HDi engine and stop-go driving...

h2ocooler · Post by **h2ocooler** » 26 May 2009, 23:28

As the fitter said to me, diesels are not designed to run as slow revs all the time and should be loaded to keep them clear, modern driving isnt good for them.
Even the manual on my HDi says it needs to be run at over 3000rpm to heat the particulate filter up to burn off temp, in top (4th on my auto) that is over 100 so i have to lock it into 3rd to do it (once a week with out fail)

When i think back to the day of the old XR2's, a woman next door to me had one (XR2) but it never went above 40mph, she was complaining one day how bad it was running, I had it for a week when she went away and thrashed it, when she got back and drove it she came to pay me for doing a tune up on it commenting on how well it was running now, after i told her how i did it she gave it to me to thrash each time it started to choke up.

It DOES do an engine good to be run hard, cleans the cobwebs out as the oldies used to say.
Rob

lolingram · Post by **lolingram** » 27 May 2009, 08:47

Rather than taking the EGR out of the system, a very well respected and knowlegable Diesel fitter near me parted with this little gem to a mate of mine with a coked up and very smokey transit.
Once a week at least take a diesel car on the motorway/dual carrageway, and hold it in 2nd or 3rd gear at the rev limiter for at least half a mile to a mile, it WONT damage the engine, that is what the limiter is for, i had a diesel escort van at the time and used to cane the ass off it all the time, looking at the exhaust there was very little soot in mine, my mates transit however was coated with 2-3mm as he treated it like a baby, always short shifting and only ever going 55mph max, he took the advice and i looked a few weeks later and most of the soot had gone, he also said it was running much better with hardly and smoke.
With turbo diesels if they dont get to rev out all they do is produce soot from incomplete combustion with the EGR valve making it worse (it recycles exhaust gas to reduce the amount of O2 in the cylinder charge to reduce emmissions)
DO make sure your engine is well maintained with regular oil changes/cambelt done on time air filter changed etc etc etc.
Rob

All the above is true, but surely MUCH better to remove the source of the problemm, by de-activating the dreadful EGR system, which is an anachronistic work around to reduce certain residuals (mostly under artificial conditions)?

Revving the the engine balls out in a low gear for ~1km can do the engine no good at all IMHO.

Post by **Paul-R** » 27 May 2009, 09:45

I wouldn't give a car the rev treatment for that distance either. A few hundred yards is usually all that's needed and then again if needed.

lolingram · Post by **lolingram** » 27 May 2009, 09:48

Wikipedia throws some light on the EGR:

In modern diesel engines, the EGR gas is cooled through a heat exchanger to allow the introduction of a greater mass of recirculated gas. Unlike SI engines, diesels are not limited by the need for a contiguous flamefront; furthermore, since diesels always operate with excess air, they benefit from EGR rates as high as 50% (at idle, where there is otherwise a very large amount of excess air) in controlling NOx emissions.

Since diesel engines are unthrottled, EGR does not lower throttling losses in the way that it does for SI engines (see above). However, exhaust gas (largely carbon dioxide and water vapor) has a higher specific heat than air, and so it still serves to lower peak combustion temperatures; this aids the diesel engine's efficiency by reduced heat rejection and dissociation. There are trade offs however. Adding EGR to a diesel reduces the specific heat ratio of the combustion gases in the power stroke. This reduces the amount of power that can be extracted by the piston. EGR also tends to reduce the amount of fuel burned in the power stroke. This is evident by the increase in particulate emissions that corresponds to an increase in EGR. Particulate matter (mainly carbon) that is not burned in the power stroke is wasted energy. Stricter regulations on particulate matter(PM) call for further emission controls to be introduced to compensate for the PM emissions introduced by EGR. The most common is particulate filters in the exhaust system that result in reduced fuel efficiency[citation needed]. Since EGR increases the amount of PM that must be dealt with and reduces the exhaust gas temperatures and available oxygen these filters need to function properly to burn off soot, automakers have had to consider injecting fuel and air directly into the exhaust system to keep these filters from plugging up.

steelcityuk · Post by **steelcityuk** » 27 May 2009, 09:54

EGR valves do seem to attract loads of gunk don't they. I think it's down to the hot exhaust gases meeting the warm oily PCV gases.

Here's what I found on a 2.5 TD.

This was the amount of gunk from one inlet port of the same engine. It didn't use any oil or smoke more than you would expect. All the inlets were exactly the same.

Steve.

MikeT · Post by **MikeT** » 27 May 2009, 12:13

EGR's are the work of the devil and should be abolished IMO. (Ok, I don't believe in the devil but you get the meaning)

The following pics are from my 116K 1.9TD which, I guess has been sedately used by an old couple until my ownership.

Click to enlarge

It's all very well giving the engine an italian de-coke (thrash) but it does increase engine wear and accelerate oil degradation while ruining the economy but having to do so even more because of this evil device is just taking the proverbial and is a poor band-aid solution which does nothing to the clear the intake restrictions caused.

Incidentally, because of the restrictions an EGR system creates, you have to use more fuel to achieve the same power output/work thus increasing pollution, not decreasing it!

lolingram · Post by **lolingram** » 27 May 2009, 14:13

Incidentally, because of the restrictions an EGR system creates, you have to use more fuel to achieve the same power output/work thus increasing pollution, not decreasing it!

But of course.

Like practically all legislation of today, it is ill thought out, and without any real logic. The monkeys in Parliament (and elswhere) are utterly incompetant in the vast majority - AND many have their noses in the trough to boot.

Bloody awful...

lolingram · Post by **lolingram** » 27 May 2009, 14:35

It's all very well giving the engine an italian de-coke (thrash) but it does increase engine wear and accelerate oil degradation while ruining the economy but having to do so even more because of this evil device is just taking the proverbial and is a poor band-aid solution which does nothing to the clear the intake restrictions caused.

Hard to see how a dynamic who's boss test (aka Italian decoke) could clear the intake side of things.....

Nuneatonrob · Post by **Nuneatonrob** » 01 Jun 2009, 14:50

Would anyone know if the EGR is fitted to the Xsara 2.0 Hdi 90 on a V plate?? I tend to drive it at it's lower end of the rev range, as I find that is where all the power is.....I have just given it a full service, including the fuel filter complete canister and it runs smoothly enough....just wondering as i want my engine to run at it's best possible for economy reasons.

I am currently getting an average of 48mpg on my varied driving down A roads and motorway and slow stop start traffic, and want it to be better.

Cheers,

Rob

lolingram · Post by **lolingram** » 01 Jun 2009, 15:35

Would anyone know if the EGR is fitted to the Xsara 2.0 Hdi 90 on a V plate?? I tend to drive it at it's lower end of the rev range, as I find that is where all the power is.....I have just given it a full service, including the fuel filter complete canister and it runs smoothly enough....just wondering as i want my engine to run at it's best possible for economy reasons.

Almost certainly... wouldn't pass the NOX [I think that's the one] test on the spec sheet otherwise.

Post by **Paul-R** » 01 Jun 2009, 16:01

I don't think that an EGR operates enough (if at all) at tickover to affect the NOx output for the tailpipe test. If it did then people wouldn't be able to remove the EGR for better fuel consumption (there's a clue!) and still past the exhaust test.

BTW our Y plate Xsara 2.0 Hdi 90 definitely does have the dreaded EGR. I think they came into common usage way back in 1991/2 for diesels. My 1990 turbodiesel Montego didn't have an EGR but ones a year or two later did.

jgra1 · Post by **jgra1** » 01 Jun 2009, 16:54

Sounds like an Italian Decoke to me

A Turin tune up ?

you can tell i am bored

Nuneatonrob · Post by **Nuneatonrob** » 02 Jun 2009, 12:35

In the xsara at least is it best to get to it from underneath does anyone know? It's a bit of a tight fit to get down behind the engine from the top...where exactly are these dreaded valves located on the HDi 90, and is it a very distinct item that is obvious?

Does it improve fuel economy with it disabled then?

Sorry for all the questions.

I think I want to intestigate and play now.

Cheers as ever,

Rob

corsehf · Post by **corsehf** » 03 Jun 2009, 10:27

Similar question to Rob's really,
Where is the location of the EGR on a C5 2.2HDi and are they best disconnected ??

steelcityuk · Post by **steelcityuk** » 03 Jun 2009, 10:40

Diesels aren't tested for NOX emissions at MOT time, just opacity (particulates). The NOX levels will be used when certifying the car for production.

If you look at this screengrab you can see the amount of EGR on a 2.0 HDi 110 at idle. Most of the EGR is done at low revs/ low load. Hence the smoke and rough idle when it goes faulty.

Be careful on what engines you disconnect the EGR valve on, on some engines it's crucial that it works so as to lower the exhaust gas temperature - as owners of some Renaults found out when their engine self destructed. Disabling it should improve response and MPG though it could be very marginal.

Personally I think the Italian tune up is only good to thoroughly heat the oil and blow the gunk out the exhaust. That said on DPF cars it's needed to allow regeneration of the filter. I certainly wouldn't 'red line' any of my cars at all, I leave that to the MOT tester.

Steve.

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HDi engine and stop-go driving...

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