Have I lost confidence in my engine?

[Earl]

Interested in other's thoughts on my growing anxiety with my engine and whether I am overreacting.  Some quick background because I know you will ask.  1986 252 with 2,300 hours TT and 500 SMOH (engine done by Mattituck).  I recently added an EDM-730 (which some of you may remember from my earlier posts). The 730 provides CHT, TIT, EGT and RPM but not MP.

Since I had the 730 installed, and maybe this is just a coincidence, but I have not been able to get 35" of MP at takeoff and climb.  I have only been able to generate 33.5".  I had the turbo inspected and it seemed OK and MSC increased fuel flow at full power to 24 gph (I was only getting a little over 21 gph before he adjusted it).  He also repaired my alternate air vent that was not seating properly.  My A&P checked cylinder head pressures and most were in the 70's with two clylinders in the upper 60's.  Oil burn has always been inconsistent which is maybe a function of my measurements (i.e., comparing a cold measurement with a hot engine measurement, etc.).  Sometimes it seems like I can fly 8 hours and burn a quart of oil and other times I will fly 2.5 hours and it is down a quart.  I also have a pretty big spread in CHT's and the two lowest cylinders in terms of compression also happen to have the lowest CHT.  The other clyinders are much closer in temperature.  I have tried running LOP but when I get below peak the engine runs rough.  My mag checks are fine (using the rich and lean approach) and each of the cylinders jump around 50 dF when I go to a single mag.

Am I suffering from too much information and imagining a problem that probably doesn't exist?  Both the MSC and my A&P have stated the engine runs great but the inability to produce full MP is bothering me.  Could it be that the MP is not accurate and something happened when he installed the 730?  Am I just being paranoid or should I be worried?  What do I need to check next?

[KSMooniac]

I would try to plumb another MP gauge somehow, either with the JPI or something else and check to make sure yours is accurate, first. 

The inability to fly LOP with that engine would bother me, though.  Perhaps GAMI jectors would solve the problem, or in the process to determine whether you need them you might discover other issues like induction leaks first.

Do you make POH performance numbers currently?

[Earl]

Quote: KSMooniac

I would try to plumb another MP gauge somehow, either with the JPI or something else and check to make sure yours is accurate, first. 

The inability to fly LOP with that engine would bother me, though.  Perhaps GAMI jectors would solve the problem, or in the process to determine whether you need them you might discover other issues like induction leaks first.

Do you make POH performance numbers currently?

[Cruiser]

you mention low CHTs and low compression but how much lower are these than the high ones? When you do a LOP test what is the spread in fuel flow? Having low compression after 500 hours would make me want to know more about the engine.

As for the oil consumption. It will change with power settings. If you run low vs high RPM you will see a difference in consumption. Is it blown out or burned up?

[Earl]

Quote: Cruiser

you mention low CHTs and low compression but how much lower are these than the high ones? When you do a LOP test what is the spread in fuel flow? Having low compression after 500 hours would make me want to know more about the engine.

As for the oil consumption. It will change with power settings. If you run low vs high RPM you will see a difference in consumption. Is it blown out or burned up?

[Mooney65E]

I've got the EDM 830 on which  MP comes standard. When flight testing after installation of the 830 I noticed an approx 1.5" discrepancy between my original MP gauge and the 830. There are adjustments on the 830 to make them equal, but it makes me wonder how accuate the original gauge is.

[Earl]

Quote: Mooney65E

I've got the EDM 830 on which  MP comes standard. When flight testing after installation of the 830 I noticed an approx 1.5" discrepancy between my original MP gauge and the 830. There are adjustments on the 830 to make them equal, but it makes me wonder how accuate the original gauge is.

[Jeff_S]

I don't really know much about turbo engines but I do know about analysis-paralysis, especially when you're getting used to a new plane and even moreso when that new plane has way more engine diagnostics than you're used to. But from the experiences I've had learning the idiosynchrasies of my new J, I'd say that if the engine generally performs well but you're seeing things you're not used to on the gauges, then the first step is to check the gauges.

In the three months I've been flying the plane, the oil pressure gauge all of a sudden started sticking, the fuel pressure gauge decides to cut in and out with a mind of its own, and now the right fuel-tank gauge has decided to start sticking. The first two of these freaked me out at first (I'm used to fuel-tank gauges not working) but I learned the value of the gentle tap. And so far (knock on wood) the engine just keeps motoring along not caring what the gauges are saying, and the JPI has been a great backup to provide confidence that the old mechanical-analog instruments are just finicky.

See if you can get an alternative MP reading before you start tearing anything down.

[Earl]

Quote: Jeff_S

I don't really know much about turbo engines but I do know about analysis-paralysis, especially when you're getting used to a new plane and even moreso when that new plane has way more engine diagnostics than you're used to. But from the experiences I've had learning the idiosynchrasies of my new J, I'd say that if the engine generally performs well but you're seeing things you're not used to on the gauges, then the first step is to check the gauges.

In the three months I've been flying the plane, the oil pressure gauge all of a sudden started sticking, the fuel pressure gauge decides to cut in and out with a mind of its own, and now the right fuel-tank gauge has decided to start sticking. The first two of these freaked me out at first (I'm used to fuel-tank gauges not working) but I learned the value of the gentle tap. And so far (knock on wood) the engine just keeps motoring along not caring what the gauges are saying, and the JPI has been a great backup to provide confidence that the old mechanical-analog instruments are just finicky.

See if you can get an alternative MP reading before you start tearing anything down.

[Earl]

Well I finally reviewed the data from my 730 and I was slightly off in my original post.  It turns out that 5 of 6 cylinders were within 25 dF of each other and one cylinder was about 50-75 dF lower which also corresponded to one of the cylinders that had a lower compression but there is no correlation.

[TonyTDMD]

My cht's are 350-360 max. My FF 24.5 at takeoff, 36/2700. Mine wont run LOP either, it gets very rough, so I just run 75 Rich. I dont think GAMI makes injectors for this installation (252's excluded for some reason).

[danb35]

Quote: TonyTDMD

I dont think GAMI makes injectors for this installation (252's excluded for some reason).

[donshapansky]

I have an EDM 930 in my Rocket 252 and had a disparity between the original MP gauge and the EDM , then I realized the EDM sensor is placed after the intercooler vs the OEM between the turb and the intercooler. What I'm seeing is the pressure drop across the intercooler.

I was involved with Machen Aerostar guys when they designed the new intercooler for the 700 Superstar, they spent 100K in design and were very happy to achieve a 1.5 inch MP drop across the intercooler at 44 inches MP. 

It's worth checking out your installation to see how it's set up, I like seeing what the engine sees. I also had to calibrate the EDM930 MP, if you have the adjustment option to calibrate the MP in the manual it's worth going through the steps. 

[testwest]

I looked at the JPI plot you have posted. If those were fluctuating EGTs instead of CHTS it might indicate exhaust valves that are hotter at one point along the circumference. As the valves rotate, the EGT values rise and fall at the same rate as the rotation.

This was written on by Mike Busch in a recent article of EAA's Sport Aviation. I have not checked, but I bet he covered it in the free webinar on his web site called "Engine Monitors" that was on line on March 2, 2011. The list of webinars is here

http://www.savvymx.com/index.php/resources/webinar

 

[Kwixdraw]

If Norm is correct you probably ought to get your aircraft in to have a borescope inspection of the exh valves done asap.  Don't wait until one of them lets go.

[jlunseth]

My vote is take a deep breath.  I don't think you have anything going on that is not pretty much normal with the TSIO-360's.  I saw several things in this thread and will try to cover them.

First, my experience is with the 231, which is the little brother to the 252, but the engines are basically the same in that they are small bore six cylinders.  I have GAMI's in mine, and nevertheless I have found it very difficult to get the engine set up properly so that LOP is possible.  If you want to find out if your engine will run LOP with the stock injectors, the best thing to do is go to the GAMI website and read the instructions on performing a GAMI lean test.  The point of the lean test is that you need the cylinders to reach peak at a fuel flow within a few tenths of a gallon of each other.  I have done the test, but it was awhile ago, and I don't remember what their standard is, I am thinking a max variation of .5 gph or something in that vicinity.  If you do not have that narrow variation then GAMI injectors may help, especially LOP. 

The reason for this is that when it comes to running LOP, your six cylinder and mine need to be looked at as though they are six separate little engines.  All 6 need to be tuned so they operate close together.  If not, let's say you go LOP and five of the six cylinders run withing .2 gph of each other, but the sixth little engine is off by 1.0 gph.  Now, when the five similar cylinders are at 60 dF LOP, which is where you should probably be with a turbo, the black sheep is nowhere close to that.  It is doing one of two things.  If it is 1 gph richer, then it is probably sitting back at peak and in constant marginal detonation, while the other five are doing fine.  If it is leaner, then it is probably choked for fuel to the point where the fuel air mixture is not sufficient to consistently support fuel burn, and it is running rough.  Either one is not good for that cylinder, the peak possibility being the worst of the two.

The problem with "our" engine (I know, yours has a better turbo system than mine) is that the small bores just do not run as consistently as the large bore turbos.  It takes a great deal of work, tinkering with cylinders and fuel flows, putting in GAMI's, and even then I am finding that the fuel flows can be made consistent only withing a certain range of power output.  Everything will look good up to about 28" MP for example, and after that the cylinders are going to start to separate and you will see more fuel flow variation.  In fact, I think it not only takes quite a bit of work, but some luck as well.  Not all the 360's can run LOP, and probably 100-125 ROP is a better choice. 

There are also possible variations depending on altitude, because the fuel pump is altitude compensated, and that needs adjustment sometimes, or repair, so the engine can seem fine at 7k or even 17k, but not at 23k.

I am going to take a guess that the cylinder that is running coldest in your engine is 6, or if not 6 then maybe 5.  The cylinders in the Conts. are numbered from back to front, and 5 and 6 are the two cylinders closest to the cooling air holes in the cowling.  That is just a perennial issue with these engines, 5 and 6 will be cool and 1 and 2 will be hot.  I wish someone would do the work to come up with a better baffle system that would correct this, as GAMI has with the Bonanzas, but it is the way it is. 

I noticed a post about CHT's being "jagged," i.e. varying a few degrees every few seconds.  If that were EGT's, as noted, you would want to have the valves looked at.  But I went through the issue with CHT's.  There is a small star washer in the connection to the sensor, and it is intuitive to a mechanic that it should be installed as a lock washer, but that creates a wrong connection and causes the jagged CHT line that you see.  I have a note from John Deakin of GAMI on this I will try to find and forward to you.  I gave it to my A & P at annual, they redid the connections to put the star washers in the correct orientation and sequence, and voila, the jagged CHT line smoothed out.

Unlike a jagged EGT, which can indicate that the temp of the exhaust gas is in fact varying rapidly (a bad thing), a jagged CHT generally indicates a bad sensor reading.  This is because the CHT probe is reading the temp. of the mass of metal that is the cylinder head, and that temp. just is not going to jump around rapidly, second by second, which is what would cause a jagged line in an EZ Trends graph (the software for viewing downloads from a JPI instrument), or a jagged reading on the instrument itself.   

On the MP, I have a thought and no basis for it except my own understanding of turbos (and I am not an A&P).  If you have thoroughly checked for induction leakage then there is only one other source I can think of and that is the turbo.  The turbo management system in the 252 is different than in the 231, but it's basic function is the same.  It "valves off" exhaust before it reaches the turbo, via a wastegate, to keep the turbo from overworking, and to manage MP at a consistent pressure.  So I would have the adjustment of the wastegate management system checked. 

If you can fly at 1,000 MSL (or a similar low altitude), put the MP at max (your 33.5) and fly to 10,000 and still have it at 33.5, then the problem is definitely not the turbo itself.  That exercise will tell you that your turbo has more capacity than it needs at 1,000 MSL, because if it did not, it would not be able to make 33.5 at 10,000.  So you either have an induction leak, or if that is completely ruled out, then your turbo management system needs to be checked and adjusted. 

To be honest though, I would not worry about that too much.  You will not miss that extra 1.5 except under unusual conditions, either a high density altitude takeoff on a short field, where you want every ounce of power the engine can produce, or possibly if you decide to try your aircraft's service ceiling of 25k, you may find you do not have the power to quite get there, it may be that the wastegate will not fully close.  Don't know.  One difference between our engines is that I can overboost mine, that is, get it to go as high as 40" and with my intercooler that would definitely be an overboost.  I think your system is more automated, so doesn't overboost.  But my point is that because of the overboost possibility, every takeoff I make is at a slightly different MP.  I aim for 36".  Sometimes I see 35.5, sometimes I see 37".  Moreover my 36" "aiming point" is a rough approximation of the affect the intercooler has on engine performance.  That effect will vary with every takeoff, because it depends on too many things such as OAT, CDT, density alt., and speed of the aircraft (airflow over the intercooler).  It does not make any difference, the engine has sufficient power to take off at any of these settings.  So I seriously doubt that being at 33.5" instead of 35 is going to be a very big deal in your aircraft. 

Those are my thoughts. 

Report back though when you have a solution.  Us turbo guys have to stick together.   

[fatalflaw]

jlunseth: that was a really interesting post, thanks.

I have a 231 (-GB) with GAMI but without intercooler or Merlyn (yet), and I am having trouble finding a sweet spot for LOP despite considerable effort from GAMI. My current issue is not being able to find a LOP setting which gives both a safe EGT/CHT and doesn't run rough. Typically I am looking at 31" and somewhere between 10 and 15 thousand feet. 13-13 1/2 gph is tantalisingly close.

I don't have any issue with MP settings but that may be because I don't have an intercooler. What I do have is a massive difference between the mechanical EGT gauge and the EDM800 - about 100 degrees hotter on the EDM. Gave me a nasty shock when I first noticed it.

My GAMI spread is about 0.7 gph which should be reasonable. Fuel pump adjustment, induction leak and iffy magnetos are possible issues I am currently working through with my A/P. Another possibly related factor is that every time I have installed new injectors it becomes more of a pig to start - requires an amazing amount of priming initially (which I dislike as I can picture all that fuel washing the oil off the cylinder walls) and finger on the primer on and off for a good 30 seconds after starting, hot or cold. Runs very nicely when it's warm though. My compressions are high 60's/low 70's, 1100 hours on the engine, 800 since a top overhaul (25 years ago).

I am going to carry on working on this and I will update this thread if/when I make progress.

Incidentally - airflow systems have stopped making the 231 intercooler, or at least until they have orders for 10 (currently there are 3 people interested apparently). Anyone know if there's one sitting on a shelf somewhere?

Also - your oil consumption seems curiously variable - and worryingly high when bad. I haven't seen anything like that on mine, though I agree > 6.5 qts serves only to lubricate the surface of the planet. I would be tempted to sort out the cylinder with the low compression.

[jlunseth]

fatalflaw, here is what GAMI would probably say about your issues.  First, an EGT variation of 100 degrees from one gauge to another is probably not a concern, nor from one cylinder to another.  The reason is sensor placement.  EGT is reading the temp of the exhaust gases when they come out of the cylinder, and at that point they are still burning, or should be.   Also, our EGT sensors are reading the average of intermittent jets as the exhaust valves open and close.  It is still usefull to visualize your sensor as sitting in the flame jet of your natural gas furnace, it is telling you the temp. of that burning jet.  However, in an engine the sensors on each of the cylinders do not always get placed in the same position in that jet because of obstructions, such as the manifolds, induction system, etc.  So sensors get placed at different locations in the burning jet of gas from each cylinder.  Those further out will read a little cooler, those further in will read hotter.  It is not at all unusual to see differences of 100 dF, but it is also not an issue as long as the EGT's are proportional.  By proportional I do not mean that the difference needs to be 100 dF at all settings, because if you reduce power enough, the burning jet on one or more cylinders may no longer be burning when it reaches the sensor, so that cylinder may be quite a bit cooler than those with nearer sensors.  What you don't want is one EGT that is suddenly significantly different from the other temps and from its own normal readings.

On your starting issue, I have the same and there is an easy cure.  The issue is vapor lock, bubbles forming in the fuel line because the engine is still hot.  That, or when the engine has sat for awhile the line seems to lose its prime.  The cure either way is to run your high boost with the throttle closed before you start the engine.  I have a fuel pressure gauge in my 930, so I watch for that to hit a stable number, usually mid-17's, but the number is not so important as the fact that the pressure stablizes, which indicates that the line is full.  According to my A & P, any excess fuel is being returned to the fuel system when you run the boost pump, so if you do not have a gauge you can just time it and run it for a full minute.  In my engine, and because we are in the cold weather in the winter and need all the help we can get, I then run the primer for 6-10 seconds, which is putting fuel directly into the cylinders I understand.  Then I push the key in and the engine will start and run without problems.  If the engine runs for a few seconds and then falters, the fuel line was not full.  The cure is to hold the primer button down while the engine is starting, that will help it through the faltering and until the line is fills.  There is a distinct increase in power when the line is full and the engine is running on its own, so you will know when to stop priming.  Works every time.  Used to have the starting issues you have, and now never have a starting issue and rarely need to use the primer button while the engine is running.  BTW, this works well for hot starts also, because it "debubbles" the fuel line.

There does seem to be alot of tinkering to do to get to the point where you can run LOP.  The GAMI people recommend 60 d LOP for turbos to protect against detonation, and my engine just won't get there.  We have too much working against us in the small bore sixes.  Yours without the Merlyn will tend to bootstrap, that is, changing one engine setting, such as mixture, will cause others to change, and then the various components chase each other.  It is hard to get it to balance at LOP.  We do not have tuned induction systems, so fuel flows to each cylinder are going to be different from the others and will vary with MP and altitude, etc. etc.  Right now, I am running 100-125 ROP and in the mid-14 gph range most of the time.  Lower if I am at 65%, but on a long trip I hardly ever use 65%, too slow.  I will use 65% for short hops, but most of the time I am in the 75-80% range.

[kortopates]

Actually, on the TSIO-360's, the primer puts fuel into the intake manifold and its the high boost that put fuel directly into the cylinders (assuming the mixture is forward, otherwise you're just pressurizing and recirculating the fuel as you pointed out which is a good thing to do and recommended by TCM prior to a hot start, yet they recommend only long enough to pressurize). You should also see some additional improvement in starting if you wait 30 seconds after priming to let the fuel vaporize in the intake manifold a bit.

I wonder if ehscott ever got his/her lack of boost problem resolved. I'd consider 2.5" below full boost a serious issue if this is all you can get at take off - full boost is 36" on the 252 (not 35") and the turbo is barely working down low. Given they checked your Turbo and adjusted your fuel pump and I assume they adjusted the max boost set screw on the turbo controller and you kept mixture in to full rich at max MP -- what did the problem turn out to be?? Wastegate or ?