the Walnut Diary

It seemed like an easy job now that I had the beauty covers off the engine, so I bought a set of the correct Bosch spark plugs and had at it. I even laid in a new 5/8″ spark plug socket with the rubber insert to help me pull the loosened plugs out of the long tubes which guide them down into the engine.

Yeah, right. The first plug wouldn’t stay on the wrench, so I recovered it with a magnet on the end of a cable/coil arrangement which allowed me to open a grappler down the tube and grab the loosened spark plug. When I installed the fresh plug, the rubber sleeve from the expensive spark plug socket stayed on it, now torqued into the cylinder head. There was nothing to do but remove plug and all, and from then on use the grappler for the handling of loose spark plugs.

My phone provided essential information: torque the plugs to 22 foot pounds.

As I removed the old ones, most looked to be in excellent condition, but #5 and #6 showed some carbon on them. It was time to do this job. #5, for reference, is the spark plug closest to the driver’s side headlight on a left-hand-drive model.

5 through 8 are very easy to change. 1 through 4 are more of a challenge.

After one removes the beauty panels which surround the engine on a Cayenne, the coils and spark plugs are covered by a pair of decorative plastic fingered things which clip and screw on. They significantly reduce injector noise and protect the wiring harness, so they are not just a frill. The only problem is that on the right side, one of the fingers slides through a complex engine mount, and another doesn’t have quite enough room to slide out from under an air pump at the rear of the engine. First use a 30 torx screwdriver to remove the screws holding the fingers down. You’ll need a tiny ratchet and the equivalent bit for a couple of tight spots, but this shouldn’t be difficult.

Needless to say, if you don’t have access to a set of triple-square male sockets, you can’t go any further. There’s this arm which reaches from the right fender well to the side of the engine. A bolt can be readily removed with a 16 mm socket at the head and a 12mm triple square thing on the other end. Then the fender connection can loosen with the same 16 mm socket and allow the torsion arm to fold out of the way. This becomes a routine operation if one is to spend any time under a Cayenne’s hood, but it’s a non-starter if one has misplaced the triple-square male socket set.

The air pump hanging over the back of the engine, one of two, is easily moved out of the way. Just remove three screws (torx #30) and let it flop loose. It’s not fragile. Unfortunately there is an aluminum frame which holds it. It has a machine screw down into the cylinder head, some sort of strange hex bolt, but an 8mm socket will work on it. Loosen that until the air pump mount can wiggle enough to let the finger out from underneath without shattering. Remember that Porsche plastics do not age well and are prone to failure when stressed. I found over several repetitions that if I removed the oil filler cap it allowed the fingers more room to wiggle without twisting. Stuff a clean rag into the open oil filler, of course.

Once you have removed the finger cover, you’ll discover that the coil for the #2 cylinder can’t come off unless you remove the rest of that engine mount. It is fastened to the right cylinder head with four hex bolts, 10 mm on top, and more of those strange green 8mm things below.

Once these obstructions are out of the way, it’s a simple job to remove the coils and change the plugs on the right side. The coils are freed with a 10 mm socket on a small ratchet to back out the the complex studs which one level up held the screws for the fingers. Once they are out of the way (Don’t lose any!) I found that the upholstery tool, a broad, angled screwdriver with a notch in the centre which comes with most screwdriver sets, is the ideal device to persuade well-established ignition coils out of their dens.

*Triple square is like a 12-point Allen wrench.

Once the plugs are in and torqued, it becomes a matter of re-installing the ignition coils. All of the old ones I had removed had 2″ vertical splits in the side that goes down the tube, but they worked well. I had new ones to install, so I cheerfully clipped them in, fastened everything back together, and fired Ruby up.

Ruby’s ignition missed quite badly, so I put the OBD II meter on. P0308, 301, 302. Ulp! Much fussing led to the conclusion that half of my brand new Chinese coils did not function. This led to an interesting afternoon of chase-the-ignition fault until at long last I had it nailed down to just P0308. With a prayer I replaced the new imported coil with the original, cracked coil which had come out of cylinder 8. Ruby fired up and purred.

I can’t emphasize enough how desperate a misfiring Cayenne V8 appears. My son says it has to do with the O2 sensors. If one detects a richer mixture because of a misfire, it leans out the entire bank of cylinders. So tic-tack-toe with old ignition coils and potentially defective new ones is a real challenge. But once it runs, it runs beautifully. It’s more like computer programming than auto mechanics.

Then it’s just a matter of putting everything back together and testing the car on the road. In my case this step occurred a few times before success. After enough repetitions the engine mount and air pump routines become familiar and strangely comforting.

And that’s how you change the spark plugs on a 2004 Cayenne S.

With the new plugs Ruby averages 12.1 litres per 100 km. That translates to a fuel consumption rate of 23.35 miles per Imperial gallon on 91 octane. That’s about what my Volvo 240’s used to do on regular.

UPDATE:  17 October, 2018.  After changing the #2 coil again last week, I re-read this blog entry.  Ruby in summer driving averages more like 11.8 litres per 100 km.  This could be the effect of summer gas.  The new coils sent under warranty were no better than the old coils.  They likely came out of the same parts bin.  I think it is time to go to the dealer and open my cheque book for a set of new, OEM coils, but still I hesitate.

UPDATE: 2 May, 2018. I notified the Amazon vendor that only half of the coils in the batch actually worked. He sent me another box of eight new coils in short order, so I get to try again.

UPDATE: 3 May, 2018. The vendor sent me eight new coils from another batch. They went in and perform flawlessly. I have become rather proud of my Porsche Cayenne tune-up skills as a result of all of the practice.

UPDATE: Mid-summer, 2018. After a month of intermittent and sporadic missing sessions, particularly while accelerating after braking on the highway, #2 began missing so badly that it popped a code and I was able to identify the culprit.  It was quite reassuring to have the CEL reader in the glove box because Ruby acted as if she was dying.  We limped home fifty miles and I had at the engine mount coil again.  Surprisingly, the spark plug was loose beneath the coil, as well.  I had torqued it to 22 lb. not long before.  Could the intermittent misses loosen a plug?  I labelled the defective month-old Chinese plug carefully and switched in a new one from the set replaced under warranty by the Amazon vendor.

Ruby is once again a pleasure to drive, though I suspect another coil failure is in the offing.  It could be my imagination, though, as symptoms are mild.

UPDATE:  October 12, 2018.  Coil #2 failed again.  I got to take everything apart again.

UPDATE:  October 18, 2018  Coil #7 failed in a spectacular manner today with the smell of burnt electronics permeating the shop when I removed it.  Enough is enough.  I ordered a set of Porsche ignition coils from the dealer.