PORSCHE TECHNICAL TOPICS
Technical problems solved
I was mildly concerned, having signed off last month’s how-to story (pages 88–91), that I might have given the wrong impression about the best method of replacing the exhaust-gas recirculation valve in a Cayenne Diesel. To put it another way, that laboriously (and expensively) removing the entire assembly – that is, both the EGR valve and its associated heat-exchanger – was the only way of tackling the job.
My doubts were based on the fact that, while Porsche seems to prefer to sell the two items as one unit (for £654.09 including VAT), the valve itself – the bit that does the work, and thus (presumably) seizes up and causes the problems – is available separately for ‘only’ £265.81 including VAT, plus about £3 for an ‘O’-ring. And in which case the labour cost would probably be for no more than three hours’ work instead of more like seven.
I suggested in the piece that I would be carrying out some sort of basic forensic examination of the first EGR valve that had come off this very same car, back in 2014 – primarily to try to find out precisely what was wrong with it, but also to assess whether or not it could be cleaned and used again. I can now report, then, that attempting to remove the valve alone, with the heat-exchanger still in situ on the engine, would probably be just as time-consuming, and arguably impossible without causing significant damage to the part you want to keep.
The EGR valve is secured to the heat-exchanger by three Torx screws. Having removed those from the old unit, I not unnaturally expected the valve to pull reasonably smoothly out of its housing, but even carefully tapping the former with a copper hammer – which would have been impossible with the assembly still in the car – shifted it no more than a fraction of a millimetre. Soaking the valve with heavy-duty carburettor cleaner, sprayed in through one of the ports, made no difference, either, and in the end I resorted, with the aid of a heavy brass drift and a bigger hammer, to simply hitting it a lot harder.
Whether that will have achieved anything, or even irreparably damaged the delicate electrical components inside the valve’s actuating mechanism, I honestly don’t know. I suspect, though, that however carefully the device is removed and subsequently cleaned, it neither can nor will ever be quite as good as new. And that while your efforts might conceivably get the vehicle going again without the basilisk stare of the CEL, or Check Engine Light (which is an Mot-test failure), the light will soon come back on again. Don’t they always?
Having said that, at least I now know that the valve can – in theory, anyway – be extracted on its own; and that, since it can physically rotate within its housing, albeit through only a few degrees, a combination of determined twisting and pulling, perhaps plus copious amounts of penetrating fluid, might just get it moving. I sincerely hope that neither Robin Mckenzie nor Terry Parker at Auto Umbau have to do this job again – and I’m sure they do, too – but I have a feeling that if it does crop up they might be willing to give this method a go.
When is what might look like a classic so-called bodge most definitely not a bodge? Answer: when in practical engineering terms it is the equal or even the better of what it replaces. And which was in this particular example designed purely for easy and cheap automated assembly, rather than for any security or longevity it might offer.
In right-hand-drive 996model Carreras, and the mechanically almost identical 986 Boxsters, there is a seemingly ever-increasing likelihood of an annual MOTtest ‘advisory’, or even the dreaded failure, due to the now perhaps inevitable corrosion of part of one of the power-steering pipes, visible inside the right-hand front wheelarch. (With the wheel off, anyway, or perhaps turned to full right-hand lock.) The pipe layout in the equivalent left-hand-drive cars is such that, so far, they appear to be unaffected – as, too, seems to be the ferrule on the larger-diameter line in right-hookers, even though it is only a few inches away from the one that does rot.
Unsurprisingly the ‘factory’ way of doing the job, and which we showed in our howto feature in November 2014, is to replace the entire pipe. And that means not only raising the vehicle on a lift, but also then lowering the front subframe a few inches. You – or your chosen specialist – will then have the joyless task of separating the pipe from the steering rack (and also the connection halfway down the left-hand sill member) and, whoever ends up doing the work, of paying for it all. The pipe alone costs well over £200 – and in our experience you might find it quite difficult to obtain from Porsche those required for certain models – and you are probably looking at a minimum of around four hours’ labour. Call it around £600–£700 in total.
The way I would now do it, however, having watched another specialist’s pragmatic approach on behalf of a customer who, justifiably in my view, wasn’t prepared to spend that much on a car that does only a few thousand miles a year, is shown in the accompanying photographs. Tools required: a trolley jack and an axlestand, plus a small pick and a screwdriver. Parts: two wormdrive hose clips. Time and cost: about half an hour (at most) and, if doing it yourself, all of about £5. Or nothing at all if, like many of us, you have ‘Jubilee’ clips beyond number stashed away in the garage. For cosmetic reasons alone do try to use two identical clips, however, and in size terms suitable for the roughly 15–20mm hose.
The technique is made possible by the fact that the aluminium ferrule where the flexible rubber hose meets the rigid steel pipe is itself nothing more sophisticated than a clamping device that, rather than requiring laboriously to be tightened by hand, can be closed up by a machine in a factory in just one swift operation. You could also use the so-called Oetiker clips favoured by Porsche for many other applications, but they too are used purely for ease of original assembly and, as in the Cayenne Egr-valve job that was the subject of last month’s how-to, might here be difficult to tighten in situ. They also require special pliers to install – and even with those are by no means easy to get right every time.
EGR valve is secured to heat dissipator by three Torx screws, but undoing those to separate the two items had no effect, and tapping and levering was going to do more harm than good. A liberal squirt of heavy-duty carburettor cleaner into both sides of the dissipator made no difference, and ultimately the only solution was to secure the casting in a large vice, and carefully but resolutely tap the underside of the valve with a heavy hammer via a non-damaging brass drift – which would have been impossible had the assembly still been mounted on the engine. Most obvious culprit is the carbon build-up that is, of course, going to be the reason why you want to separate the two items in the first place, but even without that they are almost an interference fit – and note rubber ‘O’-ring (middle). And still there remains a flap valve inside the main body (above)
Photograph top left is a common sight under the right-hand front wing of a righthand-drive 996 or 986 Boxster, and the corroded and split aluminium ferrule will likely earn the car an MOT advisory or even a failure. The factory way of repairing it is to replace the entire pipe – as we showed in the November 2014 edition – but naturally that is both time-consuming and quite expensive. Fact of the matter is, though, that the ferrule is nothing more than a cheap and simple hose clip, designed to allow it to be fitted in one swift motion by a machine in a factory – rather than laboriously tightened by hand – and it is perfectly permissible to replace it with two ordinary worm-drive clips; or, in dire emergency, by just one. All you need do is pull away the remains of the aluminium sleeve – which won’t be too difficult – and, after cleaning up the rubber, perhaps, open up and then tighten the new clips. Job done. Photo on the far right shows an air-con hose with one of these ferrules before it has been crimped and thus tightened – and how even here it is permissible to use so-called Oetiker clips instead, although those won’t be particularly suitable for the PAS pipe because of restricted access
The same car had been taken to this independent specialist’s workshop for an air-con check/regas, and possible replacement of the condensers. The latter were long in the skip by the time I got there with my camera, but the state of the main engine-cooling radiators (left) gives you an idea how bad they were. And this in a car with barely 40,000 miles on the clock