My RV-10's IO-540 went in for an overhaul in April 2025. A couple of months after it was back to flying status in Sep 2025, someone pointed out the fuel pressure readings with just the engine driven fuel pump (boost pump off) was a bit low (17-19 psi). After I complained about it to the shop that did the overhaul, they replaced it and the fuel pressure changed to around 21-22 psi which seemed to be close enough to the 22-26 psi range that seems to be "normal" based on looking through various VAF threads on this topic.
Now that the break-in is complete, I was trying to do a GAMI lean test at 0.1 to 0.2 gph intervals and found that I was having a hard time being able to control the mixture at that level of granularity (I don't think this was the case pre-overhaul). In some cases, a half-turn would result in no change to the fuel flow and at other times, a small twist was causing a change of 0.5 gph. An A&P said that it could be due to a mixture cable "stiffness" issue (possibly lubrication) or possibly due to the fuel servo. I haven't yet had a chance to troubleshoot it but if anyone has any other ideas, I am all ears.
While looking at the data for GAMI lean test, I then noticed that even though the fuel pressure (with just the engine driven fuel pump) averaged around 21-22 psi, the pressure seems a lot more "choppy" then prior to the overhaul. I have attached three screenshots. One is from Mar 2025 (pre-overhaul) and the other two are from the last couple of weeks (one of which was on a particularly hot day). When the boost pump is on, the pressure is around 24 psi in all cases but when it is turned off, there seems to be quite a marked difference between the choppiness between pre-overhaul and post-overhaul.
Is this kind of fuel pressure choppiness ok or does it need to investigated and addressed? Other than replacing the engine driven fuel pump (again), is there anything else that can be done?
The fuel flow post-overhaul doesn't seem to be obviously more choppy than pre-overhaul. Could the choppy fuel pressure issue be causing the fuel flow issue that I was seeing during the GAMI lean test ("stiffness" in the mixture control)?
Thanks.
Now that the break-in is complete, I was trying to do a GAMI lean test at 0.1 to 0.2 gph intervals and found that I was having a hard time being able to control the mixture at that level of granularity (I don't think this was the case pre-overhaul). In some cases, a half-turn would result in no change to the fuel flow and at other times, a small twist was causing a change of 0.5 gph. An A&P said that it could be due to a mixture cable "stiffness" issue (possibly lubrication) or possibly due to the fuel servo. I haven't yet had a chance to troubleshoot it but if anyone has any other ideas, I am all ears.
While looking at the data for GAMI lean test, I then noticed that even though the fuel pressure (with just the engine driven fuel pump) averaged around 21-22 psi, the pressure seems a lot more "choppy" then prior to the overhaul. I have attached three screenshots. One is from Mar 2025 (pre-overhaul) and the other two are from the last couple of weeks (one of which was on a particularly hot day). When the boost pump is on, the pressure is around 24 psi in all cases but when it is turned off, there seems to be quite a marked difference between the choppiness between pre-overhaul and post-overhaul.
Is this kind of fuel pressure choppiness ok or does it need to investigated and addressed? Other than replacing the engine driven fuel pump (again), is there anything else that can be done?
The fuel flow post-overhaul doesn't seem to be obviously more choppy than pre-overhaul. Could the choppy fuel pressure issue be causing the fuel flow issue that I was seeing during the GAMI lean test ("stiffness" in the mixture control)?
Thanks.
