So here is a new one. 1984 Mercruiser 470 bogging when adjusting trim.

[TKrause]

Did a tune up on the old gal Thurs. night. (points, condenser, plugs, cap, rotor, set Dwell gap, set timing at 4-5deg., adjust idle to approx 900 rpm, adjust fuel mixture, Dropped in the water tie it up re adjust idle in gear at launch all good.) Took her out on the water for about 6 hours or so fishing. Ran like a champ, smooth and with plenty of power however on the way in i went to adjust the trim as the wind had picked up here on Lk. St. Clair and the waves were getting bad. As i did i thought i felt the engine bog. Did it again and sure enough, as i hit the trim lever the engine would bog like she was dropping a cylinder.

I took a short cut through a canal and i could tell she wasn't running as smooth when i exited the canal i have a short jaunt where i can get up on plane before the launch area, as i powered up i could feel that she was missing and again hitting the trim switch made it worse, All of this was taking place below or around 3000 rpm as she cruises best around 2800 and i don't typically run her at WOT. Without testing (because i haven't had time since coming in) I'm guessing that this could be a sign of a coil going out? Just curious on some input before i start my diag.

 

[Eric 3.7LX Alpha 1]

maybe a spark plug wire slipped off the distributor enough to loose a cylinder, and she's running on 3? Or even on the spark plug end, not snapped on good enough?

 

[stonyloam]

The trim draws a lot of amps. Will drop your battery voltage, maybe enough to cause an ignition problem, but it is a 470 LOL. So first thing I would do is pull the plugs and take a look. Should all be tan or brown. A snow white insulator indicates coolant in the cylinder, if all is OK might as well do a compression check. If all is OK then you might have the battery checked. How old are your plug wires? You could try starting it up at night and mist a little water on them to look for sparks, if you see any then it is time for a new set. It could be the coil, try pulling the center wire lay it close to engine ground and turn it over look for a brigh blue spark. Just some suggestions based on (bad) experience ( hg and wires). Good luck.

 

[TKrause]

The plug wires are one season old (replaced last season) all the plugs that came out did not show any unusual signs of burn or fouling issues and were all the normal tan and brown color. When i get some free time today i'll take a peek at some of those. Really odd though how it started out of the blue. Came to an idle off plane to take a break from the rough conditions. closed the bimini down then took off ( no issue with miss then ) went to trim it and noticed it cutting out.

 

[stonyloam]

Yeah, it does sound like it may be an ignition problem related to the voltage drop when you use your trim. You might check your ignition grounds to make sure you are getting full voltage for your coil.

 

[Bondo]

Yeah, it does sound like it may be an ignition problem related to the voltage drop when you use your trim.

Ayuh,.... Sounds like corroded wirin' ends,... probably the Grounds,....

I'd start at the battery posts, 'n work yer way to the ignition,....

Shiny metal Clean connections is what ya need,...
a coatin' of grease will help keep 'em corrosion free,...

 

[TKrause]

Thanks Bondo and Stonyloam, i'll report back as soon as i get a chance to take a look at her, (damn Saturday scheduling of chores and stuff!! hehehe).

 

[TKrause]

Got a few mins to take a peek at it. Yesterday i had cleaned the terminals since i took them off when doing the ignition work. When i checked them today one of the nuts on the positive end was loose. (the positive battery end is one that the previous owner must have put on as it sandwiches the positive cable end with two clamp down bolts) I took it apart and took the end off, cleaned the mating surfaces and the cable and put it back together. Fired it up and let it get to operating temp and i never witnessed any missing, Maybe that was it? However being that it was on muffs and there wasn't any resistance i'll have to get her to the lake for a proper test.

 

[NHGuy]

You could have the solution with that loose connection.
Also keep an eye on your running voltage. Is it staying up to normal? If it's not charging you might have been running on battery and got voltage drop from the high load of the trim motor. Or as suggested the battery could be getting "along" in it's life cycle.

 

[TKrause]

You could have the solution with that loose connection.
Also keep an eye on your running voltage. Is it staying up to normal? If it's not charging you might have been running on battery and got voltage drop from the high load of the trim motor. Or as suggested the battery could be getting "along" in it's life cycle.

I try to keep an eye on that NHGUY, especially because she is still running on the old stator set up that the 470 had. I haven't converted it yet, i had noticed some difference in the charging that day but nothing that had me concerned. I'm hoping that the loose connection i found was it. Like i mentioned i'll have to wait til i can get a chance to get her back in the water to properly test her out.

 

[TKrause]

Finally got a chance too get her back out on the water. I'm pleased to report that there was no hesitation and or missing.
Thank you for all the comments. Now to enjoy it until this 470 does something else weird.