compression test and timing - 1994 250 hp Johnson

[adg]

Hello again,

after the mechanical things I have done on the motor I wanted to figure out why it is not running smooth. Now today I did a compression test and checked with the timing light. It is my first time ever to use a timing light so I wonder what I've got.

Compression first:

Cyl 2 (top left) 100 psi Cyl 1 (top right) 122 psi (top right and left when looking from behind the motor)
Cyl 4 100 psi Cyl 3 120 psi
Cyl 6 100 psi Cyl 5 100 psi
Cyl 8 100 psi Cyl 7 100 psi

From this I would believe after what I have read here on the forum that the 80% rule is 0,8 * 122 = 97 so the variance between the cylinders would be within acceptable range? Is this right?
I do wonder why cyl 1 and 3 are so much higher than the rest but I am not a technician so really don't know.

Then for the timing:
I checked on all the cylinders - when doing cyl 1 I seem to see only a spot close to 3 - neither can I find 1 on the flywheel - don't know why. But it lights up steady on the same spot.

The rest of the cyl light up as they should (that is how I know the cyl sequence as written above) BUT there is a problem with cyl 7.

The timing light is only rarely lighting up and it happens to be when the motor is making the kind of cough that makes it run irregularly. Does this mean I have found my faulty cylinder? or at least where there is no consistent spark when it should?

My question to you is now, what next step must I take to try to eliminate this problem? As far as I can understand it can be the spark plug cable from a little box on the powerhead to the spark plug, or it can be the little box on the powerhead? or something else? I post a picture to show you what I mean with that little box on the powerhead.
Appreciate any guidance to solving this problem - thanks.

 

[175se]

Re: compression test and timing - 1994 250 hp Johnson

that little box as you say is an ignition coil (1 per cyl) do a ohms test on the plug wire, if you have a peak reading meter check the output on the primary for that cyl.

 

[boobie]

Re: compression test and timing - 1994 250 hp Johnson

Do a cylinder drop test when running at a high idle and see if you can find a cylinder that isn't firing.

 

[adg]

Re: compression test and timing - 1994 250 hp Johnson

175se - thx I have done an ohms test on the plug wire as explained in this video (basically put the leads in each end and put the meter on 20k ohms: (youtube video showed how to https://www.youtube.com/watch?v=U27Gp_uQDLU

when doing as this guy does it I go from 1(before testing) to 0.00 (when testing) - does that mean the wire is good? on youtube the guy says I must have some 8-10k ohms per foot? I get the same reading for all plug wires.

I also have taken the ignition coil off and would like to test this one but unsure where to put the leads and what I should read? Any suggestion? the coil is marked 582508 - guess this is an omc number - and see pic below
View attachment 230814 View attachment 230815

 

[daselbee]

Re: compression test and timing - 1994 250 hp Johnson

You have intermittent firing on one cylinder as you are looking into the timing light?
OK, swap coil and plug wire with a known good firing cylinder.
Forget that 8-10k per foot resistance test crap.

 

[adg]

Re: compression test and timing - 1994 250 hp Johnson

You have intermittent firing on one cylinder as you are looking into the timing light?
OK, swap coil and plug wire with a known good firing cylinder.
Forget that 8-10k per foot resistance test crap.

thx daselbee - will go back to the harbor and try this.

boobie: I don't have such a tool to be able to take off the plug wire while motor is running (don't like voltage in my hand), if swapping coils and plug wire does not clear things up I will get such a tool and do the cylinder drop test. thx for input.

 

[adg]

Re: compression test and timing - 1994 250 hp Johnson

You have intermittent firing on one cylinder as you are looking into the timing light?
OK, swap coil and plug wire with a known good firing cylinder.
Forget that 8-10k per foot resistance test crap.

UPDATE: I have swapped coil and plug wire with the cylinder above (that would be nr 5). After swapping nr 7 still did not spark - the timing light blinked once. nr 5 worked just fine. So I guess the problem lies not in the plug wire nor in the coil. The problem seems to be before the coil.

What can I test now as a next step? Or do you know what the problem is?

 

[adg]

Re: compression test and timing - 1994 250 hp Johnson

Do a cylinder drop test when running at a high idle and see if you can find a cylinder that isn't firing.

boobie: I did this test and took off the wire plug on nr 7 when the engine was running. There was no effect whatsoever in rpm or how the motor performed as I could hear. This would confirm this cylinder is not firing at all? see also post #7 - thx for input

 

[boobie]

Re: compression test and timing - 1994 250 hp Johnson

As a guess without doing the proper testing I'd say a bad power pack. Also check ALL the wiring around the pack and ect for a loose, broken or corroded connection.

 

[175se]

Re: compression test and timing - 1994 250 hp Johnson

also as post #9 says check the pins from the timer base, had that problem before.

 

[adg]

Re: compression test and timing - 1994 250 hp Johnson

boobie/175se: ok will check all connections from the power pack this afternoon and possibly spray with some crc or so. btw what is an ECT? And where can I find the ECT on my motor?

thx for input.

 

[daselbee]

Re: compression test and timing - 1994 250 hp Johnson

Look for a pinched wire under the pack. When you bolt the pack down, a timerbase wire can get pinched to ground.

ECT is Boobie's way of saying "etc" as in "etcetera". Right B?

 

[adg]

Re: compression test and timing - 1994 250 hp Johnson

OK here is what I did this evening:

I used the cdi website checklist what to check if no or intermittent spark on one or more cylinders.

I measured the power pack resistance by checking all orange wires from the coils throughout the power pack. Here are the results:

cyl 1 orange/blue to blue 115,9 ohms
cyl 3 orange/green to green 118,2 ohms
cyl 5 orange/blue/white to blue 119,6 ohms
cyl 7 (the one with intermittent spark) orange/green/white to green 124,5 ohms
cyl 2 orange/purple to purple 148,7 ohms
cyl 4 orange/pink to pink 115,7 ohms
cyl 6 orange/purple/white to purple 146,1 ohms
cyl 8 orange/pink/white to pink 115,6 ohms

The check list mentions the typical range is 90-150 ohms but you should have approx the same reading. Would my readings categorize as approx the same?

I do not fully understand the meaning of these results, does it mean that the power pack is ok? and the reason must be somewhere else?

There is also some items where the resistance should be "Shorted" or "Open or M range". How can I measure these wires?

I also checked all other contacts I could find, none looked corroded or loose. Where to go from here?

thx for any input.

 

[boobie]

Re: compression test and timing - 1994 250 hp Johnson

Right D. :lol:

 

[adg]

Re: compression test and timing - 1994 250 hp Johnson

Any feedback on the measurement results or other ideas anyone? I would def. like to solve this issue. Appreciate yr feedback.

Maybe not said earlier, but when I run the motor on the water from approx 3000 rpm and up it will run much better and I notice more power suddenly comes in the motor. Does this explain anything?

 

[daselbee]

Re: compression test and timing - 1994 250 hp Johnson

First off, you cannot really use an ohmmeter to measure the resistance of the orange/stripe ignition primary wires.
You are measuring into what's known as an active electronic circuit, one that contains semiconductor devices.
Differences in meters, differences in the semiconductors inside the pack; both of those factors affect the readings you will get.
My meter, for example might very well give completely different readings.
This is especially true when reading into the timer base.

However, I would say that those readings, while different, do not point to a specific fault that would cause #7 to misfire.

The flywheel is spinning, and due to the magnets attached underneath, it is generating voltage/current pulses from the timer base. There are 8 pulses per revolution of your flywheel, 45 degrees apart from each other. The pack detects these pulses and fires the appropriate spark plug at the precise time.
Now, coming from the timer base, you have a specific colored wire for each cylinder. I know the colors for a V6, but not a V8. Some colors may be the same....for instance, the colored wire for the top cylinder from the timer base to the pack is blue on a V6. Might be the same on the V8. The color for the bottom cylinders is green (both sides, but different wires). Middle cylinder V6 is purple.

OK....for #7 to be flashing intermittently, either something is wrong with the pack, OR something is wrong with the input pulses from the timer base to the pack on ONE of those colored wires leading from the timer base to the pack. Only two real possibilities.

Inspect very carefully the dark rubber plugs (2) that connect the TB to the pack. Those pins can push back into the body of the plug, and look connected, but actually not be making contact. That would explain the intermittent #7.

There are very specific tests you can do with a multimeter and a DVA adapter for it. The DVA adapter collects those high speed pulses, "stores them up" so to speak, and gives you a DC voltage value that represents those pulses. Something you can use.

So, if you do not want to go further with meter testing, the only other thing you can do is shotgun the pack, and then the timer base.
Timer base is a possibility, but not likely, since all other cylinder are firing steady.

It is a crap shoot without further proper voltage measurements.

 

[daselbee]

Re: compression test and timing - 1994 250 hp Johnson

I have a story....
Got a Merc inline 4 cyl in the shop right now. I swear....every voltage from the stator, timer base, and into the Merc switch box, are reading proper DVA specs. Still have no spark. Stumped.
So I consulted the local Merc dealer. This is the interesting part.

He advised changing the stator, timer base and switch box. All three. He said he never does any DVA measurements. He simply shotguns all the ignition components to the tune of about 500 bucks for parts alone, and guarantees himself an absolute fix of the problem.

So there you have it guys....a true highly qualified mechanic's method of "fixing" engines. Shotgun the parts.

Just thought that was an interesting approach. Evinrude mechs around here shotgun injectors, EMMs, they are just guessing.....

 

[adg]

Re: compression test and timing - 1994 250 hp Johnson

Daselbee: man thanks for your reply, really appreciate you take the time to explain the basics. I definitely prefer the meter testing approach rather than the "guessing costing alot of bucks approach". After all, there must be some logic in these machines. And with the fantastic help all you guys on here give me I'm sure to be able to solve it eventually. Just takes a bit time.

I will go with all the meter tests that are necessary to find and solve the problem, learning by doing, step by step.

Will go detailed through yr reply and follow yr suggestions, will revert after that.

Thanks again.

 

[daselbee]

Re: compression test and timing - 1994 250 hp Johnson

OK...further testing is desired.
Get yourself a DVA adapter for your meter, or buy a DVA meter. EBay has them: ESI 530 Electronic Specialties Marine Multimeter DVA Peak Reading | eBay
They are probably readily available in your country...I just don't know where.
You can also make one, but the performance of the homemade ones is iffy at best.

What you are going to do is put the black meter lead on a good engine ground, and probe/measure as specified in the CDI tech document that was mentioned earlier.

This is all done at starter speed, plugs out, etc. (Not ECT):joyous:

You won't have any trouble with the orange primary wires to the coils....but you may have trouble with the readings from the timer base.
Those voltages are very low and sometimes the meter itself will lie to you on those measurements. Also, it is difficult to back-probe those rubber connectors. I use a paper clip inserted into the back of the plug deep enough to hit the metal contact. Then attach the meter lead to the paper clip.
OR, you can get a breakout box.....OMC breakout box....google it....

Study the wiring under the pack. Learn which color wire controls which plug's firing. There is a pattern to it.

Also, just to be sure, when looking at the back of the motor, # 7 cylinder is the bottom cylinder on the right side. This is the one you are debugging, right?
And, also to be sure, the exact symptom is that the timing light is intermittent and non-flashing when connected to that cylinder, and when you are looking directly into it? Right?

This is not a simple task. I commend you for going the extra kilometer here.

 

[adg]

Re: compression test and timing - 1994 250 hp Johnson

Also, just to be sure, when looking at the back of the motor, # 7 cylinder is the bottom cylinder on the right side. This is the one you are debugging, right? Yes this is correct.

And, also to be sure, the exact symptom is that the timing light is intermittent and non-flashing when connected to that cylinder, and when you are looking directly into it? Right? This is also correct.

Thanks for pointing me in the right direction, will revert when equipment is purchased and I have done some testing (or if other questions). Also found a wiring diagram for the engine so have something to study meanwhile. Together with the troubleshooting procedure from CDI should get me somewhere.