Engine misfire, very strange!

[OllyTheFrog]

Hi all,
My 97 Y60 4.2 EFI petrol has a very strange problem: I broke down (see post 840593) and had the dizzy replaced which got me back on the road.

However, since then, I've been getting intermittent misfires, usually when the engine is under load but also at idle (it's an auto box). The Nissan dealer here in France had no explanation to give, claimed to have no access to info on the 4.2 petrol engine (not sold here) and wasn't really much use at all! He did find that if the speedo wire was disconnected from the top of the transmission, that the problem disappeared.

So I now have a working engine, but no speedo!

Anyone got an idea as to what could be causing this?

What signal could the speedo be sending back that might interfere with the EFI but not affect it when disconnected? Could it be a speedo malfunction (although it seems to work ok)?

[not not]

Sounds more like timing than anything. But wont explain the speedo thing though.

[OllyTheFrog]

I'm sure it is a timing thing, but why would the speedo affect that? The EFI must be either picking up a signal, or possible the speedo is interfering in some way?

[not not]

Hopefully some of the nissan tech gurus will chime in in the next few days?

[OllyTheFrog]

Just a thought: if there was a dirty earth, would that perhaps weaken the signal from the sensor back to the timing circuit?