O/T Diesel question

[JimB]

Audi 2.0 TDI:

 

When starting, if I release the ignition key immediately the engine fires, it runs really roughly for half a minute or so. If I keep the key turned only for about one second longer, it starts fine and runs absolutely fine thereafter.

 

Any ideas what the problem could be?

[Stationary M25 Traveller]

When it runs roughly, is it that the starter motor is still engaged ? I had this on previous Octavia, and it would then stall the engine. Replaced starter motor, then fine.

 

7 related photos

[6speedmanual]

Maybe something to do with correctly "launching" the glow plug cycle. Most diesel glow plug cycles have a pre-heat and then a heat cycle which continues into the engine warm-up running, 1o, 20, 30 seconds or more depending on ambient temperatures.

 

I'm guessing here but maybe an ECU is looking for a moment when the key is turned to "cranking" position and the engine has started running???? releasing the key just when you sense it picking up the first firing stroke is maybe fooling it.....?

 

An VAG technical boffins on here?

 

 

6SpeedManual

*tongue*There's no such thing as too much BHP per Ton 😬

[Graham Perry]

A lot of people complain of this with many of the latest diesels. My Ford does it and I have seen it mentioned on various diesel websites. Theory often quoted is that you are turning the key too fast for the high pressure pump to get up to capacity OR for the multiple sensors to report to the ECU about what they find and hence it confuses the ECU. Can't comment if either of these teories is correct but as you say Just holding the car with the ignition lights on for about a second before engaging the starter avoids this temporary misfire/roughness happening.

 

Its not the glow plugs, as mine will do it on a hot summers day when the glow circuit is switched off by the ECU (I checked with a voltmeter to be sure).

 

Edited by - Graham Perry on 12 Nov 2007 17:54:10

[Frying Pan]

Ford TdCi's do it as Tony says. Well, they used to...

 

My first S-Max and previous Mondeos used to to run roughly if I did a 'key-through start' without letting the ECU boot fully.

 

If I try on my latest S-Max, nothing happens - they must have added a trap into the calibration to prevent the problem.

 

You may find your Audi Dealer can update your engine management software to improve things.

 

-----See some pictures of the build here. 13000 miles completed!

[strij]

My Audi A3 2.0 ltr TDi does exactly the same.

Local agent could not suggest a reason, but holding the starter for an extra second works everytime summer or winter. I decided to live with it rather than have them pulling it apart in the hope of finding a fault.

[JimB]

Thanks guys. I will live with it then - not a great problem. I was dreading a flood of posts talking of doom and disaster.