Before I take the Porsche in for another smog test, some work needed to be done. I went ahead and removed the dead car battery to get it properly charged. I noticed some extra wires on the positive terminal, one with an inline fuse. I suspect they are for the radio (some evidence of an amp) and maybe alarm. When attempting to recharge the battery, my battery charger, a fairly nice Black and Decker, insisted it was fully charged. I set it up on a reconditioning cycle in hopes it might bring it back to life. I speculate, especially since I am convinced the seller and Tif’s covered everything up, that the battery has been discharged many times. Reconditioning is intended to break down oxides that build up on the surface of the lead plates. I have read that deep discharging can accelerate the formation of these oxides. Luckily after a couple hours on the reconditioning cycle the, battery was able to accept a charge. I had a suspicion that the battery was not holding a charge well as the voltage gauge in the gauge cluster registered at 12 volts, even when driving (maybe my alternator is struggling too).

With the battery charged I proceeded to replace the spark plugs. I chose to go with NGK Iridium IX spark plugs. The people that know me well know that I usually choose the best when I can, especial on cars I care about. There were several plugs with a colder temperature rating than stock but since I am not looking to run any extreme modifications (turbo or supercharger) I went for the stock heat rating, part number BPR6EIX. The spark plugs I removed, NGK R BPR6ES, looked alright. Speaking with a friend that can read spark plugs like a guru, he came to the conclusion than the engine is running very well. Service records showed the plugs were last replaced 30k miles ago, and with such a mileage, the plugs are in great shape. Cylinder 2-4 had oil pooled around the plugs, which suggest a leaking valve cover gasket. Since the oil appeared clean, I was not too concerned as that will be addressed when I do the timing belt.

To aid with work on the car, I bought an underhood work light from Harbor Freight. Not exactly a byword for quality, but this lamp has been reviewed by several magazines and received high praise. It’s not overly bright but does the job. The light has a flexible magnetic attachment that works very well. The magnet is very strong, so I was cautious when attaching or removing it from the hood as it might cause a dent on thin metal.

I then proceeded to install the new spark plugs. I have read that NGK spark plugs do not require the use of anti-seize on the threads as they are coated with nickel to prevent galling. Using anti-seize on such threads can cause over tightening when torqueing to the specified torque value in the service manual. I chose to use anti-seize as it is good practice to fully prevent galling during removal. To ensure no damage occurs during installation, I used the NGK’s recommended ½ turn after hand tight. This method utilizes thread pitch to ensure proper clamping force, as opposed to using a torque wrench that is dependent on the friction at the threads. Prior to installing the plugs I also put dielectric grease on terminal points of the plugs where the leads contact. This will prevent any corrosion or potential arcing during use.

After installing all the plug wires I then replaced the air filter. The previous owner installed a K&N air filter, although it appears he chose to not service it. The opinions on using a K&N filter are mixed. The reduced flow restriction is a plus although that comes at the cost of reduced air filtration. In addition, the oil that is used when preparing the filter can coat the mass air flow (MAF) sensor that is immediately behind the air filter. This has a negative effect on the air metering which affects the engine performance as a whole. I chose to go with the OEM Mahle air filter, especially since my main goal is to pass smog. I also sprayed the MAF sensor with a sensor cleaner to ensure it can accurately measure the air flow, although it did appear to be very clean already.

The final and most difficult step to prepare the Porsche for smog was the oxygen sensor. The oxygen sense on the 968 is located right before the catalytic converter. It’s very inconveniently wedged between the floor pan and the exhaust. I purchased a special socket to assist with the reduced access, but when attempting to use it, it made the situation worse. The placement of the attachment point to the ratchet was on the wrong side, closer to the floor pan. I went ahead and gave it a go with a regular crescent wrench, and there was just enough room, from the driver’s side, to make to make it work. The location of the oxygen sensor connector relative to the oxygen sensor is rather odd on this vehicle. The connector is at the top of the engine bay, aft of the intake manifold, while the sensor is two feet away. To ensure I got the sensor cable routed properly, I used safety wire to fish it up to the connector following the old sensor. I dropped the car off the jacks, and the Porsche was ready for what would hopefully be the final smog test.

I started the car up, and it was noticeably smoother than before. I headed over to Poway for the smog test, but this time I decided to take a long way around. This would ensure I was driving on the freeway for half an hour and 15 minutes on the street. Everything was going well on the drive although the coolant temp was always low and did not want to budge even if I tried. I could only suspect it was partially caused by my cycling cooling fan, although it also resembles a stuck thermostat. When I arrived at Poway Smog Station, I had to wait about half an hour as there were many people there. During that time, I waited anxiously as my car cooled after my drive. I kept it idling to maintain as much heat as I could. When the car finally got on the rollers, my adrenaline was intense. The test began and finished without running the full time, which usually means it passed. It wasn’t until I got the paperwork that I was relieved. Finally! I can begin to work on the car without any time deadline.

To my surprise, the 968 passed with flying colors. The NOx reduced from 633ppm to 78ppm at low speed. I suspect that the largest difference was made by the oxygen sensor. Goes to show, before replacing a seemingly bad catalytic converter, replace the cheaper components first. It’s a common misnomer that the oxygen sensor does not need to be replaced unless an engine code says there is a fault. In reality, over time, the sensor becomes sluggish and does not function as intended. Luckily I did not have to resort to a new catalytic converter.

Part Numbers:

NGK IX Spark Plugs – BPR6EIX

Bosch Oxygen Sensor – 13011

Mahle Air Filter – LX407

Harbor Freight Luminar Work 120 LED Rechargeable Under Hood Work Light – 60793