My car judders

Joe_Horner

colino wrote: »

If it's juddering on the move it's pretty unlikely to be the idle control valve. Do the basics first as you really don't want to be throwing money at it.

Exactly.

Damp weather with (probably) old HT leads etc makes insulation breakdown likely, and juddering / misfire under exactly the conditions you'd expect from HT insulation breakdown.

Low engine speed / high gear = good cylinder charge = high cylinder pressure = high voltage needed for discharge at plugs = more likely flash-over at other points before the plugs fire.

Jamie_Carter

GAZ237 wrote: »

Should have.

I don't know myself. But I didn't think many smaller cars did back then.

Chickabiddybex

The WD40 worked THANK YOU SO MUCH

And I thought you guys would find this funny, a girl I work with said:
"D'you think WD40 would stop my brakes squeaking?"

... another thing, a tyre blew on my way home from work! What ridiculous timing XD
Oh well. At least I knew how to fix that one!

Chickabiddybex

Ultrasonic wrote: »

Unless you want to damage something else too, stop driving at 30 mph in 5th gear.

Why??
What would damage? The engine doesn't labour at that speed.

Ultrasonic

Chickabiddybex wrote: »

What would damage? The engine doesn't labour at that speed.

Does it really not labour at 30 mph in 5th? That's pretty amazing for a for a petrol engine.

Joe_Horner

Chickabiddybex wrote: »

The WD40 worked THANK YOU SO MUCH

And I thought you guys would find this funny, a girl I work with said:
"D'you think WD40 would stop my brakes squeaking?"

... another thing, a tyre blew on my way home from work! What ridiculous timing XD
Oh well. At least I knew how to fix that one!

Great news (not about the tyre!)

In answer to the girl you work with, yes it probably would stop them squeaking but that wouldn't be much comfort when she found they didn't work anymore :rotfl:

GAZ237

Chickabiddybex wrote: »

The WD40 worked THANK YOU SO MUCH

And I thought you guys would find this funny, a girl I work with said:
"D'you think WD40 would stop my brakes squeaking?"

... another thing, a tyre blew on my way home from work! What ridiculous timing XD
Oh well. At least I knew how to fix that one!

When did you spray with wd40?

Before or after the tyre blew?

Just wondering if the tyre was the cause of the vibration.

alastairq

Ultrasonic wrote: »

Does it really not labour at 30 mph in 5th? That's pretty amazing for a for a petrol engine.

Both of my previous motors [1300ccs....] were quite 'happy' at [an indicated] 30mph in 5th..on, or just above, idle revs...both petrol.

The key word is 'labouring'?

Now, on a reasonably 'clear' road, without a steepish gradient, even, at a constant speed, in 5th, both cars [in my hands] would be on a very light throttle.

Once freed of the 30 limit, again with a light touch to the throttle [ie, not overdoing things] both the cars would pull away.[using the torque characteristics]...without, [in my experience] causing any sort of undue delay to any following traffic [I find, as soon as they start to change gear, I leave them behind?}...

The Felicia, with a 1.3 pushrod engine [mpi] was much better than the Frord Zetec.....in this respect.

'Labouring' the engine implies placing an undue load upon it..for example, expecting it to pull uphill in too high a gear...or pull a heavy load.

But, even with my massoosive 17 stone, one-up, both engines coped admirably!

Of course, at 30 mph [limit] if the circumstances required it, I will go to a lower gear....

Often [as an example] 3rd gear is advocated when driver training [in a car] for a 30mph limit, as it gives the driver a feeling of better control over what the car does, without the added hassle of swapping gears to suit.

Like so many other techniques taught whilst learning to drive, they are not absolutes.

They are taught to help a novice driver to deal with problems in a simple manner.

Joe_Horner

GAZ237 wrote: »

When did you spray with wd40?

Before or after the tyre blew?

Just wondering if the tyre was the cause of the vibration.

That's unlikely (though not impossible) if the vibration seemed to be happening mainly at low engine speed. Normally a tyre problem will relate to road speed regardless of the gear / engine speed you're using.

Misfire from HT insulation breakdown (often caused by old leads combined with water) mostly happens at low engine speed for a few reasons, all of which are reated to te voltage required to jump the plug gap. That voltage increases for any of the following reasons:


High cylinder pressures. When the engine is running slowly, in a high gear (so relatively "open" throttle), it sucks in more air / fuel mix than when it's at high speed simply because there's more time available for it to get sucked in. That gives higher compression pressures, which increases the voltage needed to jump the plug gap.

Cool plug electrodes. A cool electrode needs a higher voltage to spark tha a hot one because the electrons in the hot one are already more energetic from the heat. Plugs cool down quite quickly at low engine speeds, partly because of the bigger, cooler, charge entering the cylinder and partly because they're subjected to fewer combustions per second. .

Air / fuel mix temperature. A cooler charge will need a higher spark voltage than a hotter one. above a certain minimum speed, a slow running engine will be cooler than one revving fast, so low revs will also increase the spark voltage here.

Humidity. Humid air will tend to cool the cylinder charge and the plug tip because of the high heat capacity of the moisture content. That means that in wet weather (high humidity) a higher spark voltage will be needed than in dry conditions.



As the voltage needed to fire the plug increases, the chance of a misfire because of insulation failure increases - the spark will happen wherever it can happen with the lowest voltage.

Damp air, with water on or around the leads, and a low engine speed weigh all the factors above in favour of insulation failure by decreasing the insulation effectiveness and increasing the voltage needed at the plug.

Often, as the speed increases (so, lower charge volume, hotter charge and hotter plug) the misfire will reduce or go away because the spark voltage at the plug decreases until it's easier for it to spark there than at the weak point outside.



(just in case anyone's interested :P )

anotheruser

If it judders doing about 50-60mph, but is okay above and below that speed, it might be wheel balancing.

Mine had this problem just recently.

However as your seems to be getting worse, best taking it to a garage for them to check and test.