REFLECTOR: EGT Temps

[Chuck Jensen]

Becks,
 
The difference in EGTs may be....nothing.  The EGT values are easily influenced by the placement of the probe, among many factors.  First, check during cruise by turn off one ignition, then the other (but preferably not both at the same time) and watch your EGT profile.  All of them should move in sync, usually up.  You probably won't notice much change if you have electronic ignition on one side, but when you run on one mag, the EGT usually rises as the gas isn't fully burned in the cylinder and converted to power, but instead, some of burns as it leaves the cylinder because of poor ignition, thus raising the EGT.  
 
If all the EGTs move in unison, then do a standard lean test.  This procedure is available on the GAMI website but in brief, you set your fuel flow to a value above your usual cruise.  Then, in 0.2 to 0.3 gph increments, progressively reduce fuel flow.  If the cylinders are well balanced, they will reach peak temperature within 0.5-0.75 gph of each other, then start to fall.  If there is a wider spread, GAMI and some other provide calibrated injector nozzles that slightly increase/decrease the fuel flow to specific cylinders to balance them, resulting in more uniform peaking temperatures across a small fuel flow span.  The absolute peak temperature difference between cylinders makes little, or no difference--only the difference in fuel flow when each cylinder peaks..
 
If #3 and #4 are running hotter because of injector problems, this likely indicates that are starting to lean out (get hotter) than the other cylinders.  If they truly are running lean (and the difference is not just probe location), then during the lean test, these two cylinder's EGT will lean out (reach peak EGT) before the other cylinders.  If your fuel flow spread is wide, by the time #1 and #2 reach peak EGT, cylinders #3 and #4 will be leaned out so far that the engine may be running rough because they are loosing significant power.
 
So, if #3 and #4 really are running leaner, then you can check the injector and fuel servo to see that there's no partial fouling.  More detailed tests is to do a jar test on the injectors in which you collect fuel from each injector to see that they are uniform across all injectors, you might remove the valve covers and check to see that the valve movement is the proper.  If everything is in order, then you may need to change the injectors to bring the indicated temps together.
 
Best guess:  Probably just difference in probe locations/indication.  EGT differences of 70-80 degrees is not unusual (in my experience).  Differences in 70-80 degrees on the CHT would be a big deal.
 
Chuck
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-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On Behalf Of Jim & Sharon Beck
Sent: Saturday, April 23, 2005 10:42 PM
To: Velocity Aircraft Owners and Builders list
Subject: REFLECTOR: EGT Temps


I now have about 30 hours on my phase 1 173 RG with IO 360A1 B6 and electric MT prop It has the armpit scoops with the cooling routed to the top & then down draft. I wrote a feew months ago about cylinder head temps and the suggestion to check for leaks was the answer. all 4 cht now run below 34o and within 3 degrees of each other.
I notice that the # 3 & 4 cylinders ( closest to the firewall ) run about 70 to 80 degrees hotter than the # 1 & 2 cylinders would this be ainjector problem or possible just a hotter location in the engine compartment ! & 2 run within a few degrees of each other and 3 & 4 run about 5 degree difference.
any thoughts would be appreciated.  I bought this from Ralph Pierce, he did a nice job building it and I am having all the fun learning to fly it.
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