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Fuel pump failure mode

gear1

Well Known Member
Our RV8 has IO360M1A and a Tempest Fuel Pump #L15473. When cleaning up the aircraft yesterday after a long cross country I found a trail of gasoline dye behind the fuel pump drain tube. As a check, I pressurized the fuel system with the boost pump on the ground and no leakage was seen. Also, when pressurizing the system with the engine driven pump by cranking the engine, no discharge from the fuel pump drain was noted. The pump has accumulated 1400 flight hours since new.

Does anyone know how these pumps fail? Does the diaphragm slowly crack, or can the final failure be catastrophic? (I had planned to attend the 75th anniversary of my Navy Attack squadron in California this weekend but feel it would be risky to attempt the 9 hours of flight time over barren countryside.)

Any knowledge that you all might be able to provide will be appreciated.:(
 
Your pump is toast. Replace before next flight. At 1400 hrs you got way more than a life out of it.

Bob burns
Rv4 n82rb
 
I'm no expert.....

....but I think that's cheating!!!! Great tip! I worked at the local car garage when I was in high school. Remember fighting the pushrod on mechanical pumps. This will take all the 'fun' out of it. :D
 
Put heavy grease on push rod ,can be done using finger , grease will help keep push rod in up position, helps to wipe as much oil off as possible, can be done without removing mag
 
Put heavy grease on push rod ,can be done using finger , grease will help keep push rod in up position, helps to wipe as much oil off as possible, can be done without removing mag

Spot on Jerry. and also a little grease on the gasket to help hold it in place on the pump helps too
 
Thanks!

Thanks all, for the great explanations, and the Tempest video. Good stuff. Now on to the replacement.....
 
Another Trick...

Another trick is to use some thin safety wire to wrap around the backside of the plunger while in the UP position. Once you get the fuel pump in place and the screws started, pull the safety wire out, then tighten down the screws. Works great!

DSCN6161.JPG
 
What Mike said!

+1

Wire lacing cord or a cylinder base O-ring works great here , too. Just snip and pull out.

Another trick is to use some thin safety wire to wrap around the backside of the plunger while in the UP position. Once you get the fuel pump in place and the screws started, pull the safety wire out, then tighten down the screws. Works great!
 
The secret super sticky grease....(drum roll please): Bosch point grease, 5700-002-005.
 
fuel pump failure mode followup

Gentlemen,

Thank you all for your most useful comments on problems with and changing out Lycoming fuel pumps.

I used the technique of safety wire to hold up the plunger, and setting the #1 cylinder to TDC. I modified it by using a loop of 14# test mono filament fishing line. I applied tension to the loop with a bungee cord to hold everything in place till the pump bolts were in place. Simply cut the line to remove it. Worked great!!

I could not resist taking the pump apart to inspect it. I found two spots on the gasoline diaphragm that might be worn spots, but they were too vague to be photographed. However, I did find a bit of blue residue in the overboard vent chamber - so no real smoking gun except for the slight trail of blue dye behind the overboard vent.

One thing that I did note was that the fuel pressure had dropped to 19 PSI on the old pump. I did not note the pressure when it was new; when I started the engine with the new mechanical pump the pressure jumped to 33 PSI. So it appears that the old pump pressure was falling. A previous post noted that Lycoming minimum pressure is 14 psi, so the pressure was within limits.

In any case, I am more confident in the new pump, especially since we frequently fly over very desolate territory....

Again, thanks to everyone who posted in reply to my first post
 
I used the technique of safety wire to hold up the plunger, and setting the #1 cylinder to TDC. I modified it by using a loop of 14# test mono filament fishing line. I applied tension to the loop with a bungee cord to hold everything in place till the pump bolts were in place. Simply cut the line to remove it. Worked great!!

Craig,

GREAT idea on using the fishing line! The safety wire was a PITA to get out!
 
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