940 taking longer to start when warm

[Eyebrows123]

Recently my 1996 940 (B230FK) has been taking longer to start (a few more turns of the starter motor before firing happily as usual). It's happening only when the engine is hot and I go to restart it. Starting from normal ambient temperature seems to be fine, I don't yet know if cold weather affects it as we haven't had any cold mornings yet. Any idea what could be causing this? As soon as it fires, it starts and runs happily.

Engine (lambda) light is not on

Last time I had symptoms like this it was the ECT sensor (which i replaced 1 year ago), but that triggered the engine light and it was replaced 1 year ago with a FEBI/bilstein item so I'm doubting it would fail that quickly?

What do you reckon it would be?

[Clan]

Originally Posted by Eyebrows123

Recently my 1996 940 (B230FK) has been taking longer to start (a few more turns of the starter motor before firing happily as usual). It's happening only when the engine is hot and I go to restart it. Starting from normal ambient temperature seems to be fine, I don't yet know if cold weather affects it as we haven't had any cold mornings yet. Any idea what could be causing this? As soon as it fires, it starts and runs happily.

Engine (lambda) light is not on

Last time I had symptoms like this it was the ECT sensor (which i replaced 1 year ago), but that triggered the engine light and it was replaced 1 year ago with a FEBI/bilstein item so I'm doubting it would fail that quickly?

What do you reckon it would be?

a classic symptom of fuel pressure draining away when you turn off , it should hold for at least 20 minutes otherwise the fuel oils in the pipes with engine het and leaves an airlock to clear through before it will start .

[Eyebrows123]

Originally Posted by Clan

a classic symptom of fuel pressure draining away when you turn off , it should hold for at least 20 minutes otherwise the fuel oils in the pipes with engine het and leaves an airlock to clear through before it will start .

Possibly but it happens if I switch the engine off then instantly try to restart it (I think, I'll check this later when I next drive the car though)

Also, I always wait for the fuel pump to do it's 2 second prime thing when I turn on the ignition before starting (you can hear it start, then turn off again), would have thought this would be sufficient to build up any lost fuel pressure?

[Eyebrows123]

Having said that, i imagine it could be a failed FPR or check valve in the in tank pump, should probably test the fuel pressure and see what it does

[TonyS9]

Also check for the rev needle to flicker while its not starting. If its flickering it means you are likely getting a spark and therefore more likley to be fuel.

The 940 normally takes along time to start due to a single reference point on the crank. The spark doesn't start until then. The hall effect or Renix systems are twice as fast.

[Rversteeg]

If the reference point on the flywheel just passed the sensor when you stopped the engine last time, it can take almost a whole revolution of the engine before the sensor spots the point again and the ECU starts injecting / firing. It could just be "bad luck" that the engine has stopped just passed the ref point a few times.
I would be more concerned if it would pick up right away, but run rough for a few moments.