Off Topic - VW Diesel Problem

tanick · Post by **tanick** » Wed Oct 19, 2005 9:44 am

I know its cheeky posting this on here, but I can't think of a better place to ask and there are some real tech wizards here.

I have a VW Passat 1.9TDI(2001) which only runs on 3 cylinders when cold. When warm, if I turn off the ignition and re-start it is fine. I'm selling it in about a month so not wanting to just put it into a dealer and let them sort it. I'm thinking that one of the glow plugs is duff? But if so why does it only re-set itself after the ignition is turned off and on again. Is it worth changing the glow plugs which sounds to me like a cheap and easy job (please correct me if I'm wrong) or is it going to be something wrong with the engine management or injection system.

Any help gratefully received, or you can just tell me to take my crappy oil burner problems elsewhere!

hmy7k · Post by **hmy7k** » Wed Oct 19, 2005 9:56 am

No idea what that problem is but you could try:

http://www.tdiclub.com/

http://forums.vwvortex.com/

I have sorted a problem using these that the garage could not resolve.

Good Luck

Ian Donkin · Post by **Ian Donkin** » Wed Oct 19, 2005 5:09 pm

Whilst not a VW, when my Merc had a glowplug fail it ran like an bag of bigger than usual nails until it sorted itself out and all five fired up. This was only at first start of the day, or after it had sufficient time to cool down.

As I understand it, the glow plug only serves to get it started, thereafter compression of the mixture and heat in the head alone are sufficient to keep it going. I'm almost certain that to stop a diesel, they in fact cut the fuel supply, otherwise it would just keep on running.

I replaced all five glow plugs on my Merc (sourced from Euro Car Parts) for £60 and an hour or so of my time (okay, make that two hours).

Should be a doddle to carry out yourself and even if this isn't the problem (although I suspect it will be), it won't have cost you a whole lot in time or money.

HTH

Barry · Post by **Barry** » Wed Oct 19, 2005 8:04 pm

Hi Nick,

like you say, seems odd that you need to re-start to sort it. The engine management usually uses an inlet manifold temperature sender to see how warm the air is, when it is below a certain temp. the ecu fires a glowplug relay for a calculated time, obviously lower temp, longer time. Usually all of the glowplugs are linked directly togther, so if one is fired, they all are: subject to the individual plugs being O.K. Once the inlet manifold hits a certain temp. they're not lit up at all, whether the engine is running, or is being started. BTW, direct injection engines fire much more readily than indirect, so some of these don't have glowplugs at all

(our 2.5 transit for example: in the handbook it actually says that below -20C you may need to use a cold start spray

)

On the face of it, like you say, if a plug has gone (or is on the way out) you would expect that cylinder to come in within a few seconds, as the engine temp comes up. Makes me wonder whether one is nearly worrking, but not enough to start that cylinder from really cold, but when you give it another shot, its just got enough guts to get that cylinder running.

Before changing them, I would be tempted to unhook the power supply to them, and put a ohm-meter across them. Obviously if one's open circuit then fine, if not see whether one has got a very different value to the others.

After that: power lead tightness/contact? Poss measure the voltage to each one as it is fired: at least you will see whether the plug harness is O.K.

After that I would start thinking about compression test (not nice finding someone to do that), plug relay/control module, slightly poor injector (supermarket fuel?) ... after that I really don't know.

Sorry, not my thing, diesels, so I'm sure this doesn't advance the investigation much

. Be interested to hear what you find though

tanick · Post by **tanick** » Sat Oct 22, 2005 11:45 pm

Thanks all for the replies.

I tried testing the glow plugs, the two I could reach had a resistance of 0.5 ohms which is OK apparently. The other two I can't reach without removing the water pump.

I'm still not convinced though. Firstly, the glow plugs shouldn't kick in when the ambient temp is over 5 degree C and secondly if it was a dodgy glow plug it would gradually start firing properly as the engine warmed. I've now checked it and it doesn't work properly until its reached normal temp then the ignition is switched off and on again. I give up. I'll see what happens. New car coming in about 5 weeks. ..

Barry · Post by **Barry** » Sun Oct 23, 2005 11:27 am

Hmmm, all beginning to sound a bit electroniccy managementy isn't it: have you had the fault codes checked?

Like you say, (and said at the beginning), you really would expect it to start to come in on the offending cylinder(s) almost straight away. Must be unusual: they're pretty good usually.

hmy7k · Post by **hmy7k** » Sun Oct 23, 2005 12:56 pm

Given that a diesel only needs fuel and compression to work I imagine that you either have a problem with the engine management system or a dodgy injector as it sounds to me that there is no fuel being supplied to one cylinder.

impmad2000 · Post by **impmad2000** » Sun Oct 23, 2005 6:03 pm

Nick,

Check out http://www.tdiclub.com/ there is some really good FAQ. Just sorted a MAF fault on mine (I'm really chuffed

) Also the VAG Com group on Yahoo. I don't know if you have VAG-Com, but it'll read the fault codes from modern VAG cars(Reads my '98 Audi so perhgaps not that modern). I have some interface leads I could build up for you to try if you'd like. Unfortunately I dont have a case so the thing sits on a bare connector, but works fine for me. Do you have a laptop (old probably) with a serial port ? You can down load a trial VAG-com and test to see if it works for you. Perhaps will give you a clue as to what is happening. From what you say, I'd suggest there is an injector problem rather than a Glow plug problem.

Sorry I've been slow to pick up on this thread.
Cheers
Tim

Robster · Post by **Robster** » Mon Oct 24, 2005 10:15 pm

Hi chaps, for what it is worth,
I would go down the VW garage, and ask one of the service bods to plug their diagnostic tool in. That should tell you whats wrong with it and could save a lot of money spent in the wrong direction....

good luck!

regards
Robster

PS my 1.9 Tdi blew it's cooling fans and needed new ones. The bloke in the garage said, 'don't worry they all do that...'. The car was only 2 months old! (mind you it has got 150hp and 320NM of torque so that makes up for it...)

tanick · Post by **tanick** » Sun Nov 13, 2005 7:10 pm

Sorry I haven't said thanks for all the suggestions on this topic. The car's still doing the same thing and I'm getting a new one in about a month so I've just got used to it. Had someone reverse into me in a car park and dent the bonnet with their spare and then I was rear-ended on the M25 last week so the car's a bit worse for wear. I guess I should just sell it while its hot although I am an honest person and doubt I can actually do it. Someone will want it i'm sure. Thanks.