Another 170 with injector problem!

[babbers21]

Hi

Found this forum after we had an injector failure. We have a 2007 A4 Avant 2.0 TDi 170 S Line and have just paid for the pump and an injector to be replaced.

My question is does anyone have any tips on how we can reduce the chances of this problem reoccuring? Also for those who have experienced this issue before did any other injectors fail after the first one?

Only had the car 5 months and cost us more than our previous 1999 Audi A3 1.8T Sport ever did!

Cheers

[dudes]

Hi i also have the quattro 07 170 with the injector and pump problem may i ask how much you paid mine has done 85000 before experiencing this problem.

[gaz1965]

It’s about time Audi recognise this problem we all experiencing with our 170bhp A4s and stop the rip off repair costs.
Apparently these injectors are like light bulbs once one go’s there are others sure to follow that’s why I have forked out for a used car warranty there’s no way I will fork out another £937.00 for another injector and Audi's over inflated labour costs.
There s always the safety issue as this kills the engine completely when the injector gives up with no clue as to when its going to happen.

[babbers21]

We paid £1350 for the repair and this was with a friend who runs a garage carrying out the work.

[Adman]

Ouch, was that for one injector? I paid £670 for the injector and an injector wiring loom including labour. it wasn't done at Audi but an Audi specialist.

[A4 Lad]

Why a pump ? What was the matter with it ?

[patrickhorton]

Hi

My question is does anyone have any tips on how we can reduce the chances of this problem reoccuring?

Cheers

My tip (based more on paranoia than fact) is to learn to detect when your car regenerates its DPF (exhaust filter) and avoid thrashing the engine at those times.

The following blurb is really there to archive my thoughts just in case someone else can build on them and make proper sense of this issue.

Cheers Patrick

the blurb...
I don't have a short theory so here's the long one...(don't read if easily bored)
The failure mechanism that seems to be agreed on is that the electrical side of the injector fails due to overheating. No matter how you drive, the exhaust gas temperature (directly linked to the temperatures reached in the cylinders) seems to stay below 500degC and is typically 200 to 400. During a regeneration cycle of the DPF the exhaust temperature is held at exactly 800degC by the ECU injecting excess fuel (the turbo casing glows dull red in the dark even at tick-over. During this process I believe heat will soak into the injectors and the whole head heating everything to higher than usual temperature - despite the efforts of the water cooling. When the driver puts his foot down, the fuel delivery to drive the car provides plenty of heat for the regen and the excess fuel is cut back to hold the exhaust at 800deg. The difference is that this fuel burn is much hotter in the cylinder than the excess fuel burn. In order to deliver power to the wheels the combustion gas expands as the piston descends and cools massively. So to get 800 at the exhaust, the temperature at the start of the power stroke will be hundreds of degrees hotter in the cylinder. In contrast the excess fuel burn function puts fuel in late on in the power stroke so that it does not give any useful bhp and the cylinder temperature will be about the same as the exhaust temp as there is no appreciable expansion. (You wouldn't want bhp at tickover but the regen still wants a hot exhaust so the excess fuel is put in late).
So the effect of driving hard during a regen could be to push the head temperature way above what would ever be encountered normally. I think this cooks the injectors. Especially since the head will already be pretty damn hot due to the regen.
Why do injectors seem to (but not always) fail at higher mileages? It could be that as the DPFs age (which they do) they regen more frequently (which they do due to ash build-up). This means that the likelyhood of the driver having a spirited drive during a regen increases.
Just in case anyone is still reading this far...cars doing massive motorway mileages may never get an injector failure. Above 70mph the agressive 800deg regen is locked out even if it has already begun at a lower speed. Instead the DPF is cleaned slowly by the naturally high(ish) temperature due to the high engine speed/power output. (I think there may be a low level excess fuel above 70 aswell but with a lower target temp). Maybe these motorway cars never see an 800 regen from on month to the next?

My car did 140k on the original injectors before I had it - (50k per year = motorways). Within a month of me doing just two 12 mile journeys a day, an injector failed a minute or so after the end of a DPF regen and a 80mph uphill blast. My theory has been built up to suit my case but it just may be right....
P

[babbers21]

£1350 was for recovery to garage after breakdown (have now invested in AA cover), fuel pump, injector and labour.

Pump was not working effectively as it should and was leaving excess oil in the diesel.

Thanks for the explanation Patrick, does make sense actually. Our car was previously owned by a sales rep and had 116k milage - mainly motorway. The DPF signal has flashed up a few times since we've had the car as we mostly do city driving.

[A4 Lad]

My tip (based more on paranoia than fact) is to learn to detect when your car regenerates its DPF (exhaust filter) and avoid thrashing the engine at those times.

The following blurb is really there to archive my thoughts just in case someone else can build on them and make proper sense of this issue.

Cheers Patrick

the blurb...
I don't have a short theory so here's the long one...(don't read if easily bored)
The failure mechanism that seems to be agreed on is that the electrical side of the injector fails due to overheating. No matter how you drive, the exhaust gas temperature (directly linked to the temperatures reached in the cylinders) seems to stay below 500degC and is typically 200 to 400. During a regeneration cycle of the DPF the exhaust temperature is held at exactly 800degC by the ECU injecting excess fuel (the turbo casing glows dull red in the dark even at tick-over. During this process I believe heat will soak into the injectors and the whole head heating everything to higher than usual temperature - despite the efforts of the water cooling. When the driver puts his foot down, the fuel delivery to drive the car provides plenty of heat for the regen and the excess fuel is cut back to hold the exhaust at 800deg. The difference is that this fuel burn is much hotter in the cylinder than the excess fuel burn. In order to deliver power to the wheels the combustion gas expands as the piston descends and cools massively. So to get 800 at the exhaust, the temperature at the start of the power stroke will be hundreds of degrees hotter in the cylinder. In contrast the excess fuel burn function puts fuel in late on in the power stroke so that it does not give any useful bhp and the cylinder temperature will be about the same as the exhaust temp as there is no appreciable expansion. (You wouldn't want bhp at tickover but the regen still wants a hot exhaust so the excess fuel is put in late).
So the effect of driving hard during a regen could be to push the head temperature way above what would ever be encountered normally. I think this cooks the injectors. Especially since the head will already be pretty damn hot due to the regen.
Why do injectors seem to (but not always) fail at higher mileages? It could be that as the DPFs age (which they do) they regen more frequently (which they do due to ash build-up). This means that the likelyhood of the driver having a spirited drive during a regen increases.
Just in case anyone is still reading this far...cars doing massive motorway mileages may never get an injector failure. Above 70mph the agressive 800deg regen is locked out even if it has already begun at a lower speed. Instead the DPF is cleaned slowly by the naturally high(ish) temperature due to the high engine speed/power output. (I think there may be a low level excess fuel above 70 aswell but with a lower target temp). Maybe these motorway cars never see an 800 regen from on month to the next?

My car did 140k on the original injectors before I had it - (50k per year = motorways). Within a month of me doing just two 12 mile journeys a day, an injector failed a minute or so after the end of a DPF regen and a 80mph uphill blast. My theory has been built up to suit my case but it just may be right....
P

Patrick, you must have sore fingers but very valid points :-)

[patrickhorton]

It would be interesting to get a bit of history from more people who have a failed injector.

Suppose my theory is right, I'm afraid there is chuff all Audi can do about it. If the same conditions arise, injectors could continue to fail. Just replacing the injectors free of charge would be horrendously expensive and would not give any of us any peace of mind that the car won't pack up in the fast lane.

The only hope is that Audi could confirm that non of the modified (post 2007) Siemens injectors have failed.

I'd be really interested if someone could design an add-on box to go in line with the injector cable which automatically disconnected a failed injector. This would let the car run on three without loosing all power.

I'd also like to know from Audi if I am likely to warp the head if I run on three as a get home measure. By carrying a torx screwdriver and a pair of pliers in the boot I could get the engine going in ten minutes at the side of the road with a failed injector. (I admit it would be a bit rubbish to have to take these measures with a quality car but it would give peace of mind) Perhaps A8tech could answer the warping head question??

Patrick