280i Cold Starting

[John042]

Hi All. Happy days, "Wesley" has again passed his MOT with no advisories I'm sure this subject has been posted before but, it's the cold starting. Starts on the first turn of the key, will idle then stop. Three or four attempt and it will idle but driving until warm is a pain. I've check the aux air valve when cold and the plate is particaly open but the rpm when cold doesn't rise above 1000rpm. So I guess my problem is with the fuel enrichment or the cold start device is not openning enough? Incidently there appears to be no voltage at the plugs of the cold start device or the aux air valve? When should there be a supply and where from? On cranking or warm up? Appart from this annoying habbit it's running very well.Thanks for any replies. J C.

[mrzigazaga]

Hi John


Can you try this and report back please..Get the car to normal operating temp and then blip the throttle via the butterfly...Does it settle back to idle smoothly?...Does it take a couple of seconds?..Or does it drop and then rise up to the base idle?

[John042]

Hi Mark, thanks, I will try what you suggest but seem to remember that throttle response was normal, however will try. I guess you're considering the adjustment of the throttle by-pass screw on the throttle housing?

[mrzigazaga]

Thats correct sir...The plate should really be fully open when cold..What is your base idle?...Can you rev it when cold?

I have a spare AAD that you could try if needed..

[John042]

Thanks Mark. Openning the throttle when cold starting will usually stall the engine until it's warmed up. The last time I removed the ADD the plate was only about half open. So I think that will be the first suspect item? However, shouldn't the mixture be enriched for starting by the cold start device unless that's bu**gered as well? Cheers J C.

[mrzigazaga]

Hi John

This may be a useful bit of info...
https://www.google.co.uk/url?sa=t&rct=j&q=...

[John042]

Hi Mark. I've done a few investigations. Removing the AAD and soaking it in brake cleaner then putting it into the fridge for an hour and the plate was open this much, is that enough?



I then checked the throttle stop and started the engine and the idle cold was about 1300rpm, higher than originally. One thing that still puzzles me is that with the ignition on there's no voltage at either the AAD or Enrichment plugs? Does the supply come from the sensor on the front of the engine? I did slave a 12v supply to both but it didn't seem to make any difference. At the moment the engine is only slightly warm and on starting is idling at 900rpm. Clamping the AAD hose does drop the rpm a bit so I guess the AAD is doing something? At this point however openning the throttle does cause the engine to hestitate before picking up making the car a pain to drive until warm. I've got a gut feeling Mark that the fuel enrichment device is not preforming, richening the mixture for cold starting/driving? Thoughts please? I was thinking of waiting until the engine was completely cold, start it and bring the idle up to 1300/1400rpm by adjusting the throttle bypass screw and see once it's warm if the idle reduces. Other than this driving on a cold engine the car seems OK. Cheers JC.

[mrzigazaga]

Hi John

Im not too up on the electrical side of the AAD, IIRC it cuts the circuit when its fully closed/Hot....Thats looks normal.

Have you checked all the hoses for air leaks?...Try this...When its warmed up remove the oil filler cap while its running, put your palm over the filler tube and blip the throttle...If it sucks on your palm then the inlet manifold is leaking...A common point is where the distributor is and usually needs a bit more silicone on the cork part.

[John042]

Mark apoligises for not thanking you for your kind offer of the loan of your AAD. I gussed it looked normal and seems free to move. I'll try tomorrow as you suggest incase I have an inlet leak. The bible and a book I have on Bosch injection systems do refer to the "Thermal Switch" I guess it must be the unit on the top of the engine, with a 2 x pin plug where the radiator hose is attached. The small single wire going to the temp' guage sensor. The circuit seem to take its supply from the coil feed via the start/pump relay. Again, assuming when cold, the Thermal Switch supplies 12v to the ADD and the Enrichment Device? Warming up gradually reduces this supply. Perhaps more investigation and a direct feed to that sensor? Thank again Mark JC.

[John042]

Just an update to the ongoing cold start saga. No air leaks evident on the check you mentioned Mark. I did, when cold wind the throttle bypass screw out to increase rpm but it remained over 1000rpm when hot. I checked the voltage at the thermo switch and there's 12v on starting. Whether that's getting to the AAD/enrichment device??? Further invest' required JC.

[mrzigazaga]

Hi John

Did you do the oil filler check?...It could be you inlet manifold leaking......

[John042]

Hi Mark, yes no vacum buildup on throttle increase. I'm still not convinced that the enrichment device is doing anything. It starts so well but just doesn't like any throttle input until warm. Stll with all this sunny weather who cares a ***k. Cheers J C.