Another puzzling XUD question...

[mat_fenwick]

Excess smoke after start up is the problem, coupled with rough running for the first 30 seconds or so. i had put this down to a duff glowplug - I assumed the smoke was down to it running on 3 for a short time after cold starting, which was difficult if attempted straight after the light went out.
I figured that I was going to take the intercooler and glowplug wiring off, I might as well replace them anyway, so I did. Now starting is a breeze, as soon as the light goes out.
But...after about 3-5 seconds after starting, the engine starts to miss (as if running on 3) and emit lots of whitish smoke (smells like unburnt diesel). It is tinged with blue initially, so I am assuming the valve stem seals are slightly worn.
There is no smoke, or any difficulty starting when warm. When I changed the camshaft I mistakenly set no. 3 inlet valve clearance about 0.3mm too large (how is a mystery, as I checked it twice after setting it as it seemed too big a shim compared to the rest - sticky valve maybe???) Therefore it was never closing, and even when cold would have been protruding by 0.15mm, more when warm. Does it seem feasible that in running like this (approx. 30 mins probably in total), that I have very slightly bent the valve? I.e. slight loss of compression causing difficulty cold running. Not so much of a problem while the heat from the glowplug remains, but if it is not firing properly, the lack of compression and heat means that it will not fire well until heat is transferred from cylinders 2 and 4.
Do you think it's worth doing a compression test, or can you think of anything else to check first?

[jonathan_dyane]

If it makes you feel any better my father's Xantia always used to do this

First thing to try is pumping the fuel priming bulb/plunger until it is hard before the cold start; if this then results in a smoke free start you have an air leak.

If it isn't that simple personally I would be inclined just to leave it but if you wish to make it right, I would check the compressions, and if they are sound have the injectors checked/reset.

I have to say, I think you would have been very unlucky if you had bent a valve in the manner in which you described; by doing a cold start with the injector union for the cylinder with the valve in question slackened, you could then see if the smoke is not present and so test that particular theory...

[ken newbold]

one other thing I've heard,

if you're on a Bosch fuel pump, it could be the injector leak off pipes that are allowing air in.

[mat_fenwick]

Thanks for the replies guys, something to check tomorrow. It does raise the question though (and I'm not doubting the fact) of why an air leak would cause excess smoke. Am I just being dense?

Ken, yes it is a Bosch pump. I did replace the leak off pipes when I did the engine swap, which is when the problem started. (No problem in the donor Xantia, but a 18 months later, after a cam change and transplant, there is...)

[Geoffrey Gould]

Hello Mat I have just caught up with this thread so could be talking a load of bo++0cks,please bear with me. When you did the swap did the pump have a switch by the throttle arm, and does the pump have a electrical connection to a solenoid on the front face of the pump near the bottom and finally are you using the Xantia or BX glow plug relay??
Right that's that part over, it does sound like an air leak, the plastic filter housings can leak round the top joint and also near the bottom there is a white 'disc' in the side of the housing that can leak also.
The rubber bulb is not above suspicion either , you are more than welcome to give me a yell if there are problems.
Cheers.
Geoff.

[mat_fenwick]

Thanks Geoff, the pump only has one electrical connection which is the fuel stop solenoid. Interestingly it has a little rubber damper on the throttle arm to slow the return to idle (presumably to stop stalling). Nothing to do with the problem though.
Are the electrical connections for altering the timing on the later Xantia pumps? I am using the BX glow plug relay which I understand (although have not measured it for myself) cuts the power to the glowplugs after cranking.
I'm also now thinking it's an air leak - I primed it with the bulb and there was less smoke, and if I kept squeezing it during the initial minute or so of rough running, it improved enough to idle without me opening the throttle. Still some smoke and slightly rough, but better.
Once it has cooled down I will slacken off the fuel to the suspect cylinder, and hopefully disprove the idea of a bent valve.

[jonathan_dyane]

Ah, good news!

My next move would be to coat around the seal of the filter housing with vaseline and also the white disc (without dismantling) to see if this provides a temporary cure, as Geoffrey says these are prime suspects... Might be worth fitting another housing complete.

FWIW, I found the father's Xantia throttle response benefited a great deal from me throwing the stupid damper mechanism in the bin; it tends to seize slightly and make progress somewhat jerky; originally there would have been both a bizarre telescopic device and a strange cylindrical thing with a plunger, would recommend binning both and returning it to what Robert Bosch originally intended!

[Geoffrey Gould]

Hi Mat, as you haven't got the extra bits then I shouldn't worry, they advance the timing and provide for the glow plugs to glow for a time after the engine has started basically. The BX glow plug relay cuts the plugs out as soon as the key is in the 'start' position. There is a mod which will give half a minute or so of plug glow after the engine has started but we are going off topic a bit.
Chucking the damper bits as mentioned by jonathan-dyane is a 'jolly good idea' they are a damned nuisance.
All the best.
Geoff.

[docchevron]

Does rather sound like an air leak, although have you checked the pump timing?
A slightley retarded pump will give those symptoms.
Changing a cam belt CAN slightley alter the static timing, and I dont know many people that bother to check the pump timing after a belt change. Unlikely to cause that much difference, but could be worth checking non the less.

Tapet clearences are a bit odd on XUD's, the get wider as the engine heats up, so a tight tappet when cold can also cause said symptoms until things warm up.

I'd be amased if you've got a bent valve TBH, a bent valve will remain bent however hot the engine gets..

I'd plump for an air leak at this point though.

[kole24]

I have the same problem with my TZD, and I don't think it is connected with air leak, because it is only present if outside temp is under 5 deg C. I think valves or compression.

[BX Bandit]

I have the same problem with my TZD, and I don't think it is connected with air leak, because it is only present if outside temp is under 5 deg C. I think valves or compression.

Or a duff/lazy glow plug! Mine are on the way out but if I preheat twice it generally fires up without coughing!
I've also read that glow plug technology has advanced so that preheating can be reduced to 3 seconds! (that's the tip of the glow plug to 1000 degC in 3 seconds!!!) I'm not sure if that technology is available for BX era XUD engines though.

[mat_fenwick]

I thought that I would have to be very unlucky for it to be a bent valve, but I am a bit of a worrier.

After disconnecting no. 3 injector, it started with a similar amount of smoke, which seems to have disproved that particular worry! Time to track down the air leak, ideally when it stops raining. Incidentally, when pumping the primer bulb, how long should it stay hard after squeezing. Mine goes soft after a few seconds, which to my mind further indicates an air leak somewhere.

I realise that I have left myself open to lots of dodgy misquotes, but I can’t think of any other way of putting it…

[mike st gilles]

never one to miss a chance....<when pumping the primer bulb, how long should it stay hard after squeezing. Mine goes soft after a few seconds, which to my mind further indicates an air leak somewhere.>
OO er mISSUS......

[Philip Chidlow]

That was a gift, Mat... (well, it is Christmas time)

[DavidRutherford]

when it stops raining

So, next June then?

Only other thing that has occurred to me is that if you had a closed-up valve clearance for a while (even for a short time) you may have burned the valve seat. I'd say it was well worth doing a leakdown test. (piston at TDC, inject compressed air into the glowplug hole and listen for where it comes out.)