406 diesel knock and poor start

Mabbs · Post by **Mabbs** » 02 Nov 2008, 00:54

Hi

I have a 406 1996 1.9 td with the following symptoms:
1. Poor starting - all four glow plugs have been replaced (as burnt out)
2. When started very load engine knock, like a transit Di;
3. poor performance;
4. Rev counter very inaccurate and sometimes not operating at all, will recommence on start up usually
5. Engine management light lit at low revs, disappears @ 2k revs

Engine has 197k, recently serviced

From what I have read http://www.frenchcarforum.co.uk/forum/v ... esel+knock
It sounds ECU related, the pump is at full advance presumably a sensor failure of some sort, where should I start to look though?

Any advice would be greatly appreciated.

Richard

Xaccers · Post by **Xaccers** » 02 Nov 2008, 03:26

Check the second injector from the cam end of the engine (number 3 injector).
If it has a lead from it, then chances are your needle lift sensor is duff, or it could be your TDC sensor which is on the top back of the gearbox by the flywheel.
Jenny had this problem where sometimes when I started her up she'd sound like a bag of nails and would have no rev counter.
Normally a restart would do the job.
Swapped the injector with a good one and she's fine.

The ECU tries to adjust the pump timing using information gained from the needle lift sensor and the TDC sensor, if they're duff then it throws your pump timing out.

Mabbs · Post by **Mabbs** » 02 Nov 2008, 22:34

ok I'll try testing both tomorrow, funny thing is that since replacing all the glow plugs she started much more easily first time, but second try completely dead, yet now the engine management light has gone out.

Could it be that the pump timing is so far out that it actually refuses to start? Didn't think these old school pumps could adjust the timing to that degree!

Xaccers · Post by **Xaccers** » 03 Nov 2008, 00:19

Mabbs wrote:ok I'll try testing both tomorrow, funny thing is that since replacing all the glow plugs she started much more easily first time, but second try completely dead, yet now the engine management light has gone out.

Could it be that the pump timing is so far out that it actually refuses to start? Didn't think these old school pumps could adjust the timing to that degree!

I'm not sure when they changed from a purely mechanical to slightly electronic pump, whether it was 96 or only from 97 onwards, hence checking number 3 injector (the 2nd from the cam) for a lead.
If it's just a normal injector like the others, then you've got a mechanical pump and the problem lies elsewhere.

Post by **CitroJim** » 03 Nov 2008, 10:13

Pugs, for some reason, changed over to the AS3 semi-electronic pump a bit later than equivilent Citroens. N plate was the transition year although some P platers can be found with mechanical.

You'd be amazed at the timing range these pumps can offer. About 20 degrees I reckon. A duff Needle Lift Sensor will either start off with the pump fully retarded or will let it advance to maximum, depending on how it feels. A fully retarded pump will make the engine harder to start from cold and fully advanced, it'll sound like a bag of nails.

Luckily, if the pump starts fully retarded, it does have a chance of putting a little advance on due to how the system works.

Mabbs · Post by **Mabbs** » 03 Nov 2008, 13:32

yes she does indeed have a lead from no 2 injector (from the right), is there anyway of testing it with a multimeter????

Post by **CitroJim** » 03 Nov 2008, 13:58

Mabbs wrote:is there anyway of testing it with a multimeter????

On a multimeter test, they should show a DC Resistance of around 100 ohms if I recall. Xac will remember if I've got it wrong.

They normally go open-circuit so if they read infinity ohms then they're dead.

Occasionally the wires fracture around the connector so if this has happened, you may just rescue an open-circuit one.

New, they're shockingly expensive but a scrappy will usually provide. Any one used with a similar Bosch pump will do but don't use a Lucas one.

You'll likely need a good a good socket specifically designed for the job to remove/replace the injector. Replace the copper washer and fire washer when replacing injectors.

Safety: Take care removing/replacing the high pressure pipe on the injector. If you have a leak, the resulting jet of diesel can cut skin like a knife and inject diesel deep into tissue. This is not terribly good for your health. Keep well away from a replaced injector until you are 100% sure there are no leaks.

Mabbs · Post by **Mabbs** » 04 Nov 2008, 23:06

110 ohms resistance - so fine
What other sensors are there in the management system?
Is it easy to test the TDC with a multimeter too?

Damn sure its the timing - fuel at the injectors, new glow plugs, sounds like its firing just seems to be at the wrong time!

Mabbs · Post by **Mabbs** » 12 Nov 2008, 16:50

the plot thickens; replaced TDC sensor, and still nothing - have cracked off the injectors and fuel is getting through and some combustion smells. Is it possibly valve timing?

red_dwarfers · Post by **red_dwarfers** » 12 Nov 2008, 18:06

If your rev counter is also off sometimes, I'd be tempted to check the resistance, rather than on the contacts of the sensor, but by finding the relevant wire on the ECU connector and see if anything goes open circuit.
The ECU connector may also be a bit grimey and maybe even starting to corrode if your particularly unlucky....like me

Mabbs · Post by **Mabbs** » 12 Nov 2008, 21:34

yeap makes sense, I'll try looking at the ECU next - possibly a broken wire somewhere in the loom either from the TDC to the ECU or needle injector sensor. I wonder if the local dealer's diags on the ECU would determine the fault?

Post by **CitroJim** » 13 Nov 2008, 13:41

Mabbs wrote: I wonder if the local dealer's diags on the ECU would determine the fault?

Yes, a diagnosis using the pukka diagnostic tool will determine it in an instant. A Peugeot DIAG200 is the best but a Citroen Lexia will do at a pinch as long as you tell it you are diagnosing a Xantia with the DHX Engine and VP20 pump.