406TD misfire/smoke.

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406TD misfire/smoke.

Post by rsjon »

I have a 406 here that is producing copious quantities of white smoke and misfiring at idle. When I disconnect the injector on no 3 cylinder (the one with the needlelift sensor), there is no difference to the running. I therefore replaced the nozzle in the said injector (several times actually) but there is no difference in the running of the engine.
I thought that if the needle lift sensor was faulty the engine would run generally badly as the ecu cannot time the injection accurately, but this does seem to be a clear one cylinder fault. I also checked compression on no 3 (400+) and the idle seems high (1200) but the high idle cable is not tight.
Can anybody give me some pointers please?
I seem to be going round in circles!
PS I believe this car has run on veg oil before, but as it has a Bosch pump I did not think this was a big issue?

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Post by evilally »

Veg isn't an issue for these engines generally. Had it been running ok on normal diesel for a while? I might try and run a line from the pump into a can of clean diesel, just to rull out any blockage or air ingress in the supply.

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Post by rsjon »

It has done 4k since veg oil and injector cleaner has improved its' running.
It has only done 68k, so barely run in!
If it had a blockage (I don't think so as it revs fine) or air in the fuel, that would affect all cylinders, but this does seem to be just one.
Nevertheless I think it may be worth using a can as a temp fuel tank tomorrow and see if it improves. I was tempted to check engine timing as well, but it's a bit of a pain so I put it off!!


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Post by Gammy leg »

I'm wondering whether the high idle speed is causing this. The idle speed mechanism can be manually adjusted. It could be that the auto adjuster may need attention. Mine doesn't work at all so i've set the idle at 900rpm which seems fine for both summer & winter


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Post by CitroJim »

Normally disconnecting the electrical plug on the No.3 Injector (needle Fift Sensor) will make a heck of a difference to the running of the engine if the sensor is good.

It can be checked with an ohmmeter and should read about 100 ohms.

White smoke is partially or unburned diesel. This suggested that at least one cylinder is not firing at all on idle.

If you have ruled out injectors then this often indicates low compression on the affected cylinder(s).

Check valve clearances and then if they are OK, have a compression test or better, a leakdown test performed...

It is possible that the head gasket has failed between two cylinders and you may find two cylinders are reading low compression.

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Post by rsjon »

Thanks for the replies.
I have checked the resistance and it is 100 Ohms.
Disconnecting it when the engine is running makes no difference (!).
I checked the comp on cyl 3 and it was 400+ which is ok.
I think I will now check all the rest and see what I come up with.

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Post by rsjon »

Thanks for all your help.
In the end it was the injection pump (!).
I got one from a scrappy for £40, fitted it, having ripped out and bypassed the immobiliser part, timed it up, and it runs well with no smoke.
It was a Bosch AS3 pump so I don't what was put in it, but I suspect it was more than just veg oil!
Obviously, I don't know what was wrong with the pump but perhaps low injection pressure?
Unusual and unlucky I think.
Jon. :D

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Post by jgra1 »

great its sorted Jon :D

be interested in knowing what went wrong with pump.. maybe with help from this forum, we could get you to disect it a bit and take a pic :twisted: