1987 85hp Force Top End Power Loss

[questar17]

Was out on lake pulling kids on tube for about an hour the other day and idled down to switch riders which took about 15 minutes (14 minutes longer than assumed) so the engine was still idling. When attempting to go to full throttle, engine would only power up to about 1/3 of what it had been.

Gimped back to dock and trailered home. Checked the plugs and they seemed a bit grimy, but all seemed to a dark color with signs of fuel. Cleaned plugs and went back out with same result. Came back, checked the compression and had ~120 lbs. plus or minus less than 3 lbs. on each of the 3 cylinders - is that good, fair or poor???)

Side note - have always wondered whether this motor was ever hitting top end with respect to rpms. Does not have a tach hooked up so don't know what the high end rpms were, but now can barely get the boat up on plane.

Have been looking through the other forums posted here and saw the mention of a couple things but for slightly different symptoms. Any suggestions as to what to look for or where to start would be greatly appreciated?

 

[roscoe]

Re: 1987 85hp Force Top End Power Loss

Welcome to iboats.

Since it appears that the compression is acceptable (110-130 is ok for that motor), and you say cylinders are getting fuel, I would check for spark on all 3 plugs.

You may have a loose wire, had a coil fail, or a cd module. Hopefully not the trigger or stator.

Let us know how the spark checks out.

 

[questar17]

Re: 1987 85hp Force Top End Power Loss

Thanks for the reply. Will try checking for spark tonight. What is a CD module and if it is bad, can one find replacements for this engine? Will post what I find out on the spark.

 

[roscoe]

Re: 1987 85hp Force Top End Power Loss

yes replacement cd modules are available.

From the sparkplug, follow the wire back to the coil, then follow it back to the blue or black box. That is the dc module.

Wiring these in can get a little confusing, I would suggest you purchase a Clymer Force repair manual, and follow the wiring instructions with the replacement part.

Hopefully it is only a coil.

 

[questar17]

Re: 1987 85hp Force Top End Power Loss

If I have no spark from a plug, I believe I saw on another forum that you suggested swapping out a known good coil with the coil from the non sparking plug. I assume this is to isolate whether the problem is with the coil or the CD module, is this correct? Is this the only way or simplest way to test a coil? Is there anything special one should know when swapping coils?

 

[questar17]

Re: 1987 85hp Force Top End Power Loss

A bit more information of where things are at... I checked for spark on all three plugs and did not have any spark on the 2nd plug. Subsequently I switched the coils for plug 1 and plug 2 and checked for spark again. Still no spark on plug 2 yet spark on plug 1 so it appears the coils are fine. Does this leave only the CD module as the problem? The coils for 1 and 2 are run off of the CD module located on the far right while the coil for 3 is run off of the CD module on the left which has a 2nd connector that is unattached. I thought I read in one of the forums that it may be possible to use this open connector of the left side CD module to run coil 2 but only with some rewiring - is this correct? If so, how would I go about it? Thanks for all the help.

 

[roscoe]

Re: 1987 85hp Force Top End Power Loss

Good job.
It does appear the coils are ok.

So it is likely that either the cd module is bad, or.... the trigger is not sending a signal to the cd, telling it to fire.

And yes, you do have an extra output on the 2nd cd.

It would be easier to swap the cd's at this point, to keep all the wires straight.

You could trouble shoot the trigger for output, but without a manual with the diagrams and procedures, it would be easier to swap the cd's.

I would label all the wires to and from, then swap the cd's.

 

[questar17]

Re: 1987 85hp Force Top End Power Loss

Roscoe,

I went back through the forums and read through what you had suggested to another individual attempting to do the same thing and not sure I followed it completely. Is there any correlation between which coils can be run off of which CD module and which 2 coils can be run off of one CD module? As it stands, the red wire is open and the orange wire of the same CD module is going to 3. As for the other CD module, the red wire is going to 2 (which is bad) and the orange wire is going to 1. Don't know if any of this makes any difference or not or changes any of what you suggested in the other forum.

 

[questar17]

Re: 1987 85hp Force Top End Power Loss

Roscoe,

One other question regarding the CD modules. Is the module that runs 1 and 2 the same exact module as the one that runs 3? I heard that if these 2 modules were swapped that one of the wires needed to be switched for it to work right - is this correct? If so, which wire would that be?

 

[questar17]

Re: 1987 85hp Force Top End Power Loss

Roscoe,

Thanks for you assistance on this - here's a final update just for the record. I successfully swapped the 2 CD modules and that appeared to resolve things, at least from a preliminary standpoint - won't be able to get it out on the water tomorrow. After the switch I fired it up and was able to rev up the throttle in neutral which wasn't able to do before so I'm optimistically guessing that the problem has been resolved.

A couple of notes though... the motor is a 1987 model 85hp and it had 2 blue coils and 1 black coil and had 1 blue CD module and 1 black CD module. As it turns out they are not directly compatible as the wire harness connecting the black CD module to the black coil had a male/female configuration while the blue CD module wiring harness to the blue coils had a female/male configuration, which meant I had to splice and switch each of the 2 connectors coming from each of the CD modules in order to make a blue coil work with a black CD module and a black coil work with a blue CD module.

I went to a link I found on another forum on this site that carried these parts, it seemed to indicate that the blue coils and blue CD modules are for 1988 and newer models. The black coil and CD modules are the replacement for the 1987 model 85hp motor, which is what I had also heard from my brother via his local outboard guru in the midwest.

Just thought I would share that in the event someone else is attempting to make use of this forum as I have done. Thanks again - nothing like some helpful information to put a smile on someone's face!