Continental GO-300 Engine Cylinder #2 not starting

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Error502

Filing Flight Plan
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tommy245
My dad and I own a Cessna 175 with a Continental GO-300 engine. When we ran the engine up, we discovered that cylinder #2 isn't functioning properly; its exhaust is cold, running at 200°F, while the other cylinders show exhaust temperatures around 800° to 1000°F and cylinder head temperatures between 300° and 350°F.

We increased the engine speed to 2000 RPM, and the exhaust temperature for cylinder #2 quickly jumped to 1000°F.

We've tried everything we can think of to diagnose the issue. We conducted a compression test, which was fine. We checked the spark plugs, and they were also in good condition and sparking. The mag timing checked out, and we experimented with running the engine both lean and rich. Additionally, we inspected the valves and found none were stuck. We also checked the balance tube and ram horns for blockages, and everything appeared clear.

We would appreciate any help in figuring this out considering we have exhausted all of our ideas.

Thanks for your time!
 
Error502 said:
My dad and I own a Cessna 175 with a Continental GO-300 engine. When we ran the engine up, we discovered that cylinder #2 isn't functioning properly; its exhaust is cold, running at 200°F, while the other cylinders show exhaust temperatures around 800° to 1000°F and cylinder head temperatures between 300° and 350°F.

We increased the engine speed to 2000 RPM, and the exhaust temperature for cylinder #2 quickly jumped to 1000°F.

We've tried everything we can think of to diagnose the issue. We conducted a compression test, which was fine. We checked the spark plugs, and they were also in good condition and sparking. The mag timing checked out, and we experimented with running the engine both lean and rich. Additionally, we inspected the valves and found none were stuck. We also checked the balance tube and ram horns for blockages, and everything appeared clear.

We would appreciate any help in figuring this out considering we have exhausted all of our ideas.

Thanks for your time!
Click to expand...

Does this happen frequently or is this a one time event?
 
Static RPM ok?

Any roughness?

Take a laser temp and “shoot” the jug/ exhaust and see if different.

If it is different use a Lead Tester to check ignition Leads and Distributor

Block. A leaky water hose may still deliver some water. Same with Leads.

An ohmmeter will not tell you if leaking.
 
Seen a cleaned newly gapped plug do this. I’d try a different plug and see if the problem moves with it.
 
Error502 said:
We would appreciate any help in figuring this out considering we have exhausted all of our ideas.
Click to expand...
Does the engine run rough when #2 indicating 200?
Is the mag check good when indicating 200?
 
Further investigation required.

What do the leads to that cyl look like? Could be a short in the harness. Is there a plug not firing under pressure? Sometimes even if they’re cleaned and gapped perfectly, they might fail when operating temperatures get to them or there’s a crack in the internal ceramic. I suspect if it’s a cold cyl, there’s a weak spark.

Fuel? Check.
Air? Check.
Spark? Check.

It should start.
 
RyanB said:
Further investigation required.

What do the leads to that cyl look like? Could be a short in the harness. Is there a plug not firing under pressure? Sometimes even if they’re cleaned and gapped perfectly, they might fail when operating temperatures get to them or there’s a crack in the internal ceramic. I suspect if it’s a cold cyl, there’s a weak spark.

Fuel? Check.
Air? Check.
Spark? Check.

It should start.
Click to expand...
Compression, too.

-Skip
 
Is the idle smooth? If so, that cylinder is firing, you have a failure in the measuring system.

Try the hand test of the cylinder head temp after a minute or so of running, see if it is close to the other cylinder heads. Start with comparing the valve covers, then cooling fins of the cylinders If the cylinder is not firing, the difference is dramatic after only a minute of running.

With magneto's, both current and voltage go up as the RPM is increased.

Both mags, leads, and plugs having a similar problem only on the same cylinder is statistically unlikely, but.....

Swap both plugs from a different cylinder. Buy or borrow a long lead, and replace one lead.

The 175 is a fine plane, and if treated as the manual calls for, long time reliable. I have only flown as a passenger, but very impressed with the smoothness and power.
 
Ignition harness? Contact springs in the distributor block? When you say cold, is that measured with a no-contact thermometer or an engine monitor?
 
So we are using a JPI to monitor the engine. We touched the jug after running and it was very noticeably cold. We have swapped plugs around still the same problem with the #2 cylinder. We also tested the sparking on the leads and plugs and they were both sparking. While idling you can tell it is skipping a cylinder.
 
Bacho said:
Does this happen frequently or is this a one time event?
Click to expand...
Yes we've run it 6 times after trying a different solution still #2 cylinder not firing.
RyanB said:
I suspect if it’s a cold cyl, there’s a weak spark.
Click to expand...
We can check to see if the spark is weaker than the others. Unfortunately, we won't be able to get to the plane until Wednesday.
 
I'm not sure if it's covered with 'balance tube and rams horn'. There are a set of boots on the intake runners. If there is a leak at the boot, or the clamp the engine will run too lean at idle to fire, and then will pick up when the MP goes up. This is very dangerous, but if you take off the cowl, and use some starting fluid you can spritz it on the intake runners, and the boots, and also the manifold flange to see if the idle changes when you spritz starting fluid in various spots.

Alternately, take off all the boots, the intake runners, and the manifold for 2, and renew it all with new seals and boots and clamps. Safer that way. I had a GO-300 and had a boot leak developed after about 20 hours of ownership. I went around and found several of the hose clamps only moderately tight, as the boots will deform and shrink over time.

Edit to add, there should be a heat flange at the boot, protecting it from the hot exhaust pipe. Confirm that those heat flange plates are present. Some rebuilders, and some mech leave them off as they obstruct access to the boot clamps.
 
Check the idle mixture. Might be so lean that this cylinder just isn't getting enough to fire.

SImilarly, an intake leak could cause the same thing.
 
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