Bottom Line Up Front: I've been flying with a one-way check valve incorrectly installed upstream of the electric fuel pump.
I purchased an RV-4 about 7 months ago. I'm a military pilot by background, so I had very little (~10 hours) experience in small, piston aircraft. I'm the third owner of the aircraft. I had the aircraft inspected by an A&P IA who is familiar with RVs and owned one for several years. When I purchased it, the previous owner always remarked that he hadn't quite figured out how to start it correctly. He would switch on the electric boost pump for ~5 seconds, it would whir away, and then it took about 5 seconds of cranking with the starter for the motor to fire. Since he had only owned it for about 6 months and flown it for about 15 hours, I just chalked it up to technique.
A couple of months after I had purchased it, I was still experiencing difficulty starting. It would always fire, but it would necessitate mixture at full rich and several seconds of cranking the engine. Upon closer inspection, I wasn't getting any fuel pressure turning on the boost pump when the engine was off. However, when I got the engine online, turning the fuel boost pump on would raise the PSI (normally ~21 - 22 psi) by about 4-5 psi. Several possibilities sprang to mind: 1) I had a leaky fuel sump, so the boost pump was just sucking air. 2) The boost pump was functioning properly, but maybe the fuel pressure was sampled after the engine pump and didn't include the boost pump. 3) The boost pump needed to be primed by the engine pump each start and then it would run.
Whatever the case, I figured the boost pump was definitely working with the engine running (bump in PSI) and I could stumble along using the engine pump to start until condition inspection time.
This past weekend, I was changing the oil and decided to see if I could troubleshoot the problem. I made a diagram of the fuel system and tried to piece how it worked together. My next door hangar neighbor is AX-O, so he came over and watched the fuel system while I ran the boost pump. Sounded like it was working, but still wasn't getting any pressure. I told him I was going to take off the fuel outlet hose from the boost pump to see if anything was getting through and then maybe clean (what I thought) was an inline fuel filter. He immediately corrected me and identified it as a one-way check valve. Upon closer inspection, with a mirror and flashlight, we saw the arrow on the valve was pointing the opposite direction from desired flow. We took off the check valve, installed it correctly, and now everything works perfectly.
There were a lot of lessons learned, but the biggest thing I took away was ownership of maintenance. The plane had been inspected by 2 A&Ps and a couple builders, but the problem still hadn't been identified. I seriously doubt the boost pump would have maintained fuel pressure in the event of an engine driven pump failure. It was my mistake to accept an off-nominal condition just because the airplane had been safely flying for 20 years.
I hope this helps someone out in the future who is also experiencing weird boost pump symptoms.
Thanks for the help AX-O!
Below is a link to the fuel diagram with the check valve installed backwards:
https://drive.google.com/file/d/1f_c-6XgFb6JNbccXTveeEvYHhSD0Q0YJ/view?usp=sharing
I purchased an RV-4 about 7 months ago. I'm a military pilot by background, so I had very little (~10 hours) experience in small, piston aircraft. I'm the third owner of the aircraft. I had the aircraft inspected by an A&P IA who is familiar with RVs and owned one for several years. When I purchased it, the previous owner always remarked that he hadn't quite figured out how to start it correctly. He would switch on the electric boost pump for ~5 seconds, it would whir away, and then it took about 5 seconds of cranking with the starter for the motor to fire. Since he had only owned it for about 6 months and flown it for about 15 hours, I just chalked it up to technique.
A couple of months after I had purchased it, I was still experiencing difficulty starting. It would always fire, but it would necessitate mixture at full rich and several seconds of cranking the engine. Upon closer inspection, I wasn't getting any fuel pressure turning on the boost pump when the engine was off. However, when I got the engine online, turning the fuel boost pump on would raise the PSI (normally ~21 - 22 psi) by about 4-5 psi. Several possibilities sprang to mind: 1) I had a leaky fuel sump, so the boost pump was just sucking air. 2) The boost pump was functioning properly, but maybe the fuel pressure was sampled after the engine pump and didn't include the boost pump. 3) The boost pump needed to be primed by the engine pump each start and then it would run.
Whatever the case, I figured the boost pump was definitely working with the engine running (bump in PSI) and I could stumble along using the engine pump to start until condition inspection time.
This past weekend, I was changing the oil and decided to see if I could troubleshoot the problem. I made a diagram of the fuel system and tried to piece how it worked together. My next door hangar neighbor is AX-O, so he came over and watched the fuel system while I ran the boost pump. Sounded like it was working, but still wasn't getting any pressure. I told him I was going to take off the fuel outlet hose from the boost pump to see if anything was getting through and then maybe clean (what I thought) was an inline fuel filter. He immediately corrected me and identified it as a one-way check valve. Upon closer inspection, with a mirror and flashlight, we saw the arrow on the valve was pointing the opposite direction from desired flow. We took off the check valve, installed it correctly, and now everything works perfectly.
There were a lot of lessons learned, but the biggest thing I took away was ownership of maintenance. The plane had been inspected by 2 A&Ps and a couple builders, but the problem still hadn't been identified. I seriously doubt the boost pump would have maintained fuel pressure in the event of an engine driven pump failure. It was my mistake to accept an off-nominal condition just because the airplane had been safely flying for 20 years.
I hope this helps someone out in the future who is also experiencing weird boost pump symptoms.
Thanks for the help AX-O!
Below is a link to the fuel diagram with the check valve installed backwards:
https://drive.google.com/file/d/1f_c-6XgFb6JNbccXTveeEvYHhSD0Q0YJ/view?usp=sharing