Fuel flow issue

[dtoelke]

I am having a fuel flow issue and was hoping y'all could help me pre-diagnose before I send it over to the shop.

 

Flew from CA to CO on Friday.  Flight went fine, no issues whatsoever.

 

I started up in CO today to take my dad around for a spin before I fly back home.  On climb I noticed unusually high CHTs, to the point that I had to back off power to 60-70 percent to keep them under 390.  Brought the plane around and landed.  Once I had my dad out of the plane and was ready to head back to CA I tried to start it again.

 

I've used a structured hot start procedure since day 1 and it's never failed me (circulate fuel line, then prime and start).  This time it didn't work.  Itook a disgusting number of tries, with the engine almost catching a couple times but always seeming starved for fuel despite a full rich mixture.  Eventually I got it going (after a jump for my dead battery) by getting on the primer after it caught.  This is something I've NEVER had to do before with the starting procedure I use.  The DA was about 8000 ft (75 deg at 6000 ft).  For reference, I've been at much higher DAs and not had this issue.

 

Anyways, I finally got it started and took off again.  First thing I noticed (should have noticed before) is that the FF was lower than usual (18-19 GPH vs the 23ish that I normally see at 36").  Bam, that explained the high temps since the mixture is too lean (by why).  I reduced power to 70 percent, pulled LOP and climbed at 300-500 FPM to cruising altitude.  The rest of the flight I noticed the following items:

 

1) The FF did not want to stay put.  It would regularly drift between 8.7-9.1 GPH with my usual cruise setting (65% LOP).  Normally it's rock solid wherever I put it.

2) The cylinder temps were not steady either.  Again, usually after 10-15 minutes in cruise they settle in and remain there for the rest of the flight.  This time they were all varying by 15-20 degrees, one of which was causing me fits because it would occasionally move up through my alarm setting of 380 into the 390s with little warning.

3) The mixture control was "soft".  By this I mean that the changes that happened to my fuel flow (as monitored by a JPI830) were not representative of my movements of the mixture control knob.  Sometimes I could turn the damn thing a half turn and get no change to the FF, other times I would move it a fraction of a degree and the FF would jump (or fall) almost 0.5 GPH.

4) The cylinder temperature spread was atypical.  I'm familiar with the temperature spread across the cylinders during cruise and today they did not look normal.

 

My first thought would be that the engine driven fuel pump is bad.  Unfortunately my M20K does not have any fuel pressure gauge or indicator so there's no easy way for me to tell.

 

Any other thoughts?

[carusoam]

See your mechanic...

Determine what is not working compared to standard settings for your plane's engine...

Check mixture control and throttle control to see if they are worn or frayed.

Look at fuel pumps and their drains for indications of fuel leaving the system.

Something is not the way it needs to be.

I am a PP, not a mechanic...

Best regards,

-a-

[N201MKTurbo]

My fuel flow was misbehaving similar to what you described. I disassembled the fuel flow sensor and all the fittings, cleaned them all up and reassembled them all with Fuel Seal. That fixed the problem. I think that there was a tiny leak and it was sucking bubbles into the sensor.

My problem had all the symptoms of a bad sensor, no anomalies in engine operation, just unstable fuel flow readings.

[carusoam]

The OP got higher CHTs to match the lower FF readings.

It seems to be an actual lower FF instead of an error in FF reading.

Definitely would be nice to have a FP gauge to go with the other instruments for troubleshooting purposes.

I'm still not a mechanic.

Best regards,

-a-

[kmyfm20s]

Did you happen to try you electric fuel pump to see if it boosted the FF?

[carusoam]

At full throttle, does the electric pump come on automatically for the K?

Look for the switch to see if it is operating properly.

KMYF, Any idea where our FT sensor is located?

Best regards,

-a-

[garytex]

Don't screw around with that, get it fixed, preferably on the field. That one could bite.

[kmyfm20s]

At full throttle, does the electric pump come on automatically for the K?

Look for the switch to see if it is operating properly.

KMYF, Any idea where our FT sensor is located?

Best regards,

-a-

Follow the fuel line out of the fuel pump it will go the the transducer which is mounted in the middle of the firewall.

[kmyfm20s]

-a- Here is a SB on some latter ovations that shows the location.

http://www.mooney.com/wp-content/uploads/2014/03/m20-290b.pdf

[carusoam]

KMYF,

Got that...

I didn't make my point clear enough...

How does the engine sense full throttle to have the electric fuel pump turn on?

If the K has this same feature that the IO550 has, the OP may want to see if it is operating.

And of course, as Gary clearly stated, on the ground prior to flight...

Running full throttle with a lean condition can melt Pistons. A high CHT is only a hint at what might be happening at the piston.

Best regards,

-a-

[Guest]

I'm not trying to be critical.

You got a way with one flight with your father on board in which you discovered a problem. Why after having a hard time starting, to the point you drained your battery and needed to boost it you manage to get it started and fly it again. I hope not home to California?

The fact that all cylinders are showing higher CHT would suggest that it's not clogged fuel injectors, 6 would be very unusual. Something has gone wrong in the fuel supply or the metering system, either the pump has lost pressure or the metering valve at the throttle butterfly. Have SID97-3 carried out on the engine, this should help determine the cause.

Lastly don't be surprised if your next oil filter contains metal, I've seen 2 similar cases where the gears in the back of the engine were damaged by prolonged starting attempts, in one case the pilot cranked until there were no teeth left on the gears, the engine was toast. The gear train is lubricated by splash oil once the engine is running.

Clarence

[wpbarnar]

Your fuel pump is highly suspect. The mixture control is incorporated into the fuel pump on a TSIO 360. As Clarence suggested have TCM SID97-3 performed first. Use a mechanic or shop that is experienced with this TCM fuel system. Trouble shooting by someone without experience will be time consuming and expensive. If the fuel pump is bad, your best bet is to send the fuel pump to TCM for overhaul. They do not sell individual components for that pump so your favorite overhaul shop may not be able to overhaul it properly. My comments are based on a recent experience with my K model.

Bill

[dtoelke]

Thanks guys.  I will pass this along to the mechanic!

[kmyfm20s]

KMYF,

Got that...

I didn't make my point clear enough...

How does the engine sense full throttle to have the electric fuel pump turn on?

If the K has this same feature that the IO550 has, the OP may want to see if it is operating.

And of course, as Gary clearly stated, on the ground prior to flight...

Running full throttle with a lean condition can melt Pistons. A high CHT is only a hint at what might be happening at the piston.

Best regards,

-a-

Sorry miss understood you. Im picking my plane up from its annual tomorrow I will ask the question. I thought you where inquiring the location to visually inspect it as suggested above.

[kortopates]

Sorry miss understood you. Im picking my plane up from its annual tomorrow I will ask the question. I thought you where inquiring the location to visually inspect it as suggested above.

FWIW, The K does not have the same switch to turn on the electric fuel pump as does the Ovation setup. Plus the fuel pump is in front of the engine in front of the #5 cyl and the transducer is also up there above #5 cyl unlike the ovation/eagle with pump in the rear. Very different, not to mention a NA fuel pump is also a different from a turbo fuel pump.

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[M252]

I have a different fuel flow issue on my M20K 252: Until recently I had a fuel flow of 10.6 GPH at 65% with TIT around 1500F and very reasonable cylinder temps (By the way ROP POH values). Recently my engine control cables were replaced with new ones, the wastegate and controller were overhauled, and a new starter adapter was installed. The fuel flow at 100% take off power was adjusted to be ~24 GPH (all work performed by a qualified shop at my homebase)

 

However, at 65% cruise I now need to to lean to 9.6 GPH to see the same TIT and other engine temps as before.

 

It looks like that my fuel flow transducer is suddenly off by 1 GPH, i.e. it shows a fuel flow that is 1GPH too low.

 

Has anyone seen that before? Any recommendations?

[Andy95W]

Need some more information.

1.) what type of fuel flow gauge, the original factory or an aftermarket fuel flow/totalizer like a Shadin or JPI?

2.) when you fill up the tanks at the pump, which value is more accurate, the 9.6 or the 10.6?

[M252]

It is the original gauge.

The fuel consumption at the pump indicates that 10.6 is more likely. Thus the indication appears to be 1 GPH too low.

[Andy95W]

Unfortunately, I'm not familiar with that gauge and where it derives its information.

We're going to need someone to weigh in who knows if there is an adjustment.