Intermittent spark at idle.

[studlymandingo]

I have been trying to use the new fangled search feature as I'm sure this has been covered many times over; however, I can't seem to filter out all the crap and don't get the responses I need.

So here's my dilemma: My 1986 150HP V-6 Mariner has been running well until the last time out. It began to idle poorly and died several times while trying to get on plane. Once I was running without stumbling, I could go to idle and back to WOT with no problems. Today I fired her up on the muffs, the motor would surge; I checked the spark, and while it was stumbling, some plugs were not firing, I could bump it up to a fast idle (1200 RPM) and I would get a constant spark on all cylinders.

Compression is within a pound across the board.

Is this the switchbox, or could it be something with the idle stabilizer? I would like to know where to go before throwing a few hundred dollars worth of parts at the motor.

 

[studlymandingo]

Re: Intermittent spark at idle.

Just checked everything here again at dusk. The spark on the starboard side of the motor (all 3 plugs) is much weaker than the port side. I doesn't seem to be intermittent like I thought, just weak. Makes me think switchbox is allright. Now I'm thinking it's the low speed winding on the stator. It looks as if the stator has been replaced fairly recently, but I am aware that this does not mean it can't be a defective part.

 

[andy6374]

Re: Intermittent spark at idle.

Do you have a DVA? It's the only real way to know if your stator is ailing. If not you can get a good idea through the resistance tests, do you have a manual? I can give you the specs if you don't.

You said the spark is much weaker on the starboard side...did you use a spark gap tester to make this accessment? You should get a blue snappy spark that can jump a 7/16" gap.

Switch all the wires from one switchbox to the other. If the "weak" spark jumps from the strb. bank to port than it's most likely an ailing switchbox. If the weak spark stays on the strb. bank than it's your stator.

 

[studlymandingo]

Re: Intermittent spark at idle.

I do have a DVA and a manual. I haven't done the resistance tests yet. I have the Seloc manual and haven't looked for the specs as of yet.

I did use a spark gap tester, the port side I got a bright blue spark definitely "snappy". The starboard side was weak, and I thought it was intermittent until I did it at dusk, where I could see it was continuous but very faint compared to the port side of the motor.

 

[andy6374]

Re: Intermittent spark at idle.

So swap the switchboxes and see if the weak spark jumps

 

[studlymandingo]

Re: Intermittent spark at idle.

in

 

[andy6374]

Re: Intermittent spark at idle.

??????

 

[ricksrster]

Re: Intermittent spark at idle.

What does "in" mean?

 

[studlymandingo]

Re: Intermittent spark at idle.

"in" means that road runner crapped out while I was trying to post. The weak spark changed sides when changing the wiring on the switchboxes....Stator? I am bidding on a new one on e-bay right now. What do you guys think?

 

[andy6374]

Re: Intermittent spark at idle.

The weak spark changed sides when changing the wiring on the switchboxes....Stator?

Nope that means it's your switchbox. Think about it. For instance.....

You have bank 1 with switchbox1 and bank 2 with switchbox 2. bank 2 had weak spark.

You swapped switchboxes and now you have bank 1 with switchbox 2 and bank 2 with switchbox 1. bank 1 now has weak spark.

The common problem...switchbox 2 !. If the weak spark stayed on one bank and didn't jump banks, then it would be the stator.

Unfortunately you should replace both switchboxes. A bad one came damage another. Go with CDI/Rapair switchboxes too, much better than merc.

 

[studlymandingo]

Re: Intermittent spark at idle.

MMM... okay, I guess I was looking at it backwards. I was thinking that by switching all of the wires on the switchbox, I was switching the input from the stator as well, throwing the weak spark to the other side. I've worked on car engines since I was 13, distributer issues are so much easier.

I'm just trying to get this right before I start throwing $200 parts at it!!
I do appreciate the help. I want to go boating this weekend; I just won a new GPS for a great price on e-bay! It will be here Friday, can you imagine the torture of having a new GPS and being unable to play with it right away? That is wrong in every sense of the word!

 

[KCLOST]

Re: Intermittent spark at idle.

Hold on!!!!!!!

Well, it sounds like you didn't actually switch the switchboxes but just switched the wires from one to the other... Is that correct???

What you should do is this... Put back everything back the way it was... Test and get your baseline condition, which should be like before where the starboard bank has the weak spark.

Now all you have to do to test the "STATOR" is to switch the stator leads from one switch box to another. Each box has two wires you need to move to the other. A Blue and Red on one, and a Blue/white and Red/white on the other. They connect at the top. Switch those two pairs of wires from one box to the other. Do not move any other wires... You have trigger leads that are only designed to stay with a particular box or bank, otherwise the engine won't run properly, that is why you want to put everything back they way it was. Right now your firing is out of sequence!

Now, if the weak spark condition moves over to the other bank, you have a bad stator. If it stays the same you most likely have a bad switchbox. But keep in mind that switchboxes don't normally cause a weak spark, they either work properly or not at all. My bet is it's the stator.

Let us know

 

[andy6374]

Re: Intermittent spark at idle.

Yeah KCLOST is right. What I told you do to only tells you if have a bad switchbox or a comb. of a bad stator and/or trigger.

But....KCLOST
If he swapped ALL the wires from one switchbox to the other and the weak spark jumped from one bank to the next it would still have to be the switchbox.

You can swap the switchboxes any time you like (not really necessary but you could), and it shouldn't matter as long as the stator/trigger/and coil wires are routed correctly. So if you literally just switch the inner outer boxes, nothing will change. Unless one box is bad and in that case weak spark will jump from one bank to the next.


Besides I don't think it's the trigger because doesn't the trigger coils control firing on 1,2 and 3,4 and 5,6. A bad trigger would cause loss of spark on pairs of cylinders not banks, right?

 

[studlymandingo]

Re: Intermittent spark at idle.

Well, I won a new-in-package stator on ebay for 103.00. I'm checking the switchboxes again in the AM, if it's the boxes, I guess I'll have a new stator for when the time comes. OR maybe I could find another V-6 that needs a stator, then a project boat, and ... I think I'm getting ahead of myself again.

 

[KCLOST]

Re: Intermittent spark at idle.

andy,

I'm sure he doesn't have a trigger problem but you don't want to switch trigger or coil wires from one bank to the other, switching the boxes is fine, but don't want to switch the wires... Now the firing sequence is messed up...

 

[andy6374]

Re: Intermittent spark at idle.

KCLOST-
Of course these types of things can get overwhelming trying to decribe in words, I wish we have things to point too.

But still (and I am not arguing by any stretch of the imagination, I just want to make sure I am not tricking myself)....

If he just switched one switchbox for the other (which would keep the same stator leads with the same bank because each set of stator leads is staying with its set of tigger and ignition coil leads, all that has changed is the switchbox), and the weak spark jumped....it would be the switchbox. Because this is showing that both stator leads (strb and port) can produce good spark and that the only thing the weak spark has in common is the bad switchbox.

 

[KCLOST]

Re: Intermittent spark at idle.

Correct andy,

 

[andy6374]

Re: Intermittent spark at idle.

What's the difference between switch the boxes and switching all the wires? If he switched all the wires, wouldn't that be exactly like switching the boxes.

We are running in circles hereo

 

[KCLOST]

Re: Intermittent spark at idle.

Ok,

Draw this on paper... You have two boxes, each with a set of stator leads that charges each box. And coil/trigger leads that should stay with a certain bank of cylinders.

Now, switching all the wires, most importantly the stator leads and the wires going to the coils/sparkplugs does this.

The stator windings have been switched from one box to another. Now if you have a bad stator winding, now the bad voltage is going to the other box. In that case you would see weak or no spark going to the same bank because we move the coil leads over also, this is true if all the wires were switched. If just the sator leads are switched only, it would move.
On the switchbox. Because by switching all the wires in this case. The outgoing coil/sparkplug leads have been switched from one bank to the other. So if a box is bad and the "out-going" wires from it are now going to a different bank, you would see the problem move to that bank also.

(This and several other of my posts have been edited)

 

[andy6374]

Re: Intermittent spark at idle.

My bet is the stator, since it is a weak spark issue (low voltage).

This I agree on for sure. I am drawing the picture