300tdi poor fuel consumption

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300tdi poor fuel consumption

Postby simesman » Sat 03 Jan 2009 1:49 pm

Anyone got any theories as to why my wifes discovery is so rubbish on fuel? Its a '98 GS (manual) and has the proper fuel pump (non-EDC)? EGR garbage went ages ago and intercooler all cleaned up, catalyst junked, brand spanker injectors fitted. Air-con always off.
We seem lucky to get 24mpg and it really bugs me, cos my mate has a 200tdi and he gets nearly 40mpg (or so he says). Now I know that the earlier Disco's are supposed to be better on fuel, but not that much, surely? I have been driving very carefully on the last £50's worth and still no better than 24mpg. There does seem to be something dodgy with the injection pump, as it is prone to smoke when cold, but more so when on the over-run. When I watch the missus drive away in the morning, it seems to pull away fine, but when she reaches the junction and starts to decelerate (ususally in third by then), the smoke just pours out. Good thick bluey black colour. It doesn't always do it either. Tickover and driveability feels fine, but I must say, the mates 200tdi is definately perkier on acceleration, with well defined boost from the turbo.
Mine does not burn oil and there are no leaks. I have messed with the fuel pump settings, playing with diaphragm position, starwheel position and smoke screw, none making any appreciable difference. As none much improved performance, I have backed off all settings to minimum with starwheel at default.
Any ideas why performance is so un-stunning and fuel consumption poor?
Before I bought it, I noticed that the head gasket had recently been done and cambelt changed. Is it possible that the pump is incorrectly timed, or would the symptoms be loads worse?
Or is the pump shot? Will the 200tdi pump fit or should I get a proper 300 pump?
Any help greatly appreciated.
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Okay lets work this out

Postby Andydisco » Sat 03 Jan 2009 3:31 pm

I do not think it is the pump - but that is not an impossibility but I would expect the cam to be breaking up and you getting problems with not switching off (overrun).

Whatever your mate says (and I believe he is partaking of too many magic mushrooms) 24 mpg is no that bad - even on a good day you will only push it to 28-30 mpg. 40 mpg is a dream for a brick.

If you have a roofrack fitted - there goes your difference, having AT tyres doesn't help. Not sure which tyres you have.

So you have played with the settings to no avail - are you sure they are now default? I take it you have done oil and filter change and air filter. Drained the sedimenter (oh yes it gets mucky in there).

Have you put any injector cleaner or boost through it?

As for the smoke - all 200TDI's are a bit smoky, my 300TDI smokes on very cold mornings and then improves once warm. My 200TDI smoked.

How many mies hasi t done and when did you last change the injectors?d If done over 60000 miles that could be the problem. I changed mine and it is amazing.

All of that said:-
I do think your turbo may be on it's way out. Or one of the pipes is internally collapsing. So I would get this checked after I had changed oil and filters and drained the fuel sedimenter.

Only then should you start to worry about the pump and ultimately the engine.

Andy
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Postby simesman » Sat 03 Jan 2009 7:03 pm

Thanks Andy. I'm pretty sure my mate must be lying. 40mpg does sound a little unlikely and I'm pretty sure he wouldn't have a clue how to work out precise mpg!
I still reckon that most of you are getting better than 24mpg when driving especially carefully. I used to run an old V8 and believe me, I know how to get the most out of a gallon!
Just to answer a few of your ideas, I don't have a roofrack, the tyres are road biased 205's (Goodyear Wranglers), oil + filters changed regularly, air filter new, did the sedimenter recently, did try some Commer injector cleaner when I first got it, but didn't make any difference. The smoking is weird. I would say it only puffs out bad smoke about 50% of the times that I observe it and then, predominantly on the over-run. The motor has done 149K and injectors all replaced 5000 miles ago.
Interestingly, I suspected the turbo might not be doing its stuff properly, so today I rigged up a boost gauge so that I could see what it did. All seems to be by the book, boosting to about 1 bar at between 2-3000rpm and with full boost loading it up hill at around 1500rpm. So I assume the turbo and wastegate are functioning correctly.
I have also just adjusted the smoke screw in 1.5 turns and turned the diaphragm 60 degrees CW, as my reasoning is that I may as well benefit from a potentail performance increase if the fuel consumption stays the same. I definately feel that the engine is having more fuel dumped through it than is used, so what could it be?
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Postby trailerfitter » Sat 03 Jan 2009 7:32 pm

simesman wrote:Thanks Andy. I'm pretty sure my mate must be lying. 40mpg does sound a little unlikely and I'm pretty sure he wouldn't have a clue how to work out precise mpg!
I still reckon that most of you are getting better than 24mpg when driving especially carefully. I used to run an old V8 and believe me, I know how to get the most out of a gallon!
Just to answer a few of your ideas, I don't have a roofrack, the tyres are road biased 205's (Goodyear Wranglers), oil + filters changed regularly, air filter new, did the sedimenter recently, did try some Commer injector cleaner when I first got it, but didn't make any difference. The smoking is weird. I would say it only puffs out bad smoke about 50% of the times that I observe it and then, predominantly on the over-run. The motor has done 149K and injectors all replaced 5000 miles ago.
Interestingly, I suspected the turbo might not be doing its stuff properly, so today I rigged up a boost gauge so that I could see what it did. All seems to be by the book, boosting to about 1 bar at between 2-3000rpm and with full boost loading it up hill at around 1500rpm. So I assume the turbo and wastegate are functioning correctly.
I have also just adjusted the smoke screw in 1.5 turns and turned the diaphragm 60 degrees CW, as my reasoning is that I may as well benefit from a potentail performance increase if the fuel consumption stays the same. I definately feel that the engine is having more fuel dumped through it than is used, so what could it be?



full 1 bar boost is at 3000pm engine under load not before...... If your engine is smoking could be lack of compression as well as worn diesel injector pump....black smoke means retarded pump timing since it has boost too it then the FIP looks like its worn. This wiggling the advance/ boost star wheel ain't a good Idea as it will whack more fuel in there. The screw on the diaphragm housing ( torq screw ) needs only to be turn just slightly to decrease smoke usually.....

you also need a very accurate guage to do the job properly

Image

Anyway to your 24mpg,...are you getting this driving around town or on a journey?....mine does about that in town but is much better on long runs!!!
Last edited by trailerfitter on Sat 03 Jan 2009 11:26 pm, edited 1 time in total.
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Postby PR » Sat 03 Jan 2009 7:45 pm

I get better than 24.8 on short runs, and much higher on long ones and I drive an 1998 auto, so that does not seem too bad. I have also get a very heavy right foot, not known for hanging about!
Get in, sit down, shut upo and hold on tight!
Paul
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Postby thebiglad » Sat 03 Jan 2009 8:01 pm

We recently sold our TDi200 manual, but over the 4 yrs we had it, it averaged 36mpg - over 47,000mls !!

My current TDi300 auto with EDC delivers 33mpg - average over 12,000mls.

Unless you are driving it very hard, I would say there is something wrong.

If you've De-EGR'd, have you De-catted? Have you replaced the air filter? Replaced the turbo rubber hoses?

Cheers and good luck

Dave
Had loads, just not now.
2010 Triumph Bonneville T100 Efi
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Postby simesman » Sat 03 Jan 2009 9:14 pm

Well Dave, I have done all the things you suggest, so I have to agree, there must be something wrong. And if Paul gets more than me in an auto (and lead foot), then I have to act!
Trailerfitter, it seems to make little difference whether running around town or long journeys. I'm convinced that the pump is worn or otherwise [half shaft]. I will have to bite the bullet and get it overhauled (or replaced).
Thanks for all the help.

Simon
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Postby thebiglad » Sat 03 Jan 2009 9:23 pm

I think it is very unlikely to be the injection pump. I would be looking for solutions elsewhere.

Do you run std size tyres? On-Road or off road? Roofrack? Snorkel? Is your viscous fan on all the time?

All ours have their fans taken off as soon as we get them, not a huge difference but a cumulative benefit.

Have you tested for brakes binding?

Cheers
Dave
Had loads, just not now.
2010 Triumph Bonneville T100 Efi
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Postby es300tdi » Sat 03 Jan 2009 9:33 pm

I get between 50 and 60 mpg :D :D
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Postby trailerfitter » Sat 03 Jan 2009 10:38 pm

thebiglad wrote:I think it is very unlikely to be the injection pump.


now its been fiddled with........???....


Is your viscous fan on all the time?

All ours have their fans taken off as soon as we get them, not a huge difference but a cumulative benefit.



Cheers
Dave


MPG calculated with viscous fan on the vehicle,.......my N reg 300tdi does 30mpg out of town with viscous fan while my 200tdi has electric fans yet has higher consumption as it has a bigger vehicle to pull along... Problem is the N reg discovery is how old now???? Mies now up for an engine rebuild at 200 000 miles...
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