Hey everyone. When I bought my plane, it wouldn't shutdown when the mixture was pulled to idle cutoff. It would sound like a normal shutdown and then spit and sputter when it hit 300-400 RPM. When I got it home, we hooked the hoses up to it and got the high and low fuel pressures set to where they needed to be. Here we are a couple of months later and it's started doing it again.

So, last night we checked everything. Mags are spot on, put new plugs in all cylinders (they were due), and we hooked the hoses up and verified that the pressure is where we set them, which they are. My mechanic adjusted the throttle idle stop as well as the mixture idle cutoff. We got it to where it was shutting down correctly and repeated 4-5 times to check for consistency. All were normal, correct shutdowns with a slight rise in rpm.

This morning I got up to go test fly it. All went well and the engine was smooth...until shutdown. It sounded and looked like a normal, smooth shutdown until it hit around 300-400 RPM. Then it sputtered again. The only difference is this time it would did after sputtering for 10 seconds or so.

Any ideas? It acts like it's still getting fuel from somewhere. My mechanic is on the verge of pulling components and sending them out to be serviced and if like to get some more thoughts on it first.

Here is a video of what it's doing.

Thanks!

https://vimeo.com/175726392


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Probably a stupid question, but to eliminate the obvious: Is the boost pump off? If you leave the boost pump running when you pull the mixture, it will do exactly as you describe.

Yes it's off, but good thing to point out. My mechanic looked through the TCM IO-520 troubleshooting and it points to a leaking manifold fuel valve. Thoughts? As we were troubleshooting it last night, he made the comment that the engine is creating suction and getting fuel from somewhere. This sounds like a likely source...but I'm not that familiar with the inner workings of this system to know.


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The fuel controller on the throttle body is what cuts the fuel off to the fuel manifold located on top of the engine. Generally the fuel manifold diaphragm being no bueno will result in external leaks. The fuel controller on the throttle body has some internal magic that can be fixed in the field by a guy who knows how it works, but most A&Ps won't touch it today. At any rate, that's where I'd look. Message me if you want to chat about it more.

so...100LL or that other stuff.....?!

Thanks. In talking to a few guys, the general consensus is either a small induction leak that is worse when things are hot and expanded. The second is a fuel manifold leak. Are the field fixes doable or is it a liability issue that makes mechanics shy away? If it needs to be sent out, any recommendations? I'd gladly chat with you. In reality, it's probably more productive for you to talk to my mechanic. If that's a possibility, pm me and we can set something up so we can both hear it. Thanks!


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Grassstrippilot wrote:Thanks. In talking to a few guys, the general consensus is either a small induction leak that is worse when things are hot and expanded. The second is a fuel manifold leak. Are the field fixes doable or is it a liability issue that makes mechanics shy away? If it needs to be sent out, any recommendations? I'd gladly chat with you. In reality, it's probably more productive for you to talk to my mechanic. If that's a possibility, pm me and we can set something up so we can both hear it. Thanks!


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Not sure how more air (induction leak) being added to an engine you are taking fuel away from will result in engine run on.

The fuel manifold is stupid simple to work on. I'd venture to guess most guys would/could do it without a service manual. That being said, I don't recall one causing this problem. But I love being wrong if I get to learn something.

The fuel controller is another animal. I wouldn't open it without and service manual (which I think I have, but I'd have to dig). If I have a manual, I'll open about anything, a lot of guys don't want to touch stuff like this either way. I'm not sure if it's liability or what that makes them steer clear of it. I do know that a lot of A&Ps are surprised to hear I do mags/alternators/fuel valves/etc in house.

I'd like to assume that you've checked the easy stuff first, because I hate when I ask a stupid question, but......

The throttle and mixture brackets and geometry on the 185 are really cheesy. I can dig up an old thread where I got some advise here that helped me fix mine. You need to be 100% confident that the anchor point for the cables is intact. The bracket bolts to the oil filter/screen housing, and clamps to the induction tube with a couple gear clamps over a tab that sometimes breaks. The bracket can also be heavily worn by the cables. In fact, the cable sheath can wear and pull right through the bracket. Mine was nearly that bad after only 1600 TTSN!

When it was working properly, were you getting a slight RPM rise before shut-down as you pulled the mixture? Just confirming the linkage from the throttle body to the controller, and looking for signs of that induction leak with this question. An induction leak can cause high idle, but once the mixture is pulled, it should still stop, so I'm going down a less relevant path with this question, only because it was brought up.

Pinecone wrote:I'd like to assume that you've checked the easy stuff first, because I hate when I ask a stupid question, but......

The throttle and mixture brackets and geometry on the 185 are really cheesy. I can dig up an old thread where I got some advise here that helped me fix mine. You need to be 100% confident that the anchor point for the cables is intact. The bracket bolts to the oil filter/screen housing, and clamps to the induction tube with a couple gear clamps over a tab that sometimes breaks. The bracket can also be heavily worn by the cables. In fact, the cable sheath can wear and pull right through the bracket. Mine was nearly that bad after only 1600 TTSN!

When it was working properly, were you getting a slight RPM rise before shut-down as you pulled the mixture? Just confirming the linkage from the throttle body to the controller, and looking for signs of that induction leak with this question. An induction leak can cause high idle, but once the mixture is pulled, it should still stop, so I'm going down a less relevant path with this question, only because it was brought up.

No stupid questions. I am trying the "low hanging fruit first" approach.

We checked that the linkage was moving it to the stops, but another person mentioned the same thing about the linkage getting worn and it will be checked again.

When it was working properly, we were getting a slight rise at shutdown. A couple people noted that the bad shutdown yesterday occurred while the engine was hot vs just warmed up after a few run ups like the night before. The idea being that if it is a small induction leak, it may not manifest itself without some expansion when warm. So, since this is an easy thing to rule out, we will fly it briefly to get it hot and do a check for any leaks. From there we will look at the fuel manifold intake calve. At this point I think that's our course of action.

Thanks guys!


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Just in case


http://occonline.occ.cccd.edu/online/rf ... ection.pdf


http://www.kellyaerospace.com/articles/ ... usFlow.pdf


TOOO much for my old eyes to read and search.

Mine will do that if I just pull the mixture all the way, but when I shut off the master and turn off the key it dies, always has been that way.

Steve

My mechanic came out today while I was doing some work on the plane and went through all the linkages and induction clamps. Couldn't find anything that was suspect. We will do an induction leak test next just to rule that out.


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...and some 520 aircraft came with a primer. Pull the two lines at the manifold and plug to block potential fuel flow from that source then test run.


Rocket

Chances are it's the fuel manifold valve / distributor valve / spider, whatever you want to call it. It has a spring loaded diaphragm valve. One side vented to atmosphere, the other to fuel pressure from the FCU. When running, fuel pressure against the diaphragm opens the valve and allows fuel to flow to the injectors, when you go to idle cutoff, the fuel pressure drops, valve closes and cleanly shuts off fuel flow to the injectors. If you inadvertently leave the boost pump on, sufficient fuel can flow past the mixture plates in the FCU and open the manifold valve just enough to get a dribble of fuel through and keep the engine spluttering at low rpm (just flick the pump off and open the throttle, engine will shut down instantly)
The manifold valve can get crud or corrosion in it causing the valve to stick, or the diaphragm gets old and brittle. As mentioned above, it's very simple, four screws and pop the top cover off, remove the spring and diaphragm and have a look inside. Not much to see... Be aware the diaphragm can stick to the valve body and cover and sometimes it tears when removing. Easy part to replace and cheap enough. When reassembling, coat the diaphragm with a little engine oil.. Also worth checking the vent hole in the cover isn't blocked.. And do a leak check by priming before closing up and running the engine.. Of course, your mechanic should know all the above and sign off the work!
Some later model injected aircraft had primers fitted, not unheard of for the primer to leak allowing fuel to suck through it(or it's not locked, hence why it's a pre takeoff check)

If the fuel system pressures and mixture is set per SID97-3 there's not much else can go wrong...


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Thanks for all the input.

Onefitty, where is the best place to buy he diaphragm? Spruce? I'll dig for a parts manual and see if I can find a part number. Thanks!


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I'm not sure if it would be helpful or if the IO360 uses the same/similar manifold valve or if I'll have time to do it before you get your problem fixed but I have a spare valve that I've been wanting to take apart. I could take pics or video the disassembly of it.

Cory, I would probably call RAM and see if they sell the Pma'd diaphram, last time I checked they were over 400 bucks for a TCM one but there was a company that had a Pma'd version for quite a bit less, I think around the 250 dollar range. If you have no luck, it actually may be more benificial to get an exchanged unit.i

Just checked their website, I would just get an overhauled unit from RAM their online catalogue is pretty good and when you call them, they actually can verify you're getting the right one.

Whee, that would be pretty useful. But I know that is also time consuming. I've got to go back to work tomorrow and will be gone for a week so it's going to be a week and change before I get to continue my pursuit of this.

Bdiazair, thanks for that info. I'll be looking today to see who makes that assembly so I can try to track down the part. Good thought on the exchange unit too. Thanks!


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I know Precision Airmotive makes pretty affordable ($280) flow dividers for RSA systems like those used on Lycomings, but not sure about TCM. I have a feeling you're going to pay.

Probably.


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