s4 hot starting problem.

[Inertiauk]

After spirited driving in my S4 if I park up for a short while, like 15 to 30 minutes, the car is a pain to start.

When cold (or just driven chilled) it fires with a tiny turn of the key and tarts no problem.

The car turns over on the ignition but doesn't seem to fire, I have to crank for 3-5 seconds and give it some throttle to make it fire up. When this happens I gat a Brakes warning flashing on my dash but that stops after a few more seconds and the car drives fine.

I have vagscan and it doesn't seem to be logging any faults.

Any thoughts?

Thanks.

 

[stu_m]

The brakes on dash is usually an early indication that the battery is on its way out

 

[quattrojames]

Sounds like fuel vapourisation, fairly common on any large petrol engine. The heat from the engine vapourises the fuel in the lines, so it has to crank over a few times when it starts waiting for new fuel to be delivered. Its just one of those things I think.

That extra cranking puts a strain on the battery, this causes a drop in pressure in the ABS system which triggers the warning, again its nothing to worry about.

 

[Inertiauk]

Sounds like fuel vapourisation, fairly common on any large petrol engine. The heat from the engine vapourises the fuel in the lines, so it has to crank over a few times when it starts waiting for new fuel to be delivered. Its just one of those things I think.

That extra cranking puts a strain on the battery, this causes a drop in pressure in the ABS system which triggers the warning, again its nothing to worry about.

Makes perfect sense. Thanks very much.

 

[cobraBLACK]

I've never had this happen and I've never heard of another S4 with the problem.

Whatever it is, I don't think it should be ignored.

 

[pauldazzle]

Hot start problems are often caused by a goosed coolant temp sensor. Have a look at the temp the ECU is seeing with vcds/vagcom.

 

[Inertiauk]

It's in fr a service now and I made them aware of the problem.

Coolant temp on dash is always as expected. I've asked them to check it in VCDS

 

[PhilW]

Does the dodgy headlight switch affect these cars as well?

Try starting it with the sidelights or headlights on.

 

[stu_m]

Does the dodgy headlight switch affect these cars as well?

Try starting it with the sidelights or headlights on.

the only thing with that is it affects all starting conditions not just hot starts! but still worth a shot to rule it out

 

[pauldazzle]

It's in fr a service now and I made them aware of the problem.

Coolant temp on dash is always as expected. I've asked them to check it in VCDS

The CTS has 2 independent outputs 1 to the dash & the other to the ECU if the ECU side is goosed it wont fuel correctly but the dash temp may look normal so it's important to look at the ECU temp reading in VCDS engine measuring blocks to make sure it's ok. ECU will only throw a fault code if the CTS goes open circuit or becomes intermittent.

 

[Inertiauk]

The light switch makes no difference.

The temperature in VCDS matches the dash gauge.

The only thing alarming is the air intake temp is reading as 45 Deg C. Is this too High? The cone filter was fitted by the previoUs owner and the car has a stage 2 map. Would a stock air box with an upgraded panel filter be wise?


As part of the full service We changed the plugs, oil, oil filter and fuel filter, we removed the cone filter and cleaned it with the airline.

Since then the problem hasn't happened. Touch wood. But I've only been using the car a bit today, and not opened it up very much.

Will report back if it happens again.

 

[pauldazzle]

Even the stock air box & filter will perform better than a cone filter in the engine bay sucking in hot air.

 

[Inertiauk]

My cold air feed is still in place and it is directed at the cone, and there is a divider around the cone filter 'separating' it from the rest of the engine bay

I would be interested to know what the air intake temp reads on a car with a stock airbox, is it making much of a difference ?
Also interested to know if the airflow gained by the cone filter is required to get the most out of the stage 2 software, or would this be no different on a stock air box ?