odd weak spark problem...???!!!

[Jawa2112]

Ok i have a spark problem i cant rationalize...

I have and EDIS4 setup, ive been troubleshooting a misfire/cutout at 4500RPM that i have had all summer and im not sure if its related to this problem although i wouldent be suprised. I have an aircooled VW type 1 engine installation and have cylinders 1 and 3, 2 and 4 are paired together and it runs, pretty good considering...

cylinder 1 and cylinder 4 are weak sparks, cylinders 2 and 3 have strong sparks "referenced by pulling off wires and placing them near ground" Weak spark barely makes it out of the boot and is yellowish blue, cylinders 2 and 3 have huge inch and a half long sparks. I suspect cylinders 1 and 4 are barely firing because the exhaust pipes are pretty cool by compairison. for reference cylinders 1 and 2 are the right head, 3 and 4 are the left head, Firing order is 1-4-3-2 and no change in spark characteristic is noted when RPMs increase.

I have swapped Edis modules, coils, and wires around on the coil, i also swapped a spare wire into the #4 spot. no changes... all i have left is to change all the wires out which i guess i should have done before posting this... i can pull 4 and 1 off together a the same time and there is no drop in RPM at idle. pulling 2 or 3 causes a stall.

anyone have any idea how this is even possible? i would think the paired coil towers should fire a near equal spark shouldent they?


Thanks,
Nathan

[simon k]

dunno how it's possible for that to happen, to summarise, you have 1 weak spark and 1 strong spark coming from each bank of the coil pack?

I'd suggest there's something going on with the supply of power to the coil, it's either intermittent, or not enough current can get through. Since you basically have 2 coils sitting side by side, with two outputs each. Both outputs fire at the same time, if there is a supply problem, perhaps the first fire of the coil for 1 revolution is OK, but there isn't enough time for it to charge up again for the second.

you can swap leads in the pairs - IE you have 1 and 3 paired, with 1 going to spark plug #1, and 3 going to spark plug #3, swap them to 1 going to #3, and 3 going to #1 - I reckon whichever one is fires second in the sequence will be getting the weak spark

something to think about anyway

[Jawa2112]

yea thats it, one weak and one strong on each bank. there has to be something im missing because it dosent seem to follow the coil towers or wires, it follows the cylinder which seems impossible.

Ive now swapped the entire wire set with junkyard wires, idle actually got worse "on the dead cylinders" i didnt look at the spark because the replacement wires has a much less substansial boot on them and i didnt feel like getting nailed, but im getting coughing and back fires up #1 and #4

I also checked, the center terminal of my coil and the edis module, it is getting a full 13.6V

I dont think current is a problem, the wiring is not undersized it does however run the length of the car so my next move is to bypass the existing wiring and run some troubleshooting wires right to the battery for the 12V and ground, just to be sure current isint the problem.

Anyone know what would occur if you were to provide EDIS/coil with 13.5V but inadequate current? The 12V source im using powered the coil for the distributor setup that i removed.

I forgot to mention previously, spark problem also exists when in limp home.

Thanks,
Nathan

[NITROPIXIE]

It must be your wiring somewhere fella, either a bad joint or what I had done seen before is the 12v supply to the coil went to the wrong pin on the coil pack, causing one weak spark and one powerful spark at the same time.

Hope this helps

Ryan

[simon k]

discovered something very odd tonight that may be related to the above - it was discovered while tracking down a misfire under load. Turned out the posts in my coil pack are almost completely corroded away

anyway...

I put a timing on each of the 4 spark plug leads, and there is a very obvious difference in the number of pulses through the spark plug leads for #1 and #2 to the number of pulses for #3 and #4. It looks like #1&2 get double the pulses for #3&4

I installed a known good coil pack - same thing

I'll see if I can get a graph of it through an oscilloscope

[NITROPIXIE]

Again this sounds like to me that the wiring to the coil pack is incorrect.

If you have the 12v power lead to the coil pack is attached to the incorrect pin then as (for instance) coil A output of the EDIS fires you get a good spark from oneside of the coil pack, but then Coil B output fires you have a weaker speaker form both sides of the coil pack

[simon k]

Again this sounds like to me that the wiring to the coil pack is incorrect.

If you have the 12v power lead to the coil pack is attached to the incorrect pin then as (for instance) coil A output of the EDIS fires you get a good spark from oneside of the coil pack, but then Coil B output fires you have a weaker speaker form both sides of the coil pack

nup, I don't think I could do 110mph (n/a) with the coil pack configured like that... all 4 plugs are the same colour and have the same mixture indications, and today with a different coil pack, it's back to very impressive performance, but still odd-sparking

but to clarify, I went and checked my wiring - my 12v goes to the middle wire

could you do the same with your timing light? just to see

[DannyP]

Try and turn around the lead on your timing light, it is inductive correct? Sometimes the lights behave funny with EDIS. If reversal doesn't work, get an old hardwired style and try that.

[simon k]

Try and turn around the lead on your timing light, it is inductive correct? Sometimes the lights behave funny with EDIS. If reversal doesn't work, get an old hardwired style and try that.

yes inductive, and no, it's not that... just with messing around and picking up whichever timing light was in the top of the drawer, it's actually had 3 timing lights on it - scratch that, 4 timing lights, we put it on the analyser too, but the secondary pickups on my mates machine wasn't working which is a bugger, it looks at all 4 plugs at the same time

messing around yesterday I swapped leads around (no, it's not that) and also swapped the pairs over (1=3, 3=1, 2=4, 4=2) and the issue stays with the coil pack post

it'd be really good if someone would pick up their timing light and give it a shot - it honestly takes 30 seconds

[NITROPIXIE]

I would but I don't have a running engine at the moment

[simon k]

I would but I don't have a running engine at the moment

thanks anyway


the other thing I made sure of when I was fiddling with this was that the plug leads were separated, so they wouldn't have been picking up pulses from the other leads - just to pre-empt that next question

[spitfire50]

Hi all,
I've been looking this thread over and noticed;
"and the issue stays with the coil pack post "
This tells me that it is always the posts that are firing in a particular direction that test weak. The reverse firing plugs will test differently than the forward firing ones.
Good luck,
Paul

[simon k]

Hi all,
I've been looking this thread over and noticed;
"and the issue stays with the coil pack post "
This tells me that it is always the posts that are firing in a particular direction that test weak. The reverse firing plugs will test differently than the forward firing ones.
Good luck,
Paul

thanks Paul - I work with an electronics engineer, and he's looked over it with me and said something similar. Does it ring true that there would appear to be "more" flashes of the timing light for the forward/reverse than the other direction?

oscilloscope next week