Not all cylinders firing...

[Blue60]

So we have an issue in that not all of the cylinders are firing. After doing a spark test with an inline spark tester, we have discovered that the following are the only ones that work.

(LHD 71 V12, D=Driver side and P=Passenger side)
B1-yes A1-no
B2-yes A2-yes
B3-yes A3-no
B4-no A4-yes
B5-yes A5-no
B6-no A6-no

Also note that A5 does not spark during ignition...

We have new plugs (all tested and work), new wires (all tested and work), Coil has spark, new advance sensor and a new rotor cap. The battery is good as well.

Any thoughts would be appreciated.

[lowact]

Left bank is B bank, Right bank is A bank. I.e. D = B, P = A Firing order is 1A, 6B, 5A, 2B, 3A, 4B, 6A, 1B, 2A, 5B, 4A, 3B.
I suspect either yr coil is stuffed, or it is the wrong one, or there is a very poor connection or wire supplying it.
When using the in-line spark tester, were all the other plugs disconnected and removed?
Testing the coil, needs to be less than 1 ohm resistance between the pos, neg terminals .
To test the coil supply wiring, could see if any better result using instead a wire directly from the battery pos to the coil pos?

[Blue60]

Ok. We will check the resistance on the coil. The coil is the original. 33k miles total on the car. Almost everything is original...

The testing was done with all plugs and wires connected during startup and while running.

[Blue60]

So we spent some time going over the ignition system and here is where we are at...

As of last night, 6B, 5A, 2B, 3A, and 4B don't receive spark from the distributor. The distributor has a new cap, new rotor cap, new timing disk, new timing sensor, and a new coil.

We have read that the ignition amplifier has two halves that send two signals and "cycles" between the two halves. If one half was bad, could this cause the issue?

What voltage should be coming out of the ballast?

I know there are mixed feelings on the Opus systems. But what are the thoughts on the Pertronix conversions? Reason being is that a conversion is under $200 and the new amplifier is $750.

[MarekH]

If I've read your post correctly, you are saying only a5 doesn't work during cranking, but about half of the cylinders don't spark during normal running.

If that is so, then I think the key here is the comparison between cranking and normal running.

The only difference between cranking and normal running is that at cranking, you run through a low ballast resistance powered by a battery voltage which drains down as the starter motor runs, but during normal running, the coil charging circuit runs through a higher ballast resistance powered by full 14.2v of alternator voltage.

What you have reported is that when you run through a low ballast resistance, 11 out 12 cylinders spark, but only 6 out 12 spark when the ballast resistance in the coil charging circuit is higher.

So you aren't charging the coil during normal running and you are barely charging it enough during cranking.

The manual shows a picture of the ballast resistances with their connections and it looks like yours, once combined with the coil resistance, are too high to charge the coil during normal running. I'd check the ballast connections and ballast resistance for normal running conditions against those in the manual.

(You haven't reported a problem with the ignition light, but I'd still also want to know whether the alternator excites and takes over. If it doesn't, then during normal running, you are trying to charge the coil through a higher ballast resistance but with only a starter motor depleted battery voltage.)

It isn't possible to accurately measure coil resistance using a modern multimeter, as anything below ~2ohms is going to carry a potential error of up to ~0.7ohms. The is guidance on Roger Bywater's website as to how to measure coil resistance accurately using Ohms law and a simple wall socket charger.

kind regards
Marek

[Blue60]

Slight correction. A5 starts working after the motor is running. The others I mentioned never spark at all.

[MarekH]

OK, so I misunderstood your post.
You are saying the same set of cylinders never fire under both cranking and running conditions, near as matters.

You said you changed the "advance sensor". I'm not sure what you mean by that, but the cylinders fire after a sensor inside the distributor is triggered by 12 ferrite rods held on the perimeter of a clear/white disc which spins past it inside the distributor. The sensor gap is important, as is the presence of these rods. If the sensor doesn't pick up that these rods have just come past, it doesn't make the OPUS fire the coil. If the coil and rotor and cap are good, and the same cylinders don't fire every time, then I'd look there, as that is the only common part of the chain, ignition wise.

The Roger Bywater website covers OPUS ignition in detail, as does one of the REOPUS websites.

kind regards
Marek

[jagwit]

Previous owner of my current S3 purchased a new OPUS ferrite disc from SNG as well as a REOPUS. The car refused to run well. With his electronic background and my PICOSCOPE he started looking into things.... and found as follows:

1. Not all the ferrite rods were located on the same radius from the centre of the disc - this led to different coil charge times for each cylinder;
2. some where so far away from the edge that they produced no spark at all or at best, very inconsistent spark;
3. Some were correctly located, but refused to generate spark - he eventually found that these rods were cracked inside the (brand new) disc - this led to the 600Hz signal being induced into the one half of the rod, not being transferred for detection in the other half of the rod, hence no/inconsistent spark.
4. OPUS and REOPUS work EXACTLY like points in the sense that charge time (dwell) is very long at low rpms but becomes less and less as RPMs rise (weaker spark at high revs) and if the engine stops with a ferrite rod directly opposite the pickup, the coil would be switched on (like points) if the ignition is left in the on position for whatever reason.

His conclusion was that OPUS / REOPUS was just a bad ignition system, period. I agree.

This led to him installating the Lumenition system that is currently in the car along with the vacuum advance unit JLM519 that brings with it all the benefits of vacuum advance. Lumenition has a system including a dedicated fitting kit (hardware) for the OPUS dissy. I can highly recommend it (no vested interests).