Suddenly running rough

[BillCNC]

Hey All,

Suddenly my engine started missing on number one making it run rough. It's a really weak spark on that distributor body terminal.

I swapped the plug with #2, spark plug wire and all the same.
I switch out the distributor body, the same.

Any other place that would make only #1 have a weak spark?

Regards
Bill

[Bigsnapper43]

A worn distributor cam will cause weak spark to one cylinder. Worn distributor bushings will give the same symptons.

[Gary WA]

Originally Posted by BillCNC

Hey All,

Suddenly my engine started missing on number one making it run rough. It's a really weak spark on that distributor body terminal.

I swapped the plug with #2, spark plug wire and all the same.
I switch out the distributor body, the same.

Any other place that would make only #1 have a weak spark?

Regards
Bill

How is the gap at rotor to cap all the same? I took a cap cut sides off and use, you can see if all 4 points have good spark or find the old clear caps.

[CT Jack]

You might have a cracked cap where the electrical path for #2 conductor is fractured internally. Also check the gap between the rotor and the cap contacts which should be .020". If there is a large amount of rotor runout at position #2 the excessively large gap could restrict the amount spark energy going to plug #2.

[nkaminar]

CT Jack has a good suggestion. You say you changed the distributor but did you change the distributor housing (the plastic part at the top that the spark plug straps connect to)?

[BillCNC]

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Yes, I replaced the distributor body (Plastic), the housing is the metal part.

Regards
Bill

[Big hammer]

A very long shot, is the plug hole clean of rust, dirt , carbon , oil ? The plug grounds through the head

[nkaminar]

How do you know it is a week spark on that one cylinder? Could it be something else, maybe a vacuum leak at the intake manifold or low compression on that cylinder? I know I am grasping at straws, but completely changing the distributor and swapping the plug would normally fix or identify the problem. The only other thing I can think of is that both distributors or bodies have the same problem.

[Will N]

I had my car start to run rough all of a sudden. I thought it was spark, as it seemed to me one cylinder's spark was weaker than the others. But I ran a compression test and found 2 cylinders down on compression. Pulled the head and found a blown head gasket between the cylinders. Run a compression test. Easy and quick to do.

[BillCNC]

OK Guy's,

Here are the FACTS.

It is a spark issue as I have ALL four plug wires raised off of the distributor body tangs by .250".

With the engine running the blue spark jumps the gap just fine on number 2, 3 and 4. Number one is intermittent and a dull yellow.

When I raise number 2,3 and 4 plug wires further up with the engine running, the spark turns white and will arc an 1." or so but #1 will stop arcing at about .312"

Grounds are fine, threads are clear, no paint under the plugs and am using copper washers under the plugs.

Plastic distributor body has been swapped and they both have had the individual paths checked with an ohm meter.

Points are at .019" and tested with a test lamp at TDC on #1 spark lever all the way up. (NuRex auto timing gizmo installed 8,500 miles ago)

Rotor gap, .025"

Plugs and brass plug wires have been swapped.

Compression will not stop the plug from firing, only igniting the fuel properly and on time, same with the valves. YES, while the engine is running, it would make it run rough, but what first must be solved is a weak spark at only #1 cylinder.

Regards
Bill

[funrunr]

I bought one of the NuRex gizmo's and it didn't work right on my car. I went back to the old school way of setting the timing and distributor. I would try setting the distributor where it just begins to touch the #1 terminal in the distributor cap when the engine is TDC on compression stroke. It's a quick, free and simple trial.

[BillCNC]

A video of the issue.

https://youtu.be/gMsGmbKRIsw

Regards
Bill

[nkaminar]

This is a real hard problem to solve, especially over the internet. Here is what I would do: Measure the compression in all 4 cylinders. Low compression may cause the spark to look different (wild guess). Find a known good distributor and upper body from a running car and try that in the off chance that both distributors you have are defective. The spark must come from the distributor and go to the spark plug. You have swapped out the plugs and distributors. The above things are the only things that I can think of to try.

[mcgarrett]

In your video, I'm seeing a stray spark that is arcing to the inside of the distributor body AFTER the rotor passes the #1 contact. Seems it is NOT feeding the voltage to the distributor contact as it should at the proper time. Enlarge the video to full screen and look at it again to confirm what I'm seeing. As others have said, get another known good distributor body from another good running car or better still, get a new one.

[BillCNC]

Originally Posted by mcgarrett

In your video, I'm seeing a stray spark that is arcing to the inside of the distributor body AFTER the rotor passes the #1 contact. Seems it is NOT feeding the voltage to the distributor contact as it should at the proper time. Enlarge the video to full screen and look at it again to confirm what I'm seeing. As others have said, get another known good distributor body from another good running car or better still, get a new one.

Hi mcgarrett,

I should have noted in the video that is the reflection of the camera light hitting the downward angle of the rotor end and reflecting it on the wall slightly after #1. Pretend your playing pool and look for the Bankshot, it lines up.

When I saw it in the video, I went and checked, no internal stay arcing.

Regards
Bill

[nkaminar]

In the video I see a reflection of a spark occurring when the rotor is near #1 cylinder at an odd place. I see the reflection at about 10 seconds into the video. I ran the video at 1/4 speed to better see the reflection. You may want to try a different rotor. I did a not-too-good screen shot of the odd reflection, see photo below.

The odd spark does not occur every time. It seems to be random. The odd spark occurs when the spark does not occur at the boss for the #1 plug. It does not seem to be a reflection from the light from the camera because it is not constant and at the wrong place for a reflection. It only occurs when the rotor is near the boss for the #1 plug and only when the spark does not jump to the boss.

Have you tried a different rotor?

[Synchro909]

Why the piece of plastic tubing on #1 lead?
I do something similar on #3 to prevent the infamous 3/4 crossfire but not #1.

[BillCNC]

Hey All,

I think I have found the problem. It's not arcing on either plastic body, it's a reflection of an arc that is happening at the condenser wire connection to the points when #1 goes intermittent.

Toasted condenser?

Syncro,

It's for when I connect a timing light it keeps the brass plug wire from shorting out the timing light wire clamp. If metal shorts the two haves together, ... bye-bye timing light. There's also a grommet on it next to the plug so I wont short out at there either.

Regards
Bill

[nkaminar]

Bill, I think you are on to something. Check that the connection is shinny metal and tightened properly. I have found that most electrical problems are connectors or terminals, especially on boats. You can test the condensor but it is probably good as the other plugs are firing OK.

[Big hammer]

The bright blue arc sure looks like high voltage, the condenser is low voltage, do you have a new rotor? I believe some have had issues with rotors , but why only the #1 ? High voltage can do funny things