Hi - perhaps some knowledgeable person can help me (technologically-challenged!) on this matter:

I have a 2007 Superb L&K (2.5 TDI) Diesel car.

Recently it has developed a problem whereby when the engine is cold and the key is turned to position 1, the glowplug/coil light illuminates for less than a second - and then the engine has to turn for 4/5 seconds before it will start. In the past the glowplug/coil light would always illuminate for 3 seconds or so and then the engine would start immediately thereafter. Ideally I would like the car to be restored to starting immediately.

I have taken my car to 2 dealers who have run the diagnostics tests and told me that the car was not registering any faults. However recently (after this problem started) the glowplugs were replaced - as was relay 202. But still this has not cured the problem.

Oddly enough, yesterday when I started the car the glowplug/coil light illuminated for 3 seconds and starting was a breeze. This is a rare happening these days - which leads me to believe that the glowplugs and relay etc work properly. But there seems to be an intermittent problem whereby the glowplugs are not being activated for long enough (or at all) in most cases.

Any ideas? Anyone?

Thanks

Jeremy

What is the ambient temperature where you are?

It's always worth checking the health of your battery. Do you have a multimeter?

Sorry - I should have added that the battery is 6 months old (recently changed) - so I think that's ok.

The ambient temperature is approx 17 degrees - but I haven't noticed any temperature differences between when the glowplugs are activated – and when they are not. Indeed, prior to this problem starting, the glowplugs would be activated at ambient temperatures higher than where they are now.

Once the car has started though, it runs beautifully!

For cold start problems, I'd always start by checking basic injection pump timing, from my testing the 2.5TDI starts best with about 0.3-0.8deg ATDC. Skoda spec says 0.8 - 2.7deg ATDC, good luck with instanst starts above 2degATDC

Measurement is via VCDS / tester, adjustment is mechanical. It is best to measure first, because if timing has changed it could be your timing belt on the way out / stretching.

If it is not the timing, and you had glow plugs and relay replaced, then the next point I'd look at would be temperature sensors - inlet, coolant, and fuel temperature. With faulty temp sensor the ECU might still think it is hot when it is not

Again, way to check this would be to hook up VCDS or similar and see if temp readings in various measurement blocks look sensible.

I had a bit of delayed start problem when the car was new, on wet days it would take 2s of cranking and a puff of fuel out the exhaust to start. I set the basic timing at 0.6deg and never had the problem since.

Thanks for this - I'll try this and report back!

my garage has told me that apparently there is only one temperature sensor (which has a double function?) for my car . . . . .I'm not sure I'm convinced (any comments from anyone?) but this was apparently changed this morning - with no effect.

Timing belt is apparently fine as is injection pump.

Any other ideas?

Have they actually measured basic injection timing? If yes, please quote the numbers (e.g 2.3deg ATDC).

Nothing to do with timing belt condition (unless it is really bad). Even good belt over the years can slip timing by 1 deg or so. Anyone who tried to change basic injection timing on this engine knows how fiddly it is (though simple to do), 1mm belt movement is probably about a degree.

The problem is that according to Skoda service book, timing in range 1.2ATDC-2.7ATDC is just fine, but in fact on 2.5TDI engine anything above 1.5ATDC results in occassional cold start problems, and timing above 2deg ATDC is almost guaranteeing cold start problems. My advice is do not rely on brush-off answer "timing is fine", ask for the numbers.

The only other thing I may suggest is placing a clamp type amp meter on glow plug leads and confirming they actually do take current (yes, I know they were changed, and so was the relay).

Failing that, initial fuelling can also be increased using VCDS, there was a Skoda bulletin on how to do that, login code to your engine is 35342.

Edited 8 October, 201213 yr by dieselV6

Right well the puzzle continues. . . . .

My car has, all of a sudden, begun to start correctly. The glowplugs are heating for several seconds once the key is in position one and then the car starts immediately. Ostensibly there has been nothing really done to the car since my last post - certainly no timing adjustments. The temp sensors seem to be fine, the glowplugs are doing their bit. . . . .now my mechanic is completely confused.

Both my mechanic and another one nearby have speculated that the ECU is intermittently giving off faulty signals - and wondered whether it should be replaced to ensure constant correct operation? I'm told it's quite an expensive part to replace - and I would only like to do this as a last resort. That said, I don't want to endure a Swiss winter with a car which might fail to activate its glowplugs at any time for an unknown reason. Given that it appears that all the parts CAN work (at times), could it be anything OTHER than an intermittently faulty ECU?

Thanks

Jeremy

Have you checked for water ingress?

err. . . no - I don't think so. Where should we be looking for that? (please bear in mind my technical knowledge about cars is almost zero!).

Water or damp under carpets. You could search water ingress on the forums and you should get plenty of results. :-)

No water ingress or so I'm told. Nothing is wet IN the car, and the ECU and surrounding area are all dry. The garage said they checked the seals etc and all is fine there as well.

However after three days of perfect performance, the glowplugs were no longer being activated for more than a fraction of a second as of this morning (now they are back to as they were a week ago). It is apparent that the glowplugs CAN work properly - but most of the time, they aren't being activated for long enough.

The starter mechanism is being changed next week - apparently it was no longer turning (?) within Skoda tolerances (it was too slow). Maybe this will resolve the glowplug problem - although I'm a bit sceptical. . . .