Turns over but slow to fire

[TomPaine]

The latest pain. The car (MY04 Aero) has always been a prompt starter but at the weekend I noted that it took longer than usual to fire. It was fine on warm restarts and I forgot about it. But then today it took even longer. I backed off the first try (5 seconds?) and it went after a bit on the second try. Again warm restarts fine, and runs fine.

It didn't seem particularly sluggish - turned over but reluctant to fire as promptly as customary.

Battery giving an early warning? I thought they just tended to fail these days. I've checked and it's 3.5 years old, measured 80% at last service (May).

I assume if it was other suspects - starter motor, alternator, fuel pump, injectors - the symptoms would be a bit different? Any thoughts gratefully received.

[sgould]

Is the cold start improved if you turn on the ignition and wait a bit before starting?  If so the fuel pump may be slow to pressure up.  Tip the back seat up and listen to the pump.

[sgould]

You often need an accomplice as the pump may only run for a brief period.   But, if the pump is OK, a blocked fuel filter might cause a slow build up of pressure.

[TomPaine]

From Off to On and before St - difficult to be very clear because all of the bongs - and with seats and bonnet up:

I can't hear the fuel pump doing anything.

There are some rapid clicks which then stop; they sound like they're coming from the back / central of the engine bay. The car then starts fine if I proceed to try, as it's still warm.

[sgould]

The pump is under the back seat. 

[TomPaine]

Aye I lifted the rear seats but couldn't hear it doing anything. I assume if it was acting up I'd have problems when driving? The car drives completely normally once started.

I'm wondering about starter solenoid.

There's a strange rapid but finite click at On.

[sgould]

Lots of clicking could be a failing relay.

[TomPaine]

That was my thought. I also wonder whether this coming on after the welding was done is a diagnostic clue - a bit of Googling made me wonder about the ground wire.

[sgould]

I'm not a welder. but I understand that a welder would disconnect the battery, etc, if he's using an arc welder.  But i'm happy to be corrected!

[TomPaine]

Sigh, it's getting more complicated ...

Swung by Cartech today and the car was completely normal; I couldn't reproduce the rapid clicking between Off and On (and since it was warm it started fine). So I headed to my destination. Got back in the car 90 mins later and again while it turned over briskly it was very slow to catch; and moreover there's a completely new symptom, a loud click/clunk which you can feel through the gear shifter (auto) when you touch the brake pedal in Park. Google says shift lock solenoid. It's like I've got some migrating electrical gremlin.

[sgould]

The click/clunk when hitting the brake pedal is indeed the shift lock solenoid releasing.  It's what stops you pulling the selector back from "P" until you put your foot on the brake.  It's normal. My old car had a noisy solenoid.

[TomPaine]

But is there some reason it would go overnight from a barely audible click to a loud clunk? I mean, I would have expected something like that to get imperceptibly louder over time but it's a dramatic shift.

[sgould]

Not really.  The switch itself may have come loose.  I was worried about the noise on my old9-5, but the garage listened and said that it was "normal".

[TomPaine]

Shift lock solenoid back to normal (inaudible). So, that was weird.

Still turns over briskly but only fires on the second or third turn. Idles fine. I was starting to convince myself that hard acceleration was slightly under par.

So, although hot starts are ok for the moment, I'm starting to wonder about [1] the CPS, which seems to generate various issues, or [2] the fuel check valve, which a bit of Googling suggests can cause my issue, i.e. difficult cold starts but fine thereafter.

[carrera]

If it's slow to start, but is OK once running then I would be looking at the fuel pump ability to get the fuel rail to the required pressure

CPS risk of failure normally shows when the engine is hot, not cold

No error codes ?