One for the experts: Bizarre power increase

spider · Unread post by **spider** » 10 Apr 2010, 19:31

205TD (so XUD7T)

This is difficult to explain and intermittent, although a concern.

If I corner right and then left, as soon as I straighten up (well, about a second or two after) there's a big power increase, by not moving my foot there's a burst of acceleration.

I should add, you only get this if you corner eagerly, so it tends not to happen that often, although I can reproduce it if I really needed to.

Now, this 'extra' power lasts about 3 or 4 seconds, there's no smoke noticeable and it does not run on oil (I'm saying that as there's no knocking or unusual noise and no smoke)

It happens regardless of fuel level. It seemed to start after I had changed the rear flexi pipes (from the sender unit area to the metal pipes underneath) although I had to take a couple of inches of metal pipe away due to corrosion)

I'm actually thinking its air-ingress somehow, although with a clear pipe fitted and normal running there are no bubbles. Obviously I cannot 'see' it when it happens.

My only theory is a crack or break in the actual pickup pipe inside the tank that allows a bit of air in possibly.

I should add it will idle (and accelerate / decelerate) perfectly normally when its having is power surge, its just as though its gained a few bhp

Any thoughts appreciated (no it is not overfull with oil!) although as I say having had heard a few that decided to drink some oil, it does not behave that way at all.

Confused

Xaccers · Unread post by **Xaccers** » 10 Apr 2010, 20:10

Change of angular velocity, and there for change in momentum.
Velocity is a vector rather than scalar value, it's made up of speed and direction.
Change direction and you change velocity, stop changing direction and you get an increase in speed due to the momentum.

In MK's shopping centre, a bunch of Israelis sell MagiCars ("Batteries not needed").
They're 4 wheeled kids ride on cars, where the steering handle connects to the smaller front wheels which are very close together.
Turning the handle left and right produces a forward tacking motion.
Swing one way and quickly straighten and you're launched forward at speed.

Unread post by **CitroJim** » 11 Apr 2010, 20:21

That's got me for an explanation at the moment Andy but I'm not unfamiliar with this phenomenon actually and on a 205D too...

I think you're onto the right sort of area with the air ingress theory...

I's explaining the mechanism though, how and why it happens...

I'll be thinking about this all night now....

hammerong · Unread post by **hammerong** » 11 Apr 2010, 21:10

Got power steering? I only ask because that takes some engine power, as you steer hard it drops power so you rev it up and when it's straight the pump isn't using power and it feels like you get a little boost. With the car on idle turn the wheel and you can hear the engine note drop.

spider · Unread post by **spider** » 11 Apr 2010, 21:49

Thanks for the replies so far.

No PAS, its the early (but a facelift, so one of the first 'facelift') D-Turbo models with no PAS (or electric windows come to that) , I 'think' they were initially optional. I know the late Mardi-Gras had them all, but this is the 'real' one if that makes sense

Off topic: Someone stole the D-Turbo badge off the tailgate a few months ago, did not fall off I could see the actual scrape marks (screwdriver maybe?) where it was prised off. Maybe a MK1 306 one will fit as its more or less the same I think.

Unread post by **Dommo** » 11 Apr 2010, 23:21

My 306 used to do this when it had a Lucas pump fitted, definately not related to PAS or angular velocitymentumspeed, the fuel pump definately injected more fuel every so often (probably only once every 2 weeks) and you got a kick up the arse as it came onto boost. Only for a couple of seconds, and because the times it did it were so far apart every time it confused me initially so I couldn't react to it and see what stopped it. I've never had a problem with it since changing the pump to a Bosch pump to run on veggie oil, so I'd say it's likely to be a fuel pump issue.

spider · Unread post by **spider** » 06 May 2010, 15:30

For the curious, I think I have located the cause.

Porous (metal) fuel pipes, must be taking in a little air but not much.

The leak (now they have got a bit worse) has alerted me to the area of concern

, as they did not actually leak (or even get slightly damp) before.

I asked for them to be changed about 2 years ago but they just cut a few inches off the 'rear' ends and used longer rubber pipes 'to save me money' , which is good in a way but I'd rather they had been changed back then, as its not practical to bend steel pipes or fit them here at the roadside (no garage or driveway!) , as back then chopping a bit off is only delaying the inevitable...

dieselnutjob · Unread post by **dieselnutjob** » 08 May 2010, 11:01

maybe you can use plastic pipes instead.
the pipe is available from diesel injection specialists

spider · Unread post by **spider** » 08 May 2010, 11:39

I was thinking about plastic piping, although the run under the car has bends etc.

I then thought about larger bore copper piping too.

I'm actually letting my garage friends do this, as I have no driveway or garage and its not very nice anyway and 'on the floor' even worse.