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[Elmstoneboy]

Now and again I get an engine rattle which sounds a bit like a diesel rattle, Yes me again, other times runs sweet and smooth. I have posted before on this subject, and I have narrowed it down to what I think is pre-ignition or pinking, and therefore possible Knock sensor problems. Tried changing MAF which improved it slightly, my thinking being, that if mixture is wrong pinking could also occur. I have now taken an ECU reading which is showing that knock sensors are not activated and there are no values reported like voltage etc, all values reading 0.  All visible wiring and connectors checked. ECU was upgraded a year ago from 3393 to 3412.                   WHY        I will solve it,  I will.   

Ian

[tigers_gonads]

The knock sensor on the V6 is bolted to the block behind the alternator.
If not clipped properly, the wire has a habit of getting trapped between the alternator and engine block.
Also another good place it may get damaged is around the utility belt tensioner pulley but tbh, a trapped / knackered cable will put the light on.

[Elmstoneboy]

Thanks for the input.

I have had a look at the cables but only as far as I can see from the top, but as you say, if they have been damaged, the light wood come on, or fault codes, but these are clear.
There has got to be something intermittent as sometimes it runs quiet and smooth with noticeably more power, and then
pull up at the lights or whatever and when you pull away, the rattle is back.

Any more ideas out there.

[Temetsy]

Are the knock sensors tensioned to correct Nm? As what I've heard they're very strict about the Nm they're tensioned at. (25Nm IIRC)

[Andy H]

Now and again I get an engine rattle which sounds a bit like a diesel rattle, Yes me again, other times runs sweet and smooth. I have posted before on this subject, and I have narrowed it down to what I think is pre-ignition or pinking, and therefore possible Knock sensor problems. Tried changing MAF which improved it slightly, my thinking being, that if mixture is wrong pinking could also occur. I have now taken an ECU reading which is showing that knock sensors are not activated and there are no values reported like voltage etc, all values reading 0.  All visible wiring and connectors checked. ECU was upgraded a year ago from 3393 to 3412.                   WHY        I will solve it,  I will.   

Ian

I wonder whether the knock sensors are functioning as they should but no codes are stored. The system is intended to run close to the point where pinking occurs but is prepared to retard the ignition slightly when necessary (maybe a bad batch of petrol). I suspect that if you were to read the codes after pinking occurs (but before switching the engine off) you will find a 'knock sensor actuated' code.

My last manual Omega (with a cable throttle) was prone to bogging down just as I was finding the biting point of the clutch - I suspect that the springs in the dual mass flywheel were weak and the ECU was also shutting the ICV because it didn't like me holding the revs at 1000rpm. When it did bog down it would either stall or keep going but knock slightly.

When yours knocks is it during gentle clutch starts? or grand prix starts? or is there no obvious pattern?

[Elmstoneboy]

Hi Andy

I know how the knock sensors work, but I don't know how often they are put in to action, I assumed that they were constantly listening for a knock and adjusting ignition timing constantly, maybe they only operate at start up, so wouldn't show any activity after. Can anybody advise me on this.

I have put a meter on the sensor connectors and both read the same, also no readings to earth, so cables seem ok.

Regarding the rattle, Mine is an Auto box, but the rattle, when it does it, is more pronounced with a lively, but not excessive pull away. It sounds just like the piston slap you get with a diesel but not so loud. In fact I doubt if you can hear it outside the car. It never happens if you just rev the engine when stationary, even to max RPM, it sounds good and smooth. Strangely I have noticed recently with the weather we are having, that when it's warm and humid, the rattle is considerably reduced. This partly led me to thinking timing.

Maybe I'm going up the wrong path. Could it be the cam shafts ? It's not the lifters or injectors as the pitch is to low. I don't think its the crankshaft as the rattle frequency is to fast.  Shouldn't be oil starvation as I had the sump dropped at the last oil change,  checked and cleaned including the pickup pipe filter, which wasn't blocked anyway. MAF has also been replaced with genuine replacement, and cambelt set replaced last year soon after I bought it.

My main concern is, is it causing any damage. I hope not, as the engine has only done a genuine 63K with bodywork to match.

Is there anywhere I can get a guide of what the ECU readings should be. At the moment I don't know what they should be or if they are good or bad.

[Andy H]

Oops - auto, so not a problem with the dual mass flywheel.

Assuming that the knock sensors are torqued correctly and that you read the codes without switching off after hearing the knocking you seem to have checked everything you can related to knock sensors. The loss in performance would indicate that the sensors were doing their job but doesn't explain why you are getting the knocking.

Other things that can make unpleasant knocking noises are:
- rattling cats/heatshields
- loose torque converter bolts
- fractured flex plate
- worn big end & main bearings (probably not likely in your low mileage car)

I think there is a thread on the old website where someone had a cracked flexplate which made unpleasant noises and also triggered the knock sensors but I cannot remember who started it

[Elmstoneboy]

Thanks for the input Andy and pointers to other possible causes. I am pretty sure it's not the heatshields but I will check.
Loose torque converter bolts, mmm, hadn't thought of that one so will investigate and check it out. Not sure what a fractured flex plate would sound like, but my feelings say probably not. I tend to agree with you on the crank bearings, as when the engine is revved up to around the 7000 in park, there is not a hint of rattle or rumble. This maybe a clue that leads back to the gearbox. As there are no stresses or torque in the drive train in park, the bolts, if loose, would probably not rattle. The same would go for when just cruising.  Worth looking at.

Onwards and upwards.