XUD engine problem

[crossy2425]

This lump is in my '98 406.

Its the Bosch As3 semi auto system.

It was purring like a cat on 90/10 WVO (dewatered and filtered to 1 micron) until recently.

Symptons are intermittent knocking/loud engine noise, predominantly at tick over. Intermittent in so much that a small amount of throttle can either produce the symptons or stop it.
Also when the engine is upto temperature if stopped it will not re-start until its cooled down.
There is NO noticeable loss of power when driving.

I have done the usual, changed fuel filter, checked for air intake, checked the fuel etc etc with negative results.
I tested the ECU coolant temp sensor (using a multimeter), this was within spec from cold to cooling fan operation, so I suspect thats OK( 3400-2300 ohms). The wiring of same to ECU was also checked (pins 4 and 21)and found to be OK.

I checked the operation of the cold start mechanism and found it works at the IP BUT there is no vaccum coming from that little unit that is attached to the brake servo (?) though I think that is a seperate issue as it only controls the fast idle and idle speed.

I cracked each injector and found the engine 'stumbled' but carried on running when 1 and 4 were cracked open. When 2 was cracked there was a slight change in the engine note but when 3 was cracked the engine stalled. Could it be a sticky injector? Would that prevent a warm engine from starting though?

I really would apreciate any (cheap) ideas to try and any literature n this engine or fuel system anywhere so I can get an idea of HOW the cold start system wrks and how the varius sensors work with the ECU and each other.
A lot to ask from a 1st post.

Crossy.

[AndersDK]

I checked the operation of the cold start mechanism and found it works at the IP BUT there is no vaccum coming from that little unit that is attached to the brake servo (?) though I think that is a seperate issue as it only controls the fast idle and idle speed.

Not quite -

The coldstart mechanism works by altering the injection timing, NOT bv altering the idle speed alone.
A sticking coldstart mechanism therefore constantly alters the idle and low rpm injection timing, commonly noticed by increased diesel engine clatter noise.

The injection timing is altered by either a lever arm or by way of a solonoid controlled by a vacuum operated switch.

Such a problem may very well come in suddenly from a clear sky ...

[crossy2425]

Thanks for the reply Anders.

Could you explain HOW the cold start alters the timing?

I cannot see a link on this engine.
I'm guessing its done electronically and not mechanically.

There is only a cover on the IP where some models have the vacuum operated switch.

[CitroJim]

Timing on these pumps is entirely electronically controlled. The cold start device only serves to increase the idle speed.

Your symptoms point to either a failed needle lift sensor on No.3 injector or a failed TDC sensor. Either failing will prevent the ECU setting the correct timing. The pump may fail to the fully advanced condition (knocking) or fully retarded, leading to poor running generally and hard starting.

The problems you are experiencing are very similar to what was described in this thread from a while ago.

It tells you how to check the sensors and saves me typing much the same text again

Take note of the possible blockage in the return line restrictor that can give rise to this sort of problem and does occur from time to time when running WVO.

In the case of the thread under reference, the problem was a pump internal fault. I suspected a blocked passage to the timing piston but never had the chance to investigate further.

Bosch pumps can wear their HP pumping element (moreso when running veg) and this can lead to the hot-start problem whereby the pump cannot pump warm, thin fuel as effectively as it can pump cold, thicker fuel. Some people experience this difficulty if they have habitually run on veg and then go back to running on diesel. Generally, a Bosch pump often fails to start the engine as eagerly warm as it does when cold.

Incorrect timing, especially if the pump sticks in the fully retarded setting, can cause very difficult starting.

Hope this gives some pointers. Keep asking any questions...

[CitroJim]

Some more useful information in this thread...

[crossy2425]

Thanks Jim.


Tested all the sensors........all fine.

I'm convinced its one of the injectors.....injector 3 to be precise. There is NO change in engine tone if this one is cracked open...there is on all the others, too much of a coincidence.

So, where/who can re-con them for me, quickly and cheaply?
I'm in Lancashire.

[Peter.N.]

Intermittent knocking could well be a sticking open injector, dribbling fuel in at low revs, you have tried the correct diagnostic procedure, slackening off each pipe in turn but you need to do it while you actually have the knocking - this is assuming that it is only knocking on one cylinder. Ideally, you need to increase the tickover speed to stop it stalling but if its an electronically controlled pump, you can't of course.

[AndersDK]

As an aid fault tracing the problem, you may unplug the #3 injector electric sensor plug.
If this then immediately emits the knocking engine sound you are experiencing intermittently, then you may have found the problem.

[Peter.N.]

Good thinking

[crossy2425]

Thanks guys, but as I posted above ALL sensors tested and working.

[Peter.N.]

Ah but if you have an intermittent fault on the injector with the sensor in it, it will only send the wrong signal when the fault is present.

[CitroJim]

Crossy,

Are you anywhere near any of us with a Lexia diagnostic machine? If there is anything going intermittently, the ECU is very likely to store a fault code which the Lexia will read.

Also, the Lexia will be able to subject the pump to a set of actuator tests and check it is timing properly; basically. give the injection system a good health check.

If you're not near any of us, consider having diagnostics carried out but do ensure you only have them carried out withe the pukka Lexia/DIAG2000 tool and that the operator knows his subject well. These tools do not give answers on a plate.

[crossy2425]

No Jim, I'm near Blackpool....but if your coming for a day out soon....... 8)



Basically, I tested the resistance values of the sensors and they were all within spec.
The one in the injector was tested with the engine off. Then unplugged with the engine running...there was a subtle change in engine note both when it was unplugged and when it was re-connected. I did this several times. Also the tacho continued working, so as per the other threads I believe all is well with the sensors...I unplgged the bottom plug on the pump (from memory the blue one) that I think controls the pump timing and there was a definate change in engine tone.
From this I deduced the timing device (not sure really what its called or how it actually works ) is working correctly.
As an aside I actually took the pump off and replaced all the seals approx 1 year ago. I completley stripped the pump and cleaned it before replacing the seals following the article on the VW forum (was it written by you Jim?) so I'm sure theres nothing seized in there and it worked for a good few thousand miles after the rebuild, I'm certain its not a result of any errors when rebuilding the pump.

I've used the age old 'screwdriver to the ear' trick and that one injector is noisy.

As far as I'm aware, the injectors are original and the car has done approx 113k....so more than ready for doing.

I appreciate everyones help and welcome any other ideas to try, but I'm pretty certain I need new nozzles etc.

Does anyone know anyone who can re-con these injectors ?
I'd have a go myself but dont have the knowledge or the equipment.

[crossy2425]

Oh...whoever invented the armouring on the IP wants shooting.

[Peter.N.]

GSF do the ordinary injectors for £38.00 each but the one with the sensor is £148.00! it must be worth getting at least that one reconned.

Try your local friendly diesel specialist, you might be pleasantly surprised.