Misfire and Weak Battery

[DrRobin]

I had a problem last summer and through autumn, my 2001 2.7L Boxster 94k miles developed a misfire as follows:

Under deceleration (engine braking) in 4th or 5th gear, probably for 5 seconds or more (so no fuel going in) then feed the power back in at 1,500 - 2,000 RPM and I got a random misfire, different cylinder every time.

Over the summer I changed:

- All six coil packs
- All six spark plugs
- Cleaned the throttle body
- Changed the air filter
- Changed the MAF sensor
- Changed all four O2 sensors (they were on the way out)

At some point fairly early on in all of this the misfire stopped, but my Boxster ran a bit rough, all of the above work was to get it running sweet again, which it did.

The misfire stopped when I charged the battery. I fitted a new battery in April 2020, but in lock down it had got a bit flat.

Roll on to Jan 2022 and I had a misfire on cylinder 6, just once but under deceleration again, about 1,500 rpm but with headlamps on. I checked my battery it was failry low. I charged it up and the misfire has gone, again.

There has been lots of discussion on here and elsewhere about batteries and misfires, seems to be a emotive subject.

I think one of the following is happening:

A weak battery causes low voltage/low current available and

- this leads to a weak spark?
- one of the sensors or ECU gets an error or signal confused?
- one of the coils produces a weak spark?
- one of the injectors doesn't open correctly?
- the fuel pump doesn't give enough fuel?

Perhaps the weak battery is not the real problem, it might indicate another component is on the way out and with a good charge in the battery that other component is hanging on in there and still working?

Any one had a similar experience?