Manda

Hi.

I have an issue that the dealers seem to have no idea how to sort. It has had the problem from new. (shame we don't have the 'Lemon-Law' here!) The problem occurs just the same regardless of what fuel is used, V-power, Tesco 99, Morrisons poverty petrol etc....

From cold, when I accelerate (not neccessarily hard-just to progress in traffic, so to speak) the car surges on acceleration. It pulls then dies, pulls then dies and so on.

My boyfriend suspected either throttle oscillation (it's electronic of course), a lambda issue or knock retard issue. After connecting a graphing scan-tool it shows that the throttle opening is steady, that the problem still occurs when in 'open loop'- eliminating the lambda but that the ignition timing oscillates from eighteen or twenty degrees down to practically nothing as the car pulls then dies, indicating an ignition-timing related issue.

Telling the dealer what we found, they fitted a new knock sensor, but the problem remains, though it does seem to be a fair bit better. When it is fully hot, ie when the oil temp is high -rather than just water up to temp, it is very much better, almost right even.

My boyfriend's suspects either:-

Excessive piston clearance causing 'noise' that the knock sensor perceives as knock and thus retards the timing. The reason this is suspected because the pistons fill the bores better when they're hot, and the problem is much better when it's hot.

or

The torque setting on the knock sensor is too high, causing the crystal inside to be over-sensitive

or

The knock sensitivity level in the ECU is set too high and thus, is over zealous retarding the timing to soon and too far in response to engine 'noise' (piston slap) rather than in response to detonation.

Has anyone had the same issue and, if so, how was is sorted (assuming it was sorted)?

dynamix

iTrader: (3)

I would doubt it is the first option as the pistons are a very tight fit and not really subject to piston slap in the way that older forged pistons were. Possible for number 2 or number 3 but I would say the best option is to let your car warm up before properly putting your foot down.

If you don't want to do this then there are always options in the map to smooth out the level of interference from the ecu's knock control strategy in certain areas of the map whilst still retaining the protection. The 32bit ecu is very sensitive to how much general noise is going on and because of the location of the placement of the knock sensor can pick up some drive train noise too (particularly when cold).

If you are reasonably local I could datalog it for you to check ?

MrNoisy

iTrader: (28)

Might be a silly comment, but this sounds very similar to the behaviour the cars generally exhibit when they have a duff or knackered spark plug or coil pack.
I assume the dealer has checked that too? Just a thought.

Manda

I would assume the pistons are a tight fit (the assumption being that they are Hyper-Eutectic Silicon alloy castings these days and not a High-copper content forging...) as long as the pistons are the correct grade for the bore they live in, there usually being several grades (sizes) of piston for a given 'nominal' bore size. It could have been built incorrectly, is the suspicion. It has had this problem from brand new, it's not something that has developed over time.

I agree that any car needs to be warm before 'really' putting my foot down, but my car has this problem simply when progressing up to speed, accelerating - but nothing like accelerating hard. It does it when I have my mother in the car with me for instance..... I can drive it around town for several hours and still it does it, it only stops (virtually) when it's been given some thrash and the oil temp is up. As soon as it cools down, the problem is back.

It has had a software 'update' at the dealers, which did nothing. One would have to assume that, if it was a mapping issue with the knock sensitivity, then all cars the same model would have the same problem to some degree. Fifth gear is 'whiney', but it has been the same from brand new and I would doubt gear whine would be in the same frequency range as that being looked for by the ECU.

My boyfriend owns an engine management mapping company, but he won't touch it because he doesn't want to give the dealers an excuse to renege on the warranty. He personally knows Merv Carrol and Dave Power of ECUtek, and has done work for them (actually for Prodrive, via them) in the past, so getting the knock control turned down would be a simple task for him. However, it's the cause OF the noise that needs to be fixed, not the symptom caused BY it, although the symptom is what you actually feel of course....

It's really aweful to drive, even normally.

Thanks for the offer to log it, but I am North of Manchester and we have logged the 'usual suspects' already, to try and give the bewildered dealers some idea what to look at next...

Thanks for your input anyway....