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Fuel pressure too high; fuel servo, part numbers ending in -9 vs -11. And everything else.


chrixxer

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Hoping to unravel this mystery. Plane is still at CMA getting its going-through after the emergency landing at Pt. Mugu and the "on the ramp, during mosquito season, overseen by some poor enlisted guy who had to stand watch, while Hawkeyes taxied past" fuel system repairs. Mechanic found a bunch of issues, and I had some concerns, so I green lit anything he found that needs doing ("blank check maintenance"), culminating in a full, several months early, annual. One of the squawks was the fuel pressure when I departed Mugu (reading about 34 PSI, above the green arc). (We replaced the fuel servo - RSA-5AD1 2524054-11, same part no. that came off the plane, and the mechanical fuel pump (LW15473).) Mechanic thought it was air in the lines, or a sticking gauge, green lit me to fly it, but it's not doing anything more than that 6nm ferry flight until it's 100%, including showing fuel pressure in the green arc.

Mechanic (a referral from another MooneySpacer, local to CMA, who was able to jump in and do the expedited repairs required when it was parked on the Navy's ramp) now thinks the wrong fuel servo was / is installed. Pacific Continental told him the 2524054-9 is required. But as I read the TCDS, what comes after the dash is sort of meaningless in this context. For the M20F (p. 22 of 58), Engine is specified as: "Textron-Lycoming IO-360-A1A (Bendix fuel injector, Model RSA-5AD1, P/N 2524054-1) See Note 20." Note 20 reads: "The dash number following the injector setting number indicates manufacturing revision level of the injector and does not change or dictate the setting of the injector."

The only 4-cylinder "-9" part I see in the Application Guide is the 2524450-9 for the IO-360-C model, which, interestingly, this engine was, originally, circa 1978 (at which point it was equipped with a 2524450-2). In 1985 this engine was converted from a -C1C to an -A1A, with a 2524054-10 fuel servo (among other changes), and installed in this Mooney. (There's no indication as to why, just an entry 8/12/1985 that mentions removing the old -A1A, and a 10/21/1985 entry that documents: "Installed Lycoming IO360C1C change to IO360A1A" with the serial numbers for both engines.)

So, am I right in my understanding the -9/-11 after the 2524054 part number is a non-issue?

Wonder what else could be going on.

 

 The mechanic's summary (pieced together from text messages and edited for flow): "You have a solid airplane however some basic maintenance things have been neglected. You have already paid for the expensive things like the fuel servo and the fuel pump which looked like it was due to be replaced, based upon the cracking I saw on the outer edges of the diaphragm. The mags are long past due for an IRAN check, about 600-700, and new wires are in order, about $350. The front baffle need to be properly installed to eliminate the rubbing on the flywheel (that seems to be happening since the cylinders were replaced?), and a few cracks in the nose gear inner we’ll need to stop drilled. The mag P Leads are ancient. And should be looked at for replacement. The fuel pressure gage seems to be sticking but it makes full fuel pressure. I replaced one of the scat tubes for cabin heat since the internal spring was missing and the hose was completely collapsed. The brake pads haven’t been changed in a very long time and are worn enough to warrant replacement. It looks like the rear elevator bungees were not cleaned or lubricated in a really long long time. They are supposed to be removed, cleaned and repacked with grease. There are a couple of flat spots on your mains tires but otherwise they are in good shape [this would have been the result of my landing at Mugu; I kept altitude maybe a bit too long and slipped it down over the arrestor gear, but came into the flare at about 100-105 mph, and only had 3500' to work with ... I know I stood on the brakes once I finally got the wheels down]. The compressions are really strong which is very good news. You have fine wire plugs on the bottoms and massive electrode plugs in the top. They cleaned up fine and tested good so that’s good too. One of your magneto coils was badly cracked. They do that with age and is a precursor of failure." Most recent updates were earlier this afternoon, prompting this post: "The plane is almost done, mags are in and we are sorting out fuel flow, pressure issues. I did a compass swing and am preparing the new correction card. The landing lights are tight and the covers have the mounting screws all in place. There were two missing screws missing from the corner mounts. We solved the VOR antenna mystery in that the other side is almost broken the same way the other one was. I never would have expected stainless steel to fracture like that. I will send the video of gear swing and manual gear deployment. Both were perfect." Followed by: "So we could not understand why the airplane was not behaving as it should, in terms of fuel flow and pressure. It turns out that your airplane requires a 2524450-9 fuel servo. What we took off and what we put on was a 2524450-11 [sic]. It appears that your airplane had the incorrect fuel servo." ... And this, ladies and gentlemen, is why you buy a plane that costs about 80% of your total purchase budget... 

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I'll keep my fingers crossed for you!

Wasn't there another thread about the incorrect fuel pump for the IO-360?  IIRC, ordering the "correct" LW15473 pump gets you a pump that has different specs than the one in the M20 maintenance manual, despite the fact that it is the correct part number, with fuel pressure in the 35 psi range instead of around 25 psi.  IIRC, that is still within the IO-360 TCDS so should not affect operation, but it falls outside the specs in the maintenance manual, so people with primary fuel pressure gauges with fixed alarms end up with a headache.  IIRC, somebody confirmed Tempest(?) sells refurbished pumps that meet the old pump specs.

So my understanding is the fact the pump puts out 34 psi is probably not a causative factor, and may not even be a contributing factor.

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Hmm, I'm not so sure.  Depending on how you read note 20, I could still see that the dash number is important for the particular application; i.e., IO-360-A1A.  If it was me, I'd call Precision Airmotive and ask...maybe even a call to Lycoming.  Doesn't seem like this is something to leave to chance.

DISCLAIMER: I am NOT an A&P

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20 minutes ago, MIm20c said:

 the exciting landings you enjoy so much ;)

You know what I like? Shooting instrument approaches that break out 50' above minimums, with the rabbit right there waiting for me. Greaser landings on a 2325 x 50' runway next to the beach, with a moderate - challenging, but not white-knuckle - crosswind. Popping into KLPC to pick up a wine shipment from Babcock then popping into the Ghetto. Seeing a rescue dog meet his/her forever family for the first time. Cruising into the sunset at <8 gph, faster than 140 ktas. Bopping along to Taylor Swift with stereo headsets wired into the PMA450 (Bluetooth FTW).
 

You know what I could do without ever doing again? Make an emergency landing, no matter how reusable the plane is. I really want to hear nothing but purring engine for the rest of my flying days... At least until the STC for the electric conversion. (George Bye, where you at?!)

13 minutes ago, jaylw314 said:

Wasn't there another thread about the incorrect fuel pump for the IO-360?  IIRC, ordering the "correct" LW15473 pump gets you a pump that has different specs than the one in the M20 maintenance manual, despite the fact that it is the correct part number, with fuel pressure in the 35 psi range instead of around 25 psi.  IIRC, that is still within the IO-360 TCDS so should not affect operation, but it falls outside the specs in the maintenance manual, so people with primary fuel pressure gauges with fixed alarms end up with a headache.  IIRC, somebody confirmed Tempest(?) sells refurbished pumps that meet the old pump specs.

I'm aware. :)If you click the links I provided, you'll see the one I bought was the correct LW15473 pump, refurbished by Tempest. (The other SKU is 07-00705, which used to say (on one webpage; ACS confusingly had two different product pages for what turned out to be the same SKU) it was the LW15473 without mentioning 62B26931, but after I ordered that one and it turned out to be the 62B26931, Aircraft Spruce updated their website and gave me an RMA.) So that shouldn't be the problem.

IMG_2736.JPG

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4 minutes ago, M20Doc said:

From what I read you need and have the 2524054 servo, the dash number denotes mod/ revision status.

Clarence

Yeah, I said all that: "But as I read the TCDS, what comes after the dash is sort of meaningless in this context. For the M20F (p. 22 of 58), Engine is specified as: "Textron-Lycoming IO-360-A1A (Bendix fuel injector, Model RSA-5AD1, P/N 2524054-1) See Note 20." Note 20 reads: "The dash number following the injector setting number indicates manufacturing revision level of the injector and does not change or dictate the setting of the injector.""  :)

Just making sure there's not a particular reason why a -9 revision would be required instead of a -11 (especially when a -10 or a -11 was installed originally).

 

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47 minutes ago, N803RM said:

Chris, has the fuel pressure gauge been checked?  Gauge always showed in the green for me.  

Ron

Yeah, and it was fine (in the green) before all this happened. It was only after we replaced the fuel servo and mechanical fuel pump we started seeing this. July 1st it was at ~26.5 psi, electric pump off, at idle. July 31st (after the emergency landing and the servo / pump replacement), electric pump off, 11000 rpm, ~34.5 psi.

 

 

 

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Chris, have you tried a different gauge?
 

We don't think it's the gauge (which was working perfectly before all of this).

Current plan per A&P: "We are soaking the fuel injectors in Hoppies and will install them and lean the fuel servo in the morning. Everything else is correct so we will get it right. We will measure fuel rail pressure but the high reading is air in the line from the system being opened up."


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6 hours ago, chrixxer said:

I'm aware. :)If you click the links I provided, you'll see the one I bought was the correct LW15473 pump, refurbished by Tempest. (The other SKU is 07-00705, which used to say (on one webpage; ACS confusingly had two different product pages for what turned out to be the same SKU) it was the LW15473 without mentioning 62B26931, but after I ordered that one and it turned out to be the 62B26931, Aircraft Spruce updated their website and gave me an RMA.) So that shouldn't be the problem.

Doh!  :D  That was your thread, now I'm embarassed!

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3 minutes ago, carusoam said:

@chrixxer

See the next post I left with a copy of the thread in it.   By MichMooney201 

He was having the same issue while getting his engine OH’d...

Best regards,

-a-

Read through it. I made it a point to buy the Tempest LW15473 pump, after reading about such issues here.

 

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Seeing if @jetdriven knows the answer to the high fuel pressure in the IO360 situation...

Its over a few threads by a few people... and it’s been too long for my feeble memory to keep it straight...

I’m pretty sure this challenge has a solution.  Both Mooney and Lycoming shared the ability to make the necessary change...

hope that sparks an idea or two...

Best regards,

-a-

 

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4 hours ago, chrixxer said:


We don't think it's the gauge (which was working perfectly before all of this).

Current plan per A&P: "We are soaking the fuel injectors in Hoppies and will install them and lean the fuel servo in the morning. Everything else is correct so we will get it right. We will measure fuel rail pressure but the high reading is air in the line from the system being opened up."


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Air in the fuel pressure line will not cause higher pressure indication.  Normally the fuel pressure line/ hose from the finger screen bore on the servo to the gauge will have air in it.  This helps to dampen pulses from the diaphragm pump.

Dirty nozzles in a Bendix fuel system won’t raise the fuel pressure on the Mooney gauge as the pressure pickup is not taken from the flow divider.

Clarence

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6 hours ago, M20Doc said:

Air in the fuel pressure line will not cause higher pressure indication.  Normally the fuel pressure line/ hose from the finger screen bore on the servo to the gauge will have air in it.  This helps to dampen pulses from the diaphragm pump.

Dirty nozzles in a Bendix fuel system won’t raise the fuel pressure on the Mooney gauge as the pressure pickup is not taken from the flow divider.

Clarence

So, what do you think it is? It’s the right pump and appears to be the right servo (I’m assuming the -11 is okay)...?

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So, what do you think it is? It’s the right pump and appears to be the right servo (I’m assuming the -11 is okay)...?


It does not take much to clog up the line to the FP gauge or the gauge itself. If you have crap in the servo, there is a good chance it is elsewhere in the fuel system.


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3 hours ago, chrixxer said:

So, what do you think it is? It’s the right pump and appears to be the right servo (I’m assuming the -11 is okay)...?

Step one, confirm fuel pressure value with a test gauge.  Confirm with Precision Airmotive that the -11 is correct.

Clarence

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5 hours ago, Marauder said:

It does not take much to clog up the line to the FP gauge or the gauge itself. If you have crap in the servo, there is a good chance it is elsewhere in the fuel system.

 

The "crap in the servo" was a solid 4"x1" piece of rubber gasket, I don't think it got anywhere else, but I'll pass the thought along, thanks!

 

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