Spark on cyl 1,2 but not 3,4?

[asm_]

Hi,

I am working on a Mercury 850 (85HP) 1974. The best information I have gotten from previous owner indicates there no spark on all cyl. After hours of testing and checking all connection, I now have cyl 1 with weak spark, cyl 2 with strong spark, no spark on cyl 3 and completely dead on cyl 4.

Here is some of thing I have already done to the the ignition system. CDI unit was replaced with after market CDI Electronics unit. Trigger unit was also replaced. I have followed CDI's instruction and confirm the CDI unit is putting out big fat spark on its high tension wire to the distributor. Each plug will fire if I manually turn the distributor to each contact, and force CDI to fire by jumping white and brown wire and strike black wire on the motor ground. Still, no spark on cyl 3 and 4. Naturally I suspected the spark plug wire on cyl 4 are at fault. Switch spark plug wire from cyl 2 to cyl4. Still no spark on cyl 4. Cyl 2 still have big fat spark with spark plug wire originally used on cyl 4.

I am guessing the contact point inside distributor cap may have to big of gap of cyl 3 and 4. However, I don't think they are adjustable.

At the point, I am out of idea to try, any comments are welcome.

thanks

 

[Faztbullet]

Re: Spark on cyl 1,2 but not 3,4?

It its got hot spark on one of the cylinders it should have it on all of them unless:

A) disc rotor installed improperly (tells trigger when to fire)
B) carbon in distributer cap bad/damaged
C) spark plug wire damaged where screwed into cap
D) spark plug wire rotted/damaged on spark plug boot

You can drop cap and ohm the wires from inside the cap back to boot and they should read within 75-150 ohms of each other.

 

[asm_]

Re: Spark on cyl 1,2 but not 3,4?

A) disc rotor installed improperly (tells trigger when to fire)

This one I can't be sure. Trigger's installation instruction shows the disc should have 'rotor side' wording installed facing rotor. I can't find such writing on the side I can see, which is the rotor side. However, it doesn't mean it wasn't there before as it may have gotten rubbed off by the coil pickup. Any one got a picture of what it suppose to look like when it's new?

B) carbon in distributer cap bad/damaged

I don't think this is the case. Carefully look over the cap for any crack. Also check to make sure carbon contact are all in place with no obvious damage.

C) spark plug wire damaged where screwed into cap
D) spark plug wire rotted/damaged on spark plug boot

I think I have already rule these out as I switch the spark wires from working cyl to none working cyl. It still wouldn't fire.

You can drop cap and ohm the wires from inside the cap back to boot and they should read within 75-150 ohms of each other.

75~150 ohms!!?!? Is that a typo? isn't that a bit high?? My measured less then 0.8ohm each.

Thanks for help

 

[CDI Tech Support]

Re: Spark on cyl 1,2 but not 3,4?

This one I can't be sure. Trigger's installation instruction shows the disc should have 'rotor side' wording installed facing rotor. I can't find such writing on the side I can see, which is the rotor side. However, it doesn't mean it wasn't there before as it may have gotten rubbed off by the coil pickup. Any one got a picture of what it suppose to look like when it's new?

If you've installed a CDI Electronics 134-3736 trigger, you MUST use the disc that came with it. You cannot use the OEM disc. Reference: 134-3736 installation guide:

NOTICE: THIS TRIGGER REQUIRES THE STEEL DISK INCLUDED WITH IT. IT WILL NOT WORK WITH THE FACTORY DISK!!

Per the 134-3736 installation guide:

Misses on one or more cylinders:
Connect spark gap checker to all cylinders, align the rotor to each cylinder in turn, and trigger the pack using the 511-9701 Battery CD Tester. If a cylinder fails to fire, or if another cylinder fires besides the one that the rotor is pointed to, replace the distributor cap. Watch for spark plug wires arcing to the engine block.

Service Note: On a double notched shaft, the wide notch is for a 4 cylinder disk and the narrow notch is for the 6 cylinder engines.

Mercury 4 and 6 Cylinder - 332-2986

NO SPARK OR INTERMITTENT SPARK ON ONE CYLINDER:
1. Connect a spark gap tester to the high-tension leads coming from the distributor cap and set the gap to approximately 7/16?. (Use of a CD Tester is recommended).

2. Align the rotor with #1 spark plug wire. Disconnect the trigger wires and connect a jumper wire from the Brown trigger terminal to the White trigger terminal.

3. Connect another jumper wire to the Black trigger terminal turn the ignition switch on. Strike the jumper wire from the Black terminal against engine ground ? (DO NOT HOLD THE JUMPER AGAINST ENGINE GROUND). Only the #1 spark plug wire should spark. If any other spark plug wire has spark, there is a problem in the distributor cap.

4. Repeat the test for the other cylinders.

 

[asm_]

Re: Spark on cyl 1,2 but not 3,4?

Thanks for posting the CDI instructions. However, I have already followed everything on those sheets. Since I did not install the trigger, I can't be sure if the disc is the one supplied by CDI or even if it's installed with the correct side facing the rotor. As far as I can see, there appear to be two notchs on the rotor shaft. And they are the same size. Therefore, even if the disc was installed in correct orientation, it could have been installed aligning with the wrong notch.

Is there any way to determine, without removing the disc, if the disc is supplied by CDI and installed in correct orientation?

 

[CDI Tech Support]

Re: Spark on cyl 1,2 but not 3,4?

Thanks for posting the CDI instructions. However, I have already followed everything on those sheets. Since I did not install the trigger, I can't be sure if the disc is the one supplied by CDI or even if it's installed with the correct side facing the rotor. As far as I can see, there appear to be two notchs on the rotor shaft. And they are the same size. Therefore, even if the disc was installed in correct orientation, it could have been installed aligning with the wrong notch.

Is there any way to determine, without removing the disc, if the disc is supplied by CDI and installed in correct orientation?

To identify if the trigger is a CDI Electronics trigger, check the trigger's wire sleeve. If it's a CDI Electronics trigger, there will be a white piece of heat shrink wrapped around the wire sleeve with part# 134-3736 on it.

If so, then:

If it's a genuine CDI Electronics trigger disc, it will have "Rotor Side" either written or stamped on one side AND more importantly, be steel-colored, NOT brass-colored.

If it is a 134-3736 trigger & you do not see "Rotor Side" written or stamped on the rotor side, you will need to have the disc taken off to see if it has "Rotor Side" written or stamped on the opposite side. If so, flip the disc & re-install.

 

[asm_]

Re: Spark on cyl 1,2 but not 3,4?

Thanks. I'll check that tonight.

 

[asm_]

Re: Spark on cyl 1,2 but not 3,4?

Just checked the trigger during lunch time. The trigger is made by CDI.

Before I go throwing more money at this motor by buying a fly wheel puller, does any one know if the trigger suppose to fire when the coil passes over the open portion of the disc or the close portion? My search seems to suggest it sends firing signal to the CDI unit on the transition into the open portion of the disc. Some one please correct me if I'm wrong.

Thanks

Brian

 

[CDI Tech Support]

Re: Spark on cyl 1,2 but not 3,4?

Just checked the trigger during lunch time. The trigger is made by CDI.

1. Does the top of the disc say "Rotor Side" on it?

2. What color is the disc? Brass or Steel colored?

My search seems to suggest it sends firing signal to the CDI unit on the transition into the open portion of the disc.

This is correct.


What happened when you followed these steps?

NO SPARK OR INTERMITTENT SPARK ON ONE CYLINDER:
1. Connect a spark gap tester to the high-tension leads coming from the distributor cap and set the gap to approximately 7/16?. (Use of a CD Tester is recommended).

2. Align the rotor with #1 spark plug wire. Disconnect the trigger wires and connect a jumper wire from the Brown trigger terminal to the White trigger terminal.

3. Connect another jumper wire to the Black trigger terminal turn the ignition switch on. Strike the jumper wire from the Black terminal against engine ground ? (DO NOT HOLD THE JUMPER AGAINST ENGINE GROUND). Only the #1 spark plug wire should spark. If any other spark plug wire has spark, there is a problem in the distributor cap.

4. Repeat the test for the other cylinders.

 

[asm_]

Re: Spark on cyl 1,2 but not 3,4?

1. Does the top of the disc say "Rotor Side" on it?

From the side I can see (the rotor side), there is no writing on it. However, there are some what look like ink smudge there. Assuming if the 'Rotor Side' was written with sharpie, it may have been rubbed of during installation.

2. What color is the disc? Brass or Steel colored?

steel color.

This is correct.


What happened when you followed these steps?

NO SPARK OR INTERMITTENT SPARK ON ONE CYLINDER:
1. Connect a spark gap tester to the high-tension leads coming from the distributor cap and set the gap to approximately 7/16?. (Use of a CD Tester is recommended).

2. Align the rotor with #1 spark plug wire. Disconnect the trigger wires and connect a jumper wire from the Brown trigger terminal to the White trigger terminal.

3. Connect another jumper wire to the Black trigger terminal turn the ignition switch on. Strike the jumper wire from the Black terminal against engine ground ? (DO NOT HOLD THE JUMPER AGAINST ENGINE GROUND). Only the #1 spark plug wire should spark. If any other spark plug wire has spark, there is a problem in the distributor cap.

4. Repeat the test for the other cylinders.

I don't have CD tester, so I used spark plug instead.
These steps were performed last night using a spark plug for each cylinder, while holding the plug's business end 1/2" away from motor ground. Each cylinder resulted in big fat blue spark. This is what confused me, if the plug fires when I manually align the distributor, why only some cylinder fire when cranking??

Oh, in case if anyone is wondering, I am using a deep cycle battery with 900ca rating that is fresh off the charger with 12.8v open voltage.

 

[CDI Tech Support]

Re: Spark on cyl 1,2 but not 3,4?

It's either going to be the distributor cap or the trigger...not sure which one.

If the trigger's manufacturing date is within 2 years of the current date, CDI Electronics will test it for free. If not, we charge $35-$50 + return shipping. Obviously, the difficult process would be disassembling the distributor, then reassembling once you received the trigger back. If this is a mild inconvenience, ship it to us.

Perhaps the more inexpensive, convenient "gamble" would be to replace the distributor cap, since it's both inexpensive & much easier to uninstall & installing a new one. We sell 6 cylinder distributor caps, but unfortunately not 4 cylinder distributor caps.

 

[CDI Tech Support]

Re: Spark on cyl 1,2 but not 3,4?

Oh, in case if anyone is wondering, I am using a deep cycle battery with 900ca rating

Deep Cycle batteries are great for trolling motors, but not ignitions with flywheels. They offer great reserve time, but do not last as long as a cranking/starting or dual purpose battery due to constant discharging & charging.

 

[Laddies]

Re: Spark on cyl 1,2 but not 3,4?

If your system will fire any time, then the problem is not the plate all it does is cause a magnetic flux which fires the system so if it fires for 1 hole it will fire for all holes. you can acttully fire the early system by moving a feeler gauge back and forth thru the gap. Having the plate in upside down only changes the timing and does not effect the systems ability to fire. You need to ckeck the wires, cap and rotor and you will find the problem, then if the engine won't time properly check the disk

 

[asm_]

Re: Spark on cyl 1,2 but not 3,4?

If your system will fire any time, then the problem is not the plate all it does is cause a magnetic flux which fires the system so if it fires for 1 hole it will fire for all holes. you can acttully fire the early system by moving a feeler gauge back and forth thru the gap. Having the plate in upside down only changes the timing and does not effect the systems ability to fire. You need to ckeck the wires, cap and rotor and you will find the problem, then if the engine won't time properly check the disk

Thanks Laddies. I perform the spark test again last night by manually align rotor to each contact point on the cap. All cylinder fires when I strike the black wire from CDI against the engine ground. So, I'm thinking the cap/rotors are fine.

I also did a few test fire with the rotor purposely lined up in between distributor cap contact. It still fires, but with very weak spark. My guess is, some of the energy was lost to jump the big gap I purposely created in the cap.

Well, Since I do not have a CDI trigger test, that only leaves the trigger as the questionable component.

I have being searching for hours on line, looking for the design schematic of a typical trigger with no success. I'm thinking the schematic may be helpful as I do have access to a scope.

If the trigger's manufacturing date is within 2 years of the current date, CDI Electronics will test it for free. If not, we charge $35-$50 + return shipping. Obviously, the difficult process would be disassembling the distributor, then reassembling once you received the trigger back. If this is a mild inconvenience, ship it to us.

In any case, How would I know the mfg date for the trigger?

 

[CDI Tech Support]

Re: Spark on cyl 1,2 but not 3,4?

In any case, How would I know the mfg date for the trigger?

On the side of the trigger housing, there will be a white CDI Electronics date code sticker. Look for the manufacturing date.

 

[asm_]

Re: Spark on cyl 1,2 but not 3,4?

On the side of the trigger housing, there will be a white CDI Electronics date code sticker. Look for the manufacturing date.

Thanks!! Since I can't seems to find any sticker with the trigger still installed in the motor, am I assuming correctly that the sticker is only visible after the trigger is removed from the motor?

 

[CDI Tech Support]

Re: Spark on cyl 1,2 but not 3,4?

Thanks!! Since I can't seems to find any sticker with the trigger still installed in the motor, am I assuming correctly that the sticker is only visible after the trigger is removed from the motor?

Correction. The date code is hand-written on the white heat shrink wrapped around the trigger's wiring sleeve.

Date code as follows -> month - week - year

 

[asm_]

Re: Spark on cyl 1,2 but not 3,4?

Still can't find the date code on the wire. There is, however, a white shrink wrap on the trigger output wires with the wording "Installation Date" Of course, that wasn't filled by the trigger installer.

In any case, I found cause of the problem. The disc was touching the trigger pickup magnet on 1, 3 and 4. Since the disc does not look like it is bended, I can only guess perhaps it is not 100% true flat.

After observing this problem, my first hypothesis was the original installer used the taller spacer supplied by CDI when it should have used the original space, which is 0.010" shorter. However, after thorough inspection of the entire assembly, I noticed a vertical play of almost 0.040" of the entire distributor shaft in the trigger housing appears to be the culprit. When the shaft is pull all the way up on the pulley side, the disc clear both the trigger base and lower pick up magnet. This allow all four cylinders to fire as it should. However, allowing the gravity to take over and lower the shaft, the disc is now rubbing over the lower pickup magnet. Further inspection shows the play on the shaft is cause by the movement of the lower bearing in trigger housing, which is in turn caused by the bearing shim that is 0.040" too thin. Unless I'm missing something here, since both the lower bearing and shim were pre-installed by CDI, it look like my trigger may have gotten a wrong size shim.

I'm going to call CDI on Tuesday to see how we can solve this problem.

Any for those who may be having similar problem with Mercury distributor ignition motor, you may want to check this as well. It took me nearly 2 weeks to finally crack this puzzle.