Induction Leak Test: Interpreting Results

[Jeff_S]

Hello all,

Yesterday I had occasion to try out Mike Busch's induction leak test just for fun, to see what my results might be. This appeared in the January edition of the EAA Sport Pilot magazine. To quickly summarize the test, at an altitude of ~5000' MSL, he says to run the engine at WOT and a reasonable RPM and record the EGTs for each cylinder, then reduce MP by 10" and repeat measurement. What matters are not the absolute EGTs but the differences between cylinders, as this determines whether or not there is an induction leak (less change indicates possible leak because cylinders are still getting close to full MP even with throttle reduction). Oh, all tests also run full rich mixture.

That said, here are my readings from my IO-360 in my J, which at 5500' yesterday was showing 24.5" MP at WOT:

                 Cyl 1       Cyl 2       Cyl 3        Cyl 4

WOT         1129       1155       1141         1148

14.5" MP   1165       1147        1157         1186

Delta         +36         -12          +16          +38

So interestingly, #1 and #4 were pretty close, and #2 & #3 were also pretty close with #2 the only one showing cooler temps. There was no guidance in Mike's article about how much change in EGT would be meaningful, and I'm curious why the #2 would be cooler while all others are hotter. The engine is running as fine and smooth as it ever has so I'm not concerned about anything, but just curious how others may interpret this data.

Any thoughts are welcome....thanks!

Jeff

[MooneyMitch]

Hi Jeff. 

Below is the quote from the induction leak section of Mike's article.

Here's the principle behind this test: At the high-power setting, the induction manifold pressure is very close to outside ambient pressure, so any induction leak will have little or no effect on engine operation. At the lower-power setting, the manifold pressure is considerably lower than outside ambient, so any induction leak will cause the affected cylinder (or cylinders) to run substantially leaner than the others.

It's quite possible I am misunderstanding his information, but based on the following section of his writings, your colder cylinder is leaner and could be an indication of an induction leak on that cylinder.

so any induction leak will cause the affected cylinder (or cylinders) to run substantially leaner than the others.

I'm open to learning of course.

[carusoam]

Stating what might be obvious by observation....

 

I see that cyl #2 is not inline with the other three.

 

Possible suggestions:  Chech intake runner seals for age effects.  Take a look at thermocouple placement compared to others.

 

Running ROP, the leaker should run hotter.  Your data indicates the opposite.

 

Other thought....

How balanced are your fuel injectors? how many hours since the balance has been checked?

 

 

Best regards,

 

-a-

[KSMooniac]

I'm having trouble envisioning how this test shows anything useful.  The GAMI Lean Test is a better place to start IMO, and if it runs LOP smoothly down to 50 LOP (or greater) then you don't have an induction leak.  Most IO-360 Lycomings seem to run fine LOP provided the ignition, fuel and induction systems are up to spec.

[Shadrach]

Quote: KSMooniac

I'm having trouble envisioning how this test shows anything useful.  The GAMI Lean Test is a better place to start IMO, and if it runs LOP smoothly down to 50 LOP (or greater) then you don't have an induction leak.  Most IO-360 Lycomings seem to run fine LOP provided the ignition, fuel and induction systems are up to spec.

[jackn]

I also ran the same test the other day.

first, let me address your results; Three of your EGTs increase approx same. I have TCM not Lyc so not sure of your cyl config, but if #2 is in front & exhaust pipe is in the front(exposed to the air coming into the cowling), that would certainly account for 2 getting colder when power is reduced by 10".

On my turbo I dont want to pull off 10" so I used 3". this gave me an equal EGT rise in all 6 cyl, Therefore no leak.The reason I was tring this, is because I cant seem to get my plane to fly LOP, was trying to find out why. Can't seem to get leaner than 11 LOP before engine runs rough. Even at that I am losing 4-5 kts. I appolocize for hijacking your thead, but I posted a few photos of my LOP test. Maybe someone has any insights, especially Parker, who has a almost identical plane to mine, and who flys LOP all the time.

I used a low power setting so as not to hurt anything while experimenting.

Regards

Jack

 

 

[KSMooniac]

Jack, did you perform a full GAMI Lean Test?  It involves recording all of the EGTs and fuel flows while you lean in small increments (like 0.2-0.3 GPH).  That is the only way to determine if your cylinders have balanced fuel:air ratios, and if not, the data will be needed for GAMI to make a set of injectors for you.  That is the first step in answering your question...

[jlunseth]

@Jack - Probably you realize this, but the power settings in the first and second picture are identical, 2400, 24.9 MP and 9.5 in one and 9.4 in the other. The JPI is displaying in Rich mode in the 9.5 picture and in Lean of Peak mode in the 9.4 picture, but the tenth of a gallon difference in fuel flow is too small to be significant.  The third picture is the same power setting at 25 MP but fairly rich at 12. I agree you need to do a lean test and get GAMI’s if you don’t have them already, if you want to run LOP. That is a big first step.  The other equally important step is to make sure your spark is strong. Fine wire’s are much better than massives, mags need to be in good order and so does the harness. It does not take much in the spark system to prevent LOP running, and on the other hand, a good, strong ignition system will let you run well lean of peak in that engine.