RV-6 VM1000 RPM Indication Fluctuations

[rvmills]

Thanks Scott, all makes sense. Buttoned up the plane after installing a new #3 EGT probe, and run-up checks showed no RPM flux. Too gusty to fly at 4SD (Reno-Stead) today, so a longer check for RPM indications will need to wait til the next flight. Meanwhile, still checking for the actual RPM sensor wiring, so if it shows itseld again, I'll be able to hit the source. Thanks again to all for all the great feedback! The VAF forum is a great source for info from pilot bro's!

[N733JJ]

Another fluctuating instrument to watch for is the MP.

In the past I have had the MP fluctuate or be very slow to respond. I was told by VM tech (back in the pre-JPI days) that it was likely moisture in the MP line. You want the transducer as high as possible with respect to the pickup on the engine to prevent this. Though mine is mounted as high on the forward baggage bulkhead as possible, this is still a bit marginal. Removing the transducer and blowing it dry takes only a few minutes and was something I started doing during an oil change while the oil was draining (along with checking the connections on the VM CPU, lubing the tailwheel and a few other routine chores). I started getting lazy and have not done this for the last couple years but have had no further issues with it but can not explain why.

Scott A. Jordan
N733JJ
695 hours

[JoeBlank]

Using the VM-1000 on an Aerosport IO-320-D1A, I was encountering fluctuating Oil Temp, Fuel Flow, CHT, & EGT readings after about 50-60 hours. What I discovered is that those crappy little red spade quick disconnects begin to fail in about that time period. (Despite using a GOOD crimping tool) I think one of the root causes is all those corrosive gases running around in the engine compartment eventually attack the attach points and crimps of those fittings enough so that an electrical signal is impeded. The solution? Remove the spade quick disconnects, solder all of the connections, and encase in shrink wrap on ALL FWF engine monitor connections. 430 hrs later, I haven't had one problem since making that change. The only downside is that the connections must be cut to replace a sensor, but for me, that is a small price to pay.

I'm not sure why the engine monitor mfr's still use the spade quick disconnects for that sort of an application. Ease of installation probably... I'm sure there is a more expensive solution that would prevent this sort of thing... YMMV

[rvmills]

Joe and Scott, thanks for the info on the MP and other fluctuations. Haven't seen any yet (knock on wood) but that will sure help if they appear. I'll look for the MP transducer (still doing a lot of learning about where everything is...part of buying, not bulding!)...good info. And I do have the spade connections...the solder/shrink wrap solution does sound time intensive, but sounds worth the effort! At 490 hours TT it is great shape for an almost 10 yr old, but gotta keep the preventitive upkeep going so it stays tip-top! Thanks again for all the great words of wisdom!!

Cheers,
Bob
N600SS
RARA Hangar, 4SD

[RV8N]

Originally Posted by N733JJ

Another fluctuating instrument to watch for is the MP.

In the past I have had the MP fluctuate or be very slow to respond. I was told by VM tech (back in the pre-JPI days) that it was likely moisture in the MP line. You want the transducer as high as possible with respect to the pickup on the engine to prevent this. Though mine is mounted as high on the forward baggage bulkhead as possible, this is still a bit marginal. Removing the transducer and blowing it dry takes only a few minutes and was something I started doing during an oil change while the oil was draining (along with checking the connections on the VM CPU, lubing the tailwheel and a few other routine chores). I started getting lazy and have not done this for the last couple years but have had no further issues with it but can not explain why.

Scott A. Jordan
N733JJ
695 hours

I've also had quite a few problems with MP. I'm pulling MP off the right rear cylinder, braided flex hose to the firewall and aluminum tubing to the MP sensor. Unfortunately it is a down hill run for a taildragger. I was getting oil fouling of the sintered fitting on the sensor. I guess there is some residual oil that somehow drains thru the intake valve bushing after shutdown. Every 15-20 hours the MP would stop reacting to throttle movement. I would take the fitting out and soak it in Avgas for about 5 minutes.

I finally got tired of this and started looking at changing the routing of the hose to prevent the fouling. I was able to route it up and over the oil cooler instead of around it. Hopefully this will solve the problem. Not enough hours yet to know if it worked.

Karl

[pvansrv3]

Hello, I have had a VM1000 on a Bucker biplane for about 10 years and am installing one in a Harmon Rocket project now. It is one of the first engine monitors but I still like it a lot.

I have had an occasional intermittent read out a couple of times and it has always been the terminals at the "brick" DPU end of the sensors wiring. Those screws somehow loosen over time and need an occasional tightening.

Since your system was working good, it might be as simple as that. Get the manual and figure out which terminals are for the tach sensor and check those carefully, maybe loosen, and tighten those.

As for the tach sensor, it screws into a threaded port on the side of the mag case and is basically a hall effect sensor that notices when a magnet passes by each rotation. No moving parts and only two wires. Hard to imagine it would fail with intermittent readings, more likely a broken wire would fail it completely.

Good luck, don't give up til you find it.

Peter