Pinking underload

Hi All,
got a problem that's just reared its ugly head - car ( 99 thor, 4.6) used to run fine - but now under load it produces a distinct pinking from the drivers side of the engine. The car does not overheat.
Thought it was the exhaust manifold - but can't see any problems with that, no chuffing on idle - all gaskets replaced anyway. Was thinking that the injectors after 173000 miles might need some attention though. No faults being shown, and the head gaskets were all replaced 2 years ago ( top end rebuild, magnacore leads, new plugs, arp stud kit and comp gaskets fitted - block OK - new engine at 135000), idles smooth, it allways has good fuel in it and as I said this one has come out of the blue.
Any suggestions are as always apprieciated.

Bad fuel, worn plugs.

What makes you think its from the drivers side only? As Wammers bad fuel, worn plugs and leads. Have you tried the super unleaded 97 octaine? any difference. But it should run correctly on 95 octaine.
If after having changed the plugs etc it still pinks then I would advise a diagnostic. This might say that one or two banks are running lean and give a clue why?

Dodgy MAF sensor? Mine was down on power and when I used to compensate with more throttle it used to Pink. New MAF sensor cured the power and pinking instantly.

Pre ignition is usually caused by glowing embers in the combustion chamber igniting the fuel early as the charge is compressed. Old worn or too soft plugs can cause this, as the deposits on them glow, as well as poor quality fuel with a lower octane rating than is needed. Or a combination of the two.

Thanks all for the thoughts - stuck some fresh petrol in and made no difference, also it had become more pronounced- around cylinder 6. Couldn't go for the injectors just yet so, I bit the bullet and removed the drivers side exhaust manifold (what a fun job), only to be greeted with a crack in the weld at the union of the 3 exhaust pipes. Only about 5mm long but under further investigation a second leak within the same area inside the central join. Manifold now off to somone who's more able to get stainless steel to go back together. Checked the Passagerside to make sure and that one was, of course, sound. Will let you know how it progresses.

forthbridge said:

Thanks all for the thoughts - stuck some fresh petrol in and made no difference, also it had become more pronounced- around cylinder 6. Couldn't go for the injectors just yet so, I bit the bullet and removed the drivers side exhaust manifold (what a fun job), only to be greeted with a crack in the weld at the union of the 3 exhaust pipes. Only about 5mm long but under further investigation a second leak within the same area inside the central join. Manifold now off to somone who's more able to get stainless steel to go back together. Checked the Passagerside to make sure and that one was, of course, sound. Will let you know how it progresses.

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Well done finding it. Would be drivers side I had the same thing a while ago. Once you have worked out how the small stearing shaft comes out and just getting the heat shields and then the manifold off is not easy. I didn't refit the heat shields and have had no problems with heat. Hope you have new bolts and no thread problems. Mine had been butchered on, several bolts were wrong pitch and cross threaded had to helicoil 3 in situ!! nightmare. When I did my head gaskets I ran a tap through every thread on the heads before putting them on the car. The muck that came out was extraordinary. Good luck. Oh and be careful with the gaskets its easy to put them on wrong and restrict the exhaust opening.

Hi Stopover, thanks for the info. I've been a bit blessed with the car as it goes, 2 owners from new ( I'm the 3rd) and a service history as long as your arm. Certainly seems to make a difference. The steering rod was a pain - which was surprising since I only fitted it 2 years ago, but as I take out the driverside wheel arch, it all becomes a bit easier. Interestingly, the passangerside manifold flew off the car, the drivers side required the removal of the starter motor ( battery off and easily done once the manifold is free of the engine and front pipes). I did fine that the 12mm socket was binding on the headers on the 2nd lower bolt in from the rear of the car - this happens both taking off and putting on, just a bit short on clearance - loosening all 4 bolts on the 'front' part of the headers solves this though, as the pipe just moves sufficiently to get on the bolt with a long extension.
Yes a very interesting job but one I hope I don't have to do again anytime soon.Hopefully the welder will be able to sort it.

Glad the manifold came out OK, I too wanted to take the starter motor off but as with the butchered manifold bolts the starters bolts are all round and no way to get them out without a great deal of bother so to get the manifold out had to saw through one of the studs this gave enough clearance to get the manifold off without removing the starter motor, and on replacing put in three new ones. Not sure I would bother with welding as there are plenty of good secondhand ones, but your man might be brilliant, hope so. Should have a nice quite car with a bit more umph!