Scirroco Cold Starting Issues.

[BlazeMaguire]

Hi everyone, this is my first post here, and it is on behalf of a friend.


He has an 1985 1.8 GTX Injection Scirroco, but its recently started having problems starting when the engine is cold (and also problems starting when the engine is warm and been left for say 10 minutes).


When you try to start her, the engine catches and fires, but almost immediatly cuts out, if you try and keep it going by pressing on the gas, it splutters and shakes like crazy - almost as though its only firing on 3 cylinders - however I have checked spark at all cylinders and this is fine.

Obviously the engine dies, but if you keep repeating the 'start - splutter - die' process (I assume its the engine slowly warming up ) it will eventually get to a stage where it will keep running, albeit roughly untill its up to normal operating temperature - when its at normal temperature, it will run, and idle on its own fine.

If you then leave the car when its warm, for more than 10-15 minutes, the same problems occur again.

My money is on the automatic choke, but i'm not sure how to prove this (i'm afaid my knowledge on engines is limited to the carburretor A-series engine, and classic mini's!) hence I dont want to comdemn this without some other peoples opinions first.

Also, the haynes manual doesnt make mention of an automatic choke, but it does explain about a cold start valve, a warm up valve and various other things that all sound like they could be an auto choke.


One thing that does concern me, is we pulled the injectors out, and fired the engine with the injectors in a jam jar - we diddnt get the 'even conical spray cone' that the haynes manual explains, just more of an uneven, weak mist that wasnt visible untill you put the injector right against the side of the glass.

- Now, the trouble is, I dont know enough about VW engines to know if this is the injectors playing up, or just the fact that the injectors are not getting enough fuel on startup due to a dodgy automatic choke!

Anyone else had a similar problem? - I gather its the same engine in the golf GTI's of the time.... - Or is there anyone on here who is a bit more knowledgable about VW's than I am and can suggest some ideas?

Many thanks for reading this essay!

Cheers

Rob

[Crasher]

The DX engine doesn’t have an auto choke as such, it has a cold start injector operated by a Thermo Time Switch (very reliable apart from wiring fractures) in the water housing on the head between cylinders three and four, a Control Pressure Regulator (reliable as long as it doesn’t get contaminated) on the front of the block which controls the mixture according to temperature and an Auxiliary Air Valve (rather prone to failure, especially the wiring which gets damaged by the clutch cable on right hand drive cars) behind the cylinder head which allows in extra air when the engine is cold, supplemented by an Idle Boost Valve (ultra reliable apart from wiring problems) on the right hand strut housing which allows in extra air when the engine revs dip under 800 rpm approx.

The main cause of problems like this is fuel system contamination so the first thing to do is remove the fuel filler cap and use a low voltage battery powered torch to examine the state of the fuel filler neck to see if it has rusted through.

[BlazeMaguire]

Thanks Crasher,

Surely if it was fuel contamination, then it would happen when the engine is warm as well? - however this only occurs when its cold, once its up to temperature its fine.


I did check the cold start injector (the one on the side of the inlet manifold) and it was spraying fuel out as described in Haynes manual - I also checked the control pressur regulator (i think thats what it was) - and it measured 20 ohms across the contacts which was in the tolerance specified in the Haynes book.

Any other suggestions?

Thanks so far.

Rob

[Crasher]

Fuel system contamination is the enemy of any fuel system, the K-Jet is extremely sensitive to fuel system contamination and it causes the injectors to not seal when the fuel pump shuts down, therefore they dribble and fill the cylinders with fuel and this wets the plugs on start up. The contamination also prevents the fuel non-return valve on the pump from sealing as it is designed to keep the system under pressure until the engine bay cools down, so the fuel in the lines boils and causes a vapour lock which takes time to crank through, especially when hot as the cold start injector won’t help the engine fire up. The CPR can only be tested with fuel pressure measuring equipment to analyse the CPR pressure from cold to hot, the resistance test is utterly meaningless as all that is measuring is the resistance of the heater coil on the bi-metallic strip and all the heater coil does is supplement the engine block heat to apply pressure to the pressure regulator to increase the control pressure as the temperature rises. The CPR works in a way you would not expect, it increases is pressure as the temperature rises, so pushing down the metering slit regulator plunger and in doing so, covers up the slits and reduces fuel flow. Check the fuel filler neck for corrosion. If this is brand new and clean, suspect that the tank is already full of debris and water has already got through and caused damage. You will be able to change the injectors and check valve if the system proves to be clean, other than that you need a fuel pressure check for which specialist gear is required.

I have been a VAG specialist working on and modifying the K-Jet for 25 years and have owned my heavily modified 83 Golf 1 GTI since 1991.

[BlazeMaguire]

Cool - thanks crasher, that makes a lot of sense!

Thanks for your detailed reply.... - i'll have a look at the filler neck. - Is this a big / expensive job to replace? (I would give it a go if it can be tackled at home - not afraid of mechanics, but have no experience of old cars other than my mini) - how much are new injectors likely to set him back also? - assuming this is the problem..

Sorry to keep asking questions, but my friend (the car's owner) is not especially mechanically minded when it comes to cars, so i'm going to be the one who ends up fixing most of it! - need to know how big a job it is, and whether it could be done in a saturday afternoon, or would it require the car being off the road for a few days in a garage.

Thanks so much,

Rob

[Crasher]

The fuel filler neck is available from companies such as GSF and they are quite easy to do but I prefer genuine ones (533 201 129 C) as they fit better but at £202 they are expensive. Injectors should be 026 133 551 and are about £ 35 each from GSF but as a lot of these cars have been modified, there are three possibilities depending on cylinder head casting number and the thread pitch of the injector lines-with these cars you can’t take anything for granted. The fuel pump check valve (893 906 093 £21.56 genuine) is quite easy to change in theory but again, the car is getting old and may have been messed around with and snapping an injection high pressure line down at the pump can lead you into a world of hurt. If a line snaps, you must not bodge the lines with normal fuel hose as they are running at 5 bar (70psi).

[Captain Answer]

As crasher says above this is very common on theses cars if they are allowed to run quite low on fuel and have any contamination in the fuel systems. Inspect the filler neck from inside but i'd have a look outside as well by jacking up the car and taking off the wheel you can acess the neck, its quite common for moist dirt to be sat on it (handfuls when i first got mine). Might be worth popping the back seat cushion out, should only be 2 screws then take the plastic inspection cap off thats underneath and have a fish about with a magnet.