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Juddering under acceleration

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Old Feb 21st, 2021, 09:04   #11
ITSv40
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Is this something that would have suddenly happened though? I mean, it is a very noticeable problem and severely impacts the experience of driving the car. I'd of already investigated it had I noticed it before.
Yes, it could although one would expect it to be noticeable before it completely collapsed. However, it is a known fault and most cases of vibration are cured by replacing those bushes. It is also a quick and easy thing to check at no cost. The other mounts to check - and a little more difficult - is the pad under the crank pulley, engine to chassis, and the two mounts - one in front of the engine block and one on the rear of the block. These two are hydraulic and can leak.
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Old Feb 21st, 2021, 09:44   #12
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Still sounds like a misfire to me - when it does it, is there any loss of power at all? If so then even more likely to be a misfire, but if it's still pulling just as strongly when it judders, probably not. Does this car have dizzy cap and rotor? If so then I'd be checking those, if it's the ME7 engine with the individual coils, then it's not uncommon for one or more of these to fail (or the wiring to them) also giving a misfire.
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Old Feb 21st, 2021, 10:54   #13
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Tested revving while neutral and it appears nothing is wrong stationary, everything is as expected.

Popped the bonnet and tried rocking the engine.. Seems almost totally solid, minimal movement. Could it be drive shaft related?


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Still sounds like a misfire to me - when it does it, is there any loss of power at all? If so then even more likely to be a misfire, but if it's still pulling just as strongly when it judders, probably not. Does this car have dizzy cap and rotor? If so then I'd be checking those, if it's the ME7 engine with the individual coils, then it's not uncommon for one or more of these to fail (or the wiring to them) also giving a misfire.
What do you mean by dizzy cap? It revs happily and smoothly in idle which is what makes me think it isn't misfiring? It does feel like a loss of power but if I watch the revs when it happens it seems normal so maybe its just an appearance of loss of power or the power is there in the engine but not getting to the gearbox / wheels?
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Old Feb 21st, 2021, 12:56   #14
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Tested revving while neutral and it appears nothing is wrong stationary, everything is as expected.

Popped the bonnet and tried rocking the engine.. Seems almost totally solid, minimal movement. Could it be drive shaft related?




What do you mean by dizzy cap? It revs happily and smoothly in idle which is what makes me think it isn't misfiring? It does feel like a loss of power but if I watch the revs when it happens it seems normal so maybe its just an appearance of loss of power or the power is there in the engine but not getting to the gearbox / wheels?
Dizzy cap = slang for distributor cap, distributes the HT spark to the right cylinder, and has a rotor arm that (obviously) rotates to do this. It's not a standard service item, so often gets forgotten, but the points in it can get corroded and worn and it'll become very inefficient. Early engines had a distributor, later ones did away with this and had a separate HT pencil coil above the spark plug on each cylinder - as mentioned, these tend to be less reliable and can fail individually, as they're necessarily small and are permanently sitting on top of a hot engine. The wiring to them can wear and short out too.

Revving the engine without load doesn't necessarily mean there isn't a misfire potential, as a weak spark will usually fire OK with no load but break downs and misfire under load, so testing it as you have done isn't conclusive.

It could indeed be engine mounts etc. as mentioned above, I'm just saying that from what you've said so far IMHO I definitely wouldn't rule out a misfire.

If it was driveshaft related I'd expect some sort of graunching noise at the same time as the judder to be honest, although anything's possible.

Hope that helps?
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Old Feb 21st, 2021, 14:16   #15
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It has a lot of judder when under load accelerating which seems to calm down when you're coasting
I had EXACTLY the same symptoms on my C30 T5. It turned out to be a truly knackered CV joint. I would start there for sure.

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Old Feb 22nd, 2021, 14:31   #16
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This morning I could be bothered to boot up the VIDA laptop and look what we have..


So ignition coils at fault.. I'm about to check all the wiring in case it's a problem down the line rather than the coils themselves but assuming it's the coils. Should they all be replaced or just cylinders 3 and 4? And which brands are decent or is Genuine Volvo the only thing worth considering?

Cheers.
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Old Feb 22nd, 2021, 14:39   #17
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Aha! I'm surprised it didn't put the engine management light on, is the bulb working? No matter, you're wise to pursue this line of enquiry in my view. In my opinion it's up to you and your wallet whether you replace just the two coils or do all five, if it were me i'd do all five as it's probably a preventative measure for the future, but I should imagine that just doing those two would at least get the car working properly for now. If you've got the time you could clear those codes, swap those two coils for other cylinders, and see if the error codes appear for the new cylinders - this would confirm the diagnosis.

I think you're wise to check the wiring, however my money would be on the coils themselves, as misfiring only under load is less likely to be a wiring problem I'd have thought.

As for sourcing, I don't have individual coils on my car so I've never had to buy any, but I expect others on here will have good advice on this. If it were me though I'd just order some from PartsForVolvo online and get them delivered, I've always found their stuff to be of reasonably good quality.

By the way, running the car to test it for a short while is OK, but don't run it too long or too hard with a misfire, as the unburnt fuel will often ignite in the catalytic converter and overheat it, then you're into a world of poor emissions and having to replace it, which can be expensive. I learnt this the hard way on a Saab 900 when the rotor arm disintegrated while blasting up the motorway, I found that the cat was completely destroyed and just full of shattered bits - duh!
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Old Feb 22nd, 2021, 16:50   #18
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Aha! I'm surprised it didn't put the engine management light on, is the bulb working? No matter, you're wise to pursue this line of enquiry in my view. In my opinion it's up to you and your wallet whether you replace just the two coils or do all five, if it were me i'd do all five as it's probably a preventative measure for the future, but I should imagine that just doing those two would at least get the car working properly for now. If you've got the time you could clear those codes, swap those two coils for other cylinders, and see if the error codes appear for the new cylinders - this would confirm the diagnosis.
I did exactly that! Swapped coils 3 and 4 over with 1 and 2. Cleared codes and reread with the car idling.. Then still no error codes. So I drove for about 10 mins down some 60mph roads doing some hard accelerations to try and trigger it but the car now seems fine and when I re read it again there's no codes... I don't know whether I should just leave it now and see if it comes back or replace all the coils to be sure or what?
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Old Feb 22nd, 2021, 23:11   #19
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Hehe - murphy's law eh? Well, at least you've confirmed the "juddering under acceleration" diagnosis. Difficult one to know what to do next, not sure what I'd do, it depends on whether you can afford for the car to be off the road for a day or two while new coils arrive if it happens again, or if you absolutely must have it 100% reliable at all times - personally I can do without my car or use another one, so I'd wait to see if it happens again, but I can completely see the logic of replacing at least a couple of coils as a precaution if you want the peace of mind. Depends on the depth of your wallet too I guess!

Nice one - glad you've finally got somewhere with this. Cheers!
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Old Feb 22nd, 2021, 23:12   #20
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Hehe - murphy's law eh? Well, at least you've confirmed the "juddering under acceleration" diagnosis. Difficult one to know what to do next, not sure what I'd do, it depends on whether you can afford for the car to be off the road for a day or two while new coils arrive if it happens again, or if you absolutely must have it 100% reliable at all times - personally I can do without my car or use another one, so I'd wait to see if it happens again, but I can completely see the logic of replacing at least a couple of coils as a precaution if you want the peace of mind. Depends on the depth of your wallet too I guess!

Nice one - glad you've finally got somewhere with this. Cheers!
I think what I'll do is, wait to see if it happens again (maybe something had just vibrated loose..?). If it does happen again I'll replace the whole lot.
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