Good morning all,

I've noticed that at low revs and only lightly touching accelerator, the Panda judders. This happens when the engine is hot, not so much when its cold.

Any ideas?

Thanks in advance

How low revs are we talking about here?

Does it do it when crusing at a steady speed like 30 also James?

Sisters 1.1 does, I've got to get around to changing the injector bar.

Yes, also at cruising at low revs. Could it be fuel filter problem?

KozmoNaut said:

How low revs are we talking about here?

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Around 1000 - 1300, something like that

james2609 said:

Around 1000 - 1300, something like that

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You're running the engine too low in the rev range and lugging it. Even if it was a diesel, I wouldn't run it that low.

Basically, the only times you should be below 1500rpm is when you're stopped or you've released the accelerator and you're using engine braking. Even then, you should push the clutch in at around 1200rpm to prevent judders.

The engine will wear significantly more if you're constantly at super-low revs, giving it some revs is much much better for it.

KozmoNaut said:

You're running the engine too low in the rev range and lugging it. Even if it was a diesel, I wouldn't run it that low.

Basically, the only times you should be below 1500rpm is when you're stopped or you've released the accelerator and you're using engine braking. Even then, you should push the clutch in at around 1200rpm to prevent judders.

The engine will wear significantly more if you're constantly at super-low revs, giving it some revs is much much better for it.

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How will the engine wear more??

And regarding engine speed there's nothing wrong with running at that speed IMO. And it certainly can't be helped in stop start traffic in 1st gear.

Most Easterly Pandas said:

How will the engine wear more??

And regarding engine speed there's nothing wrong with running at that speed IMO. And it certainly can't be helped in stop start traffic in 1st gear.

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Lower engine speeds mean more torque on the crankshaft and whole bottom end of the engine to maintain speed. HP is made from torque+revs, if you don't have revs, you need more torque to produce the needed HP to move the car, hence more stress on the engine. Hardly any stock engine dies because of revving too high unless something like an oil failure happens. Engines are almost always killed by lugging them.

James wrote "cruising at low revs" and 1000-1300 revs. Of course you need to do this in first in really slow traffic, but I take "cruising" to mean driving around town at normal speeds, 30-35mph. Which he would be doing in fifth gear and that's just murdering the poor engine.

Small update, on the way home from work last night it was juddering again. I put my foot to the floor and revved it up to the limiter for a couple of seconds.. the juddering stopped for a couple of minutes!! I will change the fuel filter and see how I get on.

KozmoNaut said:

Lower engine speeds mean more torque on the crankshaft and whole bottom end of the engine to maintain speed. HP is made from torque+revs, if you don't have revs, you need more torque to produce the needed HP to move the car, hence more stress on the engine. Hardly any stock engine dies because of revving too high unless something like an oil failure happens. Engines are almost always killed by lugging them.

James wrote "cruising at low revs" and 1000-1300 revs. Of course you need to do this in first in really slow traffic, but I take "cruising" to mean driving around town at normal speeds, 30-35mph. Which he would be doing in fifth gear and that's just murdering the poor engine.

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I'm not running the engine down past below idle at all, which I know is bad. Cruising at 1300rpm through town is safe for the engine, and also better for fuel economy and environment. If I have to accelerate hard for whatever reason, you have to change down anyway, not floor it in 5th Cruising on light load at 30-35mph in 5th gear doesn't require masses of HP so surely, if the engine was struggling to pull at this speed, it would be using more fuel to compensate and labouring? But it's not.

Anyway, will let you all know if fuel filter change cures my problem

Most Easterly Pandas said:

Does it do it when crusing at a steady speed like 30 also James?

Sisters 1.1 does, I've got to get around to changing the injector bar.

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MEP, why the injector bar? I thought if there was a problem there, it would much more likely be the injectors themselves rather than the bar.. just wondering as i'm not entirely sure myself

james2609 said:

MEP, why the injector bar? I thought if there was a problem there, it would much more likely be the injectors themselves rather than the bar.. just wondering as i'm not entirely sure myself

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Just easier to change the whole bar as I've got one from a donor motor rather than each injector one by one

james2609 said:

Cruising at 1300rpm through town is safe for the engine, and also better for fuel economy and environment. If I have to accelerate hard for whatever reason, you have to change down anyway, not floor it in 5th Cruising on light load at 30-35mph in 5th gear doesn't require masses of HP so surely, if the engine was struggling to pull at this speed, it would be using more fuel to compensate and labouring? But it's not.

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It's extremely hard to feel when a modern fuel-injected engine is on the verge of labouring. I'm not going to chide you for wanting to save the environment, but you have to look at saving the car as well

Obviously, you don't need much power to cruise at town speeds, but when the revs are that low, you're pulling on every single ounce of torque your car has at those revs, which isn't much. Therefore, your engine is working right at the limit of what it can produce, you're running the engine at maybe 8 or 9/10ths of what it can produce. It may not make a whole lot of noise, but it's working very hard to produce enough HP to keep you moving. Whereas the engine has a much easier job pulling you along in 4th gear at maybe 1800-2000rpm at those speeds.

Obviously, the slower the engine is turning, the less fuel you use, but every engine has an optimal rev range that you need to stay in. Which is why you change gear at 2000rpm in diesels, but at 2500rpm in petrol cars when you're trying to save fuel.

But I know I wouldn't want to drive around below 2000rpm every day in my diesel. I did it one time for a full tank to test the mileage I could get in ordinary driving (69mpg, mostly towns and motorways), but you should have seen the cloud of soot I produced the next time I pulled onto the motorway at full throttle. Engines need to rev to live, otherwise they get blocked up, bog down and need more frequent service.

If you don't give your car a good blast on the motorways once in a while, I'd recommend the "Italian Tuneup". Warm it up, get on the motorway and run it right at peak power (5500rpm for the 1.2 and 4000rpm for diesels) for 10-15 minutes. That'll clear out any crud and the engine will feel so much better afterwards.

Most Easterly Pandas said:

Just easier to change the whole bar as I've got one from a donor motor rather than each injector one by one

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I dont suppose in this donor Panda that you have, you have a blue drivers seat?
:worship:

Before I replace the filter, I think I should dump a load of cleaner in the tank, just to see if it will shift any cr*p blocking it and the injectors.

Picture attached from ePER shows the filter outside.. will take a look underneath if it's not raining tonight.
I haven't done a lot of work on fuel systems, sorry if I seem a bit dim

If you do use some redex James use a full bottle and put it in as reserve light comes on and trash it for a bit before filling up. Adding 1/5th of a bottle to a full tank won't do much cleaning in the concentration it'll filter through in.

I've got tbh, it just sound like you are labouring the engine which is about the worst thing you can do to it really. It's akin to trying to cycle at low speeds in top gear, think how difficult that is, then think what the engine is having to cope with.

There is no benefit whatsoever really in terms of economy. I would never cruise below 1500rpm as an absolute minimum, I prefer to cruise at 2000rpm in all honesty and find it bonkers to think that changing up a gear will drop the rpm by say 200 or so at the most.

Your car and your engine. If you are going to be one of those mpg nutters, then remember to give it a good thrashing once in a while.

trackdayqueen said:

I've got tbh, it just sound like you are labouring the engine which is about the worst thing you can do to it really. It's akin to trying to cycle at low speeds in top gear, think how difficult that is, then think what the engine is having to cope with.

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I use that very example when explaining the gear/engine/rpm relationship to students

Sadly, fewer young people these days seem to have ridden bicycles with gears.