The FF to each cylinder are 1) 7.25 oz, 2) 6.75 oz, 3) 7.00 oz, 4) 6.75 oz, 5) 6.5 oz, and 6) 7.0 oz within 2 minutes and 30 seconds." #3 is tied for the second highest fuel flow and #5 has the lowest fuel flow. I would be looking into what that is the case.
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