Coil Firing All The Time

[Bassin_Bob123]

Have a Merc 150 XR2 SN: A114595. Just got back from my boat Doc and he was unable to fix the problem. Evidently, this year 150 has it's own style of trigger assm and what is happening is #6 coil is trying to fire all the time. Sort of like an electric starter on your stove. I initally took it in to have the timing checked and the RPM "in gear" checked which I assume is related to the timing as well.

Does anyone have a clue as to what might be the problem here with the coil #6 only doing the constant firing? I don't want to toss parts at it to fix and hate the thought of the 240 miles trip to the closest Merc Dealer that knows this system. Could the trigger assm be defective or should I concentrate on looking at the outer or inner box controllers?

HELP

 

[Laddies]

Re: Coil Firing All The Time

There is nothing speical with the XR/2s trigger it's the same trigger that most V/6s of that time used so you might want to find a good service shop and have it checked out.

 

[CharlieB]

Re: Coil Firing All The Time

You can verify that diagnosis with a spark tester and a clip on inductive tach.

Test each cyl for spark AND rpm with the tach.

IF #6 is continually firing the tach will obviously read about at least twice that of the other cyl's.

If so then replace that ignition module as that trigger also fires a cyl on the other box, if all other cyl's read good then the trigger is good, the ignition module is bad.

VERIFY the diagnosis BEFORE ORDERING ANY PARTS.

NO RETURNS etc.....................

 

[j_martin]

Re: Coil Firing All The Time

To help
Coil affects 1 cylinder.

Switchbox affects 1-3 cylinders, all on one bank, with the caveat that very rarely it'll affect the other bank through the bias circuit. Easily isolated by removing the bias jumper.

Trigger affects 2 cylinders, one on each bank, opposite in timing, ie 1 and 4.

Coil can't fire without switchbox input, so I'd hazard a guess that it's a switchbox. You should be able to move the bug by swapping the switchboxes and see if the bug goes with the box.

hope it helps
John

 

[Bassin_Bob123]

Re: Coil Firing All The Time

My UTMOST thanks to LADDIES, CHARLIEB and J MARTIN for all the great help on this issue. I certainly will be trying out the helpful hints. THANKS GUYS! Much appreciated.

 

[Bassin_Bob123]

Re: Coil Firing All The Time

Opps -- FOR CHARLIEB

MY unit has both a High Speed Spark Advance Module and a Idle Stabilizer or Low Speed/HighSpeed Advance Madule. The Inner Switch Box and Outer Switch Box assm. may be the ones that Martin were talking about but I don't see a Ignition Module per say on my unit other than the 2 modules and the Trigger unit

 

[CharlieB]

Re: Coil Firing All The Time

We are talking about the two ignition modules stacked one atop the other, with two wires from the stator, three wires from the trigger three wires to coils and the bias wire linking the two boxes together.

 

[Barnacle_Bill]

Re: Coil Firing All The Time

We are talking about the two ignition modules stacked one atop the other, with two wires from the stator, three wires from the trigger three wires to coils and the bias wire linking the two boxes together.

To avoid confusion, Merc calls them switch boxes.

 

[j_martin]

Re: Coil Firing All The Time

The two little ones are called modules, advance module, and idle stabilizer module. Both mess with the bias to alter timing under some conditions, and both are completely disposable, especially for troubleshooting. Disconnect them till you get it to run reasonable, then hook them back up one at a time.

In truth, the idle stabilizer isn't needed if the engine is in decent tune running decent gas. The advance module, if it's the one I think it is, advances the timing from 19 to 25 degrees at 5000 rpm, then retards it back to 17 degrees at 5500. Unless you are running at half throttle a lot of the time, (like pulling skiiers) you can safely discard it and set the timing to 23 degrees at WOT. The engine will likely spin up to 6000 rpm and like it.

Hope it helps
John

 

[Bassin_Bob123]

Re: Coil Firing All The Time

Thanks again for the replies. Most helpful! Bill -- I do have the manual that came with the boat and it's pretty detailed. Being a mechanic makes things a bit ez'er but this old boy aint that sharp on a outboard. Basics are pretty straight forward but when you pick up a manual for timing the unit, see the necessary tools you need like a special dial indicator to insure the piston is set at .462 and aligns with the mark on the flywhell at 462, it gets pretty scary. Aint like a good old ez gas or diesel motor out of a truck so all the replies really help guys and it is much appreciated.

I will try the 'module' elimination trick and see how it runs.

TY and thanks again guys.

Bob

 

[j_martin]

Re: Coil Firing All The Time

Here's my "dial indicator" setup.
1. home made adapter
2. adapter installed
3. Cheep digital caliper strapped on.

 

[j_martin]

Re: Coil Firing All The Time

4. Swing past top and set to 0
5. Find .462 BTDC
6. Set the pointer

hope it helps
John

 

[Bassin_Bob123]

Re: Coil Firing All The Time



Martin you are the man! Nice little and ez setup to check the timing. Kwel invention! Sometimes the easiest is right in your tool box and you just can't find a way.

Thanks a TON!

Bob