Sudden jolt when pressing on

[mhurley]

Lately on a few occasions my V8V jolts when i put my foot down. Think it tends to occur in 2nd gear
Any one had this issue?
It's as if the engine is starved of petrol for a split second

[LordBretSinclair]

Dirty throttle body ????

[Bincenzo]

mhurley said:

Lately on a few occasions my V8V jolts when i put my foot down. Think it tends to occur in 2nd gear
Any one had this issue?
It's as if the engine is starved of petrol for a split second

Yes, did happen to me on my V8V. Sadly didn’t get to the bottom of it before it went. Only happened once or twice, on acceleration off a roundabout as I recall.

[mjk1]

Yes it occasionally happens on my 06 V8V and it’s a far more violent pause than if you were to just lift off the throttle. No idea what is going on but it feels like the engine is quite violently braking the car for about half a second during acceleration usually going round a corner. Anyone any idea what could cause this?

[V8V Pete]

mjk1 said:

........ during acceleration usually going round a corner. Anyone any idea what could cause this?

Is it not just the DSC cutting in? If you're still running the Bridgestones then get some decent rubber fitted and it won't happen anywhere near as often.

[Bincenzo]

Pete, if it’s like I remember, it’s much more aggressive than that, throws you forward in the seat. Very disconcerting.

[mjk1]

V8V Pete said:

Is it not just the DSC cutting in? If you're still running the Bridgestones then get some decent rubber fitted and it won't happen anywhere near as often.

I think you may be right Pete, it does feel like a sharp jab on the brakes. I was always assuming it was the engine but bar it seizing up for half a second and then running normally as if nothing has happened, I don’t think it can be the engine.

It does always happen under acceleration and cornering but at a point where the car is nowhere near the limits of adhesion so if it is the DSC it must be some sort of bug within the system.

I’ll try with DSC switched off for a few weeks and see if the problem stops.

[mhurley]

mjk1 said:

I think you may be right Pete, it does feel like a sharp jab on the brakes. I was always assuming it was the engine but bar it seizing up for half a second and then running normally as if nothing has happened, I don’t think it can be the engine.

It does always happen under acceleration and cornering but at a point where the car is nowhere near the limits of adhesion so if it is the DSC it must be some sort of bug within the system.

I’ll try with DSC switched off for a few weeks and see if the problem stops.

A sharp jolt on brakes is a good analogy

I'm running Bridgestones on the front and Michelin Pilot Super Sports on the rear

[mjk1]

I think this is a eureka moment, thanks to Pete. We have been searching for the root cause of this problem for the best part of a decade! Now we just need to identity why the DSC is cutting in at a point well before it is required. Does anyone have a technical contact within AM?

https://www.pistonheads.com/gassing/topic.asp?h=0&...

https://www.pistonheads.com/gassing/topic.asp?h=0&...

[telum01]

I've had this issue with my grey '07 V8V for at least a couple years now. Same frequency; once every few months.

For the fuel vapor valve: from what I've seen, that usually causes a complete engine stall while coasting to a stop in neutral with a mostly-full tank of gas. If not the valve, then the rubber hose attached to it:
https://www.redpants.lol/blog/2015/12/1/the-infamo...
But the valve or hose could be related to the hesitation as well. I have fixed the hose, I have not replaced the valve. So if the valve is the problem, I'll need to replace that to test... and wait 1-3 months to see if the problem reoccurs lol.

I've changed the battery, spark plugs, and coil packs with no impact on the hesitation problem. Same with cleaning the throttle body.

At one point I had a starting issue, where the car would sometimes have zero power at all. Turned out the stud on the chassis where the battery grounds was broken clean off. When the stud or ground cable rested against the chassis, the car would turn on. If it wasn't resting against it, zero power. I switched the ground cable to another stud and it's been fine ever since. Having had this issue, it makes me think the issue is electrical. Bad connection, intermittent grounding issue... something that is momentarily unable to carry the current needed for smooth acceleration.

Or it's the accelerator pedal, or it's the throttle body itself - I've heard of each of those being replaced by other people. Either would make sense.

Just my thoughts and experiences, not sure if I'm on the right track or completely off.

[mjk1]

I now realise the problem with my car is too violent for it just to be the engine momentarily loosing power. It really is a jolt that forces me forward in the seat. The only explanation for such momentary retardation (for an engine that is running normally) is a jab of the brakes. As mine happens under moderate acceleration with a small steering wheel angle I suspect the DSC/TC is momentarily applying the brakes.

There may be other problems with engines cutting out but I’m now convinced, after 7 years of thinking otherwise, mine is not an engine problem at all.

[rancidswan]

Interestingly, I have experienced the stalling issue about three times in the last 6 months. Always a very low speed situation (thank goodness) but it's extremely disconcerting.

Then last night, as I came out of a junction in 2nd gear onto a lovely straight road, and floored it - I experienced the sudden jolt, and my god what a jolt it is. I thought for a second that my foot must have overlapped the break as I got on the accelerator.

I'll get the fuel vapor hose checked out shortly and report back.

[mjk1]

I’d try switching your DSC off, there’s no way a loss of power, ie coasting engine can provoke such a violent jolt. Just try taking your foot off the accelerator during a brisk acceleration to see what I mean.

[KiwiSG]

what is the DSC ?

[JK_vantage]

KiwiSG said:

what is the DSC ?

dynamic stability control

[Big Brin]

What about the limited slip diff? Oil should be changed every 4 years I think....as it becomes too viscous. I had an old DB9 that ‘ground around’ corners rather than was violently pulling back, but I had the diff oil changed and it solved it. If your symptoms are happening as you pull away / at roundabouts it might be a consideration? Just an off the wall thought.

Regards Brin

[petop]

My (V8V 4.7 08) car does it.....or should i say used to as its not done it for the past 6 months and in the time of 4 years of having it its probably done it 5 or so times. Its the same as what you say, a sudden jolt on pick up at slow speed. I would say its nothing to do with the brakes but more like a fuel cut out. I think though ill chance it and assume it wont happen again but if it does ill look at the hose by the fuel tank.

[JK_vantage]

The engine cutting at low speeds can be fixed by updating to the latest software.
Please don't ask me what this technically does but it worked on my 2010 v8v

[Tom_GGG]

I think this may be the same issue i was having here : https://www.pistonheads.com/gassing/topic.asp?h=0&...

[Damianos]

Anyone got to the bottom of this?

Just had this happen to me for the first time, was in third gear with low RPMs, small steering angle, and felt the power cut when tried to give a bit more throttle.

I had the DSC off, so probably nothing to do with that...