So, it is finally fixed :-))))
I will explain the fix for the detonation, but I will first explain how I stumbled upon the fix.
I actually found the detonation fix, as a result of trying to get the car to even idle again, after messing it all up a few days ago
Since a few days ago after seriously retarding the timing, the car hasn't ran properly.
Like I said I put everything back to standard and it was still a dog.
I had to drive with my heel on the throttle and my toe on the brake to keep it running.
I searched around to see if had forgotten to connect some hose or something but couldn't find anything.
I then remember testing that my EGR passages were clear a few weeks ago by simply energising the EGR solenoid with two jumper wires a few weeks ago, with the engine on idle.
As expected the engine stuttered and stalled, proving my passages were clear.
I then realised that the car was now acting a bit in a similar way so I removed the EGR valve and there were some carbon boulders stuck in the valve keeping it open.
These particles have probably become dislodged as a result of the fuel additive I recently added in case there were some hot spots of carbon in the combustion chamber.
When I was cleaning these carbon lumps out, I detected that the EGR return spring wasn't really very powerful, and in fact if I pulled the poppet valve out, then released it slowly, I could release it and it would just sit about 0.5mm off the poppet being seated. If I released it suddenly it would spring back home and whack against the seat okay, but doing the slow release test proved my point, i.e. that maybe this valve was not sitting properly on its seat, at the times when the detonation was happening.
I then tried to disassemble the EGR valve from the solenoid but couldn't see how it could be done.
I had intended to try to make the poppet spring do a better job at keeping the valve hard on its seat.
The next best option I could think of was to add an extra gasket at the split plane where the actuator meets the valve.
I then thought this would be too awkward to make and install so I thought about just adding a few copper washers instead.
I did this and immediately both issues where solved.
The car was idling perfectly and the detonation was gone !!!!
There was a slight glitch in that the car stalled again, and I immediately knew I had a few more boulders stuck in my valve.
I took it off again and true enough there they were.
I bought a tin of throttle body cleaner and gave it the best going over that I could, and so far so good.
I think I have got it sorted.
I know now that if it does misbehave again that it is an easy fix, and I am sure it won't be very long until the carbon deposits just begin to stick again, since the additive has just about finished going through my system.
Here are a few photos.
The copper washers are 0.9mm thick.
Edited by HONDALEO, 10 July 2019 - 07:09 PM.