If the spread of cylinder peaks is too great your engine won’t run smoothly lean of peak.
Next time you fly do the GAMI lean test:
But plan on buying GAMIs. You’ll be very lucky if you can run LoP without them.
Yes to above.
I suggest Howard you go up for a flight, on a nice smooth day, say 5000ft, set 24"/2400 like at present (which at peak EGT is somewhere around 65-70% of max rated power for you), start with the fuel flow at 60 litres/hr (which should be well ROP), wait a minute for the EGTs to settle, and write them down. Then reduce fuel flow by 0.5 litre/hr, wait a minute, and write them down again. Repeat this until the engine starts to run quite rough, or the airspeed starts to really drop off. Probably about 35 litres/hr…
You can fly on different headings; the plane or the engine knows nothing about that. But keep out of cloud because both OAT variations and moisture will bugger up the data collection.
You should get something like the first picture in this thread e.g. the individual cylinders will be peaking at different points.
Then send that to GAMI and they will send you a new set of injectors. These are just like the standard Lyco injectors (but they are shiny 
) and you just get your mechanic to screw them in.
Then repeat the above flight test.
A more lazy procedure is to use the EDM700’s data logging feature to record the EGTs while you are very slowly leaning the mixture from 60 down to “whatever” litres/hr, but (see that thread) that produces pretty rough data, because – stupidly for the 21st century – JPI don’t log any change until it exceeds 5F from the last value. It’s still possible to do it that way, espcially if you are just looking for a crude indication, but I would recommend the manual way.
Thanks everyone.
In answer to the questions I was measuring EGTs, and leaning to rich of peak.
I’ll do the data logging that Peter helpfully suggests and move forward with GAMI injectors. I’ll report back because that might be helpful for others.
Howard
Howard,
What engine monitors sometimes do is when you are a bit too fast and sloppy, it shows a “phantom peak” and if you then focus around that peak while setting 100 ROP, you might actually end up at 200 or 300 ROP.
When the numbers don’t make sense, just start over and do it again, a little more slowly.
What I also always say is that pilots, especially owner pilots, should not only focus around peak and the relative numbers around it, but also every now and then take note of the absolute numbers. In other words: know at which absolute EGT your engine normally peaks. Then, you will also know what say 100 ROP should look like on your EGT gauge.
Another possible reason for what happened is that one injector was partially blocked, leading to it peaking very early and then leaving you with a way too rich mixture, even though, technically speaking you were 100 ROP.
What I also always say is that pilots, especially owner pilots, should not only focus around peak and the relative numbers around it, but also every now and then take note of the absolute numbers. In other words: know at which absolute EGT your engine normally peaks. Then, you will also know what say 100 ROP should look like on your EGT gauge.
That’s a good tip, but the peak EGT value varies a lot with altitude.
So it may be 1500F at low level, say 5000ft, and 1400F at say FL170. And it is a lot more important at FL170 to be able to set 130F ROP (best power) fairly quickly – when trying to set up a climb above some wx.
I find it more convenient to memorize fuel flow values instead of absolute EGT values
Before fitting GAMIs, I would ensure that there is no other issue causing fuel/air ratio imbalance, such as an induction leak, dirty injectors, or spider issues. Otherwise the GAMIs injectors may just mask another problem.
To exclude an induction leak you can do the following:
Fly at two different altitudes, first at 9,500 feet, and the second at 3,500 feet.
At 9,500 feet:
You have an induction leak if the EGT peak order is different at 9500 and 3500, unless your GAMI spread is very low (unlikely without GAMIs, but possible out of factory for IO540 if lucky).
To exclude other fuel imbalance issues, you can do a jar test. Stick fuel lines (with current injectors attached) into a jar, turn on electrical fuel pump for a few seconds, and squirt fuel into jars, then measure amount of fuel collected in jar, which should be the same.
Only after induction leak has been excluded, all other components function as expected, and fuel/air ratio imbalance is indeed sub-optimal, would I consider GAMIs.
We had a meeting at my club yesterday with a discussion about leaning techniques. One of the participants was a mechanic with 40+ years experience in maintaining light aircraft and who did all maintenance for my club until he retired last year. He is also a pilot and owns a number of aircraft.
He was strongly of the opinion that you should not lean to peak EGT as that would cause burnt exhaust valves. He conceded that it would be all right if you had CHT gauges and were careful with the temperatures, but if you didn’t have that, you should not lean to peak EGT even on relatively low-powered engines like a Lyc. (I)O-360.
Instead, he said that it was best to lean to 50°F on the rich side if you wanted better economy than maximum power (typically 100°F rich).
I have a lot of respect for his experience, but both these pieces of advise are counter to most of what I’ve read about engine handling – particularly 50°F rich of peak EGT should give the highest cylinder temperatures!
If we had the minute by minute operating data (all CHTs, all EGTs) for 100 engines that were consistently operated in a uniform way for 1000 hours each, we might be able to compare their conditions at the end of the test period, and come up with a hazard ratio for the different methods of operating. No one has a small fraction of that data. Your mechanic has probably seen a lot of burnt exhaust valves and is creating his own narrative as to the cause.
Without good data, one can only hypothesise based on underlying mechanisms. The mechanic seems to be saying that 50 degF makes a significant difference to the lifetime of the valves, even though he doesn’t know what the absolute values of the EGTs are. The EGTs on our engines have a greater spread than that between cylinders, and there’s certainly a greater difference over a range of power settings.
Lycoming permits leaning to peak EGT based on 50 years of service experience. I see no reason to doubt Lycoming’s guidance.
It is interesting to talk about temperatures and an aircraft without an EGT gauge in the same discussion, because of course the reality is that without a means of monitoring the EGT and CHT of each cylinder you really have very little idea of how each cylinder is running. As you probably know it is virtually impossible that every cylinder will be running at the same temperature so inevitably one will be running at a higher temperature than the rest.
You will read a lot of very good technical discussion on here about the best approach, but you will find the discussion between pilots is in cases where they have very good instrumentation for monitoring each cylinder.
Unfortunately with most rental fleets the aircraft are less well fitted. Also most engineers will tell you that inevitably most rental fleets are far more “used and abused”. It is not that everyone doesnt care, I dont believe that for a moment, but there are some that dont, and more that have been poorly taught how and when to lean an engine.
So, for all of these reasons, I think most engineers will support running an engine cool of ideal so there is a healthy margin built in and the risk is not run of overheating a cylinder which will be far more costly than the extra fuel consumed and the other issues associated with running the engine cooler.
