Intake Leak?

apkp777 · #1 08-27-2010, 06:34 AM

My indication.
Full power WOT all my EGT's are even about 1250-1300. #3 cylinder leads the rest by about 50 degrees (hotest). If I bring the throttle back about 1" and 80-85% power the #3 EGT skyrockets to as much as 1500, while the others remain around 1300. If I continue to power back to 70% or so all the EGT's come back together.

My steps so far
Now I know that this is consistent with an intake leak. So I disassembled my intake and cleaned and reinstalled. The tube seal was fine and no evidence of leaking. The intake gasket, also fine and no evidence of leaking. The tube flange also looks fine. I really can't see any evidence of a leaky #3 intake.

Thoughts
My #3 cylinder does have the manifold pressure pick off for both the sender and the P-mags and it also has the primer nozzle (also on #1) I did read someone suggested spraying some ether around the intake while the engine is running. I will do that also. I also realize that this could be a EGT sensor issue.

Question
Is it possible that the MP and or Primer has anything to do with this? My next troubleshooting step will be to disconnect both, but is seems like a real "shot in the dark". Does anyone have any thoughts.

647jc · #2 08-27-2010, 05:59 PM

If you have an electric primer solenoid valve insure it is installed with the flow in the correct direction. If installed backwards it will work but the valve can be "sucked" open under certain circumstances. I would also swap plugs between #3 and another cylinder if you have not already done so.

apkp777 · #3 08-27-2010, 06:44 PM

Quote:

Originally Posted by 647jc

If you have an electric primer solenoid valve insure it is installed with the flow in the correct direction. If installed backwards it will work but the valve can be "sucked" open under certain circumstances. I would also swap plugs between #3 and another cylinder if you have not already done so.

That's a thought. I will double check the primer installation. I do know that the #1 and #2 ports on the primer solenoid are backwards. #2 is in and #1 is out. I will take a peek. Swapping plugs is also not a bad idea.

174Bob&Nancy · #4 08-27-2010, 06:58 PM

I have bee having similar problems along with the engine stumbling a little on the take off roll after it gets warmed up,pulled the intake tubes replaced the gaskets,checked the timing,slick mags set on 25deg.tonight i pulled the plugs and found 3 with cracked insulators,dont know whats causing this, i had a top plug do this earlier this spring,i ussually run 23" and 2350-2400 on the rpm,and ussually keep the egt below 1350,i am running a constant speed prop,long story short i would clean and inspect the plugs.

aerhed · #5 08-27-2010, 09:14 PM

Aircraft engines don't have perfect induction systems. Most will exhibit substantial flow variations at different throttle valve positions. It is quite normal to see fuel flows and temps shift around at different power settings. Some engines way more than others.

apkp777 · #6 08-28-2010, 05:53 AM

Quote:

Originally Posted by aerhed

Aircraft engines don't have perfect induction systems. Most will exhibit substantial flow variations at different throttle valve positions. It is quite normal to see fuel flows and temps shift around at different power settings. Some engines way more than others.

If I had to make a conclusion right now, I'd like to say what I am experiencing, as far as indication goes, is "just the way it is". I just can't find a leak. Knowing a bit about NA induction, I totally agree with your statement. Still it makes you crazy when you see the pretty green bars turn to yellow then to red while your flying around.

I recently read somewhere that as long as your CHT + EGT is below 1800F you don't have anything to worry about. Does anyone have any thoughts on that?

AK4x4 · #7 08-28-2010, 08:49 AM

I would recomend the following Max tempurature limits:
Cylinder head 500? F (well-type thermocouple)
EGT 1500? F (probe ~3" from exhaust flange)
for cruise flight:
Cylinder head 400? F (well-type thermocouple)
EGT 1350-1400? F (probe ~3" from exhaust flange)
Good Luck, Russ

apkp777 · #8 10-05-2010, 05:30 AM

An update on my "induction leak". Here's what I did and the results

1. Disassembled and reassembled with new gaskets induction tubes - nothing.

2. Disconnected primer system - nothing

3. Switched to BR8EIX plugs from BR8ES - ran smooth at LOP.

4. Used the "Larry Vetterman" 2 cycle oil induction leak detection method - Nothing

5. Compression test - 78/80 (cold)

Now here's when I broke the rules for troubleshooting and made a "shotgun" approach.

6a. Removed "jumper on P-Mag" now running most advanced setting
6b. Installed Vetterman Mufflers
6c. Relocated EGT probe on #3 cyl from 5.75" from flange to 2.5".

Results: #3 cylinder EGT now is peaking at 1380 or so. Before I could easily see 1475 at part power settings. For the first time in 100 hours of flying I am very happy about my EGT's. #3 still leads the rest until I am leaned out and all of the cylinders come into balance.

Unfortunately....Now my cruise CHT's are high! (#4 cyl. 413 at 55 OAT) So, the story of the "intake leak" ends and now begins the "High CHT". I will start to tweak my air inlet air dams and see if I can bring #4 down and #1 up. Next, I am going to reconnect the "jumper" on the P-mag.

N54SG · #9 10-05-2010, 03:13 PM

3 things..

#1 All of your EGT probes should be EXACTLY the same distance from the port. If not, you can't really compare anything between cylinders.

#2 Adjusting timing always changes EGT's. More or less "fire" in the pipe generates higher or lower EGT's.

#3 Advancing the timing can result in detonation.. Oil temps go up? Be careful.. Peak cylinder pressure happening early makes a good grenade. (And lower EGT's from my experience)

apkp777 · #10 10-05-2010, 05:40 PM

Quote:

Originally Posted by N54SG

3 things..

#1 All of your EGT probes should be EXACTLY the same distance from the port. If not, you can't really compare anything between cylinders.

#2 Adjusting timing always changes EGT's. More or less "fire" in the pipe generates higher or lower EGT's.

#3 Advancing the timing can result in detonation.. Oil temps go up? Be careful.. Peak cylinder pressure happening early makes a good grenade. (And lower EGT's from my experience)

#1 Correct - However, I wanted to see if moving #3 had any effect before I relocated the others (rather have 1 extra hole rather than 4). Now that I see the results of the relocated probe, I will go forward with relocating the rest.

#2 Correct - I expect the EGT's to come down and CHTS to go up. I didn't expect #3 to drop by 100F. The others changed marginally. CHT's went up significantly. 20-30F. I am a bit concerned about that.

#3 Correct - Excessive advance can lead to detonation and I am concerned with that. However, many P-Mag operators are have great success with the full timing advance features. I didn't see any change in oil temps.