Rough Running Cold Tdi

[JDHogg]

I'm sure someone out there will be able to answer this one...

 

On a cold morning (we've had a few recently!), when I try to start my Gal, the engine does usually start ok, however it sounds really rough for the first few seconds until it gets going. After that, it runs fine, with no hint of a problem.

 

Could this be something to do with the glowplugs ? They do seem to operate, however I guess its possible that one could have failed ? Is it possible to check this easily or will VAGCOM tell me? (I have it somewhere but had a failed installation - could try it again though)

 

Any thoughts that may assist ?

 

Mucho grassy bum..

JD

[Richard gal]

Would vag com tell you which one it is?

I suggest you disconnect the wires and test for open circuit on each glow plug, ie power should flow through it to earth.

[Mirez]

Would vag com tell you which one it is?

I suggest you disconnect the wires and test for open circuit on each glow plug, ie power should flow through it to earth.

 

No Vagcom can't tell you - they are all fed from the same supply down one cable with no comms, it wouldn't even know if they were all faulty as its an unmonitored circuit.

 

You can test them though, remove the engine plastic cover and you'll see them - remove the wiring connectors to all of them and then (with a multimeter in resistance mode) put the red probe on the top of each plug in turn and the black one on any part of the block. You should expect a reading of no more then 6ohms but ideally less then 2ohm. Generally though you'll find they fail open circuit in which case you simply won't be able to measure a resistance.

[zorgman]

no meter then spark test them. get at plug tops by pulling off the covers to each one, get a wire from battery positive them touch top of each one, good ones spark dead ones dont, are you waiting till light goes out. if you have a meter also check that the relay is working by testing if supply is going to the plugs, i wouldnt worry myself mines done that for 2yrs in all temps

[seatkid]

no meter then spark test them. get at plug tops by pulling off the covers to each one, get a wire from battery positive them touch top of each one, good ones spark dead ones dont,

 

NO! DO NOT DO THIS!

 

Dangerous thing to do as a glow plug can take 100 amps! And slipping onto the block could spell disaster (shorted battery).

 

Use a lead with a lamp in series - faulty glow plugs are high resistance/open circuit and the lamp will not glow.

Edited March 9, 2010 by seatkid

[Scorpiorefugee]

Not sure about the 100 amps but it might just be possible as an initial surge until the plug heats and the resistance increases. I think the fuse for the circuit is 60 amps. SK is absolutely right about the short circuit risk. A splash to a ground conection can give a flash which could leave you blinking for some time and, as a battery can provide currents in excess of 1000 amps, the wire could get hot pretty quickly and leave a nasty burn on the fingers. As things go in 3s, you might just bang your head on the bonnet as you leap back. :ph34r:

 

Having said that, It's probably sort of thing I would do as it is a quick easy check if you're careful and wear welding gloves.

 

More to the point, how long does the glow plug light stay on and do you wait for it to go out before cranking the engine.

 

My 115 '52 Ghia does much the same but, by the time I've cleared the ice it's OK so I suspect it's reasonably normal diesel behaviour. These engines start pretty well on the button under most conditions with or without glow plugs so, even if the glow plug light is on for several seconds and it starts OK, you may still have a problem.

Edited March 9, 2010 by Scorpiorefugee

[zorgman]

if your carefull using short bared wire no problems have used flash test process for years when ive forgot my avo

[Stoneblade]

On a cold morning (we've had a few recently!), when I try to start my Gal, the engine does usually start ok, however it sounds really rough for the first few seconds until it gets going. After that, it runs fine, with no hint of a problem.

 

Have you checked the lines for air? I had a problem with air getting and making the engine rough for about 10 secs until all cyinders firing without air in them. I found once leak was found the car starts first turn now. But dont forget there will be a small fluctuation in engine until ECU compenstates for all cylinders to hit norm.

 

I dont know what the threshold is for the plugs to work, but how cold is the ambient temp outside when the light comes on? Mine only flicks at about 1c, only ever seen it come on for about 5 secs at -4c.

 

Hope that helps

Rob