What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Replacing Engine Fuel Pump

AlexPeterson

Well Known Member
Is it just me, or are these engine mounted fuel pumps a real PITA to install? I have rotated the engine until the plunger is as far up as it goes. I can get the pump in all the way, as long as it is tilted a little bit. So far, so good. The problem arises when I try to get the socket head cap screw started. Because of interference between the screw head and the pump casting, I'm not able to get it properly aligned for starting the threads. The only way to get alignment of the screw is to pull back the fuel pump a little, which causes the lever to pop up above the plunger. AARRGG.

Any tricks would be appreciated. I have glued the gasket to the pump, so that "trick" is already used.

Thanks!
 
You Need a Lackey

I think you need a lackey to hold the thing in place while you wrestle the screws. I know a guy that is qualified to hold the pump. Give me a call.
 
the safety wiring doesn't look like fun either. maybe get religious if the cussing doesn't work.

Is there a certain side to work from to get it back up in there? looks like the left side of the engine is the easiest?
 
Yes, the left side. Access really isn't a big problem, although I'm sure this would be easier with the engine on a stand. The biggest problem is that the casting of the pump will not allow the bolts to be aligned with the holes in the accessory case when the pump is far enough forward for the pump lever to clear the plunger. I.e., the bolts, when pulled back to allow the pump to almost contact the access. housing, hit the casting and are forced into misalignment.

While I'm whining, another compounding problem is that the socket head cap screws' hex socket fits very tightly on the allen wrench. I've tried a couple wrenches, and I may grind one slightly to allow for a little wobble. Even the Bondhus style won't hardly go in.

I will be happy to tackle the safety wires, since that means a victory has been had. I may go back to the airport for another try tonight.
 
Good description. So with the pump perfectly installed on the case; you can't just reach up and put a cap screw in.

So, that means you can't get everything started with a shorter bolt and swap them out.

A shorter cap screw design? That cap looks like at least an 1/2" long. Obviously a hex head would bump also.

Is the washer too thick?

Sounds horrible. Good luck.

edit-- washer wouldn't make a difference initially since you're pulling the bolts back just trying to get pump in and lined up.
 
Last edited:
Lubrication

When the cussing doesn't work, I recomend tequila.... won't get the pump on, but you won't care....:p

sorry - couldn't resist!
 
I had the same issue. I don't know if this is ok but here is what I did. Took the machine screws to the sander and ground off about 1/4" ... I also used an allen that has a ball end. If you try this, try a little less, like 3/16". Also go slow on the sanding or it can enlarge the threads making it difficult to screw in ( not a nice thing to do to the assy case threads ). Perhaps put a nut on before removing any material then make sure it threads off easy. Might be good to put some anti-seize after a solvent rinse to remove any particals that might be on the threads.

Before you install the pump you can put your index finger up in the case and feel the plunger. Have someone turn the prop until it is as short as possible. Then do not push the pump straight on; a little low then up to make shure the arm is under the pin and not pushing on the pin.

Mike
 
Great advice all, thanks. (Paul, I have some great To-kill-ya someone left me...)

The short bolt idea is great, what I'm going to do is buy a couple shorter bolts, get the pump tight in place, and then remove and replace the shorter bolts one at a time with the proper bolts.

Plunger is all the way up - see earlier post.

I'll keep you posted....
 
Maybe...

Hi, I'm a sure rookie but had to pass this idea. I've used a piece of rubber tubing to start aggrevating bolts and spark plugs before. Just cut a short piece of flexible tubing that fits over the bolt head??? and then you have flexibility to maybe get it started then drive with tools. ?????
Good Luck!!
Greg
 
Victory

Ok, Pete Howell and I beat this thing into submission. So, the short bolts to start and then replacing with the long bolts idea doesn't work. If the pump is tight against the housing, it is not possible to put the full length bolt in, because the housing doesn't allow for the proper angle for starting the bolt. The trick seems to have been to keep the pump about 1/4" away from the accessory case, while starting the bolts. Some sort of shims might make this easier. Pull the pump back too far, and the lever slips off the plunger. A balancing act.

It is probably a good thing that whoever designed the dang thing has probably croaked. I've worked on a lot of cars, etc., and I'm not sure I've seen a dumber setup.

Thanks for the tips.
 
Some minor swearing was required....

Alex is right, the design is just stupid from a maintenance standpoint.

It was a good evening in the hangar with Alex and my kids. Hard to beat that.
 
Fuel pump blood brother

...If the pump is tight against the housing, it is not possible to put the full length bolt in, because the housing doesn't allow for the proper angle for starting the bolt. The trick seems to have been to keep the pump about 1/4" away from the accessory case, while starting the bolts. Some sort of shims might make this easier. Pull the pump back too far, and the lever slips off the plunger. A balancing act.

It is probably a good thing that whoever designed the dang thing has probably croaked. I've worked on a lot of cars, etc., and I'm not sure I've seen a dumber setup...
DSC04587.jpg

Yep, what Alex said. This thing is just unbelievable.

First the decision to use hex bolts. That means you have to come in straight but you can't do that because the housing is in the way. Those bolts also make it much harder to safety wire, because the wire goes astray whilst it is in the cavity. Oh, and if the safety wire holes line up sideways you have about 1/8"clearance to the case which also greatly adds to the safety wiring challenge.

As has been said, it is critical to have the pushrod engaged with the arm when you install the pump but you can't just put the pump in position because then you can't start the bolts. The canny designer made the position where the bolts can be started almost exactly the position where the rod jumps off the arm. Probably none of this is a huge deal if you can get to the back of the engine, but it is hard when you can just get part of one arm in and don't have clearance to even operate safety wire pliers or dykes.

Anyway, I actually got the thing installed today and made two failed stabs at the safety wiring. I'll come back at that tomorrow with hemastats. The tips from this forum were a big help; in particular the round end allen wrench was a huge help.

The reason I changed the pump out is not because it failed; it is because it was working too well.

...I had five A&Ps tell me a fuel pump couldn't fail to a too-high situation, but mine did. It overflowed the carb. The fuel pressure will never go higher than what it takes to force fuel past the float valve, something around 9psi, at least on my carb...

I have been using the pump for 10 years but for the last 6 months the fuel pressure has been too high, like Bob's. For me this has only intermittently caused a problem, and only while taxiing for takeoff. The fuel pressure would go up to around 8 or 9 flooding the carb and causing very rough running. I would keep it running by fiddling with the mixture, near idle cutoff, and after the runup the pressure would be to an acceptable, but still high value, and there would be no problem until the next cold start.

Also like Bob, I asked many mechanics about this (myself, I'm not one of them mechanical guys) and none of them felt like it could really happen. If anything, an older pump should put out a lower pressure, they would say. What could I do though? All I could think of was a new pump. After I finally got it on today, I ran the airplane and it ran great. The fuel pressure was 5 PSI, which I just haven't been seeing. Even when it was within limits, it was usually around 7 or 8 on the initial start of the day.

So I don't have enough experience to say for sure the new pump solved my problem, but it looks good so far.
 
Last edited:
Larry, when I saw the picture I thought maybe you had gotten into a fight with a cat. Thanks for the laugh - and for commiserating with me (and confirming that it wasn't just me not knowing what to do!).

I think next time I'll figure out a way to hoist the plane in a way that I can turn it upside down. Seems like less trouble.
 
I'm facing this right now, and concur that the pump housing design is AWFUL.

I've heard that one can add some grease to the pin inside the engine, helping to stick it in the up position. I haven't tried it, and I'm not going to.

I want to be VERY confident that during installation the pin in the engine has not slipped down, with the associated possibility of a mismatch with the pump plunger.

Since I haven't yet mounted the engine, I will tip up my engine (as if it were on an engine stand). This won't eliminate the wrestling with the bolts, but at least I can be sure the pin has not slipped down while installing the pump.

Roger, Tucson, 7A finishing.
Premium Concrete Coatings
Hazebuster Aviation Sunglasses
 
...Anyway, I actually got the thing installed today and made two failed stabs at the safety wiring. I'll come back at that tomorrow with hemastats. The tips from this forum were a big help; in particular the round end allen wrench was a huge help...
FYI - The other day when I was looking at the Lycoming OH manual I found a drawing of the fuel pump installation. Guess what, the drawing only showed the safety wire going through the side of the hex head and out the middle, not through both sides as mine is currently wired.

If you wire yours this way, just make sure you pick up the left side so it can't loosen.
 
FYI - The other day when I was looking at the Lycoming OH manual I found a drawing of the fuel pump installation. Guess what, the drawing only showed the safety wire going through the side of the hex head and out the middle, not through both sides as mine is currently wired...
Bill, I appreciate the tip. I am planning to go at mine again this weekend and that may help.
 
I've taken the fuel pump off twice now (dont ask) and fully agree that installing this bugger really sucks - it really wasnt any easier or quicker the second time. The one thing I have learned however - stop worrying about holding the plunger in the up position while you cajole the pump into place and struggle with the socket head screws. Focus on getting one screw started (the outside one is easier - duh) while holding the pump flange just off the engine. When that first screw is just started, it will help you keep the pump positioned, while still allowing enough movement for you to manipulate the lever and get the second screw started. If you can push the pump flange flush up against the engine in its correct postion by hand, the lever IS in the correct position (under the plunger), and you have it made. If it wont go up against the engine by hand, its not, and you need to back off and manipulate it around until you can get it into position. What you absolutely must avoid is forcing the pump into position by cranking down on the screws with your allen wrench - bad juju there. If the screws arent going in easily and smoothly and/or the pump flange isnt mating up flush against the engine case, you do not have it positioned correctly.

A small mirror properly postioned (I taped it in place) to let you see the inside screw is very helpful. One last warning - be sure to use a sealer on the screw threads, as the holes for them penetrate through into the interior of the engine case, and you risk an oil leak (the reason for my forced second removal/reinstallation).

erich
 
Last edited:
interesting thread

As I do not recall this being as big a challenge as stated in this thread I wonder what the symptoms are of an incorrect installation. If I remember correctly my installation was similar to the previous post i.e get it lined up and push against casing to install bolts. The pump has been delivering around 4.5 psi for the past 65 hours of operation.
What happens if the pump is not installed correctly?
 
The Trick

Is it just me, or are these engine mounted fuel pumps a real PITA to install? I have rotated the engine until the plunger is as far up as it goes. I can get the pump in all the way, as long as it is tilted a little bit. So far, so good. The problem arises when I try to get the socket head cap screw started. Because of interference between the screw head and the pump casting, I'm not able to get it properly aligned for starting the threads. The only way to get alignment of the screw is to pull back the fuel pump a little, which causes the lever to pop up above the plunger. AARRGG.

Any tricks would be appreciated. I have glued the gasket to the pump, so that "trick" is already used.

Thanks!

Alex,
I apologize for giving advice "after the fact". :( The problem you describe was also common on auto engines (prior to 1986) when they had engine driven fuel pumps. One trick to keep the push rod from falling down is to coat it's length with grease prior to inserting it. This will prevent gravity from lowering the push rod.
That will allow you to back the pump up that critical 1/4". I still have nightmares about the first time I tried to install an engine driven fuel pump (age 19) I spent hours, only to have a "real" mechanic come over and install it in 15 minutes! That's how I learned about the grease trick! :eek:
Charlie Kuss
 
Here's the scanned image from the Lycoming OH manual:
lycoming%20fuel%20pump%20safety%20wire.jpg

Note how the wires are on the left side of the bolts.
 
Last edited:
Alex,
I apologize for giving advice "after the fact". :( The problem you describe was also common on auto engines (prior to 1986) when they had engine driven fuel pumps. One trick to keep the push rod from falling down is to coat it's length with grease prior to inserting it. This will prevent gravity from lowering the push rod.
That will allow you to back the pump up that critical 1/4". I still have nightmares about the first time I tried to install an engine driven fuel pump (age 19) I spent hours, only to have a "real" mechanic come over and install it in 15 minutes! That's how I learned about the grease trick! :eek:
Charlie Kuss

Charlie, thanks. I've put quite a few of the old auto fuel pumps on - they are a piece of cake compared to this monster. I absolutely could not get grease to hold that plunger up - too much oil all around that area. Larry V. called me today with his tip - again, after the fact! He said you need a bubba helping, pushing and snorting on the pump (I can't use the exact words here on this family site) until it is done. Something about getting one screw started.

It has been a while since I had to do it, but I do remember it went quite well when Pete was there to help. Solo is a non-starter unless the engine is not on the plane.
 
FUEL PUMP BOLTS

I HAD TO REPLACE MINE ALSO, ENDED UP GRINDING THE HEAD OF THE CAP BOLT TO A ROUNDED SHAPE. ALSO DID A LITTLE CLEARANCING ON THE FUEL PUMP CASE. THE BALL ALLEN WRENCH REALLY HELPED. DENNIS. RV-6/IO-360 ANGLE.
 
Fatal installation

Bill R, it was good of you to post the scan of the safety wiring as per the Lyc OH Manual. That was very interesting indeed.

Incidentally for those that might be tempted to take the fuel pump installation lightly here is an NTSB report on an RV7 that crashed in Feb 08 killing the pilot. Compulsory reading. This is not an area where it is good to learn from your mistakes.....because you might only get to make ONE.

http://www.ntsb.gov/ntsb/brief.asp?ev_id=20080221X00223&key=1
 
Last edited:
One last warning - be sure to use a sealer on the screw threads, as the holes for them penetrate through into the interior of the engine case, and you risk an oil leak (the reason for my forced second removal/reinstallation).

Erich,

What did you use to seal the threads when you put your pump back on? I didn't think to seal mine and now I'm pondering taking the bolts out and putting on some permatex (or other?).

thanks,
mcb
 
A couple of years ago I engaged in a two-day struggle to install a new pump on my RV-4. It was complicated by the RV-4's tight engine compartment. I had to remove the lower two engine mount bolts and lift the engine to get clearance to the firewall footwells. After I did that, I ran into the same frustrations as you are having: keeping the plunger up and out of the way and lack of clearance between the bolts and pump body. I spent a lot of time cussing the designers of the pump. Why couldn't they have built the flange a little wider? Ugh.

One thing that caused me some grief: I had turned the engine until I thought It was in its most upward position. When I sought help from a mechanic, he found that it still had a ways to go. So be really sure it won't go higher.

Using grease on the plunger didn't help me either. It was just too slippery for that to work. We finally got the plunger to stay up by wrapping a loop of waxed lacing cord around it. We ran the lacing cord to the top of the engine where I held tension on it while the mechanic worked on getting the pump in place and the bolts started. He ran the bolts in most of the way until just before the lacing cord started being squeezed. Then I released one end of the lacing cord and pulled it out. After that it was relatively straight-forward to tighten and safety-wire the bolts.

My arms looked like Larry's after the ordeal but I took it to another level. Before I test-ran the engine I decided to turn it over to see if I could detect any binding in case the fuel pump arm was riding on the side of the plunger. I was tired by that time and not exhibiting proper respect for the prop. As I pushed the prop past a cylinder's compression stroke, the blade jumped out of my hand and the other blade came around and struck me on the back of my upper arm. Ouch! I jumped around and cussed for a few minutes. It felt like I might have cracked the bone and there was a fair bit of blood from a cut. I had never seen anything like that. At first I thought it was just the compression giving the prop enough momentum to push the blade around and into me. When I ran the engine, I found that the left mag would not turn off. At some time in the two days of struggling with the pump, I had put tension on the p-lead and pulled it out of an improperly crimped terminal. This was before I reworked the electrical system and found many problems. The builder just doesn't know much about electrical stuff. I went to the emergency room later and found that the bone was OK but the cut in my arm was nearly an inch deep. So lesson learned: always be on guard of the prop when moving it. If my arm hadn't stopped it, the engine might have started and the outcome might have been even worse.
 
To late, to late!!!

Charlie, thanks. I've put quite a few of the old auto fuel pumps on - they are a piece of cake compared to this monster. I absolutely could not get grease to hold that plunger up - too much oil all around that area. snipped.

Alex,
I often run into problems like that. I always keep at least a case of aerosol brake parts cleaner around my shop. It's available at any auto parts store. It's essentially trichlorethylene. It absorbs oil and grease, evaporates and leaves no residue behind. It's great for cleaning off oil & grease. It also works well as a cleaner prior to using Locktite on parts. A few squirts of brake parts cleaner would have cleaned off all the oil in the area.
I also use it to clean grease and oil off of clothing, since it's basically dry cleaning fluid!
Charlie
 
Here's the scanned image from the Lycoming OH manual:
lycoming%20fuel%20pump%20safety%20wire.jpg

Note how the wires on the left side of the bolts.
I didn't notice, until I saw this diagram, that the pump does not mount level. Not realizing this probably made it harder to get the bolts started as the far hole is hidden and I was probably trying to make it go on with the pump level.

By the way, for any future person that runs on to this thread because they are having trouble with high fuel pressure and carb flooding and can't figure out why, swapping the engine driven pump out does indeed seemed to have solved those problems with my engine. Today, all I saw was 4 and 5 PSI and a great running engine (go figure). Before the fuel pump swap I was often seeing 8 and 9 PSI right after a start and around 7 most of the time. When it would get to 9 after a start, I could barely keep the engine running.
 
Erich,

What did you use to seal the threads when you put your pump back on? I didn't think to seal mine and now I'm pondering taking the bolts out and putting on some permatex (or other?).

thanks,
mcb

Matt, I did not use any sealant and haven't seen any leaks in somewhere around 300 hours. I sure as heck wouldn't take the rotten things out (which means pulling the pump itself back about 1/4 inch or so...) unless they were leaking - a lot. Even then, some sealant around the head would likely cure it after cleaning with solvent, since the flange is gasketed all around.
 
I've added a URL to my post #25. It leads to the NTSB report on the 2008 RV fatality caused by a faulty fuel pump installation(by the builder).
 
I used Permatex. I would try loosening, but not removing the bolts to apply it rather than go through the hassel of re-installation. However, if its not leaking now, leave it alone. No need to ask for trouble.

erich
 
Last edited:
symptoms

so reference my earlier post, what are the symptoms of incorrect install and can the electric pump pump through a failed engine driven pump on a carburated engine? The NTSB report implies that the restart with the electric pump was a problem because the engine was fuel injected.
My pump supplies 4.5 psi and has so far run for 65 hours without a hitch, can I assume it was installed correctly (probably by luck as I did not have the problems referenced here)
 
Don't take this lightly

I've added a URL to my post #25. It leads to the NTSB report on the 2008 RV fatality caused by a faulty fuel pump installation(by the builder).

Yes please go to the link in post 25, this happened in my backyard (so to speak) very chilling, I read the whole tread to make sure someone had included this information.
 
revisit?

I removed the fuel pump to put an air cooler housing (with an adapter to run cool plenum air to it) for cooling purposes. This is on an engine that has not been run yet. When I was putting it back on, I too noticed it was a major PITA to get those two bolts in, so I just got the next smallest length (and put no sealant on them). I noticed nothing in this thread about smaller length bolts (probably because it is not even a correct consideration). Is it safe to assume that I need to put those original bolts in? I think the ones I put in are 1/8", and no more than 1/4" in length shorter than the original. It seemed like there was plenty of grip length. Thanks. Dave
 
Last edited:
I removed the fuel pump to put an air cooler housing (with an adapter to run cool plenum air to it) for cooling purposes. This is on an engine that has not been run yet. When I was putting it back on, I too noticed it was a major PITA to get those two bolts in, so I just got the next smallest length (and put no sealant on them). I noticed nothing in this thread about smaller length bolts (probably because it is not even a consideration). Is it safe to assume that I need to put those original bolts in? I think the ones I put in are 1/8", and no more than 1/4" in length shorter than the original. It seemed like there was plenty of grip length. Thanks. Dave

Someone, probably many decades ago dead of old age, chose the length knowing that a shorter one could more easily be installed. I'd stick with the original obnoxious length. Besides, then you have a story to tell once you fight your way through it.
 
The problem you describe was also common on auto engines (prior to 1986) when they had engine driven fuel pumps.

I'm wondering, because I had to replace my engine driven fuel pump on my RV-6, and not looking forward to doing it again on my RV-8 - is there anything inside the accessory case that would run amuck if you didn't have and engine driven fuel pump installed? Why not get or make a plate to cover the opening and just not have to deal with the cantankerous, poorly designed thing at all? I'm sure there are plenty of full-time automotive fuel pumps (electric of course) that will work just fine. Might want to power it alternatively from a back-up battery system, but it might be better....

Scott
RV-8 FB
 
Hehe

I'm wondering, because I had to replace my engine driven fuel pump on my RV-6, and not looking forward to doing it again on my RV-8 - is there anything inside the accessory case that would run amuck if you didn't have and engine driven fuel pump installed? Why not get or make a plate to cover the opening and just not have to deal with the cantankerous, poorly designed thing at all? I'm sure there are plenty of full-time automotive fuel pumps (electric of course) that will work just fine. Might want to power it alternatively from a back-up battery system, but it might be better....

Scott
RV-8 FB

If you want such a system see here http://www.vansairforce.com/community/showthread.php?t=30402&highlight=wingroot ..Vapour lock is virtually impossible with a properly designed electric fuel pump system


Frank
 
fuel pump replacement

I am a new RV8 owner and this is my first post. I want to say thanks for all the valuable insight that is posted here, it has saved me a huge amount of frustration trying to reinvent the wheel. I recently had to replace the engine driven fuel pump (0 360). What a miserable job, poor access and a masterpiece of poor design.
I want to single out Kcameron for thanks for the tip on using waxed lacing cord to hold the drive shaft up while starting the hex bolts, it worked when all the other tricks failed. If you ever need to do this nasty job try this tip first and save time and hide on your arms.

Many thanks John Deaton
 
Indicators that fuel pump needs replacement?

What indication did you have that the mechanical fuel pump needed replacement? I have an O360 that has the fuel pressure drop below 1 psi during climb out. Am I pushing my luck if I don't replace it immediately?

Thanks
 
I am a new RV8 owner and this is my first post. I want to say thanks for all the valuable insight that is posted here, it has saved me a huge amount of frustration trying to reinvent the wheel. I recently had to replace the engine driven fuel pump (0 360). What a miserable job, poor access and a masterpiece of poor design.
I want to single out Kcameron for thanks for the tip on using waxed lacing cord to hold the drive shaft up while starting the hex bolts, it worked when all the other tricks failed. If you ever need to do this nasty job try this tip first and save time and hide on your arms.

Many thanks John Deaton

Unfortunately, I've had to do this nasty task twice; once on each LongEZ I've built. I use an old green cylinder base O-ring instead of the waxed lace as KCameron did - but essentially the same idea. The O-rings are manufactured out of really strong and stretchy rubber and you simply stretch it to fit on something higher on the accessory case, and then remove it at the last minute. Removing the left mag helps (especially in safety wiring) but then you've got extra work to do.

deek
 
15 minute fuel pump install

Hey Gang,

Here's how I installed the fuel pump in 15 minutes (engine on the plane). First of all, my engine came with a plate over the hole, so the bolts were the wrong length. I decided to use studs instead of bolts to help guide the pump on. So, I put permatex on the studs and installed them, then slid the gasket into place. Now comes the 'trick' I read on this thread bout using waxed string but I don't have any so I used a piece of 20g wire tied into a loop. I hooked the end of the plunger rod then hooked the other end to a ball bungee and clamped it to the top of the engine under tension. Now I reached in the hole and pushed the rod up and it stayed put. With the studs, there was just enough tilt down to get the pump in (with the arm clear) and start the nuts. I tightened them some, leaving just enough room to cut the wire and pull it out. Then I tightened it the rest of the way. It took me longer to type this that to do the install! I read all the depressing stories and studied the advice, and used some of it to make the job easier, so thanks to those of you who posted previously. I hope this helps.

Lance
 
fuel pump install

I have to thank all those whom did this job and posting their problems and results on this list. It helped me to easily do this repair.

I have an IO-360 on and RV-7A. I was seeing intermittent low pressure warnings, with the fuel pressures dipping randomly below 20 PSI (normal is 25-30 psi). Ground test resulting in fuel flows of 30 GPH using the AUX pump, so it wasn't a restriction. Running the engine at lower RPM's and leaned appeared to lessen the issue, but didn't completely eliminate it. Also, when fuel pressures dropped, with the engine leaned way back (two PMAGs allows this) RPMs would fall off with low fuel pressure, indicating it wasn't a sensor error, but a real low fuel pressure (and injector flow) issue.

So I ordered a new pump and a shroud and installed them today. Removing the old pump required me to remove the left P-MAG and some other hoses that were restricting access to the pump. The shroud from Spruce did not have to be modified as long as all the fittings were put onto the pump while it was on the bench.

I tried using the grease trick to hold the actuator in the UP position, but, in the Florida heat, it didn't work out. Instead I looped .020 safety wire around the actuator and had a helper put tension on it after pushing the actuator into the UP position. After installing a new gasket with a sealant onto the accessory case, I was able to insert the pump into position and, by hand, get both cap screws started, and turned then further in with a 5/16" ball Allen wrench. Before snugging up the cap screws the .020" safety wire was pulled out. The cap screw safety wiring job was tricky, but given the access with the left P-MAG removed, went smoothly. Then all the fuel lines were again connected.

To test the pump functionality, I removed the lower four spark plugs and turned the engine over with the starter, resulting in 29-32 PSI fuel pressure indications. I then reinstalled and timed the left P-MAG, and connected the other hoses I had disconnected. There were no oil leaks after running the engine...

I did not use a sealant on the cap screws, so will be looking for any oil leaks in that area.

I hope this write up helps others too.....
 
Fred,

I have had intermittent low fuel pressure warnings haunting me for months. In the process of chasing it down I have replaced all of my fuel system components, eliminating many restrictive fittings etc. I thought I had the problem solved when I replaced the Kavilco sending unit and then could not re produce the problem. Months later it is back again.

Mechanical pump experts tell me the pump cannot fail on an intermittent basis but your experience seems to indicate otherwise.

Did the new mechanical pump solve the issue for you?

Anybody else have experience with intermittent low fuel pressure due to faulty mechanical fuel pump?

Charting fuel pressure after the events shows the pressure would drop down to around 13 PSI from the normal 25 PSI. My engine has never run rough during these events but that may be because I was quick to turn on the electric backup when I get the warnings, (Dynon System).

I may install a backup mechanical gauge to have a way to verify the pressure is actually falling. Precision Aeromotive tells me that the engine may actually keep running OK in cruise conditions with the low fuel pressure I have experienced due to the way the servo adjusts to different pressures. This makes it difficult to verify the pressure reduction is real...

Randall in Sedona

RV7A, IO-375, WW RV200
 
I have had intermittent low fuel pressure warnings haunting me for months.

From experience, low and erratic fuel pressure indications may be caused by ground loops. A ground loop comes from having the sender and the instrument grounded at different points. The small difference in ground potential between the two points will cause all kinds of spurious indications in a sensitive gauge. You might look at that.
 
Mechanical pump experts tell me the pump cannot fail on an intermittent basis but your experience seems to indicate otherwise.

I had a low pressure mechanical pump (O-320, carb) that definitely failed on an intermittent basis. Engine would lose power and immediately regain it when the electric boost pump was turned on. This was in cool temps with 100LL.
 
Last edited:
Thank you all for the tips

Just replaced the mechanical fuel pump using the safety wire trick. It was quite easy to get the pump on and bolts installed. As suggested before I used a loop of safety wire connected to a bungee cord. After looping the safety wire around the plunger I hooked the bungee cord and created a tension. Pushing the plunger up and it stayed. The first time I installed the pump and had the bolts almost in before taking it out. Using the mirror and later my finger I confirmed that the plunger did not drop. It was just to verify for myself that it is working. Second time I pulled the safety wire out before it got pinched by the pump. I did not have to take mag or anything else out to safety the bolts. I did have to move around the engine to tighten the bolts.

It is raining and I have not run my engine yet so I can not report the outcome. My 1,800 hr fuel pump (O-320, carb) intermittently drop pressure to 0.1 psi. It also start leaking oil. Even after I tightened all screws it still leak a few drops (shown on my nose wheel pant) each time I fly.

Without reading the experiences from others on the forum I would not have known what to do. Now, I have a new fuel pump on the engine and my arms are not even scratched. It all because I read the forum!
 
Last edited:
fuel pressure vs flow

can I ask a newbie question? there are a few references in this thread that are about mechanical, low pressure, hi-pressure pumps....so bear with me.
My mechanical pump is about 120 hrs old, but 10 years of age.
the fuel flow was good when tested in the climb attitude, but the pressure on the van's gauge is often in the 1psi range, if the scale is to be believed. Never had an operational problem, so is it safe to assume all is well? volume being more important than pressure, in a carb?
also, I thought something was strange, as there was always a drop of oil on the pump lower case bolt heads. Apparently, not that unusual for a little to seep thru the studs? the gasket seems dry, as far as I can see.
 
Laugher.....

I replaced my pump over the weekend - wow what a diff a few years and a few tricks make. When Alex and I did this back in the day, there was swearing and blood. On Friday using bundling lace to hold the plunger up, and an unregistered, sawed-off, 5/16 ball-tipped hex driver, I had the pump on and safety wired in 35 min, and I stink at safety wiring anything.

Don't fear da pump!
 
Back
Top