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Strange Failure Signature


Andy

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I had a very strange failure signature this afternoon and I'm hoping someone might be able to help me point my A&P to the cause.

 

Flying at 1500-1600 feet MSL at cruise (5200 RPM) with air/surface temps about 78 degrees. Lots of turbulence. After about 20 minutes of flight time, we hear noise over the communications system (like a noisy radio). I turn off the radio to see if the noise goes away but it doesn't. Lasts about two minutes and then quits. Shortly after that I notice that the oil temp is running high at about 230. Doesn't make any sense since we've been in cruise for a while. Check oil pressure and it's in the green but down on the low side--about 35--normally runs around 50. CHT in the green but also high. Engine still responsive to throttle and continues to operate smoothly. By this time, we are close to our home field so I hold us high and continue while looking for a spot to land if needed. Make a successful right base entry to landing with the power back at idle. During taxi, engine oil pressure falls to about 20 psi. I think by now we have a serious problem with the engine until I start shutting down avionics. As we shut off the avionics master and the intercom, the gauges all "pop" back into the normal range. We play with turning on gear and watching the gauges and notice some movement when powering on the transponder but nothing definitive. Shut down is normal. Restarted the engine and everything appeared normal. This looks to me like something electrical.

 

Talked this over with my A&P and he thinks it is electrical and was wondering if there was a common junction. That makes me wonder...especially when coupled with the turbulence of the day..that there might be some kind of grounding problem. Has anyone seen anything like this before? Do you think we're on the right track? (Obviously, we'll do an engine check...)

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You most likely have a poor ground connection. There are 5 to tighten and they are all on the battery side. The highest one up on the firewall goes through to the inside panel. All grounds are considered hand tight and wrench loose until you put a wrench on them. All the ones in the engine compartment next to the battery are easy to tighten. The top one that goes through just needs he passenger side panel removed and look all the way back to the firewall and you'll see the bolt for the through the firewall screw. Tighten this tight.

I highly doubt you have any real issue.

My money says after the ground tightening you'll be good to go.

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Andy,

As Roger pointed out, grounding would be the first item to check.

 

We experienced the same sort of electrical ground issues with our plane from the first day we purchased it and used recommendations from Roger and others in this group to improve the grounding scheme on our aircraft . Since the improvements our electrical system has been rock steady. Much to the delight of those who fly it.

 

Look thru the postings about grounding issues and you will find a myriad of items which will eliminate this issue from popping up again.

 

One area to pay close attention to is the ground bus located inside the mushroom on the firewall and its connections. Focus on both the connection to the main ground and the stakon connectors attached to it. During an inspection we found many of these connectors loose and some barely hanging on.

 

The beauty of this aircraft is its simplistic wiring scheme. Makes for easy troubleshooting.

 

One last note. I would remove the grounds, scotch brite them and then re-assemble. This will guarantee that the connection is both tight and clean.

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  • 2 weeks later...

That did the trick. In addition to tightening the grounds, I had my A&P add the extra grounding strap Roger Lee discussed a while back. Thanks everyone for your help.

 

Gotta tell you this was a real education on this subject. Never would have thought I could see what appeared to be correlating indications of an engine problem that didn't really exist. Only my previous experience with the airplane kept me on the right track...

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Andy,

This problem is probably the number one item that causes the most heartache for us owners. Once you get the grounding squared away the other items will be normal maintenance items.

One thing I would suggest is to spend as much time on this board as you can and read most if not all the posts in the maintenance section. It will be well worth your time.

 

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You are absolutely right about that, Chris! I've been doing that and, in fact, had printed out several discussions about the problem and solutions, mainly from Roger Lee, that I handed to my A&P before sending him down the rabbit trail. He did use it and we seemed to have gotten it (and maybe have prevented it from happening again for a very long while) in one session.

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Andy,

That is good news. I have handed my guy more print outs than he has ever gotten. He went from a folder to a binder for our aircraft.

If there is a weakness in our aircraft it is definitely in the electric system. And possibly with the oil cooling. (My opinion)

 

The correct sizing and placement of the grounds goes a long way towards the elimination of that problem. I am sure that like any other aircraft other issues will come up. The beauty of this group is that most of its members have experienced problems at one point or another, and they are more than happy to give some advise.

 

At the end of the day we all fly a great plane.

 

 

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