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Please help Low fuel pressure IO 360 M1B

N

nbachert

Well Known Member
I started the engine for the third time today and noticed a drop in fuel pressure from 23 to 14psi then the engine ran rough and died. I started again and it did the same thing. I unhooked every line in order from the firewall to the spider and turn the boost pump on and pumped fuel into a bucket and everything looked good. Started it again and it ran for about a min before dropping to 14psi again. I turned the boost pump on and fuel pressure went to 27psi and the eng ran fine. I tried a bunch of rpms and turned the pump off and every time pressure dropped. I checked the filter for the boost pump and there was two very small shavings, which I cleaned out. I ran it up again and leaned it out but it still wanted to die without the boost pump. This is a brand new experimental engine from lycoming. Can it be anything other than the eng driven pump? Please let me know, thanks

Nick
 
Check (with a wrench) all of your connections from the boost pump to the engine driven pump. If you still have a problem after that, carefully check the flares on all your lines. A small crack on a flare can be difficult to detect. You can also check for leaks at each connection by putting the mixture to idle-cutoff and running the boost pump before you start investigating with a wrench.

Jerry Esquenazi
RV-8 N84JE
 
I forgot it in my post but I also put it to idle cutoff and ran the boost pump searching for a leak of some sort but found nothing. I also rechecked with a wrench all of the connections.
 
There is a very recent thread very similar to your described problems.

Found it see page 2 of this section
"Mechanical Fuel Pump Pressure Problem"
http://www.vansairforce.com/community/showthread.php?t=111097

If your fuel tank(s) are mostly full it could be blocked fuel vents. A miniscule air leak in the selector valve or connections anywhere upstream of the boost pump could also be the cause, even if there is no evidence of leaking fuel.

Good Luck
 
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I did a search but only found the one on the -10. I was thinking about boost pump forward. I gave up and was messing with the cowling when I saw a spot of green on the seal between the wing root and fuselage. Pulled it off and sure enough more green. Very little residue on the tank fitting but after inspecting its the only possible culprit. I took it off to look at it but how do you know if a flare is bad or cracked like other post have mentioned? It looked ok to me so I tightened it down and hopefully tomorrow it will prove to have been the problem.
 
Nick, I had a similar problem on my M1B before the first flight. Wouldn't idle, low fuel pressure. I looked for fuel line leaks and found none. Finally called Lycoming Tech Support and went over the possibilities. He said that it had to be an air leak before the engine fuel pump. When I said that I had looked and could not see any fuel leakage, he said that more often than not there is no fuel leak even though the system is able to suck air into itself. Since I had tightened (and retightened) all fuel line fittings, I went back and looked at my fuel line flares. A couple of them were poor and not well centered. When I redid those fuel lines, everything was fixed. FYI.

-John

nbachert said:
I started the engine for the third time today and noticed a drop in fuel pressure from 23 to 14psi then the engine ran rough and died. I started again and it did the same thing. I unhooked every line in order from the firewall to the spider and turn the boost pump on and pumped fuel into a bucket and everything looked good. Started it again and it ran for about a min before dropping to 14psi again. I turned the boost pump on and fuel pressure went to 27psi and the eng ran fine. I tried a bunch of rpms and turned the pump off and every time pressure dropped. I checked the filter for the boost pump and there was two very small shavings, which I cleaned out. I ran it up again and leaned it out but it still wanted to die without the boost pump. This is a brand new experimental engine from lycoming. Can it be anything other than the eng driven pump? Please let me know, thanks

Nick
Click to expand...
 
Was this with a hot engine?

Is this a tail dragger?

How much fuel in the tanks?

Were you using 100% pure Avgas 100 / 100LL?

I suspect a heat soaked fuel pump and vapour locking. I get this in about 99/100 taxi's back from the fuel pump after a flight and this is what the boost pump is for. ;) 100% normal.

If the engine was cold.....and I mean first flight of the day cold or with many hours between starts, then start looking.
 
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