A4 Runs fine for hours then gets rough

[jkenan]

Got it! And thanks for the helpful explanation of how the 'dark side' of the coil works. Even after tearing the A4 down to the last bolt and rebuilding it, it still amazes me how much I still have yet to learn about it

The great thing about these engines is they keep us engaged maintaining them. If I had a diesel chances are I'd have to to hire out the heavy lifting.

Thanks for all the feedback!

[dvd]

Coil

dvd

[jpian0923]

pcv failure or clog...for Neils sake!

[jkenan]

Finally got back down to the boat after 2 months. Notwithstanding it was blowing 40 knots today, I did manage to get the boat from mooring to dock without incident.

So, back to the topic of the engine running fine for hours, then running rough/loss of power: Checked the fuel line, no clogs there. When I started the engine back at the dock with the intention of letting run for as long as it took until the roughness started up again, I did so with the engine cover removed. I noticed immediately that smoke was continuously coming out of the the #1 cylinder plug hole. As the the engine warmed, the smoke subsided somewhat, but never diminished completely. Then I noticed a black soot around the base of the plug itself, so and also around plug #2 but less so. I have attached an image of the plugs removed - Left is #1, then going right to #4. Notice that #1 is heavily sooted around the base, and #2 less so, but still more than #3 and #4. Then look at the gaps, and all but #3 are blackened. These plugs are relatively new, replaced last fall, and probably have not more than 100 miles on them. They were all torqued using a proper wrench to Don's spec when installed, and gapped properly as well.

I do not see any indication of a cracked head, but am concerned by this. If the #3 plug always runs clean but the others come in and out of service, this would seem to seem to explain the roughness.

Blow head gasket? What would explain noticeable smoke coming out of #1 plug? Even if no smoke is seen out of #2, it is sooted at base too, but less so. Need some help please.

[Marian Claire]

Is the soot on #1 a continues ring? Looks that way. Just thinking if it is that may indicate that it is not seating properly. A streak at one spot might indicate a crack. Check the head right at the plug holes. That is a good spot for crud to accumulate and may be preventing a good seal. I always have to blow that area out before I remove my plugs. Bad crush washer? Try a new plug and see if you still have smoke coming out.
I had a plug that would intermittently drop out, loss of power/fouled plug, and it turned out to be the plug itself. I chased that for days before I found it.
Dan S/V Marian Claire

[jbsoukup]

when you saw the smoke, was the plug not tight?
when new ones are installed they need to be re-torqued after run for a while.
does't really explain your problem though.

[hanleyclifford]

It is easy to eliminate the plug hole threads (or confirm). Go to the Auto Boutique and get a 14mm tap or thread chaser and do all the plugs. Use a shop vac to suck out any carbon fragments.

[Dave Neptune]

Seating

John, I would like to confirm that the plug is not seating properly!!!! It may be a build up on the head where the plug "metal gasket" compresses for a seal or the threads have a carbon build up and the plug is torqued against the carbon not the seat. A tap will clean it up or a longer reach plug with a groove filed in will also complete the task. The surface at the top of the plug hole should be "flat & clean" to insure full circular contact.

Another thin is if the plug was not weated properly the spark can also be compromised due to a lack of proper seating against a good metal ground!!!

Dave Neptune

[edwardc]

I'm still not sure I buy the loose plug theory. Especially with two of them showing symptoms. Are you sure it was smoke and not steam? Any little leak, either from the head itself, or from overhead that drips on the head, will generally collect in the wells around the plugs, boiling off and leaving behind a dark residue of whatever was dissolved in the water.

[Dromo]

I think I read a thread a while back and they had the same issues that your describing .
I think that went on for a few years also.
Turned out to be the gas tank had a lot crap/sediment in the bottom of his tank .
Whenever He was out for any length of time the gas & crap in the tank would get all stirred up from the motion of the boat.
If I recall correctly, his gas filters all looked OK.
Do you have a sending unit on your tank ?
If there is access to the sending unit, I would remove it to inspect and clean the tank if necessary.
How old is the boat?
cheers Rick
P.S. Please no Shop- Vacs!

[jkenan]

Dave, Dan, Rick, Edward,and all others following this post:

Thanks for your input! Update is this: I scraped clean the seats to the four plug holes which did have a good bit of crud around them, and then replaced the plugs with new ones (Autolite, from Don), and no more steam, so I think that was a crud issue (not a water issue around the plug base, edward). After replacing plugs, I ran the engine for a couple of hours, went for a sail (cold, but nice weather, not blowing 40 like it was the other day), and have no issues to report. But it has run fine for hours before exhibiting symptoms in the past, so I'm not convinced the problem is solved. Tomorrow, I'm setting her on the mooring for the winter, and will remove the new Autolite plugs after sucking the pink antifreeze through the raw water intake, then apply the MMO to the valves, etc. If there is any soot or otherwise suspicious indicators on the plugs after running them for only an hour or so, I will report such.

I guess my main question is this: could poorly seated plugs cause the rough running that inevitably presented after running fine for hours? Also, could poorly seated plugs cause the the soot buildup on the gap (I understand why this issue would cause soot buildup around the base of the plug)? I verified the fuel vent was clear so no clogs causing fuel starvation. There is brand new coil I installed in the fall, installed because of the same symptoms. Until the problem reappears, I can't really test the wiring (jumping positive coil terminal to battery). So, I don't really know if problem is resolved. So again, my main focus will be on plugs, and their sootiness, unless any one of you think I should be looking elsewhere. Compression seems good (I left my gauge at home, dammit) - when she's running, she's running just fine.

[hanleyclifford]

In your situation I would verify that voltage to coil+ does not exceed 12 volts. This should be tested at cruise rpm fully warmed up.

[ndutton]

In your situation I would verify that voltage to coil+ does not exceed 12 volts. This should be tested at cruise rpm fully warmed up.

Once again, this ignores a key element in the ignition system current formula, the coil resistance. As an example only, if you purchased your replacement coil from MMI and it has an internal resistance of 4.3Ω (typical), you'd still be within the proven formula including a margin of safety with voltage at the coil + terminal of 14.6 volts. I'm not advocating a voltage that high but rather pointing out that depending on the coil resistance (IMPORTANT and ignored in a pure voltage approach) there may be a wide functional voltage range without risk of damage to the coil or EI, a range that may include voltages well above 12 volts.

[Marian Claire]

What is your normal operating temp? Do you have the adjustable main jet? Cool running and a rich mix can cause soot.
I pass Efland on my way to the coast. Where do you sail out of if you don't mind my asking. The MC is on the Neuse River near Oriental.
Dan S/V Marian Claire

[jkenan]

Normal temp is 180 degrees, and is consistent. In the summer, it gets to 180 pretty immediately (and is when I experienced the worst of the problem). Went for a sail yesterday out of Oriental, and it got to 140 pretty quickly but took a little while longer to get to 180, but eventually did - due to cooler water temps I presume. I don't have an adjustable jet installed, but have one in my array of parts.

The coil is from Indigo with the external ballast resistor, and was the replacement I installed in October after symptoms were experienced. Did not seem to help any. I will check the voltage just to be certain.

Dan- I sail out of Smith Creek in Oriental, and would certainly enjoy meeting you. I'm here now but will need to leave in the next few hours due to family commitments. The boat is back on her mooring, and all I need to do is winterize the engine. I'm planning to haul out in March at Sailcraft for a new coat of bottom paint before recommissioning, along with some other maintenance (need to replace the rub rail). Send me a back-channel line if you would like to meet sometime, in Oriental or Efland. My email is johnkenan@gmail.com