J with fuel control problems

[cliffy]

I got this from a friend who's fighting the issues. He keeps his airplane in good shape (or tries to);

I thought this might be a good read of issues that can pop up even with good maint.

The names have been changed to protect the innocent :-)

 

In Dec17, XXXXX fitted an IO360 A3B6 engine in place of an A3B6D.  The engine was a Lycoming factory overhaul that was completed on 25 October 2017 and installation was complete on 1 December 2017.  The initial startup was good except that the fuel pressure was pegged beyond maximum.  The cause was that Lycoming had used a different model of mechanical fuel pump that was supposedly functionally equivalent to the pump on the previous engine.  That was not true as the pump ran at 35psi when the maximum for the Mooney 20J was 30psi.  XXXXXX then paid for the fuel pump to be replaced by XXXXXX with the pump from the old engine and for its replacement in January 2018 with a new fuel pump of the original model.

Ever since this engine had been fitted, the Shadin fuel flow system had indicated flows at 10-15% higher than actual.  The attached graph shows fuel flows on flights with the previous and current engines.   I have attached EGT, CHT, FF and Oil Temp data for a flight on 7Jul17 and another on 23May19.  They show EGT and CHT about the same but with a tighter spread on the new engine (prob due to new baffles).  Oil temp is a bit lower on the new engine and fuel flows in cruise (75 ROP) are 11-12GPH indicated vs the previous 10.5GPH.

In April 2017, XXXXXX cleaned the injectors to try to correct the issue but no change.  Shadin suggest that such over-reads may be due to air getting into the system upstream of the transducer and subsequent investigations have sought to identify and rectify such leaks.

With the previous engine over 1500 hours in 12 years of flying, I'd never had any occasion where it would not start hot or cold so it seems to be a quirk of this engine, not technique.  Also, for the first 5 months and 70 hours, the new engine started normally hot or cold. 

The hot start problem first appeared on 30 May 2018.  After re-fuelling, the engine would not hot start.  The engine coughed but would then not respond to future cranking.  The Shadin indicated zero fuel flow when the fuel boost pump operated.  The pump did not sound like it was pumping fuel and extended use (two minutes) of the fuel boost pump had no effect.  Even after repeated cranking there was no sign of any fuel overflow.   After waiting about 30 mins, the engine started normally.  This pattern had continued right up to the present. 

The tight cowling of the engine is part of the problem.  It can be demonstrated by simply leaving the aircraft for 10 minutes after a long flight and 90% of the time it will then not start.  However, in the time it takes to remove the cowls and belly panel, the problem will have gone away. 

On 23Dec18 (after 131 hours since install) the aircraft was at XXXX and would not start after re-fuelling even after being left to cool.  XXXX XXXX removed the LH magneto and XXXX then inspected and tested it.  He also cleaned the injectors and checked the fuel distribution but found no fault.  When re-assembled and started, a new issue presented itself.  The engine ran very rough, would not shut down using the mixture control and had to be shut down using the fuel selector.  The FCU was removed and went to XXXX for repair (see account attached).  The mixture lever connection to the FCU was found to have disconnected internally.  When I spoke to him, the repair technician was uncommunicative about the likely cause of the problem as I think he suspected it might become a warranty claim.

In April 2019, the Boost Pump appeared to show signs of leakage and was replaced by XXXXXX with an overhauled pump.  In May 2019, XXXXX inspected the fuel lines for correct routing and evidence of leaks but there was no sign of any fuel leaks. 

In November 2019, XXXXXXX replaced the seals on the fuel selector and the gascolator o-rings, cleaned the injectors and removed the fuel boost pump for specialist inspection (no fault found).  He also fitted a heat shield to the Shadin transducer as it is installed close to the exhaust.

On 24 December 2019, painting work had just been completed at XXXX and I started it and taxied a short distance and re-fuelled.  The engine (after 235 hours since install) showed the usual pattern where no fuel flow was indicated on the Shadin.  After about 45mins of occasional checking, fuel flow again showed on the Shadin but the engine would not start.  XXXXX tried starting it but the engine would not respond to hot start or flooded start technique.  He removed the cowl and the lower plugs were clogged with fuel.  After clearing and re-fitting, the engine would still not start and a significant quantity of fuel was running out the overflow.  This pattern was identical to that experienced at XXXX a year earlier (I have a video showing the sequence from that time).

On 25 December 2019, XXX tried and the engine started and ran normally.  Note that he’d not usually working on Xmas day – he had to feed the cat!  

On 26 December 2019, the engine started normally but as I was doing my pre-takeoff runups, the engine suddenly began to run VERY roughly and was not making enough power even to taxi.  I noticed during this time that the MP was at atmospheric.  Cylinders 2 and 3 were intermittently showing on the EDM700.  When I decided to shut down, I found that the engine would not shut down with the mixture retarded to idle cutoff.  Instead, keeping the mixture at idle cutoff meant that the engine, while still very rough, produced enough power to taxi back.  I was told by people watching that the exhaust was emitting black smoke throughout the 10 minutes that the engine was running.  The A&P checked that the mixture and throttle were operating to the stops as well as checking the plugs, etc.   Both A&Ps that saw it believe that it was an FCU issue and the unit has been removed for service.

 

 

[elimansour]

OMG.  That is a terrible ordeal.   Hope the FCU repair will take care of this.  

[ArtVandelay]

So much for factory overhauls being better.

[takair]

from reading a bunch of threads on fuel servos, it seems like a number of them go back for service multiple times.  In another thread, we discuss max fuel flow.  It seems it is ill defined and I didn’t even find it in the servo service manual.  When he gets it back, I would try to compare fuel flow to the independent airframe and engine power to flow charts.  Previous experience may not be right either....although it sounds like it was close.  Hope they sort it out for him.

[larrynimmo]

I installed a factory rebuilt IO360A3B6D engine September 2018....over time my Fuel Injection Servo got to be almost too stiff for the linkage...under warranty through AirPower back to Lycomming, I sent my servo next day air to a company in Florida and they next day aired it back to me the same week.  Airpower paid $380 for labor and shipping.  Havent had any issues since.

To me....your issue is in the Fuel Injection Servo and it needs to be rebuilt....when you pull the mixture button out, it should 100% starve the engine to quit...period.

When I shut down my plane, it will maintain its fuel pressure for at least 12 hours before it finally bleeds down.

[PT20J]

It sounds like a few things might be going on.

The fuel pump high pressure problem happened a few years back. Lycoming had solved it by the time I got my A3B6 in October 2018. Anyway, it appears that issue is corrected by replacing the fuel pump.

Fuel flow transducers can get flakey after 20 years or so. Was it replaced at the time of the engine replacement? I would check the actual fuel burned from the tanks with the Shadin fuel used to see if it is reading correctly. It sounds like it is reading zero during priming when in fact fuel is flowing and flooding the engine.

At some point, Lycoming switched from Precision Airmotive RSA fuel injection systems to Avstar (which is a copy of the RSA). I have the Avstar on my factory rebuilt and it has worked fine. But, it sounds like the idle cutoff at a minimum is a problem. This should have been a warranty issue with Lycoming, but it looks like it is out of warranty now. I'd find a good shop (maybe not the last one you used) and have the system thoroughly checked out on a flow bench.

Good luck,

Skip

[cliffy]

The fuel servo is in a shop now from what I was told