Lumpy idle v6
 

I have got a lumpy idle caused by the front right cylinder not coming to the party on my V6 (Cylinder 5) mainly during idle.
The spark plug fires, the injector injects, and compression is fine. (11.5 Bar on cylinder 5 and cylinder 3 for comparison)
I have replaced the spark plug and also swapped the injector just for safety, but the problem sort of remains.
The engine runs well at higher speeds, which is evident when the spark plug lead is removed.
I will put some injector cleaner in the tank and drive a bit with the new injector (which came off my spare engine and has been sitting for a couple of years. I have triggered it and sprayed brake cleaner through it. It gives a fine mist under pressure)
The engine light comes at times and is currently on. No code reader, yet.

Anyone seen anything similar?:shrug:

First thing that comes to mind is a damp IMG even though you coat them with paint:}, any evidence on no.5's spark plug, although with your reputation I would guess you've already checked.

Regards

Funny. I haven't even thought of that! To be honest.
But there is no loss of water, and the spark plug seems to covered in petrol, not water.
When we did compression test there was no water ejected, so I doubt it could be that. But I will check.
Good thinking.!;)

Leaking cam cover gasket contaminating the plug with oil:shrug:

No, no oil at all on the plugs.

If it's got leads,they are known to break down (early mk 1's)

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No, there is spark at all times!

No, we have swapped the spark plugs between cylinders 3 and 5 (middle and right) and the misfire stays on cylinder five.

So to recapitulate:
Compression is good. Spark plug is good. Spark fires at all times (checked by pulling plug lead at different revs). Cylinder fires at higher revs (also checked by pulling plug lead at different revs). The injector has been swapped (which didn't seem to make a big difference).

So by elimination, the idea of water getting into the cylinder fits the bill, except there is no evidence for that. Which leaves the possibility that the injection control can be faulty.

Is it possible for the control to one cylinder to be out of spec? Either too long or too short delivery, or wrong timing???? But only at idle.

That is about the only logical option I can see left.

The only other option is that the swapped injector has a fault as the original must then also have had. The only way to make sure is to also swap the injectors like the spark plugs and see if the fault follows the injector or not. That is possible, but I guess unlikely.

its a long shot but maybe an o2 sensor?
had somthing similar when i bought a dud new o2 sensor.
try unplugging the front o2 sensor, plug is next to the aircon pipe
near fire wall so easy to test
The car will still run fine but this will make the car revert to a default fuel map .
may be worth a shot!!