Hello All. I have just signed up .....

[RayPooley]

Hello All. I have just signed up to see if I can get some input from members about a problem I have that I am struggling to diagnose and resolve. But I can't see a lot of that type of interaction going on here. Is this not the kind of site for that sort of thing? Is there a particular forum that I should be looking at perhaps?

Thanks

[Trevor]

Hi Ray

WHat is the particular problem you have with your A4?

[RayPooley]

59 minutes ago, Trevor said:

Hi Ray

WHat is the particular problem you have with your A4?

Thanks for the response Trevor.

Intermittent fault. Starts then immediately stalls. It's a mechanical fuel pump with a sender unit in the tank.

It's an old girl. A4 Estate 1.9L TDI 1999. So there is virtually nothing on the net about it.

The notable think about this symptom is that when it happens the fuel and the voltage gauges on the instrument cluster

show empty although there is plenty of fuel and voltage available.

Here is what I have done so far.

Pulled and tested the sender unit and all works fine throughout the range of float travel.

Checked the wiring from ignition switch to sender and all good.

Replaced ignition switch with a new one. Problem persists. Checked ignition switch connector for signs of shorting but looks ok.

All four glowplugs are knackered but this isn't the cause of this problem. Car starts fine when gauges are working. I just though I would check them anyway.

Pulled and tested all relays from under bonnet and behind the dash. All fine.

Pulled and tested all fuses from under the bonnet and behind/side of the dash. All fine. But replaced them anyway.

Pulled the ECU looking for signs of damage in pins and connectors. All fine.

There is fuel pressure when this happens. I checked by loosening one of the injectors. So it's not a fuel pump issue.

It's a head scratcher for sure.

Last thing I did on Saturday was pull the instrument cluster to take a look at the internal components. There are only three

capacitors on the board one of them looks a little convex. Only slightly though. Not obviously blown but could be

about to fail completely. Hoping to change that this afternoon, if the caps arrive, and generally re-tin other solder joints while I am at it.

So, been busy but still no joy. It is, however, working at the moment. It has a mind of it's own.

One thing I don't know is how the ECU responds to an empty tank signal. Does it care? Does it refuse to run if it thinks the tank is empty?

Any thoughts would be appreciated.

Thanks

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[Magnet]

Hello Ray,

It seems like you have worked really hard to rectify this issue.

From the initial symptom of starting and immediately stalling it might point to an immobiliser issue - if the car is fitted with one, which I would suspect it is even though it is 20 year old. 

Perhaps you could let us know if an immobiliser is fitted, and if so, if you have investigated this as a possibility. 

Kind regards,

Gareth. 

[RayPooley]

55 minutes ago, Magnet said:

Hello Ray,

It seems like you have worked really hard to rectify this issue.

From the initial symptom of starting and immediately stalling it might point to an immobiliser issue - if the car is fitted with one, which I would suspect it is even though it is 20 year old. 

Perhaps you could let us know if an immobiliser is fitted, and if so, if you have investigated this as a possibility. 

Kind regards,

Gareth. 

Hello Magnet

Thanks for the response.

You would think so wouldn't you given it was regsistered in 1999 12 months after immobilisers became mandatory? BUT it could well have been built in 1998 before it became a legal requirement. On the cusp as it were. It was on my list but I only have one key and it looks like an ordinary key to me with no transponder in the head of it. I have had a good look around too under the seats and the dash. Also, I did manage to find a list of fuses and their locations that match what's on the car and there is no reference to an immobiliser. So probably not got one.

I have actually just replaced the capacitor in the instrument cluster that I refered to above. I refitted the cluster to the car and it has certainly had an impact. The digital display in the center of the cluster was not working before. Now it is. So that's a good sign. The petrol gauge is also working now, but not the voltage gauge, and the car runs. But I'm not celebrating yet because that happened before. I have to wait and see if it stays like that before flying the flag.

[Demixl]

Hello,guys,glad to come here)

[Trevor]

 

 

 

 

 

 

 

 

 

 

9

On 6/24/2019 at 12:33 PM, RayPooley said:

Thanks for the response Trevor.

Intermittent fault. Starts then immediately stalls. It's a mechanical fuel pump with a sender unit in the tank.

It's an old girl. A4 Estate 1.9L TDI 1999. So there is virtually nothing on the net about it.

The notable think about this symptom is that when it happens the fuel and the voltage gauges on the instrument cluster

show empty although there is plenty of fuel and voltage available.

Here is what I have done so far.

Pulled and tested the sender unit and all works fine throughout the range of float travel.

Checked the wiring from ignition switch to sender and all good.

Replaced ignition switch with a new one. Problem persists. Checked ignition switch connector for signs of shorting but looks ok.

All four glowplugs are knackered but this isn't the cause of this problem. Car starts fine when gauges are working. I just though I would check them anyway.

Pulled and tested all relays from under bonnet and behind the dash. All fine.

Pulled and tested all fuses from under the bonnet and behind/side of the dash. All fine. But replaced them anyway.

Pulled the ECU looking for signs of damage in pins and connectors. All fine.

There is fuel pressure when this happens. I checked by loosening one of the injectors. So it's not a fuel pump issue.

It's a head scratcher for sure.

Last thing I did on Saturday was pull the instrument cluster to take a look at the internal components. There are only three

capacitors on the board one of them looks a little convex. Only slightly though. Not obviously blown but could be

about to fail completely. Hoping to change that this afternoon, if the caps arrive, and generally re-tin other solder joints while I am at it.

So, been busy but still no joy. It is, however, working at the moment. It has a mind of it's own.

One thing I don't know is how the ECU responds to an empty tank signal. Does it care? Does it refuse to run if it thinks the tank is empty?

Any thoughts would be appreciated.

Thanks

Can only think it may be crankshaft sensor and the signal is dropping out

[RayPooley]

Update. It has been 8 days since I swapped out the suspect cap in the cluster. The problem has not occurred since I did so. So it looks like that was the problem. This is what I conclude. The cap in the cluster was faulty resulting in intermittent charging. When it failed to charge there was no voltage to the stepper motor of the fuel gauge circuit. So as far as the ECU was concerned there was no fuel in the tank resulting in it disabling the fuel pump causing the non start condition. I don't have any confirmation of this but it makes logical sense since the pump is mechanical and lubricated by the diesel fuel that flows through it. Disabling the pump when there is no fuel in teh tank is protecting it from damage. Bottom line: If you get this kind of symptom put the cluster circuitry on the to do list.