Turbo Arrow III Rough Idle
Hello all,
New to this forum and a new aircraft owner.
I purchased a 1977 Turbo Arrow III a month ago and have had an issue with a rough idle. When RPMs are under 1000 the plane shakes and runs rough. Adjusting mixture doesn't help. I contacted the previous owner to see if this was an issue during ownership. It was. His shop checked the prop and figured it was OK. They never figured out the cause.
The plane has a merlin waste gate and intercooler. Compression values are all good and a bore scope found no problems.
Any help on this problem is appreciated.
Thanks,
Todd
Comments
Hi Todd,
sorry to hear about the problem. How many hours are on your engine since major, both tach and calendar time?
Bob
Hi, Bob
The engine has about 400 hrs and was overhauled in 2009.
Thanks
Todd,
Those times make sense.
A reasonable concept to keep in mind when an engine is running rough is that one (or more, but probably only one) cylinder is making less power than the others. So, then the question becomes, "which one, and why?"" Actually, that's two questions.
The checklist usually starts with enriching the mixture, on the theory it might be too lean. Then cleaning the plugs and checking the timing, sometimes even if L/R/Both shows no change. Then cleaning the injectors and checking metered and unmetered fuel pressure per Continental M-0, both at idle and full RPM. Then move on to differential compression checks, and borescope. Often there's a run through the Dynavibe, and occasionally a review of the engine monitor data looking for an errant temperature profile. Finally, a leak check on the induction system.
I'm very familiar with the checklist, since I experienced this problem a few years ago, when I was unfortunately 1800 miles from my home base. Over a period of a couple of months, I watched as the two local maintenance shops, a company that specializes in maintenance consulting, and a factory engineer repeated this checklist a dozen times, each time unable to identify the source. Finally, after a desperate plea to the local engine shop, they dispatched their lead mechanic. It took him all of five minutes to conclude, "you have a bad #6 exhaust valve," based upon the slight darkening of the factory bronze paint. We pulled off the valve cover, and sure enough, the overhead space was black with blow-by products, despite passing compression and borescope with flying colors. We replaced the valve and the guide, and the engine has run like a champ ever since.
It's curious that both compression and borescope have insufficient sensitivity to detect what is probably the most common cause of rough running in Continental Turbo engines. Maybe someday there will be a cost-effective test that reproduces actual combustion temperature and pressure as part of the annual inspection. But for now, we need to rely on the crackerjack mechanics, and hopefully avoid those who pontificate!
Bob
Thank you Bob. That's good info. I'll have to take a look at the engine a little closer. I'm assuming the discoloration on you plane was on the valve cover? I'm going to forward your info to my mechanic.
Thanks again
You can also probe valve covers with a non contact thermal probe - just need to run uncowled and check soon after.
For the TSIO-360 series the turbo doesn't really spin up until around 1000 rpm. Both of my engines in the Seneca run better at 1000+
Also check the engine mounts. Is the MP or Fuel Flow bouncing below 1000. After the engine is warmed up can you pull the power back and hit idle speed with the engine still running? Does it make a difference on L/R or both mags?
Eric
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)
Todd - yes, darkening was on the #6 exhaust cover. Honestly, it was so subtle I didn't notice it until the mechanic pointed it out to me. I tried to take pictures with my DSLR and a ring light, but unless I got the lighting perfect (which I never managed to) the illumination difference dominated the shading difference between the valve covers.
Under the valve covers was a different matter. The #6 rocker space was so full of soot it looked like a bomb had gone off; whereas the other 5 were clean and soot-free. Bob
Thanks for the info guy's,
I'm going to the airport today. I'll let you know what I find out.
Thanks again,
Todd
Also Eric,
Not sure about Mp and fuel flow bouncing. And pulling back to idle under 1000 rpm the engine runs rough. The previous owner had the problem and never figured it out. He just kept the idle high enough.
I haven't switched mags to L and R mag at idle. Only during run up. Minimal drop equally on both.
Follow up on the vibration issue. The shop did a track check on the propeller (McCauley MPC-11) found one blade off track about 1/8 of an inch. The prop was installed in 2008. The prop has 630 hours on it and the logs show 100 hour inspections every year or two. Nothing else.
I am learning the the prop should have had an overhaul at 5 years or 1500 hrs. Being brand new to aircraft ownership I am learning the hard way. The shop is suspecting this could be the cause for the vibration.
I only have 7 hours of flight time in this plane. Needless to say I'm not having fun yet :(
Shempinator:
First, welcome to aircraft ownership. Second, it's very safe to state that every owner of a used airplane has been where you are now. The only way to completely avoid repairs on an older aircraft would be to purchase brand new with a warranty, but that will set you back a half mil or more.
More than likely you have a list of squawks. There are 2 approaches to address them. The number and the severity of the squawks should be taken into consideration when choosing one of the approaches below.
Pros:
Cons:
2. Park the plane for a while and fire the money cannon at it.
Cons:
Pros:
As I mentioned, we've all been where you are now. My experience? Despite having a pre-buy inspection, my engine needed (2) jugs and an alternator replaced during my very first annual.
Whatever path you choose, stay close to this forum and ask lots of questions. There is a ton of knowledge here, and the members are very happy to help. You'll get through this, and you're going to love flying your plane.
Jim "Doc Griff" Griffin
PA28 - 161
Chicago area
Regarding then prop. I would say most of general aviation ignores calendar time for props and engines. So, not unusual at all to have a prop in since 2008. If there was only 630 hrs in 15 years that is an average of around 42 hrs a year which is also fairly typical for GA these days.
Did they want to do something about the prop track? Is the blade loose? What is the spec? I am not convinced it would have anything to do with vibration. If it was the prop would likely get worse vs better. Rotationally it is the same mass spinning around, just offset in the non spin direction.
I would have it balanced vs overhauled and would not overhaul is only based on calendar time. A good prop analysis can help rule out a number of engine related items too as it will look at the nature of the low rpm vibration as well.
Have you flown with any other Piper pilot? That might be able to offer feedback on how unusual (or not) your engine vibrates. If you ground run with the cowl off you might be able to see it too. Perhaps your exhaust is hitting the fuselage at low rpms? Could be any number of things.
FYI: If I had a shop that insisted on overhauling prop or engine just based on the calendar age than I would drop them.
Back to your earlier comment on roughness not improved with mixture. Are you referring to the mixture knob or the idle mixture setting? I think they idle mixture setting responds differently vs the idle control at low speeds. Do you get the expected rise in rpm right before cutoff at shutdown when slowly moving back the mixture lever at idle? If not, could be the idle mixture circuit. Did they do the full fuel system set up?
Eric
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)
Hi Eric and Griff,
Thanks for the info. The shop suggesting the prop be sent out to a prop shop and have it checked. Then repair it if they find any problems. Also the shop told me there is adjustment needed regarding the MP. Can't remember exactly what he meant. The mixture I was referring to is the one in the cab and there is a rise then drop in RPM as I slowly pull back to idle cutoff. The shop did not do a fuel system set up.
Another thing is I found out the previous owner had the same vibration. He had it checked but they couldn't find the cause. So he just lived with it. The rear of the plane shakes quite a bit when it is running around 900 Rpms but totally smoothens out as you increase RPMs. My instructor who was a previous Arrow owner thinks it could be injectors.
Another squawk is my amp reading goes up as high as 50 with all electronics on (including wing tip lights.) I have two Dynon sky views on my panel and I'm not sure if the range in the green is set properly. Volts in flight are 14.2.
Thanks again with the help.
Todd
Hi Todd,
That seems really high for amps. Is this on ground and in flight? How old is the battery? You could isolate one breaker at a time to see what is driving the current. These days usually it is a blower motor. The Dynon's sip power in comparison.
I ask about the battery as it might be old enough that it is having trouble accepting charge.
Crazy idea but what if you leave the alternator off and start it? Do you still get the vibration? I ask because at low rpms the alternator struggles to put out current and it is possible it could be cutting in and out at low rpms. I have seen this in an experimental IO-540 with AC.
Anything on the valve cover appearance or were they popped for inspection of the exhaust valve seals?
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)
My ammeter barely moves when everything is running. I do my Pitot heat check and the increase is barely enough to move it albeit it does move.
I am wondering if something is shorting or has a major issue. On the ground, start the plane and run it 1200 rpm, brakes on and chocked. Start shutting down appliances one at a time and look for the big drops. When You see that meter drop substantially, note what the item was and turn everything back on. Do the same procedure except skip the offending appliance and look for any other high amperage users, if any.
When you find the offending items, now you can trouble shoot them. This is just an easy way you as an owner can help narrow down the problems your Mx can now focus on. You can also connect an ammeter to the actual appliance and confirm it’s within spec or if an anomaly in current usage present itself.
I own and fly a 79 PA32RT-300T. Previous aircraft are a 79 Archer and 76 Arrow.
Todd,
I fly a 1977 Turbo Arrow III as well. When I purchased my Arrow, the engine did not idle below 1000 rpm. I also experienced the engine quitting when landing and pulling the throttle to idle.
To solve these issues I had my mechanic readjust the fuel system. This requires gauges to be hooked up to the engine and adjust unmetered pressure at 700 RPM and full power, and also adjusting metered pressure at full power. After these adjustments were completed, the engine would idle at 700 rpm. The engine does idle smother once it hits 1000 rpm, but it will idle at 700 RPM.
Here is a link to a document that describes how this adjustment is done. https://www.lancairowners.com/files/wp-content/uploads/ContinentalFISystemAdjustment.pdf
Ken
Thanks for all the good info everyone. The battery is less then two years old. The amp issue is also intermittent. A few times it stayed in the normal range for a while. Then, back to high. As for the prop, I'm having a hard time accepting the possibility that a prop blade being off track only1/8" could cause that much vibration. Especially when you throttle up and after about 1000 rpms and higher it runs smooth as heck.
The mechanic called me to give me the potential cost of the service for the prop. Best case $3,700 worst case $5,800.
I'm going back to the airport tomorrow to talk to the mechanic. I'll mention the info provided here. I'll let you know any new developments regarding this.
Thanks again.
P.S. Thought I would show the aircraft in question.
Wow, she's a beauty!
Glad you are skeptical about the propeller theory. I'm not aware of a principle of physics whereby propeller-induced vibration mitigates above idle speed.
BTW, after my valve-induced vibration odyssey a few years back, my A&P (who has a lot of Adam Savage in him) and I performed an experiment trying to evaluate the potential impact of all the different vibration causes the experts had proposed. One-by-one we replaced my low-resistance Tempest plugs with high-resistance Champion ones, tuned the fuel system to the extremes of M-O, deliberately put the GAMI injectors in the wrong cylinders, adjusted the ignition timing to the extremes of range, removed intake gaskets to cause leaks, and everything else we could think of except maybe drilling holes through the cylinders or removing the crankshaft balance weights. Then we evaluated the results of each configuration by observing vibration and engine monitor readings throughout the entire range of RPMs with the engine de-cowled. The results....wait for it....nada! None of these defects made any visually observable or measurable difference in engine performance.
I was reminded of this experiment by Scott's article in the magazine this month, evaluating the performance of speed modifications. If you haven't seen his article, you should! I am hoping to repeat the vibration study, fully-instrumented and on the dynamometer, and write an article like Scott did. We all can benefit from more objective (and factual) troubleshooting information.
Any update? How old are the engine mounts? Did anyone do a prop balance? What is the minimum MP at idle? Still seems suspicious that the vibration is right around the turbo spin up rpm. What happens if you hit prime at idle? does it have the alternate prime where a solenoid opens and fuel is injected via two spray nozzles in the intake runners?
If you pull the mixture back quickly do you get a sharp cut off? There are some problems that can occur in the spider that might impact low speed operation.
Can you send your Dynon engine data at idle, takeoff, cruise settings? Have you done a GAMI lean test?
I think of roughness only at idle as mostly inconsistent fuel/air mixture. It is more likely to be variations in fuel delivery vs air.
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)
Hello all,
I apologize for my absence and late response. Been out of town for a few weeks. Seneca and empannin thanks for responses with good info, I just read them today. An update on my issue. Since my last post, I went ahead and had the prop sent in for evaluation and repair as needed.
After looking at the logs and contacting previous mechanics and the last owner, turns out the prop has never been removed from the plane ever. It was installed in 2008 and has 600+ hrs on it. Not sure if it will fix the issue but at least I won't have to worry about prop issues in the future hopefully.
I will keep everyone updated and thanks for all the excellent responses.
Good luck, and keep us posted.
Initial findings on the prop is evidence of red dyed oil leak.
Is the leak in a seal, or from a crack?
No crack. Bad seals or "O" rings.
Heres what they found:
One blade is off a 1/4" off. There is corrosion in the snap ring grooves. The blades had too much play/ they were too loose. The prop was installed in 2008 and all the new stampings are still there. It has never been overhauled. Red dyed oil is leaking.
I'm sure there is more, I went ahead and gave them the go ahead to perform an overhaul.
A mis-tracked prop might not impact vibration but a loose prop could. The engine sends a series of power pulses to the prop and if the prop blades are loose this could potentially translate into vibration.
Seems like regardless it is time for the prop to be overhauled.
Eric
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)
Thanks Eric, A few weeks ago I was with one of the head mechanics and we were checking the prop. He grabbed one blade and it rocked it back and forth enough so you could hear a metal to metal clang.
I'll let you know what I find out after the overhaul. Probably two weeks from now.
Todd
Todd, those props take a beating and as soon as there is any play it gets progressively worse. Regardless of the impact to vibration (and I hope it solves it) this was the right call to inspect and overhaul.
Eric Panning
1981 Seneca III
Hillsboro, OR (KHIO)
Todd:
I've seen fixed pitch props with tracking less than 1/4 inch off cause pretty serious vibration. Drove the owner nuts trying to find the cause. I don’t know how poor tracking manifests itself a constant speed prop, but it's never going to be beneficial.
Now that we know there was loose hub/prop interface, it made me think. If the slack (let's say) was biased toward the rear of the plane, the prop may not track at idle/low RPM's, and could cause vibration. At higher RPM, the prop is pushed forward by the opposite force of pushing air backwards. The slack is taken up, the prop tracks correctly, and the vibration goes away. There are a multitude of other dynamic forces at play, so this is just a theory.
Had a very reputable prop shop do a presentation at our pilot's group. They told us that the forces on a constant speed hub are enormous. In cruise, each blade of a Bonanza prop exerts something like 8 tons of force on the hub trying to tear itself free. Your T-Arrow can't be too much different.
Agree 100% with Eric. Once that hub/prop gets loose, it's never going to get better or fix itself. Having it overhauled is a very wise call.
Please follow up and let us know how it turns out.
Jim "Doc Griff" Griffin
PA28 - 161
Chicago area
Thanks Eric and Jim.
I appreciate the info. Makes sense on the prop tightning up as you throttle up. I am going to the shop tomorrow to check on progress. I'll keep everyone updated as I get more info.
Thanks
Todd
Hello all,
I wanted to update everyone on the status. I had the prop overhauled last week and according to the shop manager it was definitely in need of the service.
The prop was installed yesterday and according to the mechanic, the test run was a success, no more vibration at idle!!! Smooth at all rpm's. A big sigh of relief. I haven't flown it yet but will let everyone know how that pans out next week.
The last problem I am still trying to figure out is the high amp reading I encounter during flight.
Thanks everyone,
Todd