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Pinking under load - what to check? FIXED AT LAST

kerb scraper

25 May 2012
Think I need the benefit of your accumulated wisdom please guys.

Pretty much ever since I have owned my C4 she's had a tendency to make a noise which I've only recently realised is probably pinking.

This noise is heard only at about 2000 RPM with throttle opened more than just a gnat's. Worsens when the engine is really warm.

Sounds like the classic 'marbles being poured into a tin can wrapped in a blanket'

Dropping a gear or two enables acceleration without the noise.

Oil just changed and no obvious performance issues and disconnecting the primary distributor king lead doesn't affect the idling (so hopefully distributor belt is still in one piece). Always used BP Ultimate fuel. Oh and I changed the rubbery connecting piece in the vacuum system behind the heating inlet but no real discernible difference.

Is it just the Hall sensor in the distributor, the two knock sensors and the ECU that control ignition timing or should I check the position of the distributor relative to TDC? Are there any centrifugal weights to lubricate? Should I check and clean all the connectors on the knock sensors?

I noticed one of the two Dzus fasteners has fallen out of the transmission undertray and have a new one on order but am not optimistic that's what I can hear rattling.

Am I barking up the wrong arboreal species altogether? Please help; it's driving me nuts
Does it only do it when you are loading the engine?..i.e pulling in a high gear on an incline?..or will it still do it when the car is stationary and the revs are raised to 2k.
Try some different fuel.
Thanks for the responses.
Just to clarify - no it doesn't occur revving up when stationary only when pulling in highish gear on the flat or incline.

Will try another fuel - is Shell V-power nitro + unleaded the highest octane? (in addition to being the most stupid brand name)

Sebastien - yes very topical! Re the dizzy belt - as I said idles well with primary disconnected but guess to be sure I'll have to look under the secondary cap and twiddle the rotor arm at the w/e.
High octane fuel should be used as standard (with regular unleaded being the option if the higher octane stuff isn't available) - I can't remember whether the manual suggest 97 or 98 RON.

A slightly left field thought..... could the noise be rusted heat exchangers? A rattle could be caused by low engine speed resonance.
If it is pinking you can hear then thats very unusual as these engines have knock sensors installed which automatically retard the timing on the onset of predetonation. Way before you hear it actually.
If the fuel change does not work I would get the car to a good Indy and have them check the valve timing and fuel mixture, the camshaft can sometimes move from its optimal position certainly enough to lose power, maybe to cause pinking.
I wonder whether your car has been remapped (badly) by a previous owner. It might be worth getting it on a rolling road and run some diagnostics.
Wayne at Chipwizzards recommended Tesco 99 fuel over the Shell V-Power

My 95 c4 cab has been pinking or pinging as they call it here in Canada, it started immediately after fitting a Steve Wong chip to cure the LWF stalling issue ( which it hasn't done ). Pinks for a second or two if I apply throttle in a high gear at lower revs, say 4-6th at 35 ish MPH , ***** fuel out here mind, vpower 91 :D

It's going in tomorrow to be checked for vacuum leaks etc, however was fine with factory chip, just stalled occasionally, now it stalls,pinks and hunts

Gonna end up removing the chip and replacing the oe item,

Anyways I would second the advice regarding a check for an aftermarket chip
Ridders said:
Wayne at Chipwizzards recommended Tesco 99 fuel over the Shell V-Power


Sorry to digress, but I thought supermarket fuel was a no no. However, if Wayne says it's good, who am i to argue.

Can yoy elaborate on the Chipwizzards recommendation?
Thanks for all your interesting suggestions gentlemen.

For now... I'm discounting the 'badly remapped or chipped' solution because I've owned this car for 12 years am only the second owner and have the impression the original owner wasn't a remapping kind of guy. Plus the noise wasn't apparent for the first part of my ownership.

Here is an update after further investigation at the weekend.

As per OP I needed to fit the missing Dzus fastener and receptacle for the transmission undertray and whilst under there decided to have a good look around for possible causes of the rattling sound including removal of the n/s wheelarch liner for inspection and cleaning.

Turned out to be a bit like the aftermath of the Tottenham riots i.e. no shortage of suspects viz.:

1) The missing Dzus fastener

2) One of the self tappers at the bottom lip of the rear PU securing the heat shield was loose

3) The outermost self tapper for the n/s forward PU support bracket was missing

4) The heatshield fitted to the pipe connecting the n/s muffler to the cat is severely corroded and flapping in the breeze

5) The half-moon shaped fairing piece welded to the n/s exhaust tip was making contact with the bolt of the clamp securing the muffler pipe to the cat. (see pic below with contact point ringed in red n.b after remedial bending). The pic is taken from within the n/s wheelarch, with liner removed, facing to the rear

The chief suspect for me was (5) above and I shamefacedly admit this probably stems from an inept bit of reversing into a dwarf wall early in my
ownership necessitating PU and exhaust repair .

Am happy to report that after levering the fairing piece away from the clamp bolt and fixing suspects 1-3. The 'pinking' sound has all but disappeared and I have to try quite hard to make it manifest itself by using wide throttle in 6th gear at less than 2,000 RPM. Driving the car is much more pleasant

Would I be right in the opinion of the jury to think that the engine is labouring at this RPM so best to avoid that situation?
The owner's handbook torque curve seems to show that torque only really picks up post 2,500 RPM after all.

Any residual noise maybe is associated with the rust-riddled heat shield that can be clearly seen in the picture but I can't see a quick way of dealing with this – or if indeed the heatshield can be renewed.

So thanks again and perhaps this was not pinking although the sound is similar.
As above apologies for going off-topic....

Pickled Piper said:
Ridders said:
Wayne at Chipwizzards recommended Tesco 99 fuel over the Shell V-Power


Sorry to digress, but I thought supermarket fuel was a no no.

There is no such thing as 'Supermarket fuel'. They don't have oil refineries. In your local area (wherever that is) all the fuel in ALL of the petrol stations comes from the nearest distribution point, which comes from the nearest refinery.

So your Esso Sainsburys BP ASDA Chevron Texaco whatever franchise all sell the exact same fuel. What is different is the additives package which is erm added at the distribution point into each tanker.

Strangely Tescos is a different fuel - they have been souring it from Greenergy for many years, and that is why you couldn't get the 99 RON everywhere in the UK because of distribution limitations in the past. Now you can.
I have reverted back to my factory chip and now have no pinking unless like you I severely lug the engine, I guess keeping the engine in a more suitable rev range is the obvious avoidance technique

Well it looks like you have found your culprit, and i have never heard a 993 pink,without something seriously and obviously amiss. Engine issues with the basic injection system are very rare in my experience, I almost never see engine faults codes in any 993 i see ,although granted its not the most sophisticated electronics system around so wont capture everything. These engine are well engineered and basic and that makes them tough old lumps!
I agree full throttle in top at 2000 is an unusual situation and not desirable, but your unlikely to cause to much wear as its impossible to maintain that as the engine speed increases with the torque and you begin to accelerate, the engine is a very torquey low revving unit in sports car terms and i'm quite happy to bumble mine along in top at say 35 plus on level ground riding on a whisker of throttle to no detriment of the engine. Its nearly a four litre engine! not exactly your family car average.


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