Diesel Smoke Test - what's 'normal'?
I knew that the truck would fail today's MOT because of the fog light switch and had just expected to retest on Weds, but it turned out that the test would have failed anyway on smoke emissions which averaged @ 3.2 m-1 - I was suprised because last year it passed with a lower value and no problem.
The guy doing the test said that he thought that it was simply that they'd picked the car up from cold in the morning (garage is 100yrds from my driveway so they just collect) and that if it had warmed up for a few minutes it would have gone through fine (which we'll do for the retest on Weds).
I am wondering though whether the valve adjustment I did a few weeks ago was a factor though. They were all very tight and although I think I was quite careful with the slkip guages, it was a stinking cold morning and the advice I was given was 'err on the side of loose'. Having said that, too much clearance and I would have expected less smoke (more air in, logically).
Otherwise, the engine has always been one of the strong points of the vehicle and I use a diesel injector cleaner religiously and all of the plugs, (harness and relay too) were changed before christmas. I guess I wouldn't expect it to have 'suddenly' got worse and the only thing I can think of is the valve adjustment.
Anyone got any other ideas?
MOT test rules require the engine and oil to be at normal operating temperature before the emission test is done.....the garage should have warmed the engine up before doing the emmision test. Diesels also take longer to heat up than petrol, even the new genration cdi's have prolongled warm up, hence some have engine heaters to assist the warm up.
White smoke on a cold morning coud just mean condensation, like you would see from any vehicle on a cold morning.....but if its heavy white puffy smoke....that means unburnt diesel..
Have you checked the pump timing after doing the valve clearances, the timing might be slightly out from wear and tear from the rotating components, chain tensioner/cogs and timing chain guides. By adjusting the vave clearances you have altered the mixture settings.
Hope this helps and good luck with the retest.
I would like to fine tune G Singh's comments on a few points. Adjusting the valve clearances has no direct affect on pump timing or fuel mixture settings. Valve adjustments may have an effect on emissions but repeat, does not alter the fuel settings. I agree, ignition timing and valve timing can minutely alter due to chain and cog wear.
In my opinion and declaration of limited Diesel experience; if the valve timing and pump timing were to be excessively out due to chain wear, I would very much expect additionally, complaints of difficult starting, high fuel consumption and a lack of power complaints. None of which you have made.
The valve adjustment you have conducted should have worked in a positive way rather than a negative fashion. It is probable the MoT station had not warmed your vehicle enough, check on the sheet what the oil temperature reading was. Before taking the vehicle to the test station again, rev your engine high for a about five minutes to clear the exhaust system out or go for a long fast run. Constant short runs in town chokes the exhaust with soot.
One could argue we both are saying the same thing but differently. You can rest assured that your valve adjustment would not have made worse, the smoke test.
Cheers,
Had it been driven genty before test? May be needed a bit of a hard drive just before test to clear out any residue.
You are right Rakesh that the engine is otherwise in very good shape - starts immediately, 'sounds good' and clearances were tight so opening them up should have made things better I think.
I'll take off the rocker an look at the timing chain stretch. My feeling is that is will be in good shape though (the vehicle has been very well looked after with documented oil and other service intervals observed).
The other thing now I think about it is that vehicle has been standing idling a lot (often for an hour or more) over the past few months while I have been rebuilding and testing things (in fact its only had 3 short trips out of <10M since June when I first took the body off).
Because the MOT station is so close by an extended 'blast' might be tricky 'well officer.. you see I was on my way to a pre-booked MOT 100 years down the road, but my Sat Nav told me I needed to detour via Guildford' probably won't wash (and not Taxed at the mo for this reason either). But I'll see what I can do.
I'll report back here!
Rakesh wrote:
"I would like to fine tune G Singh's comments on a few points. Adjusting the valve clearances has no direct affect on pump timing or fuel mixture settings. Valve adjustments may have an effect on emissions but repeat, does not alter the fuel settings. I agree, ignition timing and valve timing can minutely alter due to chain and cog wear."
Just to point out that I never wrote alter fuel settings, I wrote mixture settings, air and fuel mixture to be precise. Taking in more air or less by adjusting the valve clearance has a direct link to 'mixture settings' as you are altering the amount of air entry into the combustion chamber which has a direct link to the compression created and the burn achieved as a result. This is where injection pump timing should be checked and adjusted to further fine tune the engine and get the adjustable components of the engine within the closest tolerance that the manufacturer recommends. Setting the timing of the pump will set the correct fuel injection time at the correct point in cycle, not too early and not too late. Setting the pump timing is as neccessary and routine as it is for setting the valve clearances etc.
I also agree that the spill timing method is difficult and not very accurate, hence many engines are not set corretcly, I have an elctronic MB tool for this job, I've done many whilst working for MB(18 years) and also as an independent repairer. Its takes some patience to get it 100% right but once its done you will feel the difference straight away, starting from cold and hot, smoother engine running, better pick up performance, smoke reduction, emissions and mpg.
Sorry for any confusion in previous posts/comments!
No confusion - all helpful input.
I'll see how we get on tomorrow. I expect it will go through as I say. If not then I'll probably just bit the bullet and have someone else do the timing as I need the vehicle off the driveway.
REPLY TO THREAD NO: 6
Point taken, I should have read it again.
Truck re-tested for emission yesterday and went through 1st pass.
The answer was that it just needed a short run out to clear the cobwebs before :-)
The work I did on the power steering has also transformed it.. No longer is Heisenberg hiding in my steering geometry!
Also, the move to a slightly reduced diameter pressure side (I went from 7mm to 6.5mm stainless when I replaced/ rerouted the hard lines) and getting rid of the MB rubber hose (replaced with braided PS hose) has firmed it up a and is all the better for it. The 33" BFGs still make it a little bouncy, but what a difference :-)
Good to hear the News.
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The old 617 takes while to warm up and since it was 1st slot this AM (7.30) its possible that they didn't wait. They'll retest on Weds for free in any case and I expect it will go through one way or the other.
Of more concern is why its like this - I'm not to be truthful even sure where the figure of 3.2-m sits relative, other than that 3 is pass. Is the scale linear or logarhythmic for example? Runign the engine up tonight there is no substantial visible smoke
Re. timing - no I haven't. Diesel engine tuning (and building) is something I'm learning a bit about as I got along.
I know that checking for timing chain stretch is a matter of cranking to #1 to TDC, lining up the marks on the back of the camshaft sprocket and looking at the readings from the gauge behind the crankshaft pulley?
I also know of the 'drip' method of setting timing, but it doesn't seem that easy to do (one of those things that once you've done it a few times I'm sure it is). Any other suggestions though?
The only other thing I must check is that I reassembled the air filter correctly after having it powdered... that would be an easy way to make it smoke!