Slow Avantage? Or fast Aura? SORTED.

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James.UK
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Slow Avantage? Or fast Aura? SORTED.

Post by James.UK »

Some of you may recall me complaining that my ZX was rather slow. As it was my first diesel I asumed they were all rather slow, but..The Aura is noticeably quicker than the Avantage! [:0]
Starting from 40 mph at the foot of a local hill the Avan- manages to make 65 mph without my helping, if I use the gears it manages to make 75, (the hill is 2.4 miles long).
When I tried this in the Aura (with a heavy passenger) it made 85 mph with no help at all.. hmmm.. I repeated the experiment when on my own with the same result, the Aura accelerates up the hill much better than the Avantage.. I did think it was faster the minute I first drove it but needed to confirm it.. [:0]
So I checked the fuel pump settings and all the paint marks on both engines are as set when built, i.e. they have not been altered.. Both engines appear to be identical, the Avantage is about 4 months older than the Aura according to the log books.. Aura has done 83K Avantage 107K both cars run well at 70 with engine temps of 85 ish..
Oh I also checked that the throttle is fully open when the pedal is on the floor.. Both are wide open.. The only visable diff I can see on the two engines is the Aura has a small plastic pipe from the diesel filter over-flow (front, just above the thermo housing) running down to below the engine and open at the end, this pipe is missing from the Avantage...
I intend to hire a ramp at my friends garage shortly so I can check the wheels etc. Any ideas as to what else might be causing the difference would be appreciated.. Thanks. [:)]
[:)][:)]
David W
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Post by David W »

James,
I wonder if the auto box is better/different in the Aura. Does it hold the gears a little longer or in any other way keep the engine in its best power band?
Perhaps a better test of the engine power alone would be to take a shorter test that is all in one gear.
Of course there could be other factors like tyre type/size, brakes dragging etc??
You haven't T-Cut and polished the Aura by any chance? ;-)
David
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Post by rabenson »

Have you tried the "good blast up the motorway with a bottle of injector cleaner in the tank" tune up? I've known this liven up many a tired diesel that has been run overly gently for some time.
Ron
James.UK
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Post by James.UK »

Yes, the Aura does hold its gears longer, but I thought that was because the engine was giving out more power? The Avan changes gear very quickly, too quickly in my opinion..
Wheel size. Aura 13 inch ally's with 165-70-13's (original).. Avan 14 ally's 175-65-14's (off a Volcane).. The Avan corners better, less rear end swing and tilt.
I use Forte's injector cleaner about 4 times a year in the Avan, and have done South coast to home M5-M6-M56-M67 270 miles in erm under, WELL under, 4 hours. [:I] so it does get some welly at times. [:D]. I am no boy racer, but I dont hang around either! [;)]
Re the brakes, I fitted the Aerated discs and callipers from a Volcane not long ago, and changed the brake fluid, new nipples, pads, and overhauled the rear brakes as well. but I am going to check that no brake is touching asap, just to be sure..
From stationary, plonking my foot straight to the floor, The Aura takes off noticeably faster, and changes into 2nd at a higher speed. [?] is it the gear box? or, as I think, is the Aura engine holding the gear down by producing more power, faster? The two gearboxes appear to be absolutely identical.. [xx(]
Anyone got any other ideas I can persue please?
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Post by Simon Canfer »

Are the injection systems the same? (Lucas/Bosch?)
My K reg TD was definitely faster than my R reg TD, I put this down to extra safety equipment and weight, but it could just as easily be variability between injection set-ups.
You could have brakes dragging in the slower one?
Simon Canfer
James.UK
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Post by James.UK »

Both have Bosch injector set-ups. How do I get the injector-fuel-timing etc. checked out?
I intend to have a good look at the wheels asap, but I dont think there is any drag, the cars are about the same to push when in neutral.. No cuddley toys in the Avantage thou? lol..
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Post by David W »

James,
Your larger wheels on the slower car will raise its gearing a little and cause slightly more drag, but I wouldn't have expected it to make that much difference. You could try swapping the wheels over and doing the test again though.
The other point is that you confirm the faster car is holding its gears longer. So this is a gearbox issue surely, no need to go looking at the injector pump.
Why not do as I mentioned above and do a shorter test that takes place within one gear and between the same min/max engine revs. That would give a more fair comparison of engine power. Do it with the small wheels on each car in turn for a 100% fair comparison.
David
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Post by peter1138 »

Hrmm, wouldn't the slightly larger wheels cause the speedo to read a tiny bit lower as well? Not by much mind you, and assuming they weren't that size originally...
James.UK
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Post by James.UK »

Re wheel sizes, I thought the %70 down to %65 ratio in tyre thickness compensated for that extra inch? or so I was told when I bought the wheels? [:I]
Having checked the tyre pressures on both cars with my elec pump, marking the tyres with a chalk mark, then rolled both cars forword a full turn of the wheel, both cover the same distance when measured with a tape measure, I know thats not terribly accurate, but they appear to be identical. Measurements taken by marking off the top of a house-brick, one full turn untill mark was again level with the top of the same brick. [:I] [8)] Engineers? TUHH !! lmho.. [:o)]
As I understand it.. the gearbox holds its gears longer because it is getting more power input, i.e. if I accerate gently they both change at about the same speeds. With my foot hard on the floor they both hold their gears much longer but the Aura changes up later and covers a given distance faster.. I think if you fitted a 2 litre petrol engine in them, they would both hold their gears almost into the red zones?
Locking both cars in first gear, and from a standing start, the Aura is about 3 car lengths ahead of the Avan as it touches the red zone, approx 48000 revs!!.. the Avantage was still back on 4000 revs when my mate hit the brakes on the Aura!. we tried several times, and swopped cars, but the results were the same every time.. the pesky Aura is at least %20 faster!! [:I]
In top gear side by side on the M67 doing 80 mph (just after midnight, empty road [:)]) The Aura still out-accelerates the Avantage with ease, and no gear changes are involved as they wont change down at that speed.. [?] Interestingly they both have about the same top speed of 108 ish...
Is there anyway to check the actual engine out-puts?
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Post by Kowalski »

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by James.UK</i>

Is there anyway to check the actual engine out-puts?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
Dynomometer run ?
James.UK
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Post by James.UK »

Thanks Kowalski, [:)] erm, but whats a Dynomometer?? [:I] And what does it do/check exactly? [8)]
philhoward

Post by philhoward »

AKA Rolling Road...
James.UK
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Post by James.UK »

Hmm.. my mate has one of those, but I dont see how it can help? What I really need is the engine tested in some way that does not involve things like gearbox-wheels etc, just some means of testing its unladen performance? power output?
philhoward

Post by philhoward »

That'll be an engine dyno, then. A rolling road can approximate the engine power by subtracting the transmission losses from that put down to the road.
James.UK
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Post by James.UK »

Hi Phil, thanks for the info, but if David is right, and the powerloss is being caused by the Avantage gear box, would it show up as just less output from the engine? i.e. we still wont know if the problem lies in the gearbox, wheelsize, or the output from the engine itself? also I wont have both cars available for testing-comparing, and.. If I did it would only prove what I already know. e.g. the Aura is faster. [8)] [:o)] and before someone sugests swopping gearboxes and re-testing.... pfffttt!! [:D] [:p] [}:)]
I am going to check the brakes, tyres, tyre pressures (again), compare linkage measurements, cable movement-travel, try it on the rolling road in case anything usefull shows up, and replace the back exhaust section, over the weekend. I did the front section about 3 months ago, the back looks ok, but it will be one less possible cause to investigate....
Gearbox, engine oils may well be diff, but I can't see that having too much effect and I have no way of knowing whats in the Aura anyway. [:I]
If I fail to find any faults, then I will leave the Avantage as-is, I dont intend to start messing with injectors and stuff as the car runs very well, and is nice to drive.. I might put half a ton of bricks in the back of that pesky Aura thou... [}:)] [;)] lol..
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