252 MP and Fuel Flow

[JC252MB]

New to the forum and I've tried the search function for this issue. 

I've owned my M20K for about six years .  It's been very reliable and trouble free.  I have noticed that my MP available for takeoff has dropped to roughly 31 inches and while I thought that replacing the cracked #3 intake tube might help to recover some of the MP, it has not.  The cracked tube was an "ah ha" by the way and was not found on the most recent annual.  Engine time since OHV is 550 hours.

I'm seeing a fuel flow on take off of approx. 22 gal hr but when I lean to a TIT of 1450 in the climb I see about 16 gal hr.  CHTs are all hovering in the 340-360 range and the engine is quite smooth.  I just can't explain the loss of about 3 inches of MP.  Can this be an issue of the engine being set up too lean?  All of my compressions are 70's.

I run the airplane in cruise flight at 28 inches MP, 2500 RPM with a TIT of 1450 or so with a fuel flow in the vicinity of 12.5-13.0.  CHTs are right where I expect them to be and all the EGTs appear quite uniform.  True airspeed is within a couple of knots of what I'd expect as well.

Anyone have any thoughts as to where my MP is going and where to focus my search if this is indeed unusual given what I've passed along here?

Thanks in advance!

[Piloto]

Check that the waste gate is closing properly. Also on hot days the pressure will be lower.

José

 

[roundout]

Yep, sounds like a boost problem. Maybe a leak, maybe the wastegate not closing. I don't know a whole lot about the 252, so here's a question:

On the Bravo and Acclaim, the boost controller can only govern a certain number of inches of MP - outside of that it has to be manually adjusted. In climates where the airplane may operate in an extreme range of temperatures, typically it needs to be adjusted twice a year - once when ambient temperatures get cold and once when it gets hot. I don't know if the 252 has an adjustable controller like this. If it does, it might be set up for winter (cold, dense air) operations.

[jackn]

Roundout's comments are good. In my experience, I found the ships guages in my 252 not to be too reliable. If the plane is doing the book #s, you are prob ok.

[vasco]

i drive an O3.  What is your typical KTAS for your "... in cruise flight at 28 inches MP, 2500 RPM with a TIT of 1450 or so with a fuel flow in the vicinity of 12.5-13.0...." and what altitude do you typically fly.  Thanks.

 

[FlyingAggie]

On takeoff, I see MP of 36" with a fuel flow of 21.3 GPH and 2700 RPM in my 262.   In criuse and below 10K ft, I am leaning to a TiT of 1550 degF at 2500 RPM & 24" MP which gives about 10GPH and 155 knots.

At full throttle and full rich, what TiT do you see?

 

[roundout]

Quote: jackn

Roundout's comments are good. In my experience, I found the ships guages in my 252 not to be too reliable. If the plane is doing the book #s, you are prob ok.

[JC252MB]

Thanks to all so far.  Appreciate it!

The only time I'm really ever at full power and full rich is for take off which right now looks like 31 inches MP, 2700 RPM and about 1200 TIT assuming I don't lean to a more typical 1450 on the go.

I don't believe I'm running a reduced power setting as what I'm running in cruise is right out of the book for 75% power at 28 in. MP, 2500 and pretty much 12.8 gl/hr.

Yep, no doubt about the turbo spinning up on the takeoff roll.  Problem is....I only get 31 inches of MP.

I think tomorrow I point my A&P towards a possible sticking wastegate and/or a set-up issue at the boost contrller.

Flew the airplane today BTW from Northern WI to Southeastern MI (1:30).  Everything was very satisfactory at 9K (28 in. MP, 2500, 12.5 gl/hr, TIT of 1450 and all CHTs 340-360.

Thanks to all!  This is a great site.

[roundout]

Quote: JC252MB

Thanks to all so far.  Appreciate it!

The only time I'm really ever at full power and full rich is for take off which right now looks like 31 inches MP, 2700 RPM and about 1200 TIT assuming I don't lean to a more typical 1450 on the go.

I don't believe I'm running a reduced power setting as what I'm running in cruise is right out of the book for 75% power at 28 in. MP, 2500 and pretty much 12.8 gl/hr.

Yep, no doubt about the turbo spinning up on the takeoff roll.  Problem is....I only get 31 inches of MP.

I think tomorrow I point my A&P towards a possible sticking wastegate and/or a set-up issue at the boost contrller.

Flew the airplane today BTW from Northern WI to Southeastern MI (1:30).  Everything was very satisfactory at 9K (28 in. MP, 2500, 12.5 gl/hr, TIT of 1450 and all CHTs 340-360.

Thanks to all!  This is a great site.

[Earl]

I am glad to hear I am not the only one with this problem on a 252.  Right after I installed a JPI-730 I noticed I can only make 33" to 34" MP at max power on takeoff (i do not read MP on my JPI and use the OEM gauges).  Have been troubleshooting the problem and it seems the best explanation is the wastegate is sticking.  You have all the same facts as me - other than the MP being low the plane appears to be running fine.  I spoke to one MSC and he thought that either the controller was not working properly or the wastegate sticking was the problem.  Exchanged emails with Mike Busch and he thought the wastegate sticking was the more likely cuplrit.  If it doesn't close all the way at full power you won't make full MP.  But it works fine at altitude.  I miss that little boost of power when the turbo kicks in on takeoff and it hits 36" MP.  Will have it checked at my next annual unless something else seems to go awry.

[glbtrottr]

You may find that you're running a little hotter than you want.  

Book max for the TSIO360MB is right around 22.8/23GPH on full power takeoff if you look at the back of your TSIO360 manual. 

I used to lean to 1550 based on Krom's and other's previous settings.  

Now, I fly 150ROP or 50LOP, 28/24.  If you're flying at such low power settings, you may consider flying LOP and check your results...

Quote: FlyingAggie

On takeoff, I see MP of 36" with a fuel flow of 21.3 GPH and 2700 RPM in my 262.   In criuse and below 10K ft, I am leaning to a TiT of 1550 degF at 2500 RPM & 24" MP which gives about 10GPH and 155 knots.

At full throttle and full rich, what TiT do you see?