A6 Intermittent Starting Problem

Dear All
Some time ago I posted about my A6 2.4 Auto that has an intermittent starting problem (details below). Since then, my garage (an independent
Audi specialist) has checked over all of the obvious things (spark plus, cleaned the injectors etc), however the problem persists and next week the car is booked in with them to have the fuel pump replaced - purely on a speculative basis. However, I have been in contact with another A6 owner whose car had a similar problem, and his was diagnosed as a faulty immobilizer.
I'm now wondering if replacing the fuel pump is the right thing to do at this stage. The biggest difficulty is that the problem is almost impossible for the garage to reproduce (happens about once a week), so it's very difficult for them to know where to start. From my notes below, can anyone suggest any components that are definite candidates for replacement or any that can almost certainly ruled out as the culprit?
· A typical scenario is that the car starts fine in the morning, and I park at work after a 20 minute drive. Come to start the car in the afternoon - nothing. The engine cranks over fine, but doesn't fire up. I can normally get it started using full throttle and cranking over for periods of 30 seconds or so. Sometimes the engine will fire after just a couple of cranking periods, but on one particularly grim occasion it took 10 minutes.
· Another scenario is that I drive somewhere (short or long distance) stop for a few minutes and then try and restart and it won't.
· When the engine finally starts after a problem start incident, it doesn't roar in to life straight away. Rather, I can sense it firing but know that if I stop cranking it will die, and have to pump the accelerator to coax it in to life.
· Once started, the engine runs perfectly. No sign of any trouble at all.
· There are NO fault codes being logged.
· The dashboard immobilizer light does NOT remain lit when the car is having a problem starting.
· The most annoying thing is that the problem is very intermittent (say once a week on average) and most of the time the engine starts fine. I started to keep a log of when it happens but there doesn't seem to be any obvious pattern.
Thanks very much folks!
Cheers - Graham
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Hi Graham,
What year is your A6?
A no start scenario could be the hall sender but that would thro a 2113 code. If it's the immobiliser, check for a faulty relay. I have a C4 S6 and relay may be behind panel under steering column.
Tony
Dear All
Some time ago I posted about my A6 2.4 Auto that has an intermittent starting problem (details below). Since then, my garage (an independent Audi specialist) has checked over all of the obvious things (spark plus, cleaned the injectors etc), however the problem persists and next week the car is booked in with them to have the fuel pump replaced - purely on a speculative basis. However, I have been in contact with another A6 owner whose car had a similar problem, and his was diagnosed as a faulty immobilizer.
I'm now wondering if replacing the fuel pump is the right thing to do at this stage. The biggest difficulty is that the problem is almost impossible for the garage to reproduce (happens about once a week), so it's very difficult for them to know where to start. From my notes below, can anyone suggest any components that are definite candidates for replacement or any that can almost certainly ruled out as the culprit?
· A typical scenario is that the car starts fine in the morning, and I park at work after a 20 minute drive. Come to start the car in the afternoon - nothing. The engine cranks over fine, but doesn't fire up. I can normally get it started using full throttle and cranking over for periods of 30 seconds or so. Sometimes the engine will fire after just a couple of cranking periods, but on one particularly grim occasion it took 10 minutes.
· Another scenario is that I drive somewhere (short or long distance) stop for a few minutes and then try and restart and it won't.
· When the engine finally starts after a problem start incident, it doesn't roar in to life straight away. Rather, I can sense it firing but know that if I stop cranking it will die, and have to pump the accelerator to coax it in to life.
· Once started, the engine runs perfectly. No sign of any trouble at all.
· There are NO fault codes being logged.
· The dashboard immobilizer light does NOT remain lit when the car is having a problem starting.
· The most annoying thing is that the problem is very intermittent (say once a week on average) and most of the time the engine starts fine. I started to keep a log of when it happens but there doesn't seem to be any obvious pattern.
Thanks very much folks!
Cheers - Graham
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snipped-for-privacy@smith-hewerdine.freeserve.co.uk writes:

A bad fuel pump will give the problems you describe. Try and listen for excessive noise from the fuel pump. It should not sound like a hive of wasps in your fueltank.
The shop should be able to diagnose the fuel pump without replacing it by measuring the pressure of the fuel pump before the filter. Low or too low pressure will indicate a bad fuel pump.
On my '93 Audi 100 2.3E the pressure should be as high as 6.1 bar. I've just replaced the fuel pump myself on mine. The shop had the pump gauged to 2 bar... needless to say: The car wouldn't start.
Before I changed the filter it took it out of the tank and dropped it into a bucket of water and applied power on the pump. A 2 foot column of water shot straight in the air, but the water was black as soot. So got some fresh water twice and gave the pump a good clean. I left the pump to dry and replaced the fuel filter. I then reinstalled the fuel pump and tried to start the car. It roared into life immediately.
Albeit, as the fuel pump had excessive noise I replaced it with a new.
A clogged fuel filter is a sure death for a fuel pump, and a change should always be included in the 30k km service. It's cheap and it's easy to do. So remember to change the fuel filter if you get a new fuel pump installed. Otherwise your new fuel pump will have a short and pointless life.
Just to get an indication of much crap there is in the fuel, try and empty the content of the fuel filter into a clear bottle...
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Thanks for your replies! My A6 is a 1998, and there are no fault codes being logged. I've just heard back from the A6 owner who had a similar starting problem that turned out to be the immobiliser, and his car didn't log any fault codes nor did the dashboard immobiliser light stay illuminated. So immobiliser is still in the frame - or the relay (thanks Tony).
BBO, if the fuel pump is the culprit, is it plausible that there would only be a problem at startup? I'd have thought that the car might suffer from other problems - poor running perhaps?
Cheers - Graham
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snipped-for-privacy@smith-hewerdine.freeserve.co.uk writes:

The fuel pump is either working or not, albeit I have had my fuel pump work intermittely until it finally bought it. This showed itself as poor performance and stalling.
From what you're telling of the experience the other A6 owner had I'd have the shop check the immobiliser before they start ripping out the fuel pump.
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In case anyone else has a similar problem, the faulty component was the coolant temperature sender.
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snipped-for-privacy@smith-hewerdine.freeserve.co.uk wrote:

Now that you have it sorted, there's no need for this tidbit - The fuel pump on my 80q worked fine after it got to working. Not a problem, when it was actually operating. But it was getting it to get going that was the hassle. Replacing it solved our intermittant non-start problem.
Good to hear you got it figured out, and relatively cheaply, too.
E.P.
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"" wrote: > snipped-for-privacy@smith-hewerdine.freeserve.co.uk wrote: > > > > BBO, if the fuel pump is the culprit, is it plausible that > there would > > only be a problem at startup? I'd have thought that the car > might > > suffer from other problems - poor running perhaps? > > > > Now that you have it sorted, there's no need for this tidbit - > The fuel > pump on my 80q worked fine after it got to working. Not a > problem, > when it was actually operating. But it was getting it to get > going > that was the hassle. Replacing it solved our intermittant > non-start > problem. > > Good to hear you got it figured out, and relatively cheaply, > too. > > E.P.
Hi Graham,
I own a 1998 Audi A6 1.8L. I have the SAME EXACT immobiliser problem!
My worst experience was being stuck in a car park for three hours as the immobiliser light was flashing away.
You mentioned that the issue was with the Temperature Coolant Sender.
Please could you elaborate?
Many thanks, Lee
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