1979 Mercury 90 hp in line 6 No Spark

[mil0058]

Good Morning,

I have a new project that I am working on. It is a '79 Merc Inline 6 90 hp with serial number 5160916. Compression is in check and I was looking at a fuel issue in which I found and fixed corroded lines. In that process I made a mistake and did not disconnect the battery, when putting the starter back on I shorted out the Rectifier. Sparks flew and all. I knew at that moment I just made things alot harder for myself. I then conducted a spark test to find out I lost spark on all cylinders.

First question,can a blown rectifier cause a motor to lose spark all around, or lead to damage other ignition components.

Second Question, I had a rectifier that I bought for an 89 merc 135 and swapped it out to no avail. I assumed that the internal capacitance would be the same for all 6 cylinder engines. Could they be different?

Last question, I have never troubleshot a distributor type engine before. Does anyone have advice on where to start. The manual gives some tests but doesn't appear to give in depth instructions on trouble shooting. I have a DVA meter and some basic tools.

Thanks for all your help in advance.

 

[Chris1956]

Re: 1979 Mercury 90 hp in line 6 No Spark

The motor is a distributor ignition, right? If so, the rectifier cannotl not affect the ignition. Howeve, the wires are usually in tough shape in motors that old. Have yours been replaced/repaired?

Make sure you have +12VDC on the red and white terminals that are next to each other on the switchbox, when the key is in the run position. The red terminal should have +12VDC at all times.
The CDIElectronics web site has troubleshooting tests for that ignition. Make sure the test you choose is for the battery driven CDI systems with a distributor.

 

[Gomer50]

Re: 1979 Mercury 90 hp in line 6 No Spark

If this is a Distributor style ignition (CDI).This will give you some insight..
MERCURY BATTERY-POWERED CDI TEST FOR DISTRIBUTOR MODELS

This test is for the 332-2986 switchbox used from 1967-1979 on all the inlines.

This test assumes your coil is good (problems with CDI coils are rare).

DISCONNECT BATTERY

1. Turn off ignition;

2. Disconnect all 3 distributor wires on the Port side of the switchbox (and the “mercury switch” if present);

3. Remove the High Voltage lead from the ign coil to the center of the dist. cap (remember it unplugs from the coil and unscrews from the cap);

4. Reconnect the H.V. lead to the COIL only;

5. Position the free end of the HV lead approx. 3/8" from ground (block, shrouds etc), and find a way to hold it there;

6. Jumper the brown and white terminals on the distributor side of the switchbox to each other.

RECONNECT BATTERY

7. Check that you have +12V at the red terminal (even with the ign off);

8. Turn on ignition and verify +12V at the white terminal (same side as the red terminal);

9. Ground the black terminal on the distributor side of the switchbox - this should cause a spark each time you touch ground.

If you get spark with the distributor bypassed, and it won't fire with the distributor connected, the trigger is bad and the entire distributor housing assy must be replaced.

If you get no spark using the test, the switchbox is probably bad. In that case, be sure to check for correct power on the switchbox, check all connections, and check the coil's resistance to make sure it's OK."

 

[mil0058]

Re: 1979 Mercury 90 hp in line 6 No Spark

Good Morning,

This is a distributor type iginiton. The wires coming from the wiring harness look terrible. I assume this is normal after 30 years of abuse. The insulation on many of the wires are just falling apart. I saw that these are still available from CDI and are modestly priced. Would the replacement wiring harness be plug and use? I will conduct the tests that you suggested today after work or tomorrow and post my results. Thanks for your help so far.

-Andy

 

[coolguy147]

Re: 1979 Mercury 90 hp in line 6 No Spark

the bad insulation is just a mercury problem, as well as corrosion.

 

[Chris1956]

Re: 1979 Mercury 90 hp in line 6 No Spark

Andy, the entire engine harness is availible on the web. I liked the price at the surplusunlimited website.

 

[mil0058]

Re: 1979 Mercury 90 hp in line 6 No Spark

Hello Everyone, after a 3 month delay I finally got some time to work on this motor. The weather was beautiful here in MD so I took out the other boat for some preseason striper. I removed the internal wiring harness which pretty much fell apart in my hands as I took it off. The battery was dead because I assume some wires were shorting out inside of the harness itself. After reinstalling a new CDI wiring harness my no spark issue is still present. I followed the CDI troubleshooting that came with the part and found that the brown wire was receiving the required voltage but the white wire was reading 0 Volts. CDI indicated that either the key switch or wiring harness is malfunctioning. Has anyone ever experienced this or know how to troubleshoot the keyswitch. My manual has a test but it is a little over my head as to where to look for some of the components.

Thanks for your help all. You helped me get my Merc 135's running and I greatly appreciate it.

Andy

 

[Chris1956]

Re: 1979 Mercury 90 hp in line 6 No Spark

Mil, On that distributor ignition motor, you must have power on the red wire on the switchbox at all times. It is directly connected to the rectifier red wire. The white wire from the ign switch need to have power on it when the key is on or in the start position.

The brown wire that runs to the ign switch is for the tach signal

 

[mil0058]

Re: 1979 Mercury 90 hp in line 6 No Spark

Thanks for the response. After looking through CDI's instruction manual for the harness you are right. I did not connect a red jumper from the rectifier to the red terminal on the switchbox. The manual does not state that this is needed. Do you know why it is omitted? Could it be a CDI thing? Okay, so next question, I do not have a solid red wire on my switchbox. I have a white wire with red stripe that is connected to the white wire from the harness. Would this be where the red from the rectifier would go. I have posted a picture of the available wires coming from the switchbox. The black, white, brown are going to the distributor. The other black goes to ground, green to the other side of switchbox, and again the white/red to the white of the harness. What a learning process.

Thanks again,

 

[Chris1956]

Re: 1979 Mercury 90 hp in line 6 No Spark

CDI sells a different switchbox. I have never seen it in person, but it appears to just have a place for the white wire to connect. Make sure you gave a solid +12VDC on the white wire, and it shoud work if the coil and trigger are good.

 

[DerekCB]

Re: 1979 Mercury 90 hp in line 6 No Spark

If this is a Distributor style ignition (CDI).This will give you some insight..
MERCURY BATTERY-POWERED CDI TEST FOR DISTRIBUTOR MODELS

This test is for the 332-2986 switchbox used from 1967-1979 on all the inlines.

This test assumes your coil is good (problems with CDI coils are rare).

DISCONNECT BATTERY

1. Turn off ignition;

2. Disconnect all 3 distributor wires on the Port side of the switchbox (and the ?mercury switch? if present);

3. Remove the High Voltage lead from the ign coil to the center of the dist. cap (remember it unplugs from the coil and unscrews from the cap);

4. Reconnect the H.V. lead to the COIL only;

5. Position the free end of the HV lead approx. 3/8" from ground (block, shrouds etc), and find a way to hold it there;

6. Jumper the brown and white terminals on the distributor side of the switchbox to each other.

RECONNECT BATTERY

7. Check that you have +12V at the red terminal (even with the ign off);

8. Turn on ignition and verify +12V at the white terminal (same side as the red terminal);

9. Ground the black terminal on the distributor side of the switchbox - this should cause a spark each time you touch ground.

If you get spark with the distributor bypassed, and it won't fire with the distributor connected, the trigger is bad and the entire distributor housing assy must be replaced.

If you get no spark using the test, the switchbox is probably bad. In that case, be sure to check for correct power on the switchbox, check all connections, and check the coil's resistance to make sure it's OK."

i have the same motor, i performed this test and i had no spark now i found a switch box (332-2986A22) that looks identical to mine but on the back it has a sticker saying 4cyl o.b. and 8cyl v8 will this switch box work or do i need (332-2986A4) switchbox?