Old Smokers

[Steve L]

We were travelling behind a lovely newish caravan yesterday which coincidentally was being towed by a L reg Disco Diesel.

The outfit was badly loaded to start with, far too heavy on the hitch which visably made the disco a right handfull to steer.

Then as soon as he hit a hill I thought he'd caught fire!!

Black smoke billowing out from the back of the car.

Now this senario could just as well of been with a deisel car or a petrol for that matter.

I'd just like to know, with all the ECo this and ECo that in life today, how do they get away with it?

Old cars are not natural smokers. It's just the poorly maintained ones that let the side down.

This one was so bad I bet he had to wash the van when he got to his destination.

 

[rob_jax]

L Reg Disco - Smoking?

Basically blame the Lucas injection units (I think that's right for that year) and the mechanical (and not electrical - and no ECU) control over the fuelling.

Mechanical control over the fuelling was always seriously defective as a technology - no feedback - no accurate control - and by the time it's this age, the mechanical parts will be slightly "sloppy" and out of specification

Robert

 

[Garfield]

Yes but look at how many times you could replace the mechanical gear for the cost of the electronic stuff, our 170000 mile pug 405 didnt smoke that bad. I was told that the injectors for a new VW sharan are

 

[colin-yorkshire]

Yes but look at how many times you could replace the mechanical gear for the cost of the electronic stuff, our 170000 mile pug 405 didnt smoke that bad. I was told that the injectors for a new VW sharan are

 

[colin(bridgend)]

With the older cars the average D.I.Y. person could service the car themself. Nowadays there is so much technology that the owner does not have the inclination or the diagnostic equipment to carry out the service nowadays and is then ripped off in a garage. A neighbour took his Renault Clio to a local dealer for service and was charged over

 

[Garfield]

Whilst my first cars had 4 gears I can imagine a 3 speed box by driving a 5 speed using only 1st, 3rd & 5th, it can de done but it's not good, I think 5 gears are better than 4 but 6 is going too far, my motorbike has 6 gears but it will still pull strongly from 20mph to 150 in top gear

 

[Garfield]

I understand your comment Colin but I was quite glad to see the back of points and carburettors, my XR2 had a troublesome carb but the electronic ignition never needed touching or re timing in the 100,000 miles I drove it, my 1.6cl golf had a carb but was gutless and thirsty so I swapped it for a fuel injected 1.8GTI which blasted the 1.6 into the weeds and did up to 50 mpg

 

[rob_jax]

Hi Gary,

There is a difference between the injector bodies, the fuel pump and the mechanical or electronic injector control.

The "old" Lucas injectors were opened and closed by fuel pressure squirted down each injector line by a rotating disk in the high pressure fuel line. Those disks (and the housing / drive) needed replacing on a regular basis - particularly as they weren't designed for low sulfur fuel and will wear even quicker now.

The nearest modern equivalent is the Common Rail Diesel engine (used by nearly everyone other than VW / Audi) where a common supply of high pressure fuel is injected by electronically controlled injectors.

The VW / Audi Pumpe Deuse injectors combine the injector and the high pressure pump in one "unit injector" - so yes these are more expensive than a CDI injector - but you don't have the cost of the high pressure system

So comparing the costs for a VW unit injector with different technology is a false comparison. Especially when a Pug 405 offered around 90 bhp? and the current Pug / Ford engine will offer 150 bhp and twice the torque, and use less fuel.

And on the subject of gearboxes and fuel consumption, my car has a 7 speed automatic gearbox and happily tows in 7th at 60 mph - and returns over 33 mpg when doing so.

If the car engine produces insufficient torque at the engine rpm for the gearing ratio / road speed, then selecting a lower gear will probably offer better fuel consumption.

But if the car manufacturer designed the engine to produce sufficient torque to support the gearbox ratio and road speed combination, then towing or driving in the highest gear possible is the most economical approach.

Robert

 

[Garfield]

Hi Gary,

There is a difference between the injector bodies, the fuel pump and the mechanical or electronic injector control.

The "old" Lucas injectors were opened and closed by fuel pressure squirted down each injector line by a rotating disk in the high pressure fuel line. Those disks (and the housing / drive) needed replacing on a regular basis - particularly as they weren't designed for low sulfur fuel and will wear even quicker now.

The nearest modern equivalent is the Common Rail Diesel engine (used by nearly everyone other than VW / Audi) where a common supply of high pressure fuel is injected by electronically controlled injectors.

The VW / Audi Pumpe Deuse injectors combine the injector and the high pressure pump in one "unit injector" - so yes these are more expensive than a CDI injector - but you don't have the cost of the high pressure system

So comparing the costs for a VW unit injector with different technology is a false comparison. Especially when a Pug 405 offered around 90 bhp? and the current Pug / Ford engine will offer 150 bhp and twice the torque, and use less fuel.

And on the subject of gearboxes and fuel consumption, my car has a 7 speed automatic gearbox and happily tows in 7th at 60 mph - and returns over 33 mpg when doing so.

If the car engine produces insufficient torque at the engine rpm for the gearing ratio / road speed, then selecting a lower gear will probably offer better fuel consumption.

But if the car manufacturer designed the engine to produce sufficient torque to support the gearbox ratio and road speed combination, then towing or driving in the highest gear possible is the most economical approach.

Robert

It seems to be the common assumption that driving in the highest gear that the car will pull is the most economical way to drive, it's what I always used to assume, but the evidence I have seen from our old 110hp Sharan tdi and our new S-max 2.0 tdci suggests otherwise.

A blowing head gasket on the Sharan forced us to travel using very low throttle openings letting the engine rev with low torque in a low gear to produce the power needed to move, we got home to find that fuel consumption was better than usual.

Travelling home in the S-max I was pleased to see the computer showing 60mpg, I then realised I was only in 5th so I selected 6th and reset the computer, maintaining a similar driving style the mpg fell to 54.

In a much more controlled experiment driving 750 miles across France at 80 mph 6th = 37 mpg, 5th = 39.5 mpg

55 mph 6th = 54 mpg, 5th = 60 mpg, 4th = 54 mpg

towing at 60 mph 5th = 27 mpg / 2100rpm

4th = 29.5 mpg / 2700 rpm

I somehow doubt that our car is a freak.

My conclusion based on this data is that, as most of us know, using too low a gear means that more fuel is used to simply keep the engine spinning,

If too high a gear is used, the cylinder pressure required to produce the necessary torque is so high that lots of this pressure is wasted once the piston reaches the bottom of it's stroke and this valuable presssure dissapears down the exhaust, this is why cars appear to give ~50% of the available power with just ~25% pedal travel, and flooring the pedal does not appear to make as much difference as it should.

With 236 lbft of torque our car will very easily hold its speed in 6th gear but it uses less fuel in 5th, it would probably hold 60mph in 6th gear towing if I bothered trying, it easily holds 60 in 5th but it does 2.5 mpg more in 4th.

There is an optimum gear ratio for efficiency, which is different for every size of engine and load applied, this ratio is not necessarily the highest that the engine can pull.

 

[Garfield]

It seems to be the common assumption that driving in the highest gear that the car will pull is the most economical way to drive, it's what I always used to assume, but the evidence I have seen from our old 110hp Sharan tdi and our new S-max 2.0 tdci suggests otherwise.

A blowing head gasket on the Sharan forced us to travel using very low throttle openings letting the engine rev with low torque in a low gear to produce the power needed to move, we got home to find that fuel consumption was better than usual.

Travelling home in the S-max I was pleased to see the computer showing 60mpg, I then realised I was only in 5th so I selected 6th and reset the computer, maintaining a similar driving style the mpg fell to 54.

In a much more controlled experiment driving 750 miles across France at 80 mph 6th = 37 mpg, 5th = 39.5 mpg

55 mph 6th = 54 mpg, 5th = 60 mpg, 4th = 54 mpg

towing at 60 mph 5th = 27 mpg / 2100rpm

4th = 29.5 mpg / 2700 rpm

I somehow doubt that our car is a freak.

My conclusion based on this data is that, as most of us know, using too low a gear means that more fuel is used to simply keep the engine spinning,

If too high a gear is used, the cylinder pressure required to produce the necessary torque is so high that lots of this pressure is wasted once the piston reaches the bottom of it's stroke and this valuable presssure dissapears down the exhaust, this is why cars appear to give ~50% of the available power with just ~25% pedal travel, and flooring the pedal does not appear to make as much difference as it should.

With 236 lbft of torque our car will very easily hold its speed in 6th gear but it uses less fuel in 5th, it would probably hold 60mph in 6th gear towing if I bothered trying, it easily holds 60 in 5th but it does 2.5 mpg more in 4th.

There is an optimum gear ratio for efficiency, which is different for every size of engine and load applied, this ratio is not necessarily the highest that the engine can pull.

 

[rob_jax]

Hi Gary,

When I was driving VW Audi saloon car products with diesel engines and 6 speed gearboxes, I didn't notice this effect. But then these were larger engined versions, and produced significantly more torque than the 4 cylinder diesels.

I don't have any documentary proof on hand for this, but the best fuel consumption figures at a set road speed, should happen when the engine is producing maximum torque - so if the plateau region of the torque curves starts at 1600 rpm - then the highest gear that lets the engine spin above 1600 rpm should be the most economical. And as you say, this may not be the highest ratio in the gearbox.

And this is how it works in my car, 550 NM torque is shall we say - substantial - and the 7 speed autogearbox has it's gear ratios chosen so that the engine should always be operating at peak efficiency. And yes, 7 speeds is substantially better than a 6 or 5 speed - each gear covers the torque plateau better

Robert

 

[Garfield]

Rob,

With 550 nm of torque you obviously have a large one, if my

theory is right then a larger engine should be most efficient in a higher gear at lower revs for a given load compared to a smaller engine, which your experience appears to back up, I expect if your engine were mated to our car & gearbox then 6th would be the most economical even when towing. If all 5 speed autos are as bad as the one in a freinds Galaxy then I would expect 7 speed would be smoother but my experience of autos is negligible and only enough to make me not want one so my comments refer only to manuals.

 

[seth1]

hi there,im very suprised at the ford that it doesnt like pulling top gear or 6th with the van on.i think your theory is partly correct or would be for older non EDC engines.ie more cc more power.but later common rails and even older design PD,s dont necaseraly work like that.for a start there,s no direct link to an injector pump or throttle body.your throttle pedal is just a petentiometer,linked to the engine ecu via can data bus.(controller area network ,j1597)the engine ecu desides how much fuel it gets.you basically give it a parametre to work in.and as you probably know these can be tailored .although i know you dont have the option on cars.

 

[lynne_374296596]

quite right older cars are infinitly repairable I still tow with a 1.6 talbot alpine and it's got 185000 on the clock

it still has points and a condensor and a carburettor remember them

no fuel injection, no ecu's, no cats,no expensive sensors to **** up, HEAVEN

and it's 100% reliable if you got a no claims discount from the AA iI would have free membership by now

happy motoring all

Hi - just want a bit of info off you mechanically minded guys. we have an old ford escort 1996 - the pressure gage is in red all the time - and my other half is constantly filling it up with water/coolant. we have been told off the garage he brought it from it's fine and it's a fault with the reader on the pressure gage, but when we went on our longest journey (4 hours there and back) it overheated! and we had to the call the AA. is this fella having us on? not been driving for long so think he's having us over!!!