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Discussion Starter · #1 ·
Hey blokes,

I've been reading forum posts for days and trying to diagnose my dual fuel (LPG/Petrol) TB42 Carby after it conked out on me on the road home from inskip.

I've tracked the problem down to ignition, the spark behaviour is really odd.
Occasionally I get a good few sparks and the engine runs for a second or two, but mostly it just cranks and throws no sparks.
I replaced the ignition coil with a Fuelmiser CC254 because that's what Repco had on hand and apparently it's compatible, but again it is working only occasionally.

I've checked:
  • Removed coil-to-cap wire and tried my inline spark tester straight from coil secondary to ground (no spark)
  • Ballast Resistor: shows 1.5Ohms impedance
  • Coil + to Battery - (key on): shows 9V
  • Coil - to Battery + (key on): shows 12V
  • I don't have an immobilizer any more (I ripped it out)
  • Fuel pressure is good
I'm not sure what impedance I should expect between coil primary and secondary, info is hard to track down on that.

I'm lead now to think it must be some gremlin in the wiring, but that is a bit lost on me. I'll attach some photos and maybe someone can see something out of place.
There is some kind of condenser coming from the resistor out to a ground strap, which I don't understand...

I'm not sure where to look next. Any guidance on what now, much appreciated.

Cheers

Video of the engine cranking (and momentarily firing):

Some photos around the ignition coil:

Hood Motor vehicle Vehicle Car Automotive tire


Motor vehicle Automotive tire Automotive exterior Bumper Vehicle
 

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Discussion Starter · #3 ·
It is points & condenser in the distributor.

After some further reading it seems that the only thing that could be preventing a working ignition coil from sparking is the wiring between the coil and the distributor.

I could try fault testing the factory harness, and the condenser and the points, but honestly it seems like a better idea to just rip that all out and install a pertronix module and hopefully never worry about this again.

I've ordered one, it is in the mail. Hopefully I'll be back on Tuesday to post about my resounding success.
 

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Check the wire to the points INSIDE the distributor, it can go open circuit or HR.
 

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There are issues you can get that even a Pertronix won't fix.
- Ignition switch poor/burn/worn contacts - had this on my old GQ
- Dry joints in harness plugs - old GQ again
Your volt meter won't show it up as it's a current / amps problem.
Check it by running a hotwire from the Battery + to the ballast resistor.

If there are still problems, check your dizzy low tension leads for breaks, dry joints or shorts to earth.
Had this on my current GQ. - broken earth wire from dizzy to coil base.

Check your points are adjusted to 20 thou and the supression condenser near the coil isn't stuffed (disconnect it to test)
 
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Discussion Starter · #6 ·
Interesting thanks guys. I don't know a great deal yet about the wiring inside/outside the distributor.

I'll certainly test these theories, but the Pertronix seems like a decent and affordable idea anyway (and I've already ordered it).

Would installation of Pertronix resolve the dizzy earth to coil problem? Or is that a different wire?

I need to find a more extensive diagram of the dizzy wiring for my GQ, the Haynes manual only has so much info
 

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Discussion Starter · #7 ·
Installed the Pertronix today and no love (sparked once briefly, then not again).

Ran a hotwire from Battery + to BallastResistor 12V, no change in behaviour.

I'm at a bit of a loss now.

It can't be dizzy-to-coil harness because I bypassed that with the Pertronix.

If the ignition switch was faulty, would the engine even turn at all?
 

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Discussion Starter · #8 · (Edited)
I just checked the terminals on the coil. It has constant 6v from Coil + to Coil - when the key is turned to accessory.

AFAIK this should fluctuate between 6V and 0V while the dizzy turns and grounds the coil, causing the spark.
It seems like the coil is just getting constant power and not breaking the circuit (which throws the spark)

I loosened the dizzy and turned it by hand back and forth and saw no fluctuation in the voltage from coil + to coil -
 

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Are the points opening and closing when the rotor button spins?
 
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Discussion Starter · #12 ·
UPDATE:

I took the dizzy out, removed the Pertronix and removed all notion of LPG systems connected to the ignition.

I installed a fresh oem set of points and condenser into the dizzy and turned the dizzy shaft by hand and voila! Spark, from coil to earth.

Its all still apart for tonight, so I'll write back in the morning when I figure out exactly where the fault was.

Thanks for the ideas! I would never have had the bravery to dismantle a distributor and debug it
 
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