TDI intermittent starting

Just something to add here guys, those that have swapped the starter motor for another one or taken it off for repair knows that the other end of the earth strap from behind the headlight connects to the starter motor body, this can also cause problems due to its location. I always give that a thorough cleaning and grease it up for protection.
 
Another vote for earth lead. Had this problem only yesterday, called breakdown service and they fitted an extra earth lead between engine block and body - now starts fine again.
Do you have a picture/locations of this extra eart lead, I would like to try it on my Fsi
Thanks,
 
>It's been a couple of weeks since I fixed this starter motor earth problem, and quite aside from rectifying the actual problem of not starting, I noticed other improvements
- it runs so much better, engine sounds better, there is more power under acceleration and cruising in 5th. I guess the deterioration happened more or less gradually and therefore wasn't so obvious, but the step improvement is very clear

[/QUOTE]

Took my car to the shops earlier a couple of hours after re-fitting the cleaned up starter earth. Noticed that the voltages reported by the colour DIS after starting (as I turned on the lights, aircon, radio, dashcam, heated screen / mirrors and wipers etc.) were markedly healthier than last week even after the new battery was fitted - at least 0.3-0.4V stronger today than the other day despite everything being switched on - and also less erratic - (last week I was wondering if the voltage regulator was playing up as the numbers oscillated between low 12s with everything on and 14.6 during a recharging drive the other day whereas today never below mid 13s with same things switched on, and sitting at 14.2V with all electrical drains turned off but engine running. Knowing how sensitive A2s are to voltage fluctuations presume this could impact on all sorts of circuits, giving spurious fault codes or limp modes etc., if not dealt with.
 
I have another theory about the starter to chassis earth lead. As it degrades due to age and corrosion, it arcs and produces spikes in the cars power supply, as the power drops the computer senses this and temporarily turns off some systems perhaps only for a few seconds. This can be enough to trigger faults in sub systems that may or may not log faults / warning lights. While the starter is sucking the life out of the car it is also not getting clean full battery power and you get a lazy starter, a side effect of this is the starter squeal, although not all do squeal. This is down to the solenoid not having the power to cleanly engage and disengage putting strain on the pinion gear and letting the gunk build up compounding the lazy starter. So a bad earth has now caused at least one other issue, who knows this may also be a contributor to other well documented issues with the petrols and diesels.
 
I'm beginning to think that every A2 I've got has a slightly dodgy starter earth.

...
This is just a thought to help diagnose the bad earth problem. In my case - when the car started failing completely (not even turning over), the alternator light (battery symbol) in the dash board was telling me pretty much the whole story (the garage and their "automotive electrician" contractor should have spotted this - but didn't). The light was going from brightly lit with key in pos II, to out completely with key in pos III whilst all other dashboard lights did not change in brightness. Also in my case the battery symbol was flickering slightly with key in pos II but this may not be the case for everyone - I guess it depends on what alternative route the current can take. If you see this behaviour, it rules out battery and battery connections because in that case the other dashboard lights would dim/go out also. The explanation is either bad earth or bad +ve supply connection to the starter. I guess the former is more common.

When battery, connections and starter are all good, the alternator symbol and all other dashboard lights remain brightly lit during cranking with key in pos III.

I think - though I did not pay attention at the time so cannot be certain, that when the earth connection is partially failing (the engine still turns over but cranking feels sluggish), the symptoms should be somewhat in between the two extremes. So the battery symbol should dim during cranking whilst other dashboard lights remain bright. Wish I'd paid more attention at the time so I could be certain about this.

I also found some general advice online about diagnosing bad connections:
https://www.fluke.com/en-gb/learn/blog/automotive/electrical-automotive-troubleshooting

Advice from Fluke is quite emphatic - check ground connections early on in your diagnostic routine, to avoid wasting time and money.
 
Last edited:
Back
Top