Missfire and backfire under no load?

[metalmonkey47]

It's on my A15.

 

Mods: New dizzy cap & rotor

MSD coil & IGN box

NGK Platinum plugs,

8MM Accel wires

Weber 32/36 DGV

 

Timing dead on @ 11 BTDC

 

It's currently running NO vac advance, because it seems like the problem is more prominent with any more advance on the timing. It doesn't usually bother me, and I've driven just fine for the last few months, but I figure I might as well get it taken care of sometime.

 

It only appears to be a problem at 2.5K - 4K RPM. I dunno if it's missing at any higher revs, because I don't rev any higher with no load.

 

http://www.youtube.com/watch?v=fo3s3NnLS3s

 

[ggzilla]

Is your plug wires. Throw the original old Nissan wires back on to confirm (the originals usually last forever).

[metalmonkey47]

Is your plug wires. Throw the original old Nissan wires back on to confirm (the originals usually last forever).

 

The old wires were shot. I'll get some OEM Nissan wires since I don't like the ugly Accel anyways.

 

 

What about the wires would cause that?

[ggzilla]

It could be something else, but plug wires are the most common cause.

 

You can check them with a ohm-meter. They should be around 10,000 ohms per foot. If you measure one that's totally different, you found a bad one.

 

Also look carefully at the end of each wire, inside where the metal end is. If you find one is corroded, you found a bad wire (or a cylinder that's not firing, a compression test will verify).

 

Inspect every inch of the plug wire. If you find a burnt spot (usually whitish) you found a bad wire.

[datzenmike]

Firing order mixed up. Cap or rotor bad or bad wires.... basically anything you just changed could be it.

 

Generally it requires more voltage to fire a cylinder with heavier throttle. The harder it is to fire the plug the more the voltage will look for another route to ground... maybe even onto another wire.

 

After dark go out and fire it up and take a look for blue sparks on the coil terminals and wires.

 

This a used coil and box????

[Wide14u]

i was going to say that last night but then i said shut up crack head

[metalmonkey47]

oops, forgot I posted this here.

 

 

All my IGN components are brand new. Cap, rotor, coil, everything except the dizzy. Firing order is dead on. All the parts look the be in perfect shape. No arcing, faulty parts at all from inspection. IGN coil's resistance was spot on MSD's specs. Box and coil are both brand new.

 

It almost seems like the problem may be timing related, because with my VAC advance connected, I have the same symptoms X10.

 

Heres an old video after a fresh install of the box with the vac advance connected.

 

 

http://www.youtube.com/watch?v=9r_oQroJHVQ

 

[datzenmike]

Pull the plug wires one at a time while running until the problem cylinder is found. Now remove valve cover and check the valve lash.