Aldon Amethyst

blitzracing · Post by **blitzracing** » Sat Aug 16, 2014 6:30 pm

Has anyone managed to get one of these to work on the RV8? Ive had nothing but trouble trying to get it work with the lucas ignition amp and constant energy coil set up (1992). Its been back to Aldon twice with no fault found- but another owner of this set up is having the same issues as me. Basically the unit misfires badly- and appears to be randomly triggering, although Ive had and oscilloscope on the case and the signals Im feeding it with are perfect. Any other sufferers out there?

ChrisJC · Post by **ChrisJC** » Sat Aug 16, 2014 6:58 pm

I wonder if your 'HT' side is correctly aligned. You can imagine the situation where the rotor arm isn't pointing at the correct HT lead, it's kind of 1/2 way between two of them, and so the spark is having to make a bit of a random jump to get to a plug.

Maybe turn the distributor 1 tooth on the cam to get a better alignment.

Chris.

sidecar · Post by **sidecar** » Sat Aug 16, 2014 7:26 pm

ChrisJC wrote:I wonder if your 'HT' side is correctly aligned. You can imagine the situation where the rotor arm isn't pointing at the correct HT lead, it's kind of 1/2 way between two of them, and so the spark is having to make a bit of a random jump to get to a plug.

Maybe turn the distributor 1 tooth on the cam to get a better alignment.

Chris.

That's a good point Chris, I've done loads of work on the Lucas dizzies over the years and the rotor alignment is pretty bad. In fact if you fit a cheap rotor from the likes of Real Steel the mis-alignment causes the insulation of the rotor to breakdown which kills the engine stone dead. Moving the dizzy round one tooth won't help because the error is all to do with the relationship of the pickup, the trigger wheel and the HT cap.

My dizzy now looks standard on the outside but hardly any of the internals were made by Lucas.

Johnny Rotton · Post by **Johnny Rotton** » Sat Aug 16, 2014 10:14 pm

Aldon installed Amethyst in March and it has worked fine ever since. I have 35 DLM8 Powerspark dizzy and Lucas coil. Is your advance determined by engine speed and vacuum ? Does the max advance box in the map equate to the total of rev and vacuum related advance ?

Wilts289 · Post by **Wilts289** » Sun Aug 17, 2014 1:08 pm

I'm the other one having no luck with this unit. Been trying to get it to work properly since Christmas! It's had two software upgrades but having changed every other part of the ignition system with no improvement, I reverted to the old spring and bob system with it's Aldon ignitor and it runs up to 6500 rpm without a hiccup which to me indicates the problem is with the unit but again Aldon says it's OK! Very frustrating. Have had the distributor(s) in and out so many times now that I can remove it/modify it/replace it/and time it in under 10 minutes.
Johnny R - I would be very interested to know what "map" you ended up with and what you set the static at etc.

DaveEFI · Post by **DaveEFI** » Sun Aug 17, 2014 1:51 pm

Can it do a log of the trigger pattern? It would be good to know whether it's that or the HT side causing the problem.

Johnny Rotton · Post by **Johnny Rotton** » Sun Aug 17, 2014 9:04 pm

The map I am currently using is as follows:

500rpm 10'
1000rpm 13'
1500rpm 16'
2000rpm 20'
2500rpm 23'
3000rpm 26'
3500rpm 28'
4000rpm 30'
4500rpm 31'
5000rpm 32'

The advance remains at 32 degrees from 5000 up to 6500rpm, which is where the rev limit has been set to. I also have some advance programmed based on vacuum, with a peak advance of 10 degrees at 10inches Hg.
The first map I tried had 5' at 500rpm and 10' at 1000rpm, but the idle was very lumpy. Much better now.

blitzracing · Post by **blitzracing** » Wed Aug 20, 2014 8:28 am

Ive been through my install with a fine tooth comb- I had considered the rotor arm position, so I cut a hole in the dizzy cap so I could see the rotor position, so I could ensure the rotor tip was near a pick up point across an effective 45' timing period- which is just fine. Ive scoped out the waveforms, and the lucas amp is providing a clean 12 volt switched waveform. Ive also scoped out the supply rails. I cant do the coil primary as Ive destroyed one ,scope already with the back emf. The software display on the laptop shows the RPM goes wild and the rev limiter kicks in even at low RPM, that causes the misfire. It looks like the unit is being spiked, but Im at a loss to know the source- Ive tried resistive plugs to reduce the primary spikes, but no difference plus new earth paths, and a different 12 volt supply. Considering the unit is designed for use in the ignition system it should not be that vulnerable to external spikes anyway. Im not conviced that having the unit in a non shielded plastic box, plus using the same ground wire for the negative side of the coil and the electronics is a good design- Im waiting to get a new unit from Aldon, and Ill set up a full ignition system on the bench and see if I can get it to fail.

stevieturbo · Post by **stevieturbo** » Wed Aug 20, 2014 9:25 pm

If you want to test the trigger output relative to what is happening at the coils, buy a cheap current clamp

http://www.ebay.co.uk/itm/Hantek-CC-65- ... 3f395455fb

This outputs a 0-5v signal based on detected current. So you can get a good view of what is happening at the ignition coil with no worries about frying anything.

You could do one channel on the input trigger, and another on the current supplied to the ignition coil. So you'd see clearly when both are triggering

sidecar · Post by **sidecar** » Mon Sep 01, 2014 4:00 pm

If I understand the posts correctly you are using a standard Lucas ignitor to trigger your ignition system, if so is it possible to trigger the system directly from the pickup within the dizzy? The reason that I ask is that in the past I have connected up two systems to a standard Lucas "box on the side of the dizzy" system and they both had issues, I suspect with noise. The first was a Accuman Clubman rev limiter, it would kick in for a fraction of a second at any revs, the second was a Summit Racing RPM window switch, again it would trigger outside of the RPM range that I had programed into it. From memory I think that I cleaned up the signal to the RPM Window switch with a zenner diode. I tried more than one Lucas amp and they all had the same issue. I sold the rev limter to someone running an SBC engine, I told him about the issue but he reported back to me that the unit worked fine on his SBC engine. I actually don't think that the Lucas systems are very good, they are OK for a standard low RPM lump but that's about all they are good for. I now trigger my programable MSD from a MSD pickup mounted on a homemade baseplate inside the Lucas dizzy, I have built four systems like this now and they all made a BIG difference over the standard setup with regards to starting and power at low and high RPM. (seat of the pants dyno only).

I know that you have looked at the output of the Lucas amp but I'd still bet money on it being the issue!

DaveEFI · Post by **DaveEFI** » Mon Sep 01, 2014 4:10 pm

Can you post a circuit of the setup? I'm interested to know just how you're using the Lucas amp.

blitzracing · Post by **blitzracing** » Thu Oct 16, 2014 11:21 am

The lucas amp simply replaces the points effectively, in so much it simply grounds the coil when it gets the trigger pulse from the pickup in the dizzy. The Amethyst draws very little current so you have to add a sink resistor between the trigger output and the 12 volt rail to bring the switch current up a bit- a 100 - 200 ohm is enough. I have tried triggering of the reluctor trigger head directly with a diode to protect it (as recommended by Aldon), but it wont fire at cranking speed. It will fire with another couple hundred RPM, but thats no use. I had to put my car in storage back in August as I was having a new garage built, so I never managed to test the new unit. I subsequently loaned to a friend to try on his TVR, but so far hes had no luck. Aldon have now been sent my spare dizzy, amp and the Amethysts to bench test as a complete unit- so Ill wait to see what they say.

DaveEFI · Post by **DaveEFI** » Thu Oct 16, 2014 12:28 pm

Be interested to know the purpose of the diode. The Lucas sensor is a VR type and as such needs a fairly sophisticated input circuit to give a consistent trigger output. So unless the Aldon unit is designed to work with one, I'd not expect it do do so. However, I'd expect the Lucas amp to provide a consistent trigger.

blitzracing · Post by **blitzracing** » Sat Nov 01, 2014 7:01 pm

The set up is pretty odd- you put 12 volts on one end of the of the trigger coil- and the other end goes direct to the amethyst trigger wire. The diode goes from ground with the positive side to the trigger wire. This simply looks like it prevents any negative spikes from the reaching the trigger input- like a fly wheel diode. The trigger head is quite a high resistance so Id assume that when the magnetic field is at its greatest as the lobe passes it can pull the 12 volts down far enough to represent points closed signal. I can only assume you can get away with this as the trigger pulse will be rising and falling pretty quickly due to the shape of the trigger lobes, so any voltage changes due to the varying RPM wont have a huge affect on the final trigger point.