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Discussion Starter #1
Over the years, there have been many things wrong with my car, some of which I have investigated and fixed.
I meant to post these findings as a reference in the hope that it may help someone (and myself, because after a long time I might not remember it anymore). It seems that some of the problems are not very common (but some are, I think).

Symptom: After turning the key to STOP position, the engine still runs for a few cycles before stopping. If I try to re-start within a few minutes, I need to crank for 8 to 12 seconds before the car can start whereas normally this will take only 3 seconds or so.

Cause: This is a clear case of dieseling, meaning additional fuel is somehow getting into the cylinder after the key is turned off. When re-starting, additional wet fuel in the cylinder will cause a hard to start condition. If one waits longer and the fuel evaporates away, then the car will start normally. Dieseling seems to be a rare occurrence in fuel injected car, so I pull out all the injectors from the intake but with them still attached to fuel rail. I then turn the key to MAR and observe. There is NO fuel leak detected, so this method cannot be used to detect the fault.

Remedy: I swapped all the fuel injectors with a set of used ones. Sure enough this cures it.
 

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Interesting. I wonder if the injectors have metal in them which ethanol attacks. Our current 95 octane has 5% bio-ethanol and so do some 98+ octane fuel. I note that in Germany, the Shell V-Power pumps state it contains a maximum 0.7% ethanol. I'm sure there is good reason for that.

Here is a pic of a carburettor which was using supermarket 95 octane. The green gunge suggests the jets were being eroded by fuel.
IMG_20210403_151755~2.jpg
 

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Discussion Starter #3
Frankly, I still do not know the failure mode on the injector. Though it was occuring frequently, it was still an intermittent issue. Since it seems that this kind of injector failure is rare, initially I thought it might be related to injector control, i.e. fault with the ECU, but I was not making any progress until swapping out the injectors.
 
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