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IP: 68.118.0.102
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Fuel pressure leak down questions
Upon reaching the 1/4 mark in the fuel tank, the fuel pressure gauge would shake and gyrate between 0-4 psi until it ranged down to 0 and after a while the engine would die of fuel starvation. Until that point, the gauge would read 3-3.8 psi and was generally steady. Adding gas to the tank alleviated the symptoms. The bottom of the tank is roughly parallel to the top of the block. The fuel pump is mounted on the bulkhead with approximately 15 inches of head to the bottom of the pickup.
Although I had a theory or two, I decided to follow a diagnostic process based on what I've gleaned from this forum rather than getting my exercise by jumping to conclusions. Following are the steps and findings:
Currently the engine runs smoothly with less than 1/4 tank of fuel, fuel pressure steady at 3.4-3.8 psi. Upon shut down, fuel pressure drops to 1.2 psi in about a minute. After two hours the fuel pressure is .8 or so, and after four hours it has leaked down to 0 psi. While I believe the fuel pump was getting weak, I also believe an air leak at the shut off valve caused the pump to overwork, introduced cavitation, and was most problematic when the fuel was lower in the tank because the pressure assist from the effect of gravity on a fuller tank is diminished. So much for background. Here're the questions: Is the leak down I'm experiencing typical? If not, what could I have missed? Thanks!
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Del ____ 1986 Com-Pac 23 (until the next boat shows up!) 1986 Pearson 34 (sunk by Florence) 1963 Morgan Tiger Cub w/original A4 engine (Sold...but not forgotten) |
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TimBSmith (08-08-2022) |
#2
IP: 24.152.132.65
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I think you have a crack or pinhole in the in-tank fuel pickup tube right at the 1/4 tank level.
edit: Sorry, it seems we didn't actually answer your question. I would not expect the carburetor float valve and fuel pump check valve to hold pressure very long so as for whether or not your fuel pressure leak down is normal, I'd say it is. This is offered without any real testing, only opinion. I still think the pickup tube needs checking.
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Neil 1977 Catalina 30 San Pedro, California prior boats 1987 Westsail 32, 1970 Catalina 22 Had my hands in a few others Last edited by ndutton; 06-25-2016 at 05:03 AM. |
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TimBSmith (08-08-2022) |
#3
IP: 108.31.90.116
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Quote:
Edit: Neil types faster than I do!
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@(^.^)@ Ed 1977 Pearson P-323 "Dolce Vita" with rebuilt Atomic-4 |
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TimBSmith (08-08-2022) |
#4
IP: 24.152.132.65
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Wow, sad. I type with two fingers. It shows we are both thinking the same thing and that it's not mentioned in Del's list elevates the confidence that this is it.
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Neil 1977 Catalina 30 San Pedro, California prior boats 1987 Westsail 32, 1970 Catalina 22 Had my hands in a few others |
#5
IP: 99.30.185.198
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This scenerio reminds me of something that happened to me many years ago involving a rather large rented generator. With about 1/4 left on the fuel gauge it died. Adding fuel solved the problem which prompted the question to the owner, "what's going on here?". His reply was that he had shortened the pick-up tube about 2" to get it away from the rust in the bottom of the "unserviceable" tank. So, my question for you is, is your pick-up removable so that you can check on Ed's and Neil's diagnosis ?
Tom |
#6
IP: 68.118.0.102
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A pinhole leak in the pickup sounds logical.
The pickup tube is mounted in a plate that also contains the fill tube. The tank is located directly beneath the cockpit floor and will have to be removed to pull the tube for inspection. It's a 25 gal cylindrical monel tank. When I first got the boat 12 years ago I pulled the tank for cleaning and pressure testing. Pulling it was a couple of hours and reinstalling was an all day job. Is there a way to confirm the presence of a pinhole leak in the pickup tube before removing the tank?
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Del ____ 1986 Com-Pac 23 (until the next boat shows up!) 1986 Pearson 34 (sunk by Florence) 1963 Morgan Tiger Cub w/original A4 engine (Sold...but not forgotten) |
#7
IP: 24.152.132.65
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Your boat, your choice but before spending hours on tank removal I'd consider an access plate in the cockpit sole. They come in a variety of sizes and colors, even stainless. I can't think of a way to confirm a tube leak other than visual inspection.
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Neil 1977 Catalina 30 San Pedro, California prior boats 1987 Westsail 32, 1970 Catalina 22 Had my hands in a few others |
#8
IP: 132.147.29.249
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I think pinhole leak in fill tube + leak in valve = too much air for the pump.
As for the leak-down, this is exactly why I shut my pump off and let the engine run until it quits when I am done for the day. When I know I will need the engine again, I just let it run until the fuel pressure drops to zero, which is only about 10 seconds or so. |
#9
IP: 108.31.90.116
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Quote:
If there's enough air coming through for the pump to lose pressure, it should be enough to see. A quick Google for "clear fuel hose" turned up this https://www.amazon.com/Motion-Pro-12.../dp/B000UKM4GI
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@(^.^)@ Ed 1977 Pearson P-323 "Dolce Vita" with rebuilt Atomic-4 |
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TimBSmith (08-08-2022) |
#10
IP: 68.118.0.102
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Great suggestion! I'll try about anything before resorting to cutting an access port or removing the tank. I can easily attach clear hose to the pickup fitting on the tank and run it to the primary filter. Observing fuel flow at that point will be easy as well. I've now got about 18 gal of gas to burn before I can try. At my usual rate that's 25+ hours of run time.
After July 4th the plan is to sail outside from Topsail to Cape Lookout and then on to Beaufort, Oriental and then Ocracoke. Then on to Little Washington before heading back to Topsail. There will be plenty of motoring along the way, and with the right stuff on board, once I hit the 1/4 tank mark I'll give it a go.
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Del ____ 1986 Com-Pac 23 (until the next boat shows up!) 1986 Pearson 34 (sunk by Florence) 1963 Morgan Tiger Cub w/original A4 engine (Sold...but not forgotten) |
#11
IP: 68.108.255.88
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Try This Before You Cut
When the engine seems to run out of fuel blow on a short piece of hose back into the tank with your mouth. If you don't hear bubbles in the tank something fishy is going on in the tank.
TRUE GRIT Last edited by JOHN COOKSON; 06-26-2016 at 02:24 AM. |
#12
IP: 137.200.32.38
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Discovered an oddity today - my fuel pressure comes back from 0 after sitting a day. I don't know if this is new or not because I only recently have a fuel pressure gauge I can see from the helm, but I ran the fuel out and the engine quit one day and the next day it was up to 0.5 PSI The engine actually started and ran for a couple of minutes with the fuel pump off, so it was not a gauge artifact. I am not sure if this is heat causing gas to expand or what, but I might turn the valve off next time and see if that changes things.
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#13
IP: 68.118.0.102
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Diagnosis/resolution
Man have I learned a lot.
First the diagnosis: air leaks. The shutoff valve that was leaking air was removed, but the problem persisted. As I've experienced too many times, there is seldom a single failure resulting in a problem on my engine. I found the pickup tube fitting at the top of the tank was a little loose. The fitting couldn't be turned 360 deg due to interference from the fill hose, so it was loosened as much as possible, Permatex Ultra Black sealant applied and it was tightened as much as possible. Then a coat of sealant applied around the base. That seemed to do the trick with the near full tank but testing was needed. I installed clear fuel line at the tank and at the Facet pump inlet. With the fuel delivery system intact, running the engine resulted in no bubbles at the tank end of the fuel line. However, the flow was negligible and at times appeared non-existent unless the line was slightly elevated. At the pump end, fuel seldom completely filled the 12" clear line, but a slight flow could be detected. The line on the tank end sagged a bit and never completely filled--there was always what appeared to be an air bubble in it, but obviously there was some fuel making its way to the pump. Fuel pressure taken just before the carb stayed around 3 psi. Side note: My pump has always run hot, around 125 deg in 90 deg air temp. I re-read the post here re: hot pumps by Roadnsky. Mine always quickly heated and until recently ran with no problem. To get the fuel level down to the point where I originally experienced the recent problem, around 1/4 tank, the line was removed from the carb and placed in a 5 gal jug. The pump was jumped to avoid putting current through the coil and immediately the fuel line completely filled, no bubbles. The pump was no longer hot, it was quite cool, about the temp of the gas in the tank. After emptying the tank to less than 1/4 full, still no bubbles. Blowing in the line resulted in bubbles in the tank--thankfully no tank removal needed to examine the pickup tube. Line reconnected to carb, engine started. No bubbles, but the fuel flow lessened to the point observed before. And the pump heated again. Interestingly enough, an occasional bubble would come from the pump back up the line at idle. Fuel pressure still at 3 psi. Just for fun, I reinstalled the faulty valve. Bubbles galore throughout the line at full flow. The line was reconnected to the carb and there were NO bubbles, and the previously observed negligible flow appeared. After just a few minutes at idle, the fuel pressure dropped to zero and the engine stopped. Faulty valve removed, full flow, no bubbles. Line connected to carb, engine runs great. Putting the clear fuel line on both ends was most instructive. It's too bad clear fuel line isn't made such that it is USCG approved. The short sections opened a window to the operation of the fuel delivery system that was extremely helpful. Here's what I learned from the experience/confirmed from reading posts here:
Thanks folks--Happy July 4th.
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Del ____ 1986 Com-Pac 23 (until the next boat shows up!) 1986 Pearson 34 (sunk by Florence) 1963 Morgan Tiger Cub w/original A4 engine (Sold...but not forgotten) |
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TimBSmith (08-08-2022) |
#14
IP: 184.0.19.114
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Quote:
Today in 101° air temp the Facet temp was 120° Note that it's been years now and the pump is still running strong.
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-Jerry 'Lone Ranger' 1978 RANGER 30 Last edited by roadnsky; 07-04-2016 at 09:22 AM. |
#15
IP: 108.31.90.116
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Great troubleshooting Del. Nice and methodical, changing one thing at a time.
Glad you didn't have to go through the pain of removing the tank!
__________________
@(^.^)@ Ed 1977 Pearson P-323 "Dolce Vita" with rebuilt Atomic-4 |
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TimBSmith (08-08-2022) |
#16
IP: 68.118.0.102
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Not having to remove the tank has been a holiday weekend gift!
Troubleshooting A4s is made easier by reading the Moyer manual and posts in this forum. And from the expertise of forum members. Remote diagnosis of a problem based on the information shared in a post is tough--but folks here give good advice to contemplate. After understanding how a system works, the next most important troubleshooting tenet for me is not to stop working through all the components in a system just because it appears that the problem is resolved. The presence of another problem in the system has occurred often enough that by checking through every component I have confidence there's not another masked by my "fix." Time to go sailing!
__________________
Del ____ 1986 Com-Pac 23 (until the next boat shows up!) 1986 Pearson 34 (sunk by Florence) 1963 Morgan Tiger Cub w/original A4 engine (Sold...but not forgotten) |
The Following User Says Thank You to dburns For This Useful Post: | ||
TimBSmith (08-08-2022) |
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