Pop, bang, whizz

[wrinx]

This is starting to bug me now....starting the Q4 is a bit of a lottery.

If it's not been used for a few days or a week it starts straight away after two pumps of the throttle.

Trying to start again after filling up with fuel, or an hour in the supermarket is a real lottery.

Symptoms include backfiring, cranking without firing, firing after letting go of the key (wtf?), sometimes needing throttle, sometimes foot flat to the floor and other times starting with no throttle.

I have noticed if the car is hot it starts better with no throttle, but if it's just warm it's variable.

I've replaced the plugs and water temp sensor. Now wondering if the air intake sensor might be at fault?

Any other ideas?

wrinx

[AlfaJack]

Air intake sensor is testable like the water one...probably best to check that first as we know on the TS engines if that sensor is too hot they wont start - if you suspect it might not start, before you try, disconnect it :)

[AlfaJack]

Also, mine back fires whilst cranking over now and again. Always done it though..

[Stuntz]

Some do some dont. It gets better when changing the crank sensor or aligening it right..

[axaQ42]

Crank sensor definitly...change it(maybe the cable is in bad shape) or set it correctly(as i remember around >1 mm from sensor to the sensor wheel(or what it is called.)).

[AlfaJack]

Actually I read recently that for starting both the crank sensor and cam phase sensor need to be reporting accurately for starting the engine - then is it true that one of these can be disconnected and the engine will stay running? - guess I could try it myself...

[axaQ42]

If you disconnect the crank sensor the engine will never start:)

[AlfaJack]

If you disconnect the crank sensor the engine will never start:)

Or if the cambelt wears through the cable:tapedshut::tapedshut::tapedshut::redface:

[wrinx]

Crank sensor definitly...change it(maybe the cable is in bad shape) or set it correctly(as i remember around >1 mm from sensor to the sensor wheel(or what it is called.)).

That might be worth checking, I've had it off the car a couple of times and just set it "near" the phonic wheel.

But the car has always done this, before I took the sensor off.

Do they cost much to buy?

wrinx

[AlfaJack]

Sensor is about ?25 from your favourite stealer..

[wrinx]

Ah, not that bad then :D

wrinx

[Juan AR155Q4]

If you disconnect the cam sensor, the car will run anyway, not smoothly and with some bangs.

I did have a similar problem (bangs starting and while driving) and the problem was solved due to a loosen wire in the cam sensor.

Worth to try it.

[Evodelta]

I would tend to go with cam sensor too, if it was the crank sensor why would it only happen at certain times?

[wrinx]

Thanks...is that the large unit on the end of the exhaust cam?

wrinx

[AlfaJack]

Yes :)

[wrinx]

Ta...will have a play then :smile:

wrinx

[Evodelta]

Like the others have said I would check the crank sensor too, first I would be playing with the gap on it to see if that helps.

[wrinx]

Manual states 0.4-1mm so quite a large difference...but I'll have a look. :smile:

wrinx