Fouled injector, or worse?

[dnsey]

The C5 (2.0 8v HDi) suddenly this evening has developed a severe misfire.
On investigation, there's little life from pot no 3 - disconnecting the injector makes a slight but minimal difference.
The injector shows electrical continuity, and there's a firing pulse from the ECU.
Quantities of white unburnt diesel smoke are emerging from the exhaust, and of course the ECU readily enters limp mode and displays the 'antipollution fault' message.
There's no obvious evidence of HG failure, but I can't do a compression test or inspect the injector without removing it, which will mean a new fireseal, which I don't have to hand.
Given that there were and are no nasty mechanical noises, and the other cylinders are working fine, I can only assume that the injector isn't atomising properly due to dirty nozzles.
Does that seem the logical conclusion, or does anyone have other ideas?

[Deanxm]

sounds like its widdling fuel in to me but then im no derv expert, can you not do a compression test through the glowplug port.

D

[woodywoodpecker]

Hi mate first thing i would do now is a leak off test this will tell you if your injector is faulty or nozzle blocked. Pretty easy to make your own leakoff test kit, I used 4 kids panda pops pop bottles then you just need 4 bits of pipe to connect to the top of the injectors. Run your car for 2 to 3 mins and compare the diesel in all four bottles. My mates c5 had this problem his turned out to be just the injector washer leaking the whole car was shuddering on 3 cylinders, new injector washers on all 4 and run nice and smooth again.

[myglaren]

Leakoff test kit:

Click for larger image.

[dnsey]

Thanks for the suggestions, chaps.
Unfortunately, the leakoff test was inconclusive - pretty similar returns from all injectors.
What's worrying me a bit is that the potentially faulty injector contributes just discernably to the running, but not significantly - you can just about tell when it's connected.
I've ordered a replacement (second-hand) injector in the hope that the old one's spray pattern is bad, but I'm just a bit concerned that it's holed a piston or something
My compression tester doesn't have an adaptor for the glowplug hole (and is on loan to someone anyway).
I could probably do a rough comparison test via the glowplug ports though. Having said that, there's no obvious unevenness about the engine sound apart from the obvious misfire.

[Deanxm]

Does it sound different when you are cranking the engine? with a bit of luck it will just be the injector, my fingers are crossed for you.

D

[woodywoodpecker]

Thanks for the suggestions, chaps.
Unfortunately, the leakoff test was inconclusive - pretty similar returns from all injectors.
What's worrying me a bit is that the potentially faulty injector contributes just discernably to the running, but not significantly - you can just about tell when it's connected.
I've ordered a replacement (second-hand) injector in the hope that the old one's spray pattern is bad, but I'm just a bit concerned that it's holed a piston or something
My compression tester doesn't have an adaptor for the glowplug hole (and is on loan to someone anyway).
I could probably do a rough comparison test via the glowplug ports though. Having said that, there's no obvious unevenness about the engine sound apart from the obvious misfire.

Hi mate, You really need this plugged in on lexia now to see what the injector flow correction figures are and if its alot higher than the others, injector is prob shot.

[CitroJim]

Normally, an injector exhibiting a bad spray pattern will cause knocking and black smoke, or that certainly was the case on the old days of IDI diesels and mechanical injection. I don't see the HDi being a lot different in this respect. Black smoke is a result of poor quality combustion in an environment starved of air or one too rich in fuel.

The fact there's white smoke is worrying as this does suggest no or almost no combustion due to lack of compression. White smoke is unburned atomised fuel. The reasons can be several but a holed piston on a DI engine is very unlikely although if over heated it could be cracked or the rings could have failed. A big clue here will be diesel in the oil. Is the level up and can you smell diesel in the oil? What is the volume of the white smoke?

Another cause could be a stuck valve. Most likely an exhaust valve. This might be caused by nothing more than a failed hydraulic tappet. A last possibility is a cracked head...

It might even be a damaged glowplug allowing compression to leak away... Can you hear any 'chuffing' from the injector and glowplug areas?

If the new injector does not fix it, a leakdown or compression test will be the next essential step.

[dnsey]

No obvious 'chuffing' or any other strange noises.
The volume of white smoke suggests that about the correct amount of fuel is being injected, but most of it's not being burnt.
The problem started suddenly, and only a few minutes after starting and running perfectly normally. No obvious signs of overheating, fuel in oil, oil or gas in coolant etc, so it seems unlikely that it's the result of another longer-term fault.
Your suggestion of a stuck valve is a good one, Jim - but as there are slight signs of improved performance when the injector is connected, some combustion must be going on, which would presumably result in 'backfiring' in that case.
I'll probably remove the injector tomorrow, and see if there's anything to be seen. Of course, unlike IDI engines, it's not really practical to set things up to observe the spray pattern. Can the old fireseals be used on a purely temporary basis? It's a pain that the stealers and factors are closed over the weekend, so I can't get any replacements (or a Lexia session) until Monday at least.

[CitroJim]

They're would be no backfires with a sticky exhaust valve. There's nowhere near enough heat in the exhaust of a diesel to burn the escaping diesel - hence the while smoke...

The old XUD7 used to suffer tight valves when cold which made the engine very hard to start, along with plumes of white smoke... never a backfire although if the inlets were well open you could detect a faint chuff...

[lexi]

I have heard that worn injectors on hdi can cause head or piston damage more readily than old school diesels. Much higher fuel pressures I assume.