A4 B7 3.0tdi misterious warm startup problem

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grimS

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Hi,

I have had this misterious problem with my 3.0tdi b7 for quite some time now, so I'm getting desperate enough to ask for help and ideas online. (have gone through several services, repairs, online threads already).

Car summary: it is a 2004 year December 3.0tdi automatic, done 170k km. A 204hp version, but I chipped it a month ago (problem started a year ago). It is in perfect condition, with all repairs done in dealer on regular basis (up to now).

Problem evolved from: during the startup the car flickers a little bit for a fraction of a second. Sounds like an electrical shortage, like a "tick" as soon as you turn the key, right after this fraction of a second it starts fine. This is how the problem started a year ago, it got a bit worse and worse as the weather got colder and also after I chipped it. Right now it is so severe, that is just fully shuts down during startup, lights/panel/music shuts down. But as I try again it starts up perfectly.

This happens ONLY when car is warm and it has been standing for 5 - 15 min off. Also, on second try it works perfectly on 100%.

I have changed all the injectors to different used ones (second hand) and back (both sets checked fine at diagnostics in specialized service). Also changed the starter. Searched for "green" problems in electric circuits and ECU. No errors show up as well. Coils have been checked as well. Today I bought a new battery, the problem changed back to the way it was a year ago (minor "tick" at a warm startup), but it is not gone.

Any ideas/suggestions (getting desperate)?
 
If this happened all the time I would suspect the chains need replacing... but as it starts 100% on the second attempt this sounds less likely.

Have you had the timing chains replaced? There is no service interval listed for them, however I think the rule of thumb is 120k miles or when it rattles on startup. You're at 105k miles so it wouldn't be unreasonable to think it's time to have it done. Unfortunately it's not a cheap job... engine out and the chains, tensioners etc are about £700 just for parts, so prepare for a £1.5k-£2k repair bill if this is the problem.

The above is a guess and without hearing the sound I wouldn't be able to say for sure. I may be way off as you believe it to be an electrical problem (with the intermittent nature this seems plausible), but if you haven't had the timing chains replaced it might be a good thing to investigate.
 
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It sounds very much like some kind of electrical problem if the dash , radio etc are turning off when the car is being started. I would have said the battery was your problem and you have changed that which seems to have helped it a lot. As you are still having issues it seems that the problem may be due to a poor connection, probably an earth or ground issue . You need to check the earth strap on the engine and all the main power connections from the battery to the car.
What size battery is in the car ???

Karl.
 
Desert storm is on the right track. It is definately is NOT THE TIMING CHAINS! (See thread "3.0 TDi death rattle on start up")
The fact that the issue has changed since you replaced the battery is a clue as you have obviously disturbed part of the problem creating the change.
I would suggest like Dessertstorm, the problem lies with battery leads or connections. Especially when you consider that the issue is worse when hot and total voltage is lost (dash etc) This indicates that heat expansion is playing its part. I would check the resistance and continuity of the main red power lead to the starter and the earth leads when cold and then again when hot and while you flex them around. Remove the earth connection at the engine and the chassis clean off any corrosion to make shiny and replace with a smear of copper grease both sides and securely fasten. The "tick" you hear may well be the electricity jumping a break like a spark plug does.
As member JMGR33N mentions, from the main leads if no problems found, next go to the relay box and check for tightness and clenliness of relay tags and for any sings of arcing or corrosion. Main power relay, ign relay and injection relay.

Good luck and let us know how you fair

Regards
 
The ticking is likley to be relays chattering due the voltage fluctuating.
 
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Thank you guys, you are helping a LOT! I did consider the timing chains, but would expect a rattle with it (which is not the case). It does seem exactly like martynash described "The "tick" you hear may well be the electricity jumping a break like a spark plug does." I find your theory very plausible.

The only problem (since I have already invested a lot of money in changing the injectors (+ diagnostics) + starter + battery, I have the feeling that checking all the leads/connections will be expensive (taking into account the fully packed engine bay).

Question: what is the risk/damage if I leave the problem as is and it is the lead/connection problem you described?

EDIT: the new battery is 100ah an 850A.
 
The battery capacity looks about right for the car. If you leave the problem as it is it's liable to get worse, it really needs tracking down.
Where abouts are you in the country maybe somebody could recommend a place where you could get this sorted.
Somebody who knows what they are doing should be able to resolve this.
Why were the injectors replaced, I wouldn't have thought that this was ever going to resolve an issue like you had.

Karl.
 
audi upgrades
I fitted a new battery to my 3.0TDi quattro avant recently and it was a ....................................................................Duracell believe it not:laugh:


If you leave the issue to its own devices, evetually it will fail all together and then you'll be able to find it easy but this will be in the pouring freezing rain or a blizzard, in the middle of nowhere at night with the kids and wife in the car and posibly the mother in law if you're really lucky.
Join the AA now!!
 
The battery is Auto Starts, AGM type battery.

I am actually from Riga, Latvia. I have ~4 reliable shops where I could go to fix this. It will not be cheap, however. Regarding the injectors, I was assured by one repair shop that they guarantee injectors are the problem "they have had many cases like this before" and it is the dripping of injectors that cause this at startup. Needless to say - burned money on this one.

Regarding solving the electric issue - I though maybe driving like this for a couple of months to see if it get's worse again or not, but only if there is no risk of damaging/frying any devices?

BTW another problem: I have noticed pulsations of RPM when I'm in 4th or 5th gear at ~1500 RPM and when the accelerator pedal is barely touched (when I'm cruising). It seems as though the car is not sure whether you have let go of the pedal and it should drop RPMs to neutral or you are still driving. It looks like the problem persists even if I switch to "manual". Any ideas?

Thanks.
 
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