Discovery TDI smoke and power loss

Had a very similar problem due to an air leak into the fuel line.

Jeff

How did you spot the leak?

Spotted fuel dripping from the sedimenter drain plug.

What was happening was at low revs air was being sucked in and because there was not a high fuel flow the air/fuel mix was quite high, but at high revs there was a greater fuel flow so proportionally not so much air. That is why things seemed better at high revs.

Jeff

Thanks. the Disco has been parked outside all night so I'll have a look. But my symptoms seem a bit different to yours. I wondered if it was air starvation of some sort as black smoke usually means too little air or too much fuel.

Keith

A collapsed air filter, a split or collapsing intercooler hose (with one collapsing internally the most likely), or possibly a blocked intercooler.

That's what I'd check first, the intercooler hoses, they're known to collapse after de-lamination inside (mine did it).

I'd also check the injector leak-off pipes, they perish and split letting air in, easy replacement .. but they normally only produce hard to start engines and lumpy all over running.

I'll check the hoses for splits today. Thanks.

Pull 'em off and check for loose flaps of rubber inside too.

Hi Keith,

I had a similar problem with my 1995 300tdi Disco, though not quite as bad as your sounds. My problem was with the EGR valve. I fixed this by fitting a blanking plate (much cheaper than a new EGR valve, and I'm not sure of the merits of putting exhaust gas back through the engine anyway). After blanking off the EGR power was restored and no more smoke. Just search you favourite online auction site. The plates only cost a few quid and might just fix your problem. I think main dealers also sell them.

Kev.

Keith wrote:

At low engine loads/speeds, it reduces the Oxygen content in the inlet air, so reducing NOX emissions.

Them that cause SMOG in the unlikly event we get enough LA type sunshine...

Regards.

Dave B.

Does tend to make one wonder at the point of using an intercooler if you're going to shove red hot exhaust into your cooled air?

The Intercooler is only realy of any benefit, when the engine is working hard, like when the Turbo is doing it's full job, and the compressed "Boost" air will be hot. Cooling it makes it more dense, and therefore more O2 to burn more fuel with = more power. At least, that's the idea and we all know that...

At light loads such as idle and overun (such as deceleration, going down a hill with your foot off the throttle) the turbo will be doing next to nothing, also the exhaust gasses will be very very much cooler too, so the EGR, as earlier, recirculates some waste gasses into the inlet to reduce the O2 content of the air therefore reducing Oxides of Nitrogen production, at a time when the Turbo and Intercooler will not be doing much if anything.

It's an anti polution control, as even on overun, the engine is still producing polutants purely due to the temperatures created by the compression part of the cycle, even though no "fuel" is being used.

If you look at such an equipped vehicle, the EGR gas feed to the inlet is directly into (or very close to) the inlet manifold, after the intercooler. It should not be recirculating anything when you are working the engine hard. It's also often "blown backwards" into the airstream to promote good mixing.

Removing or disabling the EGR will not bring about any remarkable performance increase, if it was working correctly. But on later vehicles where the ECU can sense the actual valve position, it can sometimes (ECU software dependent) cause a warning light to show.

Regards.

Dave B.

Not a "remarkable preformance increase" on a TD5 with EGR valve and EGR throttle but enough to be noticeable and give you a couple of more MPG.

On my TD5 I've settled on EGR valve connected but EGR throttle disconnected. With the throttle connected it really is rather sluggish until you get the revs well above 1500 and you don't feel the turbo start to kick in either.

Not on a TD5. There is no positional feedback from either the vacuum solenoids or the valve/throttle themselves.

In general terms and on other marques maybe...

Interesting comments.

A local farmer friend who had a TD5 90, said he had no noticable difference with it connected or not (he had to try to save fuel) as he regularly pulls a livestock trailer about, and being a "gentleman of the earth", if its economy (such as it is) was badly affected, it'd be back at the dealer all too quick.. Mind you, he's not exactly a quick or enthusiastic driver.

He's since sold the 90 at 3 years old with gearbox problems, and now uses an old Toyota pickup (more rust than body!) to pull the livestock box. He does say it has some "interesting" handling features when the trailer is heavy, but it uses much less fuel than the 90 did, and is more comfortable he said at the time. (Similar model as the TG lads tried to destroy.) I have no idea if it has an EGR, or if it has, if he's tried to fiddle...

I had an intermittently sticky EGR on a works car a while back, that did adversly affect the economy (and smoke generation!) but the performance (such as it was) was not that badly affected, at least at legal road speeds.

That was a Passat with the 1.9 4 pot common rail lump. It developed an intermittent "Engine Warning" light at about a year old, sometimes it would come on at idle, sometimes when driving, sometimes not for a few days. I figured out eventualy, that 250 smokey miles a tank was not good when that light comes on, when it could do nearly 500 a tank if the light never lit. Still took the dealer three attempts to find it, and another week to get the replacment part. I should have learnt after the saga with the alarm system, not to take it to them...

Since then, all the works cars have been Japanese. Supurb reliablility it has to be said. (OK, so they are made in the UK, but are not of UK design.)

My LR hybrid has an early X Disco 200TDi, so no such potential failure thankfully. The only "High Tech" item on that, is probably the alternator voltage regulator.

In truth, there are many things that can cause a Turbo Diesel to loose power and/or smoke. Methodical diagnosis is needed, rather than jumping to conclusions as I'm sure you agree. Some common symptoms (excessive smoke being one) can be caused by all sorts of bad (often expensive) things, or something as simple and easy to fix as a clogged filter.

Yes, EGR's can stick open. But with the 100's of 1000's of TD cars and vans about, there seem to be relatively few EGR failures, compared to the number of knackered turbos, blown head gaskets, melted pistons and snapped timing belts, that keep a mate and his pal's employed full time.

Cheers.

Dave B.

My mechanic took the hoses off and there were no splits, delaminations or blockages. Checked the EGR valve and it was OK. The air filter looked a bit dirty so it was replaced. Everything was put back together and the problem seems to have gone. The whole process took an hour of his time. So either the problem has been fixed by the old method of take it apart and put it back together or it was the air filter (which did not seem paticularly bad).

On or around Sun, 23 Aug 2009 19:57:00 +0100, Kev Ellis enlightened us thusly:

You can use a 2p piece in the pipe joint to blank the EGR...

I spoke too soon. The bugger has got the same symptoms again. So not the hoses, not the air filter. EGR valve intermittently dicky?

Have you got a boost gauge, or old vacuum gauge you can temporaraly fit? Plumb it into the inlet manifold. If you get "Vaccuum" There is a blockage, end of story. The only time I've 'Ever' seen any Vaccuum on the idiot gauge I've got on my 200TDi (there was a spare hole in the dash) was when I forgot to take a rag out of the air filter when putting it back. Trying to start it, it would catch instantly, the gauge went full -ve (1 bar vaccuum!) and with lots of smoke, it stopped...

The rag was sucked right down into the turbo! It all came out OK, no damage to anything (not even the rag!) other than to my pride...

That was after replacing the timing belt. All sorts of horible things were being thought about, but a sleep and beer (or was it beer and sleep?) and logical thinking figured it out.

Regards.

Dave B.

No blockage. Maybe it's an intermittently stuck EGR valve. We've fitted a blanking plate to stop the EGR. It was OK afterwards, but it was last time too, so I'll see what happens now.

Do you know if the lack of EGR valve affects the MOT particle emission test?