Ignition Intermitantly Fires 180 degrees out of phase

[eldplanko]

Hi All:

Hopefully this is an easy answer...

Background:

1974 Mercruiser 888: Original Block, Original Mercruiser Distro, Newer (last season) Sierra Points, Condenser, Ignition Coil, plug wires... can provider details if necessary.

Symptom:

Base Timing when viewed with timing light will intermittantly (~50% of the time) will show 180 degrees off (verified by marking balencer at 90 degree increments with a sharpie. Idle is obviously rough, and having trouble idling down below 1500 rpm.

Dwell is at 27

Any ideas?

I'm going back out to start the basic verification (correct firing order, rotor position relative to #1 plug wire, dwell, advance springs)... will follow-up with additional details, but any thoughts in the mean time would be greatly appreciated.

 

[Don S]

Re: Ignition Intermitantly Fires 180 degrees out of phase

Bad/wrong type plug wires will cause cross fire, cracks, moisture, carbon tracking inside the distributor can cause it.

 

[EddiePetty]

Re: Ignition Intermitantly Fires 180 degrees out of phase

AND....if you're using an induction timing light with a senitive pickup, real close proximity to adjacent plug wires will fire off the timing light.

Following Don S.'s suggestions......fire the beast up on muffs on a dark night and look for a lightening show along the plug wires/distributor cap terminals. Run an insulated screwdriver along each lead to isolate defective plug wires/terminals. (watch out for rotating components while working in reduced lighting though)

 

[eldplanko]

Re: Ignition Intermitantly Fires 180 degrees out of phase

Will do, and will f/u.... I'll make sure I don't wear my necktie...

Would it be reasonable to assume the cross fire is on the position 180 degrees away (when viewed from the balencer). I've also marked 90 and 270, but don't ever see these with the timing light.

With my firing order, 1372-6548, would this mean the cros fire is either on the #6 or #4 wires/posts?

 

[Don S]

Re: Ignition Intermitantly Fires 180 degrees out of phase

You can also get cross fire in spark plugs by having the running side by side in a straight line. Like having them neatly wire tied together. Twist them and separate them to keep the cross fire to a minimum. If you look at the pieces holding them apart in OEM setups, they are about 1/4" apart.

 

[eldplanko]

Re: Ignition Intermitantly Fires 180 degrees out of phase

Definitley all neat and tidy, I'll tangle them up again...

 

[Pete104]

Re: Ignition Intermitantly Fires 180 degrees out of phase

I had a 360W in an F-350, the plug wires were "specifically" routed to eliminate this issue.

 

[eldplanko]

Re: Ignition Intermitantly Fires 180 degrees out of phase

Update... checked things out:

Points: Dwell 27 deg, gap: 0.010"

Plug Wires: New, no cracks, in correct order... mostly more than 1/4 inch apart... more on this later

Cap/Rotor: #1 on rotor in correct phase (#1 TDC on compression stroke), some carbon on cap terminals, sanded down to shiny copper

Timing: Checked all wires for cross-fire:

Cylinder - ( Correct Firing (deg)) - Actual Firing (deg)
1 - (0 ) - 0 / 180
3 - (90 ) - 90 / 0 / 180 / 270
7 - (180) - 180
2 - (270) - 90
6 - (0 ) - 0
5 - (90) - 90
4 - (180) - 180 / 90
8 - (270) - 270

Looks like cross-fire is only on starboard side (Engine is Ford 302). Any ideas here? These wires are all routed close to the alternator. Is it possible this is interfering with these? It seems unlikely given the spark should be pretty high voltage compared to alternator... but I'm not completley sure. I'll look again when it's darker out for the "light show."

 

[Don S]

Re: Ignition Intermitantly Fires 180 degrees out of phase

The carbon tracking on the cap is on the inside.
If the cap is over 2 years old, replace it and the rotor.-

 

[eldplanko]

Re: Ignition Intermitantly Fires 180 degrees out of phase

Finally dark out... blue arcing was evident only on the ceramic of plug #1, no other arcing on the other wires, plugs or at the cap. I didn't do the screwdriver test, will save that for later. Tomorrow I'll inspect the plug boot for #1 a bit closer.

On the cap, meant that I sanded the terminals on the inside to shiny copper. Also sanded up the rotor to shiny. Should I still replace?