hnorber Posted May 30, 2019 Report Posted May 30, 2019 Hi all: I wonder whether anyone has any thoughts on the following 2 issues that I've been experiencing with my 1999 MSE (about 1950 TSMO): 1. My engine consistently misfires at idle. I've had this problem for a long time, but it seems be more frequent now (generally one 'stumble' every 10 or 15 seconds). I was told a long time ago that this is common in Mooneys due to the twists and turns in the intake manifolds, but I wouldn't imagine that would cause misfires with any regularity? I recently changed my plugs, but the problem is still with me. I'll also note that my oil consumption is really high (about 1Q every 3.25 or 3.5 hours), but the old plugs didn't seem fouled (one of them had cracked, causing a significant vibration that was fixed when we replaced it). 2. Lately, after setting my RPM to 2450 in cruise, I see that it'll bounce around between 2420 and 2470. It happens for about half a minute before returning to 2450 and then it'll happen again every 10 minutes or so. I guess - while I'm at it, I'll also mention that my panel back-lights went dark on me a few weeks ago. I ruled out a bad fused by swapping the 2 125v cylindrical fuses on the back-lighting and the glareshield lights - after which neither lighting system worked. When I swapped them back to their original positions, the glareshield lights were working again, but the panel back-lighting was still dark. I'm working with my mechanic to diagnose the engine issues, but would be grateful for any thoughts/advice from this group. Thanks! Quote
Oldguy Posted May 30, 2019 Report Posted May 30, 2019 Any chance you have an engine monitor like a JPI or EI where it records engine data? If so, you can load it up to savvyanalysis.com, and we can all take a look at it. But as to your OP: I have never heard this about our engines (the stumble problem being common). Do you have the IO-360-A3B3D engine, and if so, how long has it been since the mag was overhauled? If you instead have the -A3B6 engine, what type of mags do you have and when were they overhauled? Age of wires and type of plugs (Tempest/Champion, Massive/fine wire)? Prop governor last overhaul time and date? As for the lights, it sounds as if one of the fuses (the one from the back-lighting circuit) is blown and, for some reason, the back-lights did not blow the other one when it was put in, but already has a short somewhere that has killed the circuit. If you have a VOM, I would suggest testing the fuse on the back-light circuit to see if it is blown. Did you have a typo in your post? The FAA shows N7LU as a 1991 model? Somebody with more knowledge and experience than I have will likely be along soon, but these are a few of the questions/comments I think may come up in the thread. 1 Quote
PT20J Posted May 30, 2019 Report Posted May 30, 2019 If the high oil consumption is due to worn valve guides, it's possible that one exhaust valve stem might have enough deposits to cause the valve to stick intermittently. 1 Quote
carusoam Posted May 30, 2019 Report Posted May 30, 2019 1) When discussing engine issues... The JPI data is the best! Go ahead and get it loaded... It may be one cylinder is responsible for the miss and the oil use... The data can make a brief experience of the trouble shooting exercise... 2) When discussing plug fouling issues... Knowing what plugs you have is often very important. Champion is known for changing to high resistance over short periods of time... this leads to plug fowling and not firing properly... 3) when discussing age related wear... keep an open mind... farming the data can be better than removing all the bottom plugs to see what is going on... PP thoughts only, not a mechanic... Best regards, -a- Quote
jaylw314 Posted May 30, 2019 Report Posted May 30, 2019 At idle RPM, the IO-360 makes a "loping" sound 1-2 times a second. This is caused by the sniffle valve at the bottom of the intake manifold opening and closing. Each time it does, the air/fuel mixture changes. If you are having rough running every 10-15 seconds, I speculate it may be that your sniffle valve is sticky and only opens every several seconds. You might want to have your mechanic look at the sniffle valve to see if it is sticking. Obviously, this has nothing to do with high oil consumption. While Occam's Razor would suggest this is less likely to be a problem than one problem causing both, it's at least easy enough to check. 2 Quote
Guest Posted May 31, 2019 Report Posted May 31, 2019 Here is the oil consumption calculation. 0.006 x BHP x 4 ÷ 7.4 = Qt./Hr. It’s form this S/I https://www.lycoming.com/sites/default/files/Lycoming Reciprocating engine Break-In and Oil Consumption.pdf Clarence Quote
PT20J Posted May 31, 2019 Report Posted May 31, 2019 18 hours ago, jaylw314 said: At idle RPM, the IO-360 makes a "loping" sound 1-2 times a second. This is caused by the sniffle valve at the bottom of the intake manifold opening and closing. Each time it does, the air/fuel mixture changes. If you are having rough running every 10-15 seconds, I speculate it may be that your sniffle valve is sticky and only opens every several seconds. You might want to have your mechanic look at the sniffle valve to see if it is sticking. Obviously, this has nothing to do with high oil consumption. While Occam's Razor would suggest this is less likely to be a problem than one problem causing both, it's at least easy enough to check. Sniffle drains to a hose. Easy way to test for leaking sniffle is to temporarily plug line and check idle. 1 Quote
Shadrach Posted May 31, 2019 Report Posted May 31, 2019 19 hours ago, jaylw314 said: At idle RPM, the IO-360 makes a "loping" sound 1-2 times a second. This is caused by the sniffle valve at the bottom of the intake manifold opening and closing. Each time it does, the air/fuel mixture changes. If you are having rough running every 10-15 seconds, I speculate it may be that your sniffle valve is sticky and only opens every several seconds. You might want to have your mechanic look at the sniffle valve to see if it is sticking. Obviously, this has nothing to do with high oil consumption. While Occam's Razor would suggest this is less likely to be a problem than one problem causing both, it's at least easy enough to check. 32 minutes ago, PT20J said: Sniffle drains to a hose. Easy way to test for leaking sniffle is to temporarily plug line and check idle. Just to hijack slightly has anyone thought about why the "loping" from the sniffle valve is not present when the engine is cold? Quote
MB65E Posted June 1, 2019 Report Posted June 1, 2019 Sniffle valves are a joke, everyone I’ve ever tested or questioned was failed. You could measure the valve travel at the rocker arms.. However my guess, is if the cam lobes measure ok, you’ll probably need some new cylinders. Could have a cracked ring. I’m sure compression is great. If the the oil turns black after just a few hours after an oil change, it’s the valve guides. 1950 hr is very respectable for these engines. Bummer, -Matt Quote
Yetti Posted June 4, 2019 Report Posted June 4, 2019 Nope not supposed to be that way. 1. When were the last time the mags were done? 2. Could be a short on the p leads. 3. Has a baby jar test been done? Read through here and tell us which section most applies to your engine https://www.lycoming.com/sites/default/files/SSP-475.pdf Quote
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