Messy Spark On 1993 Townace, Need Ignition Advice

[nickm321]

Hi all. I've got a really messy looking spark on my 1993 Townace (import), and am utterly stumped on how to fix it. It causes poor economy from too much unburnt fuel going through. I've changed a load of stuff, and still can't get to the bottom of the problem. I could really do with some ideas from people who are familiar with ignition systems on Toyotas of this era. I get the impression they're generally pretty similar - ECU>Igniter>Coil>Rotor>Sparks, with reluctor signals feeding crank and cam postions back to the ECU. Here's what I've done so far:


Symptoms:

• Really rich running on both petrol and LPG.
• I have unplugged all the HT leads, and plugged a spark plug in to look at the spark while turning over. It gives a fairly strong blue (white when plugs are cleaned of rich soot) spark pulse that is regular, but in between the main pulses are a lot of weaker blue crackly ones. This is one of the most puzzling aspects.
• The changes below have improved the spark from what it was, but it's still not good.

Changed:

• ECU (A scrap unit from Japan).
• Igniter (Tried 4 different scrap units, one very new looking).
• Coil (On the 4th one now, I think a stuffed condenser was wiping these out. Current coil is aftermarket).
• Condenser (New from Toyota).
• Distributor cap (Aftermarket).
• Rotor arm (Aftermarket).
• Ne and G pickup coils (Sourced from a scrap distributor from Thailand. I know Toyota manual says if gap on these is not factory set, to replace distributor. I don't have that kinda £££! So I've set the gap myself using a feeler gauge. They give a reasonable AC voltage when spinning the distributor on a bike wheel!)
• HT leads.
• Spark plugs.

Work done:

• Timing with a strobe.
• Checked the following signals using an oscilliscope:
  • From Ne and G sensors to the ECU.
  • IGt and IGf between ECU and Igniter.
  • Checking these signals was difficult as there was a lot of noise, and I had no real reference of precise values to be looking for.
• Checked earthing, and ran extra earth strap from battery to star point in engine bay, and to igniter.

Car:

• 1993 Toyota Townace, grey import.
• 3Y-EU engine. Only other car this was installed in is the Hilux Surf.
• LPG kit. Problems are present on both gas and petrol running.
• Model: E-YR21G-MEZE
• Frame: YR21-0129220

Anyone got any suggestions??

Thanks in advance!
Nick.