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Help needed troubleshooting rough running O-320

TShort

Well Known Member
I'm hoping for some wisdom / assistance in helping a friend troubleshoot a rough running engine in his purchased RV-9.

Background: RV-9, carb'd lycoming o-320, dual mags, pretty much basic setup as per vans.

Jim bought the airplane earlier this year, it was pretty new with phase I flown off. Has about ~75 hours now. Aside from some warmer CHTs, the engine had been running fine.

Early Aug, he and a friend flew to a nearby airport for fuel. On return, (in the dark!) the engine began running rough. Runs rough at higher power, seems to smooth out if the throttle is pulled back.

I am going to link to engine data from 2 flights:

First, before any issues arose and the engine was running well (this was takeoffs and landings at our local airport):

https://savvyanalysis.com/flight/2718360/f4c36a28-d430-4f91-b8c4-e3f9159664d2

The flight where issues arose:

https://savvyanalysis.com/flight/2718364/e0d155ba-f206-471b-bf24-0a621ccead39

I am going to share the link with Jim so he can register / login and help answer any other questions. Not sure he is on VAF yet.

Thanks in advance for any thoughts / suggestions
 
Here are screenshots of the above flights (clicking the savvy links in the above posts takes you to the actual data, where additional parameters can be added / compared):

Normal flight:

29853592957_f07e232500_z.jpg


Rough engine:

29853591777_5a26c3cc36_z.jpg
 
Savvy analysis

Tell your mate Jim to dust the cobwebs out of his wallet and get Savvy Analysis to inspect the data. They are the absolute experts at this. Their opinion would undoubtedly be more valuable than any free opinions on this forum. ;)
 
As Kurt says, kinda high on the CHT's.
It would be very helpful to know at what time it started running rough.
There is a large FF drop at 25:52 with a small RPM change.
If that is where the problem started it sure looks like fuel flow.
However EGT #4 started wondering of about 23:30.
 
Tell your mate Jim to dust the cobwebs out of his wallet and get Savvy Analysis to inspect the data. They are the absolute experts at this. Their opinion would undoubtedly be more valuable than any free opinions on this forum. ;)

Haha. We talked about that.

There is tons of great knowledge on this board ... I was hoping for some insight or thoughts on troubleshooting.

The front page exposure definitely helps - thanks Doug!
 
Agree about the CHTs
We've talked about that and are looking at the issue.
Baffles etc look good.

Anecdotally, he's been told "this is a common problem with the RV-9 in climb" - any truth to that?
 
Loose Carb?

This may be totally off (I'm no expert) but its easy to check. Have the nuts that secure your carb loosened up? John
 
This may be totally off (I'm no expert) but its easy to check. Have the nuts that secure your carb loosened up? John

I had a similar experience, the carburetor bolts backed off that held the carb together which intern allowed the carb to split just enough to leak gas when the fuel pump was on and I'm assuming suck air when it wasn't. Anyway she ran a bit "rough" (Scary) all fixed and safety wired
 
My money would be on fuel delivery issue. New enough plane that maybe some construction debris has made its way into the fuel system? Carb should still be in good shape, as should the ignition system (still easy to check though).

Regarding CHTs, the baffles "looking good" doesn't mean much. Mine "looked good" also, but with a few hours of work I was able to shave another 15* off my CHT's. There are plenty of people who manage to design and build cooling systems that never go over 400*, and will also say you should do the same. They may be right. Personally, on a hot Florida summer afternoon, I may creep above 400* after a hot takeoff and climb. I can just pull back the power a tad and put the nose down a bit and it's not an issue. My personal redline is 425* although I start making changes at 400*, which is will within Lycoming's recommendations, and probably well below what most people flew around at for decades before 4 cylinder engine monitoring.

Chris
 
Agree about the CHTs
We've talked about that and are looking at the issue.
Baffles etc look good.

Anecdotally, he's been told "this is a common problem with the RV-9 in climb" - any truth to that?

Yes - truth to that. CHTs run a bit high on climb and then settle back down after a while at cruise.
 
This may be totally off (I'm no expert) but its easy to check. Have the nuts that secure your carb loosened up? John

Thanks for your suggestion. The carb was removed and checked for dirt and none found. The carb bolts were tight before removal.
 
Rough!

I had a similar problem with an 0-320 carb. engine. Not so much the high temps, just the rough engine at higher power. Mine traced back to bad intake gaskets.
Ck the connections and gasket condition. Mine ran great after.....
 
Agree about the CHTs
We've talked about that and are looking at the issue.
Baffles etc look good.

Anecdotally, he's been told "this is a common problem with the RV-9 in climb" - any truth to that?

High CHT in climb can be normal but it depends on your definition of high. The CHTs in the photo are what I would call high (>400). Within MFG limits but higher than I would accept in climb. Consider climbing at a higher speed (110-120 knots.
 
Regarding CHTs, the baffles "looking good" doesn't mean much.

Chris

Agree with your thoughts ... I spent a ton of time on my purchased RV-10 making the baffles etc seal well. I've done a ton of reading and research about airflow etc. Jim's baffles are well sealed ... there are a few small areas for improvement, but overall they look really good. I don't think this is the issue. But the CHTs are high in climb ... no doubt about that.
 
I had a similar problem with an 0-320 carb. engine. Not so much the high temps, just the rough engine at higher power. Mine traced back to bad intake gaskets.
Ck the connections and gasket condition. Mine ran great after.....

We checked to make sure everything was tight and sprayed starting fluid around the intakes and the rubber boots to make sure they were not leaking. Did not find any leaks. Thanks for your suggestion.
 
Send your data to the experts.

Thanks for your suggestion. The carb was removed and checked for dirt and none found. The carb bolts were tight before removal.

Dear Jim, As I said in Post #3 you really should get Savvy Analysis to look at your flight data. Sorry, but that's the best advice you're going to get on this site. There's a lot of information in that data but you need a really tuned-in person to assimilate it all. It is unlikely that anyone on this forum has the appropriate expertise and even if they did it is unlikely that they would be prepared to take the time and make the effort to analyse all of the data. People on VansAirforce mean well, but in this case you have a huge amount of data at your disposal and you need an expert to make sense of it.

This is not just a matter of EGTs and CHTs. Savvy Analysis will also look at your Airspeed, Fuel Flow, RPM, Altitude, OAT etc etc. Then they'll tell you some interesting things and you can be confident in their opinion.

If you get an opinion from them then you might like to reproduce it in this thread for the benefit of others.

Incidentally I note that others have commented on your high CHTs. There are many possible reasons for this. I see that on the flight where the engine ran rough your #3 CHT rose to 452 degrees by 900 feet AGL on climb out. That's 452 degrees before you're even at circuit height. That's ridiculous.
 
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Dear Jim, As I said in Post #3 you really should get Savvy Analysis to look at your flight data. Sorry, but that's the best advice you're going to get on this site. There's a lot of information in that data but you need a really tuned-in person to assimilate it all. It is unlikely that anyone on this forum has the appropriate expertise and even if they did it is unlikely that they would be prepared to take the time and make the effort to analyse all of the data. People on VansAirforce mean well, but in this case you have a huge amount of data at your disposal and you need an expert to make sense of it.

This is not just a matter of EGTs and CHTs. Savvy Analysis will also look at your Airspeed, Fuel Flow, RPM, Altitude, OAT etc etc. Then they'll tell you some interesting things and you can be confident in their opinion.

If you get an opinion from them then you might like to reproduce it in this thread for the benefit of others.

Incidentally I note that others have commented on your high CHTs. There are many possible reasons for this. I see that on the flight where the engine ran rough your #3 CHT rose to 452 degrees by 900 feet AGL on climb out. That's 452 degrees before you're even at circuit height. That's ridiculous.[/QUOTE

Thank you for your advice. I signed up with Savvy and will send them the data to review. I had the service bulletin addressed on the Slick mags and they tested fine. I will advise on the progress. Thanks again.
 
check primer leakage - especially if electric

If you have the standard Parker electric primer that comes with the kit, you may want to verify that no fuel is getting past the value....if even a little fuel does get past the valve it can cause rough running and fouled plugs on the primed cylinders.

You can open the lines where it goes up to the cylinders and visual verify that no fuel is going to the primer lines while running the boost pump only as a check.
 
If you have the standard Parker electric primer that comes with the kit, you may want to verify that no fuel is getting past the value....if even a little fuel does get past the valve it can cause rough running and fouled plugs on the primed cylinders.

You can open the lines where it goes up to the cylinders and visual verify that no fuel is going to the primer lines while running the boost pump only as a check.

I will check and make sure the primer is not leaking. Thanks for your suggestion.
 
Thank you for your advice. I signed up with Savvy and will send them the data to review. I had the service bulletin addressed on the Slick mags and they tested fine. I will advise on the progress. Thanks again.

So, have you been able to pinpoint the problem. I'm sure all of those who have contributed to this thread would like to know the outcome.
 
Still troubleshooting. It's been a slow process with weather and schedules.

We are actually headed back out today to do some more work ... I will keep you posted and update when we get things sorted.
 
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