oiledballs

Dear Q7 owners - I am looking for some ideas on what might be the problem.

I set in motion a string of catastrophe...possibly...but hopefully not

On a 2007 Q7 4L bug engine 3.0 TDI with 147,000 miles on clock I successfully replaced an injector seal 6 months ago on cylinder 2.
Car worked perfectly and was notably quieter in engine bay.
Wanted to repeat the operation on cylinder 6 as this one was making noise some months later.

(1) Notably on extraction of cyl 6 injector no copper seal was found...mystery as to where it could have gone..but carried on and cleaned injector hole thoroughly and fitted a lovely new copper seal.
(2) When refitting wiring loom I inadvertently plugged the cyl 5 injector plug onto the high pressure sensor and the high pressure sensor onto the cyl 5 injector. Doh
Car did not start ofc. When I realized what I had done I swapped the plugs back over but engine would not start. Assuming High Pressure Sensor failure, as it normally takes 5v and the injector plug delivers 12v,
(3) I replaced the high pressure sensor with a shiny brand new one. Car still did not start.

I could see a reasonably long air bubble above the High Pressure Fuel Pump so thought air could be the problem and bought a 1 litre can of Liquid Moly Diesel Purge and some hoses and a small rubber hand pump bulb.

(4) Pumped Liquid Moly Diesel Purge through a small filter, which i purchased new also , through the fuel delivery pipework and out of the fuel return line from engine, through another small filter, back into the pot of of the Liquid Moly Diesel Purge supply. Total of approx 200ml out of the whole 1000ml was consumed somewhere by fuel delivery system (not into tank as this was isolated). I cannot account for where this 200ml went and it certainly did not remove the bubble above the HP Fuel Pump. So still could not get the air out of the system. Car was struggling to turn over at this point

(5) Tried easy start into the air intake after opening the air box.
(6) engine seemed to partially lock ...or was it the battery failing...I could not tell.. no nasty noises just hardly any action and hard struggle to even rotate the engine

Put battery on charge and Went to work for a week and returned to the problem a week later.

(7) Removed and took injector from cyl 6 to diesel system specialist for check, they showed me it was not squirting despite 380 bar applied to it. They suggested it sometimes happens when you remove an injector that it ceases to work as the Peizo types are sensitive. Purchased brand new Bosch Injector £222 and fitted it on cyl 6. Still the engine would not start

(8) I noticed that there appeared to be very little compression when turning the engine over and it seems to turn too freely. Not yet comp tested in any way. How would this happen?

Now I am worried something else might have crept into the problem list and wonder if you guys have any ideas?
Regards OB

AudiQ7slineplus

Did you get to the bottom of this? I’m experiencing a very similar problem with no copper seal present

oiledballs

I did not get to the bottom of where the seal went, apart from it is plausible that it has all been blasted away eventually in entirety by the pressure that breaks it down in the first place.
I still have the vehicle but it is glued to the spot (has not moved) since this issue.

'10Q7TDI_Prestige'

When you swap in a brand new injector, it must be programmed into the car via VCDS or similar. You must be careful when removing/replacing injectors to get them back into the same location they came from for this same reason, or they have to be reprogrammed into the car with correct/new locations, etc.

The copper seal does eventually get consumed, but that means they've been having problems for quite a while when you've reached that point there is nothing left. Nominally, you would get to the noticing the problem long before the entire washer has succumbed to the combustion/exhaust pounding at it, and flowing past it to the vent port drilled into the head.

I'd be concerned if one was fully eaten away and be looking at all of them for damaged or missing seals, and to check the condition of the injectors, etc. There are a number of videos online showing injector services as well as what they look like when have suffered damage to the injector body, etc. Also, don't forget that the HPFP (high pressure fuel pump) is really the heart of the system, and they don't last forever. There's also the low pressure fuel pump that is mounted inside the tank that is the 'primer' for the system; if it is dead, then the car is unlikely to start. You acknowledged hooking up wrong wires with different voltage, so it's also quite likely you sacrificed some fuses and/or relays along the way

Be sure you pull all the trouble codes off the car to see if any are relevant to the fuel and/or injector system...you need a VAGCOM capable scan tool for this. VCDS diagnostic scan tool by Ross-Tech is really what you want for this more advanced level of DIY fixing.

-Wes-

Well, this is a pretty close fit regarding fuel injectors on the Q7 TDI, so I thought I'd share some images of before/after in terms of changing out the injectors themselves. I bought a set of six OE units from FCP Euro a couple weeks ago, which set me back about $1,400. For future reference for others, these come with the copper "o ring" on the injector nozzle end, the tiny rubber o-ring on the low-pressure return nozzle, but they do NOT come with the o-ring that seals the injector against the head (or the rubber seal that is between the injector and the valve cover, though that's probably not an issue in terms of needing to replace - unless it was previously leaking). If you're getting new injectors, be sure to pick up WHT000884 (x6) as well; they are $1.50 or so each.

Anyhow, here are a couple photos of what my injectors look like after nearly 150,000 miles of use compared to a new one:

-Wes-

Okay, so I finished installing the injectors tonight. I did the passenger bank (cylinders 1-3) last night and the driver bank (cylinders 4-6) tonight. I still cannot believe how easy it is to access and replace the injectors. It almost seems anti-VAG considering how difficult even the most basic things are on these cars! Unfortunately, I forgot my laptop today, so I'll need to wait until tomorrow night to do the coding and ensuring the fuel system is primed to the HPFP. I don't imagine it lost its prime with this work, since I only removed the hard lines between the injectors and the common rail, but better safe than sorry. I will then run the injector recode sequence before attempting to start it.

-Wes-

Alright! I sit here in the Q7 after successfully coding the new injectors, priming the fuel pump, and... it fired right up! Smooth as warm butter.