Now everything is clearer. All assumptions are correct except the reason for removing the head. Anyways, at this point I would recommend hooking a VAG-COM scanner to OBD port and check for errors stored by ECU. There might be something as simple as corrosion in Hall sensor connector, knock sensor connector, ECU connector, bad wiring in between or ultimately the ECU itself.

Did you turn the whole disi 180* or just the cap? Assume you left the leads in situ?

Pretty surprised the new disi didn't come with a new cap, they normally do.

You cant turn the whole dizzy 180 degrees, the mounting bolts are offset to prevent it.

Its fairly obvious to me the fault is with the cap itself, either not seated correctly, or has a broken terminal internally, or its the wrong cap

there are 2 types if dizzy, the bosch ones have an orange cap, the magneti marelli ones have a black cap.... ironically these engines normally have a bosch dizzy even though the ecu is from magneti marelli.

Its fairly obvious to me the fault is with the cap itself, either not seated correctly, or has a broken terminal internally, or its the wrong cap

Yeah, that is what logic tells us and that was the purpose of the test suggested by you. But az@ insists he bought not only a new dizzy cap but finally a new complete dizzy  I guess he can tell black from orange. What chances are both a new cap and a new dizzy have the same fault? So what are we left with? The ECU, another associated sensor or the wiring in between. The scary part is that, according to az@, the problem started out of the blue during a trip.

 

I wonder if erasing the learned values or disconnecting the battery overnight will help ECU...

No, I don't think so, it's now proven that the ht leads and spark plugs work by the fact the misfire swapped to another cylinder,the Hall effect switch is proven to be working by the fact the engine runs, all the injectors share a common driver circuit, plus there is only one ignition driver in the 4av ecu.

It is possible for a distributor cap to work when the spark plug is out or ht is disconnected, but when it's connected you could have a high resistance possibly caused by carbon build up which prevents the spark from jumping, but this can often be heard and seen as the spark traces across the inside of the cap.

The other thing I have seen is where the spark plug threads in the cylinder head and the surrounding area is dirty or corroded which prevents the plug getting a decent earth connection, but this is disproved in this case because the cylinder fires when the cap is rotated to the opposite position.

So in essence here, distributor and Hall effect switch are proven to be working, ht leads and spark plugs are all proven to work, rotor arm is working, all that is left is the distributor cap.

.in reference to what I said about the 2 dizzy types, bosch and magnetti-marelli, either type can be used on this engine, they are wired exactly the same, both fully compatible, but as I said, the rotor arm and cap are specific to each type and must be used as a complete matching set.

So in essence here, distributor and Hall effect switch are proven to be working, ht leads and spark plugs are all proven to work, rotor arm is working, all that is left is the distributor cap.

True. That is why it doesn't make sense there was no fix after changing the cap and then the distributor entirely, both new. What should we think? Foul play from the mechanic that didn't replace them and in fact he forces an engine swap because it is a job payed better? To me both head removal and engine swap recommendations for a misfire seem fishy.

I suspect the mechanic probably wants the truck, most people would bin a vehicle that requires a new engine in the uk, the value of second hand cars are tiny right now, and a ever rarer fun truck will become a classic desirable vehicle before long.

I am still waiting for his feedback after the shock of the 180 trick working hahaha. As soon as I know any more I will inform you all. However I did speak to him on Sunday to double check dizzy cap and arm are of the same manufacturer.

I suggest taking the car back quick. Otherwise you might end up with other 'mysterious' (ehem) issues that could render the engine dead or very difficult to diagnose.

Well good news we got a new auto electron to have a look (£) and it's all fixed if the phone call is anything to go by it seems there was to much resistance on the new ht leads, however this was a very brief phone call whilst I was meant to be working so will get a proper report tomorrow when I pick the car up. But as of now apparently the car is running perfect.

AZ@ said that he had sparks at all plug leads so It does not seem to be electrical so where do you look next, Apart from hole in piston or valves, camshaft!

Spark is not always equal to strong spark. It all depends how you test it.

az@

Who bought the spark plug leads? What manufacturer code?

Sorry to "believe none of what I hear and only half of what I see" (I am a fan of Richard D. Hall), but if I were you I would trust only hard evidence, figures, values, codes. Never words. Or you can let it go if the money spent and the waiting time are not an issue to you. In the latter case you will never kmow for sure what the real problem was and we will not learn much from your experience.

Edited 15 October, 201510 yr by RicardoM