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Very erratic oil pressure


Scrapman1959

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2011 CTLS with 1040 hrs TT. Oil pressure gyrations has been getting steadily worse with today's flight seeing 23 to 55 lbs In wcruise. The needle moves rapidly. Connection on the sender is clean and tight. We did the extra grounding years ago. Engine oil is full as always, and engine sounds normal. Any ideas guys? I was going to replace the oil sending unit for starters.

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It's either the sender ($39) or it's a connection or ground.

If it decreases with throttle and increase with less throttle then I'd say it was a ground. If it bounces all around and it is no correlation with nothing you do then I would lean more on the sender.

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I think it just bounces around in a lower range when idling at 2100 rpms, even going to 0 and in and out of the red up into the 40s. We redid that ground post on the firewall behind the MFD a few years ago. What other grounding improvements can be done or where do we look for a bad ground? The oil temp sometimes bounces around too, but not this crazy and not all the time like this oil pressure is doing. Thx.

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If you have a Dynon make sure your software is up to date. There was an erratic oil temp fix I believe in 5.5.0.  Tighten anything that is grounded in the engine compartment over by the battery. The ground wire runs under a couple of things. Under the reg/rec, the starting solenoid, the neg. battery terminal, under the center bolt on the engine frame. Then tighten the one that goes through the firewall that goes behind the instrument panel. Make all of these tight. Consider them hand tight, but wrench loose so everything gets a wrench and not just hand wiggled.  Did you put in the extra ground wire I posted a couple years back. It comes off the neg. battery terminal, up to the #3 cyl. screw hole and then through the firewall to the main ground bus bar or grounding screw depending on which CT you have. I have never had a CT I could fix with just replacing the sender or tightening all the grounds.

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2011 CT will likely have Skyviews, so the update number would not apply. It should also have something different than the VDO sender, maybe a Honeywell. Another sender is the Kavlico. Both of the later senders had a lower failure rate than the VDO, but they do still fail. Especially if they are mounted at the front of the engine. 

 

I have tested the VDO senders on the bench before. If you can find the specifics for your sender I would think it could be checked as well.

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It's only one ground and what problem will it cause?

The ground that are already on the plane are required grounds from the MFG's.

 

 

2011 CTLS with 1040 hrs TT. Oil pressure gyrations has been getting steadily worse with today's flight seeing 23 to 55 lbs In wcruise. The needle moves rapidly. Connection on the sender is clean and tight. We did the extra grounding years ago. Engine oil is full as always, and engine sounds normal. Any ideas guys? I was going to replace the oil sending unit for starters.

 

These extra grounds create a web of paths to ground that over time degrade and result in a a bigger problem to fix then if only the original path(s) to ground was utilized. 

 

You now have an additional point of failure and bad ground is a possible cause here.

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All the regular factory installed grounds are supposed to be there. The one and only extra ground I recommend is a much larger wire, the ends are soldered and it won't break or degrade and it's a straight path to a ground and isn't zig zagging around like the others from one connection to the other with small wires that are only crimped and have had a history of pulling out or breaking..It becomes the best most solid ground above the rest. This is one reason people that have installed this have quit having grounding issues. Now the engine has a solid ground for it's probes, but the big benefit comes to all the electrical items in the cockpit. This ground is far better than the factory one from the engine compartment.

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A properly crimped connection is stronger than solder. Connectors that are a one piece ring with a metal barrel that grab the insulation are the best.

 

In fact, solely soldering to terminals isn't allowed in many industries, including marine and aerospace.

 

Stay away from connectors with PVC. PVC is often the opaque plastic ones. Those are the worst type. I don't have much choice when it comes to the bullet connectors used by FD, but it's worth going out and buying a big connector kit with various connectors. I find those with uninsulated terminals the best as they give the cleanest crimps and ease to inspect after the crimp is finished. I can insulare with shrink wrap.

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Kudos to Roger Lee! We removed cleaned and tightened all the grounds and EVERYTHING is working great now. We had an EGT that we thought was bad and had it unplugged while waiting for a new one to stop the aural warning. Fixing the grounds even took care of that "bad" EGT.

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