No fire on cylinder 4

[BackyardKrazy]

hey guys, I have been trying to trouble shoot this myself, but some of the procedure doesn't make sense. Ill start from the beginning.

the engine is a 1989 125hp. Works like a top, untill this morning. ripped across the lake, and when i stopped I noticed a skip and my idle was really low. Great what now. Anyways I got home, narrowed it down to the bottom cylinder, #4. i switched out a known good coil pack, and still the same issue. tried a new plug, same thing.

So i cracked open my manual and looked on outboard ignition.com. Its missing on one cylinder, so i tested my stator at 725 ohms between the yellow and blue (seems in spec) and between each trigger set i have exactly 50 ohms. Tested my compression, each cylinder hitting 140-150 no prob.

So it says to disconnect a kill wire from one pack, now I'm stuck. What do they mean? I will attach a pic of my wiring diagram.


Now one other thing. I have noticed its not charging like it should. The other day my volt gauge krept up to 14.2 after cruising wide open for 4-5 mins, but this morning stayed on 12V.

I thought maybe this would show up with the stator testing but it reads 725 ohms.

please help, Its my vacation this week and now im without a boat!!

 

[Jiggz]

The kill wire is the white wire off each module. If that doesn't solve your problem, the next move is to switch the modules physically. If the problem follows then module originally feeding #4 is faulty.

 

[BackyardKrazy]

perfect, Thanks! But what about the charging issue, as far as i understand the engine should start charging above 1000rpm?

Ill switch modules this morning and try it again.

 

[jerryjerry05]

Test the rectifier for continuity.

​To test the stator you'll need a DVA meter.
The ohms can be tested with a regular analog meter but the voltage test needs a special attachment.

Use the search function and look for making the attachment or buy online?

This is from CDI electronics.

1. Check stator and trigger resistance, trigger wire sets read approximately 50 ohms between the wire sets (DVA-5V or more), stator reads 680-800 ohms, DVA 180V or more from blue to yellow.
2. If readings are good, disconnect kill wire from one pack. (white wire)If the dead cylinder starts firing, the problem is likely the blocking diode in the other pack.

Like I suggested in the other post. Check the trigger leads.

 

[BackyardKrazy]

Test the rectifier for continuity.

​To test the stator you'll need a DVA meter.
The ohms can be tested with a regular analog meter but the voltage test needs a special attachment.

Use the search function and look for making the attachment or buy online?

This is from CDI electronics.

1. Check stator and trigger resistance, trigger wire sets read approximately 50 ohms between the wire sets (DVA-5V or more), stator reads 680-800 ohms, DVA 180V or more from blue to yellow.
2. If readings are good, disconnect kill wire from one pack. (white wire)If the dead cylinder starts firing, the problem is likely the blocking diode in the other pack.

Like I suggested in the other post. Check the trigger leads.

I tested the rectifier leads, and it has continuity from both ac terminals and also between the red 12v terminal to the ground?? Does that sound right?

I also tested the trigger wires (with them still connected) and got 50 oms between each one.

So the DVA meter is required to test the stator how? I have 725 ohms between the blue and yellow, im unclear on the procedure of the DVA meter. it basically tests output voltage directly from the stator?

 

[Jiggz]

The rectifier on this motor, 89-125HP (same as mine) can be easily tested using a voltmeter. With all auxilliary equipment off, radio, depth finder, etc. Test battery terminal voltage and note it down. Next tests voltage at the rectifier output, note it down. Then start the motor, still with all aux equipment off raise the idle rpm using the throttle control by placing it in fast idle. (There are usually two type of throttle control, one had a center button that you push and then placing the throttle in forward. The other needs to be pulled straight out towards the driver and push forward) and it should idle around 1500-2000 rpm. Then take voltage reading on the AC side of the rectifier and also on the output side and take note. Finally take battery terminal voltage and note it down.

If the output voltage of the rectifier at fast idle is higher than the its voltage reading when engine was off, that tells you the rectifier is working. As such the battery terminal voltage with motor running should be higher than when the motor was off. If the battery terminal voltage remains the same or worse is lower when the motor was running, it tells you something is either draining or using battery current or there is high resistance connection.

There should be a ckt breaker between the rectifier output and the battery. Make sure it is not tripped. Remember, the charging circuit on this motor is rated only at 7 amps, which is only around 84 watts. This is just barely enough to power a car stereo and a depth finder. And if you have other aux equipment, you can bet you will drain your battery in no time even at WOT speed.

My original rectifier was broke and now replaced with a cheap Radioshack rectifier that costs less than $5.

 

[jerryjerry05]

The stator tests:
​The DVA or peak reading volt meter is used to measure the voltage output from the stator.

A regular analog meter can read the OHMS but not the voltage.

Nordin recently posted about making an attachment for the DVA to do the readings.



​

 

[BackyardKrazy]

OK. I started pricing ignition parts, big $ and i'm not positive on what component is wrong. So ai found a 1989 125 online here in Canada, complete except lower end. parts due to no compression on 2 cylinders. I bought it unseen and had it shipped to me, $460. Good deal, the power trim works perfect doesn't drop at all, and the engine is in clean great condition. Tons of great parts.

So i started with the Modules, wiring headache but relatively easy to change. No difference with the firing issue on cyl 4.

Moved on to the flywheel stator etc.. swapped it all over, flywheel stator, trigger. i swapped the rectifier as well, it was so pretty compared to mine, I just had to.

Took it out on the lake, ran a bit funny, noticed the carb were seeping some fuel and the air/fuel mix adj did nothing. took it home and i rebiult the carbs completely with new kits.

Back to the lake, started mint... adjusted idle a tad and ran like a dream in neutral and in gear, GOLDEN.... so i thought.
I accelerated to get on plane, and sputter sputter.... not too good under load.... checked a few things and drove around hoping it would "clear up". headed toward the ramp, full throttle and killed the switch. Got home pulled the plugs, and waddya know, #4 is wet and not firing. Still great at idle, just not under load.

So I switch coils 3 &4 and changed the plugs. Tried it again, same issue.

And its still not reading over 12v while running across the lake.

im thinking about getting another compression tester, just to confirm readings.

What do you suggest I do with this thing????

 

[Nordin]

As you stat it is idle great, does it runing at all cylinders at idle? The 125Hp is a 4 cylinder engine and it can be hard to hear if it is runing at 3 or 4 cylinder at idle.

Pull the boot from the plug at idle one by one for a short time (just for a second) and check if the engine sound change.
If the sound do not change at #4 plug it shows no fire.

If you have a timing light, use it instead and check for spark at all cylinders.
If all sparks and still wet plug at #4 check the reeds and also the fuelpump diaphragm for cracks.

 

[jerryjerry05]

Check the trigger leads.
​The wire is very tiny and breaks easily.
The shrink wrap can hold the wire in place and seem to be good.
Give it a good tug and see if it comes loose.

Another thing.
The fuel pump sets on #3 cyl.
It's operated from the vacuum from #3
It has a hose leading to #4 and if the diaphragm is bad it can leak fuel into #4

 

[BackyardKrazy]

Check the trigger leads.
​The wire is very tiny and breaks easily.
The shrink wrap can hold the wire in place and seem to be good.
Give it a good tug and see if it comes loose.

Another thing.
The fuel pump sets on #3 cyl.
It's operated from the vacuum from #3
It has a hose leading to #4 and if the diaphragm is bad it can leak fuel into #4

I've triple checked the trigger leads, the old one and the new (used) one I just put on. He swears the engine ran top notch, just no power.

Can You elaborate on the hose leading to #4? Not sure what you mean, but it sounds very similar to what i have going on.

the engine is running smooth, and on all 4 cyl at idle, even in gear. Its only when you load the engine and accelerate, it starts missing, and one thing i forgot to mention, my tach stops reading at 4000rms... Wierd.

 

[Nordin]

I will try to elaborate, maybe jerryjerry chime in and help.

The engine has a two stage fuelpump. most smaller engines use one stage pumps which operates from one cylinder.
But as a bigger engine needs more fuel and it has a two stage typ which operate from cylinder 3 and 4.

Stage 1 use vaccum and overpressure from cylinder 3 and stage 2 from cylinder 4.
Then there are checkvalves in the pump for inlet, output and between the two stages to lead the fuel from inlet through stage 1 and over to stage two and then out from the pump to the carbs.

In your case maybe the diaphragm in stage 2 is ripped or has a hole which will allow fuel to enter directly to the cylinder.

 

[BackyardKrazy]

Wow.. everyone I think I have a grip on this engine someone teaches me something new.

I replaced the fuel pump last year, due to a small pinhole in the diaphragm. It was bogging at open throttle. I don't suppose I should "assume" it's still good.....

Is the diaphragm that I would have replaced the same one you talking about as the second stage?

 

[Nordin]

There is only one diaphragm and it handles both stages.
The diaphragm has two areas one is larger and one is smaller.
The larger is stage one and the smaller is stage two.

They operate in two different chambers in the fuelpumpbody.
The chambers are separeted by a checkvalve.

Stage one operates from cylinder 3 and stage 2 operates from cylinder 4.

Sorry if I makes you puzzled by elaborate/explain in a strange way.

 

[jerryjerry05]

Never assume.

 

[BackyardKrazy]

Nordin... I owe you lunch!

I removed the fuel pump and found this:



Smaller diaphragm is torn. I grabbed the one off my spare engine, checked it and it was perfect.

Wow, it works better now than ever!!

I used a Sierra kit to rebuild it last year, That should be a good replacement part right?

I am going to order this this to keep on hand: waterpump kit, fuel pump kit, carb kits. Cant be missing a good weekend over simple parts.

So as far as my issue with the tach dropping off at 4000rpms, I put my old rectifier back on and that problem was solved as well. It was weird, I tested it according to my repair manual and it tested good. Although, I had to put the purple tach wire on the top AC pin, even though I know positively it was on the bottom one.
Now it works all the way up through the entire rpm.

Thanks guys, I (once again) really appreciate it. This forum has saved y butt more times than I can remember.

These force engines dont have market value like a Merc or yamaha but mine sure works good now!!!

 

[Nordin]

Well nice to hear you found the issue.

With some logical troubleshooting you will find the solution ....at last.
Force/Chrysler engines are no rocket science, only basic oldschool well working design.

Was this diaphragm replaced last year? A back blow can cause a new diaphragm to ripp. Have that in mind.
A spare diaphragm is a "must have" in the boat, and it is easy to change with only six screws.

Sierra will be a replacement part, BUT Mercury dealer or others will have the OEM part. Partnumber is F438747 and maybe better quality.
I do not know. I use them because I buy parts from a store that have only OEM.

As jerryjerry said ........ "nerver assume". Check the reality.

The advantage with a two stage pump (at a 3 or 4 cylinder engine or more) is if one fails as yours, the engine will run and take you home but not with full performance.

The smaller Force/Chrysler engines with twin cylinders 25Hp and up to about 65Hp use the same pump and will not run if one stage fail, because it has a hard time to run at only one cylinder.

 

[BackyardKrazy]

Thanks again Nordin! Im ordering spare parts today to keep on hand.

 

[BackyardKrazy]

Well I had a good few days, now its sputtering again but this time it doesnt seem to be one particular cylinder, @ issues, The green and yellow stator wire chaffed through on the flywheel. I repaired it, and it still runs crappy. 2nd, I started testing wires and found some continuity between the 12v side of the rectifier and ground.... this goes all the way back to the starter solenoid. Any thoughts? The breaker is not tripped.

 

[Jiggz]

Disconnect the rectifier (input wires) for now and test the motor. is it still crappy? Then it is not the rectifier.