Does a large EGT spread indicate fuel injection imbalance?
I have a 1972 Cessna Hawk XP II (R172K) with a Continental IO-360KB. I've been uploading my flight data to FlySto and it points out a signifiant spread in EGT for a couple of cylinders at lower manifold pressure. In particular #1 and #2 are routinely quite a bit lower. Seems to me that this might indicate a fuel delivery imbalance. I also have some challenges with keeping CHT for #3 below 400 on extended climb outs which also make me suspect an imbalance. Does anyone thing that GAMI injectors might help with this?
Comments
Based on just your snapshot here it's almost impossible to do much troubleshooting. Yes you have a big spread on one and two but as you indicated that's at a low manifold pressure so I'm going to assume that's off idle at about 12 to 1,300 RPM?
This series of engines is not known for good mixture balance especially at low RPMs. If you had this a cruise I'd be a little more concerned.
And 400 on CHT is still not too bad especially in climb. Lots of owners would love to have a temperature like that incline. Lol My questions would be when was the last time the fuel system was set up and checked, condition of spark plugs, timing there's a whole host of questions that would have to be answered. Induction leaks, sniffer valves. Condition of baffles. If that fuel system has not been checked and set up in recent memory it's probably time to at least start with a known baseline fuel pressure system.
And no my feeling would be gammies would not be an option at this point. Carl
IA 47yr A&P DAL A/C Inspector 172n
I have the GB version of same engine in my 175. EGTs are the wrong way to answer your question about fuel balance- there’s just too darn many variables. Assuming you have fuel flow capability measure it directly by just doing a GAMI lean test which in short calculates the fuel flow delta between first cylinder to peak and last to peak. GAMI website has the procedure. Mine was 0.75 gph difference which was low enough I’m not going to worry about tuned injectors.
Or just go through a couple leaning cycles and send the full data set to GAMI and they’ll analyze it for you.
My number 1 cylinder tends to run around 380F but will hit 405 on a hot day climb. I just lower the nose to climb around 110mph and run a bit richer than usual and that seems to do the trick. Make sure your baffles are a) there and b) in perfect shape plus the other stuff Carl mentioned.
BTW, when I’m at idle (on the ground) I aggressively lean until engine is on verge of quitting. The 1-3 cylinder EGTs don’t even register while the remaining are 2 or 300 degrees F. I don’t worry about the delta because they behave normally under power and the aircraft performs above book numbers for MAP/fuel flow/speed/altitude combinations.
I’m not an A&P and certainly not an expert but this is a topic I’ve studied on quite a bit. Look for YouTube or podcasts with Mike Busch or Paul New and read the articles by John Deakin at Advanced Pilot something (seminars maybe?). There are others but the above I find credible.
I do love flying this engine!
EGT spread may be totally meaningless as the temperatures displayed are not real temps. The possitioning of the probe makes a huge difference in the readings. The only way to understand cylinder balance is to perform a GAMi lean test.