Well, once again I am impressed by a Lubegard product
I only put the stuff in yesterday, when I started the car today the tappets were instantly quiet from the get go. I let it idle for 2-3 minutes to see if they would get noisy but they didn't and the engine was just purring over nicely at idle. I didn't reset the ECU or touch anything except opening the bonnet to listen to the tappets.
I then went for a longish drive and the car seemed rather zippy right from the beginning. Still a wee bit of hesitation below 3000 rpm to begin with, but nothing like it was even a day or two before.
Unlike what usually happens where it starts off running ok and then the performance goes progressively down hill the longer I drive it feeling lethargic by the end of the drive, the performance of the car just got better and better the more I drove it, to the point where it was going like a rocket with almost no hesitation after 20 minutes or so driving.
What was really apparent is just how much more responsive and grunty it was in the 2000-3000 rpm range, where it was often suffering from lack of power and quite bad throttle lag before, where you could floor the pedal and time a half second delay on a stop watch before it responded! Today, especially after the first 10 minutes or so driving, if I was in sport mode at 2500 rpm in 2nd or 3rd if I snapped the throttle down to half way it instantly pushed me back in the seat with no lag whatsoever.
Interestingly when I finished driving a couple of tappets were little bit noisy again despite the performance still being excellent.
I noticed a similar thing with the Wynns additive that I put in with the previous oil - the tappets would be silent right from a cold start but 2 or 3 would eventually get slightly noisy when the engine warmed up, and then be silent again when cold - exactly opposite to what you normally see with noisy tappets. I'll bet anything that when I start the car next time the tappets will be silent when first started but slightly noisy again when fully warmed up. (Anyone have any suggestions for why they might be quieter when cold and noisier when hot rather than the other way around ?)
Of course we all know how intermittent this problem has been, and I did let it idle a few minutes before driving which from past experience often causes it to run better, so lets see how it behaves over the next week or two, but if it continues to run as well or even improve further then I think we might have a diagnosis at last - excessive internal mechanical engine noise triggering the knock sensor! (eg "false knock")
Excessive mechanical noise apparently due to lack of maintenance of the lubrication system both before I got it and in the time I've had it.
If the additive has quietened down the mechanical noise significantly and the knock sensor was previously being triggered erroneously the progressive improvement in performance as I drove would have come about by the ECU sensing absence of "knock" and slowly creeping the timing in the knock retard table forward again. The more I drove it the more the timing would return back to normal, although I could have speed the process up by reseting the ECU.
Since a few tappets were still a little bit noisy when fully warmed up but the performance was still excellent it might not be the tappets but something else in the engine that was a bit noisy...and apart from slightly noisy tappets I wouldn't have said that the engine sounds unusually noisy to the ear either...
The fact that the oil I drained came out completely black after being in for only a month suggests its crying out for a good flush and one or more oil changes to get things back in shape, just like I did to the gearbox. This time I might try using a cleaning/flushing agent before changing the oil to give it the best chance of getting all the crud out.
Could it really be as simple as a poor oil maintenance schedule ?
Watch this space...