The engine is pinking at a steady cruise around 2000 - 2500rpm at a steady speed when the throttle is JUST open a little. If I release the throttle or put my foot down just a tiny bit further the pinking stops immediately. I have tried running 98 octane instead of 95 - no difference. I have checked the ignition timing which is set at 8 deg BTDC - manual says 10 deg so its actually retarded very slightly. A setting of 24 deg at 4000 rpm is given in the specs and this reads about 21 deg with the timing light. The mechanical advance seems OK and the timing advances smoothly as I rev the engine up. Vacuum advance seems to be working well. I tried disconnecting the vacuum advance for a couple of days. NO difference to the light throttle pinking. The engine is running very well aside from the pinking. It has the Bosch LE Jetronic injection. Is it possible there is a lean condition occurring just off closed throttle due to a vacuum leak? All the vac hoses look OK. Its a weird one - I'm almost out of ideas. The engine DID have a head gasket replacement 18 months ago by the Pug experts at Auto France Ltd and the head was planed so compression could be a bit higher than standard. I think I will take the spark plugs out and compression test the engine just to see what pressures its making. Any advice would be appreciated. Thanks.
clark20,
Dec 19, 2:26pm
Are you sure its not just injector noise?
rovercitroen,
Dec 19, 2:32pm
Hi. No I'm NOT sure. Definitely sounds like pinking but I suppose its possible its a resonance in the exhaust or something.
bjmh,
Dec 19, 3:27pm
centrifugal advance weight spring broken,allowing to rapid an advance curve ?
bwg11,
Dec 19, 5:56pm
I'd be surprised if it is pinking. At 2000 rpm in a no-load situation, even full advance of 24 degrees should not cause pinking. If it is pinking, full throttle should make it dramatically worse.
If it has done big km's I would not rule out a big-end or big-ends as a light or trailing throttle is when you will hear bottom-end noise. Is it sweet and smooth at high rpm. or a bit harsh?
rovercitroen,
Dec 19, 10:09pm
Sweet and smooth all the way through the rev range.
intrade,
Dec 19, 10:18pm
i would check each piston for bearing and gudgeon pin end play, to roole that out with spark lug out move the piston on crank and see if all move instantly back and forward. some screwdriver sipping straw as visual gague for movement
bwg11,
Dec 19, 10:44pm
Well, if it sweet and smooth at high revs and full load, I think that would rule out bottom end noise. Getting a bit obscure, but what about a loose baffle in the silencer resonating at certain rpm?
gazzat22,
Dec 19, 10:49pm
Bit of a longshot but i heard of a car that had a similar noise and it turned out it was a loose heat shield on the manifold.
poppy62,
Dec 19, 11:43pm
Hi RC! my tupence worth, My take is that around the 2000rpm (1800-2000) mark is where a motor appears /sounds the most thrashy, For me all the rattly, clinking and clonking seems to occur at this point. Whenever I check out an engine I always rev it to around this range on a light throttle and all the noises seem to be accentuated. Something about harmonics me thinks, not sure why but thats where I base some of my findings on a motors condition. A useless snippet from my engineering days, that some sage imparted to me. Are the plugs the right range NGK would be the choice.
poppy62,
Dec 19, 11:45pm
Agree with this as well, especially if there is a crack in the heat shield around the bolt/screw head. A squirt of CRC to verify wouldn't go astray.
phillip.weston,
Dec 20, 12:12am
Try changing to cooler temp spark plugs and maybe a cooler temp thermostat to see if it's temperature related (ie hot spot in the combustion chamber).
rovercitroen,
Dec 22, 11:16pm
Thanks for your replies. I'm starting to wonder if the noise IS pinking but, damn, it sounds like it. Merry Xmas to you all.
bwg11,
Dec 22, 11:42pm
Merry Xmas to you too. Be sure to post the cause and solution when you solve it.
rovercitroen,
Apr 17, 9:32pm
Update. I did an experiment. Wired the rear exhaust tail pipe in a slightly different position to the rear tow loop so that the rear muffler was in a slightly different place and much less free to move around. Noise almost completely gone! Maybe as I go on and off the throttle the exhaust pipe gets a resonance which rattles a baffle in the rear or centre muffler? I will get it up on a hoist and see if I can track it down. Sounded SO much like pinking!
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