Partially Plugged Injector

[carqwik]

Hadn't flown my bird in several weeks...and as expected, my plane always reminds after any time off that it's not happy when I don't give it enough love....This time, it started ok, and ran well at low rpm but on run-up, it ran a bit rougher than usual although on both mag checks, didn't observe any cold cylinders (as evidenced by the JPI as well as the shaking that typically occurs).  Still, the the engine wasn't running as smooth as normal....but nothing bad.  So on takeoff, watched the JPI more closely than usual...as did my pilot pax...and lo and behold, the #6 CHT and EGT were highly elevated...1500+ EGT and 445 CHT.  Whoa....throttled back and landed.  Did another run up...seemed ok...tried again...and got nearly the same result on #6 but slightly improved...did one circuit in the pattern with a climb over the field and this time the EGT and CHT went too high....throttle back and land.

 

Thankfully, the local A&P was working and he came over and we did a compression check on the cylinder...got a 65 reading which is well below where it normally reads (about 74)...and could hear air coming through the oil filler.  This suggested an intake valve problem....and he wanted to pull the jug.  But that wasn't jiving with my thought processes.  Thankfully, my hangar neighbor...also an A&P IA...came by and when I told him the symptoms, he immediately said "plugged injector." 30 minutes later he found a spec of hard crud in the injector.  And it was just a spec, like a grain of sand.  So we ultrasonically cleaned the injector in Hopps 9 and reinstalled.

 

Flew the plane early this AM in the cooler Phoenix wx (75 degrees) and it ran just fine.  So in 30 years of flying, the first time I've experienced a plugged injector.  Lesson learned...but now looking for an expert to tell me why a plugged injector causes such high temps.  Wouldn't a restricted fuel flow result in lower temps?

[jetdriven]

Whoa, he wanted to pull the cylinder for a 65/80 compresssion?  Thats ridiculous.

 

Plus, air hissing in the oil filler is rings, not intake valve. 

 

And third, a bad intake valve you can see on a borescope.

[tony]

Why would a plugged injector cause low compression and air escaping out the oil filter?  I’d like to understand the logic.  Could it be possibly you have a broken ring and the crud on the injector is a byproduct of that?

 

 

 

 

[Cruiser]

snip.........

 

Flew the plane early this AM in the cooler Phoenix wx (75 degrees) and it ran just fine.  So in 30 years of flying, the first time I've experienced a plugged injector.  Lesson learned...but now looking for an expert to tell me why a plugged injector causes such high temps.  Wouldn't a restricted fuel flow result in lower temps?

 

Look at the attached image it might help to visualize what is happening when the injector is partially clogged.

A clogged injector will limit FF and move the EGT closer to peak EGT and beyond into the LOP range if it is severely clogged. As the FF is reduced (from full maximum flow at full power takeoff setting of about 250°F ROP) the EGT and CHT will get hotter and hotter to about 40°F ROP where the EGT continues to increase but the CHT will begin to fall. (this is the point of MAX PRESSURE) it is also the point of max CHT. These temps can be well over 400°F

 

So, while the other five cylinders were operating at maximum FF and pouring excessive amounts of fuel through the cylinders keeping them cool, #6 was not getting as much fuel because of the restriction in the injector, causing it to burn much hotter than the rest.

[carqwik]

Very helpful Cruiser.  I didn't think of it that way....but now I get it...it's like leaning the engine at full power...of course the EGT and CHT would skyrocket!

[thinwing]

Better monitor # 6 for a while...a clogged injector afetr a couple takeoffs hopefully not getting into detonation or preignition range do to excessive leaning....I would be concerned about a broken ring at this point...ie if you can definitely hear air enter the crankcase from a hot differential comp test...

[carqwik]

The #6 cylinder seems to be doing fine now....oil consumption is per the usual so....I will wait until annual to have Top Gun take a closer look at the cylinder.  Let's hope it doesn't need work...this year's annual will include complete replacement of the Kevlar O2 tank (life limit reached), mag overhauls, new spark plugs, and a fix for my  broken visor (probably the least expensive of the items...still, there goes $100).