Rough Engine ---- help!

I need your advice and suggestions on this one? Background info, I just changed out spark plugs, oil, and some other minor stuff. Engine was running fine before above work was done.

In my last post "which plugs" it was determined that spark plugs on ignition module A are 1,2 top and 3, 4 bottom. Ignition module B controls spark plugs 1, 2 bottom and 3, 4 upper.

My problem is I have all of a sudden developed a rough running engine when I turn off ignition module B. I get a 250/300 rpm drop when normally I would see about 80/100 rpm drop. This makes the plugs or connections to spark plugs 1, 2 top and 3, 4 bottom suspect. I removed all plugs and they all showed signs of soot. I cleaned and checked gap for .025 and all are ok. I reinstalled plugs with torque of 22lbs and switch them all around where plugs on Mod A are on B and of course B plugs on A. I ran up the engine and problem remains the same! So in my mind the plugs are not the problem. Maybe spark plug wires? I'm told when the ignition module fails everything quits, not one plug. So I believe the ignition module is good. Is there anything else this non-mechanic can try? Has anyone had spark plugs wires go bad after 200 hrs?
Your thoughts / suggestions are appreciated.
Thanks, Steve

Sounds like spark plug wire

Steve,

Greetings from KARM

I had the exact same problem and found that one of my wires was not fully engaged on the spark plug terminal. The rubber insulators are extremely tight and resistant. Go over all the spark plug connections once again served by the ignition module that was active during mag check. Good luck.

Jersey

Tried that

Hi Gary. I thought that also, and have double checked all plug connections. They all seem to have a solid connection with the plugs and the connectors and somewhat difficult to get off the plugs, so I feel that are making a good connection. Steve

I have the same problem but not all the time. If I let the engine run for about 5 minutes after it reaches normal operating temp of 121 degrees, it seems to always smooth out. If I check the ignition immediately after the temp reaches 121 degrees, then I get the large drop and rough running engine.

Try unscrewing the connectors from the spark plug wires and screwing them back on, or at least check their tightness.

plugs

make sure you check you have the plug leads on the correct plugs
and you could try swapping all the plug positions and see if the fault follows the plug or stays with the module and check that the leads haven't been rubbing and that the plug tops are on properly

Steve, I have just gone through similar circumstances and tried similar fixes. Through the generosity of a good 12 buddy (Skunkworks), I replaced my ignition modules with his known good modules and now have my 12 back (albeit with new modules on b/o). When I would switch off the b ign., the engine would intermittently quit. I also had been noticing an increasingly rough ignition check on ign. b. It appears that all of the distributors have the new soft start kit on b/o and I was told by all of them that there has been a run on these parts over the past months (the hot months). I think there is a problem with these modules, but so far no monetary help has been offered.
Going off on a tangent here, but thankfully, we have a close group of 12 guys that help each other whenever a problem like this comes up (Skunkworks-Mark and Paul Bishoff, Dave Valcik-Smokey and Mitch (Chip) Locke). Friends like this make owning and maintaining an a/p much easier and cheaper. I recommend it highly.
Good Luck

I believe all the "new style" ignition modules have yellow labels my engine came fro Vans in 2011 with the new style that includes soft start.

Thank you all

I have the style of ignition modules that has the soft-start included. I have triple checked my connections and all are good.
I spoke with "Dean" at Lockwood Aviation today and he was great! He provided very good information and how to determine if my problem is some sort of ignition problem, timing, or possibly carb issue. He carefully explained how to reverse the connections on the modules to begin to isolate the problem. I will begin work tomorrow and report back to the forum what I find out.

Steve

Update (kind of)

I was able to determine that my problem was with the ignition system and not the carbs. I began to isolate which ignition module or coil and my problem simply went away. The engine ran perfect. I put everything back together again and I've flown a couple of hours with no problems. I personally believe I have a bad spark plug boot, but I'm not going to do anything else until the problem shows up again. All for now.
Steve

Good news

Steve, glad to hear you fixed your problem. I have noticed at idle with the cowl off the carbs and ignition modules do vibrate quite a bit. Hope it was just a loose wire and you have no more problems. Don

I vaguely remember someone talking about the dark test on the ROTAX when the cowling is removed and the engine run in a dark area so any leakage to ground from the hi voltage lines can be seen. If your problems come back it might be worth a shot.

I found this blog online which seems to detail some similar info for future reference for people doing searches:

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DEC 18, 2011

Rough Running Rotax 912/914 Engine

When we installed the new Rotax 912 in our plane 16 years and 1,400+ hours ago, it exhibited poor idle when started, uneven running up to 3,000 rpm, and worse yet, would really shake in flight when the throttle was pulled back to idle. The latter problem was really disconcerting when power was reduced for landing.

When flying on 100LL avgas on long-distance trips, the engine would quickly show the effect of lead-fouled spark plugs and run rough during start-up and taxiing.

We tried all the suggested cures, such as balancing carburetors, adjusting mixture, replacing spark plugs, cleaning carburetors. These remedies improved the problems somewhat, but performance never was really satisfactory.

Eventually, we assumed that this was just part of the Rotax performance. That is, until a recent annual inspection turned up the real culprit.

For the discussion, we need to look at the ignition system.

Each ignition cable of the Rotax engine is connected to the spark plug with NGK connector VD05FMH. The connector housing is made of rubber. Inside the connector is a threaded pin.

The ignition cable is pushed into the connector until it touches the pin, then the connector is twisted so that the connecting pin is threaded into the copper strands of the cable. The process stops when the cable runs against the bottom of the connector.

Once the cable has been installed into the connector, a tie wrap is pulled into the groove of the neck of the connector and tightened. The tie wrap seals the connector around the cable and thus prevents moisture from getting into the connector.

The rubber of a new connector is quite soft and pliable, and the opening where the ignition cable is to be inserted is undersized relative to the diameter of the cable.

When a new cable is pushed into a new connector and then the connector is twisted to thread the cable onto the pin, the dry surfaces of cable and connector induce quite some friction. Indeed, the friction may become so large that it may seem that the cable has bottomed out in the connector when it has barely touched the pin.

When this happens, the cable does not properly connect with the pin and fires with a weakened spark or not at all. In the latter case, a significant rpm drop during the ignition check points out the problem. But in the case of a weakened spark, there may be enough spark that the problem is not detected by the ignition check.

Exactly this installation mistake was made at the factory on my engine. The connector of the spark plug for the top #4 cylinder was never threaded onto the pin. After 16 years and 1,400+ hours, the cable suddenly pulled out of the connector during the recent annual inspection when we removed the connector from the spark plug for the compression test. That's how we became aware of the faulty installation. Throughout the years, the ignition check never showed a significant rpm drop.

It is easy to avoid this problem. When installing a connector, measure the depth of the hole of the connector into which the cable is installed. This is done best with a thin wire, such as safety wire, so that the depth to the bottom of the hole and not just up to the threaded pin is measured.

Mark that depth on the cable with masking tape. Now we know that the cable must be installed up to the masking tape mark.

For easier installation, apply a very, very thin coat of non-conducting silicon grease to the cable, and then push the cable into the connector and thread the pin onto the cable.

Due to the coat of silicon grease, this can be done with reasonable effort, and twisting of the connector will become impossible exactly when the cable hits the bottom of the hole and the masking tape mark is reached.

Finally, add the tie wrap to tighten the connector around the cable.

If you have a Rotax 912/914 engine where the above symptoms of roughness occur and all other remedies have been tried, you may want to test proper installation of each connector by placing masking tape on the cable next to the connector, cutting the tie wrap, unscrewing the connector from the cable, and comparing the masking tape mark with the depth of the hole.

If the installation had been done correctly, reinstall the connector using the above procedure.

If you find a faulty installation where a connector was not sufficiently twisted onto the cable, repair this as follows. Cut off about 1/2'' of the cable so that you see pristine copper strands, and install a new connector. Do NOT try to use the old connector since the pin likely is damaged due to arcing.

When we did this repair for our Rotax 912 engine, the engine had smooth idle immediately after cold start, had more power on takeoff, and ran smoothly when power was reduced to idle in the air.

It felt like a completely different engine. No wonder; for one of the cylinders, just one spark plug had been firing properly. Since that plug was at the bottom, it fouled easily with 100LL avgas use, producing a rough running engine with avgas use.

Of course, we also checked the remaining connectors for proper installation. They all turned out be correctly installed.

Posted 18th December 2011 by Klaus Truemper

Thank you

Thank you John (Catuspilot) on your posting (reposting) detailing some great information. I believe my problem will show up again someday and when it does, I'll check my spark plug connector connections on plugs associated with the "A" ignition module?. 1 and 2 top and 3 and 4 bottom. Many thanks for bringing it to everyone's attention again. Thanks to all for you suggestions and advice.
Steve

Article follow up pics!

I thought I would do a follow up to the Cactuspilot article. I google then bought a couple of the rubber NGK spark plug caps using the part number in the article. They cost $6.30 each at this web site:
http://www.ngk.com/product.aspx?zpid=20087
The cheapest I could find these from one of the three Rotax dealers was $26.00 from Lockwood so this is some good info if somebody needs one. You can save $20 bucks each. Here are a few pictures to go with the article.
The rubber cap.

Where the spark plug goes in.

Threaded end where ignition cable goes in.

Box with the Part number on it.

I had one rubber spark plug cap lose its suction and come off showing the Symptoms talked about in this thread. Now with the above article and these pics you can see how these go on.

Thanks John and John, good info.

When I took the ROTAX course at California Power Systems the instructor mentioned that these boots could be bought much cheaper outside the ROTAX supply chain. He also said that auto heater hose is a good substitute for the coolant hose and pointed out many of the specialty tools can bought for a fraction of the cost from non-ROTAX sources. One of the best examples is the spring clip cable pliers for the coolant hose clamps. The Craftsman version is less than 1/4 the cost of the ROTAX equivalent.