Troubleshooting 1993 Force 150

[HotTommy]

Jiggz, here are my assumptions and conclusions.
1. Each cylinder must get spark at the right time and that time is determined by the position of the trigger assembly. I'll call the part that sends the signal to the #1 cylinder Trigger 1.
2. Regardless of how the rest of the ignition system is wired, Trigger 1 must be used to initiate the spark to cylinder 1. Otherwise it will not fire at the correct time.
3. My wiring swap allowed the signal from Trigger 1 to go through the portion of the switch box and coil pack for cylinder 5 before being routed back to cylinder 1. All this did was test the portion of the switch box and coil pack normally used for cylinder 5.
4. As swapping 1-5 and 2-4 showed no change (i.e., cylinders 4 and 5 were not firing properly after the swap), I concluded the problem must be either the part of the trigger assembly that fires 4 & 5, or the carburetor serving 4 & 5.
5. As spraying a fuel-oil mix into the bottom carburetor had no effect, I conclude the carburetor is not the source of the problem, so the part of the trigger that fires 4 & 5 is faulty.

 

[Jiggz]

Well said! You are correct that the wire swapping only tested the coil and CDI but not the trigger signal. Well, hopefully with a new trigger coil set you will soon start enjoying the fruit of your labor. Goodluck and make sure you post the final resolution to this problem for others to see.

 

[pnwboat]

Just from a cost perspective, I would still check out the lower carburetor and reed assemblies. The triggers are typically a low failure item and since your measures within specs., I'm not sure I'd go that route just yet.

Attached is a link for a DVA made with parts from Radio Shack for less than $5. It can be used to measure the trigger pulse (as well as the Switch Box input and output voltages)

http://www.thehulltruth.com/boating-forum/370139-1990-evinrude-timer-base-sensor-coil-bad.html

 

[Jiggz]

If I have any reservations about replacing the trigger coil is because the motor runs perfect at WOT. It's only when it goes to lower rpm or speeds that it runs rough. I wonder if Tommy has observed any fuel blowing back from the lower carb at low to mid speed? Or maybe even just fuel dripping. Those would have been a perfect symptoms of broken reeds.

 

[Jiggz]

Duped

 

[HotTommy]

Jiggz,
I've already ordered the trigger assembly. But it's not much work to look at the reeds. I may do that while I'm waiting. ... Thanks for the suggestion.

 

[Jiggz]

I believe with your inspection of the reeds, we have covered just about everything about your engine issue. So we are basically down to two choices, reeds or Trigger coil. And I'm quite sure by tomorrow we would have eliminated the reeds if they are still intact.

 

[HotTommy]

Better, but still not right.

I inspected the 4 & 5 reed valves (ok), installed the new trigger assembly, reset the timing and here's what I have. The engine starts easily and idles smoothly. (If it is occasionally dropping a cylinder at idle, I can't notice it.) The engine runs smoothly at full throttle and at some reduced throttle. But as the RPM gets down to what I guess to be 2500 - 1500 RPM the engine sound abruptly changes and the power noticeably drops as what I would describe as one cylinder dropping out. That miss continues as I reduce the RPM toward idle, but it becomes less noticeable as the RPM drops. That's why I can't tell if it is there or not at idle. .... I tried several rapid accelerations from idle and the miss is there even at full throttle until the RPM gets up. That makes me want to describe it as an RPM dependent miss rather than a throttle position dependent miss. ... Subjectively, everything I've done so far has reduced the problem somewhat. It is not so bad I wouldn't use my boat. I seldom cruise at the just-above-idle speed where it is noticeable. But I am frustrated by not knowing what is causing this. Here's a brief summary of things that might help in diagnosing this thing.
- New spark plugs and wires
- New flywheel
- New trigger assembly
- Carburetors cleaned twice and reassembled with new kit parts
- Both fuel pumps rebuilt
- All fuel lines and filter replaced
- Reed valves 1, 2, 4, & 5 inspected and found ok
- Idle mixture screws set from 1-1/8 to 1-1/2 in 1/8 turn increments with no noticeable difference

 

[pnwboat]

I don't know if this would have any affect, but since you've done just about everything else, check the by-pass covers. Make sure the 4 bolts on each cover are tight and the gaskets are in place and not leaking.

 

[Jiggz]

Another suggestion will be to de-carbon the engine. Make sure you do not overdo it. It is more of a preventive maintenance than anything else.

 

[HotTommy]

I don't know if this would have any affect, but since you've done just about everything else, check the by-pass covers. Make sure the 4 bolts on each cover are tight and the gaskets are in place and not leaking.

Are you referring to the fuel recirculation system?

 

[HotTommy]

For now I'm going to run the motor as is, finish the break-in, transition back to 50:1 mix, and be alert for other signs of unusual operation that might yield a clue. I might even put a little Sea Foam in it and bury a chicken bone in my back yard. Couldn't hurt.

 

[pnwboat]

[ Originally posted by pnwboat View Post
I don't know if this would have any affect, but since you've done just about everything else, check the by-pass covers. Make sure the 4 bolts on each cover are tight and the gaskets are in place and not leaking.

Are you referring to the fuel recirculation system? /QUOTE]

No I was not referring to the fuel recirculation system. The by-pass covers. Each cylinder has one. See link below.

http://www.ebay.com/itm/Mercury-For..._Accessories_Gear&hash=item2328d2e46c&vxp=mtr

 

[HotTommy]

OK.

 

[Jiggz]

For now I'm going to run the motor as is, finish the break-in, transition back to 50:1 mix, and be alert for other signs of unusual operation that might yield a clue. I might even put a little Sea Foam in it and bury a chicken bone in my back yard. Couldn't hurt.

Totally agree. I'll say get done with the break in first and if problem persists, then troubleshoot some more.

 

[HotTommy]

Ten hours later the problem is still there, but seems to be not as bad. I have an appointment to have a marine mechanic check it out for me. In the mean time I read something that raised a question. ... When I refurbished this boat and the previous motor (1994 Force 90 HP) last year, I never got the tachometer to work. The needle jumps when power is applied, but is otherwise stationary. When I swapped in the 150 this thread has been about, I simply connected the existing electrical connections. The tachometer still acts the same. .... Is it possible/likely that a bad or incorrect tachometer could cause my intermittent misfire problem? Would disconnecting and sealing the tachometer leads have any effect on how the motor runs?

 

[pnwboat]

It's worth a shot at this point. Try it and see if it has any affect.

 

[HotTommy]

Said another way, is the tachometer an essential element of the electrical system? If I disconnect it, should the engine continue to operate normally?

 

[Jiggz]

The tach is an optional accessory and is not an essential part of the electrical or ignition system. However, when setting idle rpm's and when doing some troubleshooting it does become an essential accessory. You can disconnect it and see if things will improve and if it does, then it tells you something is wrong with the tach. It's been awhile so let me review the rest of the post before commenting further.

 

[Jiggz]

OK, finished reviewing the entire thread. So basically the ultimate problem is the misfire between 1500-2500 rpm. I have two suggestions. One, retard the static timing to 28 degrees instead of 30 degrees. Test and if things doesn't improve, replace spark plugs with BUHX. If things improve with different type of spark plugs, reset timing back to original 30-S. Let us know what happens.