Thread: Confusing - distributors for 3.9L V8

Reviving an old thread here.

I finally set about swapping the dizzy to the "new" old scorcher last night.

Immediately, the idle seems better and there's far less float in the timing advance and retardation as the motor spins up and down. Feels like it's making a tiny bit more power down low. The bloke I bought it from threw in a near new Bosch coil to suit. I just need to tidy up the coil bracket and wiring and I'll be all rid of Lucas.

This has been a most informative thread. Well done guys.

Originally Posted by bee utey

Ignition lead resistance is like shocker damping rates is to suspension. Too low and you get bounce. Too low a resistance and you may get lots of radio noise (RFI) and poor spark.

More data for this thread.

I barely ever drive on ULP and had found suddenly last month that ULP running was atrocious. Rough running generally, but surging and misfiring when coasting on gentle throttle. However LPG running was superb! Very odd I thought... Out of curiosity I tried another old coil lead which improved things somewhat. Tried yet another and things went back to normal. When I measured the impedance of the 7mm low resistance coil lead it was down below 2K Ohms. The "better but not best" measured about 5K Ohms. The best running lead measured nearly 8K. What has me confused is that LPG running is perfect, so I wonder whether the low impedance lead was starting to excite the fuel injection somewhat. The lead runs right past the MAF and close to a couple of injectors.

When I have nothing better to do I'm going to do some closer studying of what happens with different configurations of leads.

Originally Posted by MacMan

More data for this thread.

I barely ever drive on ULP and had found suddenly last month that ULP running was atrocious. Rough running generally, but surging and misfiring when coasting on gentle throttle. However LPG running was superb! Very odd I thought... Out of curiosity I tried another old coil lead which improved things somewhat. Tried yet another and things went back to normal. When I measured the impedance of the 7mm low resistance coil lead it was down below 2K Ohms. The "better but not best" measured about 5K Ohms. The best running lead measured nearly 8K. What has me confused is that LPG running is perfect, so I wonder whether the low impedance lead was starting to excite the fuel injection somewhat. The lead runs right past the MAF and close to a couple of injectors.

When I have nothing better to do I'm going to do some closer studying of what happens with different configurations of leads.

Interesting, RFI affecting the ECU readings. I suggest keeping ignition leads 50mm away from each other so away from the MAF might be a good idea too. The LPG on a D1 doesn't use any part of the ECU so it wouldn't care.

I recently found a problem with a vehicle I had put Bosch leads on, the one that was arcing read 1.5K ohms and the replacement was 4.5. Ran great after that. Seems like you have to check every new part every time!

50mm is a little hard to achieve when they are closer than that on the distributor terminals. I have them currently running neatly with spacers, taking care to keep #5 and #7 as far apart as possible and the coil lead away from both as much as possible.

As you point out, the fact that LPG is a "dumb" system makes me think that it must be an RF issue with the engine management.

Will keep you posted with my findings.

Originally Posted by MacMan

50mm is a little hard to achieve when they are closer than that on the distributor terminals. I have them currently running neatly with spacers, taking care to keep #5 and #7 as far apart as possible and the coil lead away from both as much as possible.

As you point out, the fact that LPG is a "dumb" system makes me think that it must be an RF issue with the engine management.

Will keep you posted with my findings.

Sorry I should add 50mm is only the best spacing which happens away from the dissy. Magnetic interference between leads is cumulative with length, the most important thing is not to bundle them up tight for long lengths. Sharing a clip here and there is no big deal. Sounds like you've got that angle covered.

Best thing I ever did was stop throwing parts at the 95 D1 and do a scorcher with Bosch coil and Bosch (australian) amp module.

Cheers

OK, but which leads! Because the ones sold by Performance Ignition Services who make the Scorcher distributors are not playing so nicely on ULP!