Is my Fuel Pump failing?

B

blanducci

Member
On my 14-13-2 the fuel pressure reading on my CGR-30P is erratic (multiple 2 to 7psi fluctuations within a second) unless the electric pump under the seat is running - then it's steady at 7psi. This is more pronounced at low rpm - less so at cruise. I've only got 30 hrs on the plane and it has always been doing this, but I was more focused on new cylinder break-in during the first 20 or so hours. The fuel pressure never drops below 2 psi at cruise and the engine (165) always sounds/runs great.

I temporarily eliminated the Kohler high pressure relief valve circuit so I know that's not causing the pressure fluctuations. I'm fairly certain it's not a bad pressure transducer cause the fuel flow also reads abnormal when the electric pump is not running. It reads 9 gph on the ground while idle with no electric pump, but lower (and more reasonable) at 2 or 3 gph when the electric pump is running.

I do have a small oil leak on the pump - a drip always forms at the bottom pass through bolt so it should probably be pulled. Looks like this could be a big job - I don't think it can be removed without lifting the engine off the mount.

Another theory is there's nothing wrong and the CGR-30P is only reacting to the pulsating nature of a diaphragm pump - but I assume the EI folks would have this figured out.

I imagine more likely the diaphragm has been compromised and is now less efficient at pumping. Perhaps it's even pulling in air - which might cause the fuel flow behavior (higher flow at low rpm) that I see. The carb strainer is clean - so no bits of diaphragm.

I see no leaks when I pressurize the system (7 psi) with the electric pump on the ground.

So either nothing is wrong or these are tell tail signs of a failing fuel pump.

The pump on my 165 is marked "AC Model B" and has "855228" stamped on the bottom. I see no other markings. The picture in my Cruisair parts manual looks like the pump I've got, but the p/n listed seems to be a Bellanca number - not an AC p/n.

Thanks,
Bill
 
Check all your fittings/lines/"B" nuts from the fuel valve to the carb for security and proper torque.
The symptoms indicate an air leak. I think this has been discussed on the forum in the past.
Dan
 
Since fuel flow and pressure both seem erratic I would think an electrical problem or faulty sender. Maybe check all of your connections to the instrument and sender. I would not discount air or fuel pump, but add electrical to things to check. Please let us know what you find. _____Grant.
 
I had low and sometimes eratic fuel pressure issues five or six years ago.

What follows is some fact and some opinion, from personnel experience.

One thing that is at the top of my list of regular things to check is the bolt at the top of the fuel pump bowl. The cork type gasket under that bowl can leak a little when under pressure and may not be noticeable after engine shut down. You have to have someone pump the wobble pump while you observe the engine pump. I was fooled for a while when I ran a electric boost pump and could never find a leak at the engine pump - finally realized that because of a preventive back flow valve between them, the boost pump wasn't sending any fuel there. The boost pump sends fuel straight to the carburetor.

I have found that the top bowl bolt needs tightening about every 25 hours of flying. I looked and inquired everywhere if there was a torque setting for that bolt - never found any data or recommendation. I have been tightening the bolt to 50 in/lb, it takes about 1/16 to 1/12 of a rotation each time I re-tighten it - I suppose that the gasket just keeps needing more compression. Now I must add - this bolt earlier in the pump's life stripped the threads down in the cast aluminum pump body. I inserted a helicoil into the pump body and that is retaining this bolt now, so I don't know if 50 in/lb is proper for the cast aluminum body threads receiving that bolt.

About five years ago I re-plumbed the entire fuel line system behind the fire wall throughout the cockpit area, and made sure that all of the fittings in the engine compartment were tight. That did wonders for my fuel pressure. Prior to that, my cruising fuel pressure hardly ever indicated more that 3/4 PSI (always thought that was way too low, but never had any problems for 20 years). After re-plumbing, my fuel pressure always reads around 5 - 6 PSI.

I have over the years rebuilt my fuel pump about 5 times. Each time for some perceived reason, thinking it needed rebuilding. And, each time I believe that I found the in-erds of the pump were in perfect condition and the only thing that needed replacing was that bowl gasket - and if you take the pump apart then the small fiber bolt washer/gasket on top of the pump must be replaced. This small bolt washer/gasket is hard to find that is cut from the proper type of phenolic, some will not seal and fuel will leak through it when the system is pressurized. I found a stainless steel washer at McMaster-Carr that has a type of rubber sealant bonded to the underside that has solved that problem. That washer at MC is: RS62200C 1/4", Type 316SS, BarTite Sealing Washer, 0.260" ID, 0.615" OD, 0.060"-0.075" Metal OAH; pack of 25. Don't remember price, maybe around $10 (but priceless).
 
The fuel pressure and flow are EI's CGR-30P. Going on the theory that there might be a leak allowing air to be sucked into the system somewhere between the electric pump and mechanical pump, I eliminated the electric pump, the gascolator, and the kohler pressure relief valve. In the end it's a very simple linear flow from the tanks, through the twin-valve assembly (rebuilt), through the mech pump, through the fuel flow, and into the carb and pressure-transducer.

I still observed the erratic pressure behavior and higher than normal fuel flow rates when at low rpm (< 1100 or so) and higher fuel flow rates.

Next I replaced the cork gasket at the top of the fuel pump. When I pulled the bolt I don't recall seeing a phenolic washer - I think it's just a regular AN washer under the head of the drilled AN bolt. So perhaps this is my problem....

Anyhow, I added 10 feet of clear 3/8" ID hose between the fuel flow and the carb tee (normally it's 8" from the FF to the carb tee and 8" from the fuel pressure transducer to the carb tee). I hoped I'd see bubbles in the hose. I purged the system and ran the engine. No bubbles. And - the fuel pressure and fuel flow worked completely as expected.

I've since returned everything to normal (new gaskets in the gascolator, tightened all flare fittings, and purged the lines) and although I still see the original erratic pressure and flow behavior, it's not quite as bad. Perhaps all along it was the cork gasket at the top of the fuel pump. It may need additional tightening and perhaps has a missing washer, but it is interesting that adding the extra hose 'after' the fuel flow caused the fuel flow to behave correctly.

I'll confirm whats under the head of the fuel cap bolt and check it's torque and report back.
 
If you're not sealing the hole on top of the bowl, I am sure that could be at least part of your problem.

You need to have someone pump the wobble pump (making sure that it is pressurizing the system into the engine pump and you're not plumbed in such a way that the wobble pump is going straight to the carb without getting to the pump) and see if that bolt has fuel leaking around its head at the top of the bowl. It could be a very small leak wetting the top of the bowl.

I would also be afraid to tighten down that bolt with a steel washer and not the phenolic washer under the head to the bowl. To get the steel washer to seal even somewhat might take too much torque and risk stripping the threads in the pump body.

I am certain, without looking at the pump rebuild diagram/parts list that that washer is called out as some type of fiber or phenolic sealing washer. The stainless/sealant material washer I listed in the previous post that I found at McMaster-Carr is your best option I believe, as I could not find the called out phenolic ones that were able to seal properly.
 


The attached file is the cover page for a Technical Manual that goes into some detail regarding these vintage fuel pumps and their maintenance. it is helpful and informative
Army TM 9-1828A
Air Force TO 19-75CCB-1

The entire file is around 6.5 MB and this site limits an attached file to 1 MB. If you send me a personal email address I will send the whole pdf to you [ my em > heffhane (AT) mac (dot) com ]

Or, go on-line and google it to find a download.

In a few places the top bowl gasket is not referred to as a washer but a 'gasket' - implying that it is not a steel washer, the bolt as the 'Cap Screw'.

In the rebuild kits I used to get from the Antique Auto Parts Cellar in MA included a 'soft-ish' phenolic gasket to place under the cap screw bolt head. Later I tried to get just a number of these and could not, the ones I was finally able to order from another source were noticeably harder and did not seal the cap screw. Again, the M-C sealing washers do the job.
 
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