Updating firmware in-situ: safe practice
 

Is there any reason why it would be a bad idea if I unhook the car battery then plug in an external 12V supply directly to my DIYPNP while I reflash it, still plugged into the car's loom?

Previously, I've unplugged the DIYPNP and updated the firmware at my desk. (I gather there can be issues if you try to reflash with everything still connected up - possibly damage the coils?)

I'm just looking for a risk-free way to update without unplugging the looms, as they always put up a fight and I don't know how many mating cycles it'll take before something snaps.

I can't imagine why you'd need (or want) to disconnect the MSPnP from the vehicle harness in order to do a firmware update.

The only circuit in the car which can be damaged by this process is the igniter (90-'93) or ignition coils ('94-'05) so simply disconnect this under the hood and re-flash the ECU in place.

I have a '94 and I find it's far from simple to disconnect the coils. I can't get at the connectors without unbolting the coils from the back of the head.

It's much quicker and simpler to unhook the battery and unplug the DIYPNP. I can do that in the car park when I arrive at work, and reflash on my desk at lunchtime.

I just wondered if it might be even quicker in the garage at home to unhook the battery and plug in an external 12V dc supply. Can you think of any reason it would be bad to have the DIYPNP powered while it's connected to the unpowered car's loom?

actually, it's really easy to disconnect the stock coils. It's the plug right next to the coils. Opposite side of the CAS on a 94. If you're really worried, you can disconnect the harness for the injectors too. A total of 2 plugs to unplug

^^ This.

But there is also a knack to unplugging the coils directly without having to remove them.

Having slept on it I realise I was being stupid and there must be a second connector in the loom leading to the coils. Must have been one of those I disconnected during my engine swap. Doh.

Just need to identify which one, and this may be a LHD vs RHD issue. On my left hand drive car the only connector on the CAS side of the coils is the lambda sensor. But as I recall there are two multi way plugs on the intake side rear corner. One must go to the coils.

Richy, if you can reach (let alone unplug) the coil inputs without unbolting them, you're a better man than I. :)

One hand from the intake side around the back of the engine to push the connector lock in.

Other hand from above gently tugging on the loom/connector.

They're usually very stiff at first as they've likely never been removed, do it a few times though and it soon loosens up.

Then I discovered the connector by the intake manifold you've just discovered ;)