Q – I just bought a Boxster S and it has a K & N air filter. My mechanic said that it needed to be serviced. I wondered what your thoughts are on the K & N versus the factory filter? He suggested that I go back to the original dry filter. Pete

A – Well Pete, if you are the one servicing the K & N and if you have extra time on your hands, keep it and buy the kit to clean and re-oil it. However, for my money, I recommend the original dry filter in your Boxster.

Here is my logic: Considering the time it takes (and time is money when you are paying someone else) the cost/benefit ratio does not work out. To get to the filter alone is a chore. Cleaning it is messy and then you are supposed to let it dry after you clean it. Another disadvantage of the K & N is that is uses oil to attract and trap debris. When you consider oil as a contaminant of the Air Mass Sensor on your Boxster, you need to be careful not to over oil the filter. If you do, the check engine light can set and your car might not run very well.

I have a K & N in my Carrera but that is a different application.   First of all, it is a cone (non original) style air filter rather than the conventional “panel” filter. On my older Carrera, there are also a few other factors to consider. My car does not have the same design Air Mass Sensor so a little extra oil doesn’t hurt it. My filter is easy to access. And when I service it, I can leave the car apart for however long it takes to clean it and oil it.   I usually wait for rainy weekends.

Do the K & N’s really give you more power? I defer to the manufacturers literature on that question and I am sure they can, but here’s the rub. When the filter is buried in an engine compartment, where you can’t see it, how do you know when it is dirty?

The factory dry filter has the advantage of releasing some of the dirt into the air filter housing that it collects while the engine is running. The K & N does not. It just keeps packing it in. I think that the benefits of a new K & N are real, but as it gets clogged with crud, what benefit does it have then? Frequently I find these filters neglected due to the hassle factor. Now if you still want to use the K & N, buy a stock filter and simply swap the two during the cleaning/re-oiling process and take your time cleaning it. – MC

My 928 S-4 is really frustrating me lately. I love it, but I am starting to hate it too. This past winter I installed a powder coated intake manifold because the old one was looking shabby. When I got the car out I noticed unpleasant changes. It idled a little roughly and it slammed into each gear on the up shift (it’s an automatic). Changing the transmission fluid made no difference.

Even worse, after I have driven the car for 10 to 15 miles on the freeway and parked it, if I try to drive it after sitting for 30 to 60 minutes, it will start, run fine for about 50 to 100 feet but then die! It will start right back up, idle barely and take no throttle until it goes through a succession stalls, restarts and idle fluctuations. The first time it happened I thought I was going to get creamed by oncoming traffic. So now I don’t like the way it drives and it scares me as well. Help me please, before I sell it. I can’t drive it anymore. –Daniel

Answer – I once had similarly frightening experiences in one of my project cars. When you can’t rely on your car to keep you safe, you can’t enjoy it. That quirky cutting out problem might be tough to find, so let’s tackle the shifting first. A common problem that can cause poor shift quality is low or contaminated transmission fluid, so changing it was excellent preventative maintenance. However that did not cure it, so you need to dig deeper into what controls shifting.

Your automatic transmission has a component known as the vacuum modulator. It gives the transmission feedback from the engine to determine the speed and intensity of the shift. The greater the vacuum signal (low throttle pressure) the smoother it will shift, the less vacuum signal (as in wide open throttle) the harder it will shift. Modern cars’ shifting is controlled via computers, but your 928 was designed in the 70’s.

The modulator can fail by leaking or by getting stuck. If it leaks, it can feed automatic transmission fluid into the intake and your car will smoke. You are not getting any smoke, so it may be seized or have lost the signal from the engine.

To determine if you have a problem with the modulator get under the car, remove the hose, have your assistant press on the brakes and start the engine to see if you can measure vacuum at the modulator hose. If you can, you probably need a new modulator. If you do not detect vacuum, shut the motor off, get back under the hood of the car and check under the intake manifold where there is a vacuum port which you cannot easily see. You will need a mirror and a strong light, two tools that you already have in your arsenal if you work on your own 928. If you find that hose has come off the nipple where it connects to the engine, you have found the culprit.

When you have a vacuum leak at that location, you will get rough idle, that slamming sensation in gears and your fuel pressure regulator will be inoperative in the “full load enrichment” mode. If you are really lucky this could have something to do with that hot running issue as well.

For the cutting out, rough idle and stalling when hot, my first suspicion is a phenomenon known as “vapor lock.” This is very common in carbureted cars but rare in fuel injected cars. Fuel pressure is maintained in the injection system through a series of check valves. In addition, fuel pressure regulators frequently fail and, rarely, an injector may fail. Check valves fail intermittently and this can drive you crazy while you are trying to diagnose them. Most fuel injected cars have numerous check valves. I once had a car that would act just like yours every 20th start or so. On a hunch I changed the check valve; they are cheap and easy to change. Still, the car failed occasionally. It was so bad that I added a micro switch to energize the cold start valve when it happened in order to start the doggone thing! As crazy as it sounds, it got worse and I discovered that the NEW check valve was defective. After replacement, the car started perfectly for the next five years.

The way we finally caught the symptom in the act was by temporarily installing a fuel pressure gauge on the fuel lines with the gauge taped to the outside of the windshield where I could view it in failure mode. Since then, I install fuel pressure gauges early in the process and I don’t remove them until I have had ten solid test starts in a row with no failures.

So this might take a while. And since you do not want a car you can’t rely on, be prepared for a series of long test drives and test starts. I will dig deeper into this for you and by the next issue; I hope to have the answer. –MC

Last month a frustrated 928 owner was considering selling his Porsche since he could not count on it. Here is the rest of the story: After repeated test drives (over 400 miles) a pattern failure of starting and dying become more consistent.   A dip in fuel pressure was noted during hot cranking and attempted starts and a subtle “chattering” sound was heard under the hood.   With the sage advise of “Dave K” (a 928 guru) this led to the suspicion of a failing component in the Motronic computer. We sent the computer to a respected vendor for Porsche ECUs for evaluation. Their testing revealed NO PROBLEM FOUND with function. They did note that the circuit boards inside the metal box were not for the vehicle and therefore on-board diagnostics would not work, which we confirmed. With this information, and with a correct circuit board installed, our diagnostic computer would “talk “and the car performed perfectly.   To quote the owner, “in the three years I have owned the car, it never ran better and the symptom is completely gone”.   To hear that the computer repair shop could not duplicate the problem did not surprise me since the car had to be driven many miles before it happened. The ability to scan the car for trouble codes and install the correct computer was a viable risk to take and it paid off.   He is no longer selling it and the car is now getting a new interior.   MC

Q – The brakes on my Cayman S are testing my resolve. I admit that I use them hard. I do not abuse them, well OK, I did once, but it seems like no matter what I try, they fade after a few hot laps. Driving this car is the joy of my life, it is a fabulous car but I have tried everything. I roasted my red calipers until the red turned “burnt umber” (from my Crayola days). The caliper seals were shredded and I had them replaced, I installed titanium heat shields, GT3 air ducts, flushed out the brakes after every event and I use the best fluid I can get.   Most recently my master cylinder began to cause a soft pedal and I replaced that too. Still my brakes are fading!   Tim

A – It sounds like you have suffered. Your frustration is very clear. After a test ride with you on the track, I don’t think it is how you’re driving. My opinion is that you have made all the right choices but one.   It is time to try another composition brake pad.   When you build up so much heat that you red calipers turn brown and you can only get six laps in, you need new pads.   While I do not claim to be a brake system engineer, it stands to reason that the heat which shreds rubber and boils brake fluid will also affect the brake pads coefficient of friction.   To stop you have to have both pressure and friction to get the job done.   If that fixes it, remember which pad works and which one didn’t and let me know. The best advice I can give often results from feedback I get from club members like you. MC

Q—I am thinking or selling my 944 and moving up to a 928. I wonder which one I should choose and what I should be looking for before I take the plunge. –Emil

A—Taking a plunge into the Shark Tank can be a scary and exhilarating process. My thumbnail analysis is to budget two times the purchase price to do needed maintenance and repair inevitable problems that these older classics are prone to. I suggest that any one considering a specific model should join the local Club that is most associated with that model. Join the model-specific community of motorheads who live, breathe, and sleep in that world. One group recommend is the 928 Owners Club. Attending an event geared toward making an informed decision is also a wise move. The local 928 geeks meet once a month at a local watering hole and they are a great group of guys and gals. Yes, wives and girlfriends are welcome.

Q—Should I start my car up when it is stored in the winter time? If so, how long should I let it run? –Chuck

A—I do not endorse starting the car routinely in the wintertime unless you can drive it. Starting it up without a full warm up creates more problems that it solves. During warm up, that metal parts get coated with corrosive chemicals that are eliminated when the system gets up to operating temperature. If you decide to drive it, I would recommend a 10- to 20-minute run to get everything up to temp with a few high rpm romps and some hard stops thrown in to clean the flash rust off your brake rotors. Even if it does not help your car, you will feel better; that is what it is all about anyway. –MC

Q—I am getting ready to put my car up for the winter, just after the color tour. What do you recommend? –Pete

A—This simple check list is all it takes:

1) Wash the car a week or two before you cover it up, allow all the water to evaporate.

2) Clean the wheels to remove all the brake dust before you store the car. Your best bet is to remove them first. When you do, you can clean your beautiful brake calipers with the wheels off. Brake dust contains corrosive elements. You do not want that on your wheels and calipers all winter.

3) Clean the interior, under the seats, in the map pockets, check the glove box for missing receipts and don’t forget any other compartments as well as the trunk(s).

4) Wax the car. If it needs a good buffing, do that before you wax it. Now that your wheels are clean, wax them too.

5) Use a protectant on the vinyl trim and rubber. Use a leather treatment on the seats.

6) Fill your tires to the maximum pressure allowed and for added benefit, consider tire cradles to keep them from flat spotting. Don’t worry too much about that however, my tires flat spot over the winter and when I get the car out in the spring, it takes a week or two and the problem goes away. It is important to remember to adjust the pressures back to their proper spec when getting the car OUT of storage. I will often write myself a note to that effect and tuck it in front of the steering wheel, so I’m sure to see it when I get in the car in the Spring.

7) Consider a battery cut off switch. If you do not have one, disconnect the negative terminal from the battery until you are ready to fire it up. If you have an electrically operated front hood latch, I suggest that you place something to obstruct the latch. If you don’t, and it shuts, you will have to jump power to get it open in the springtime.

8) Use a modern high quality battery tender, not a trickle charger, to keep the battery up to snuff. If the unit you have in your car was installed by the dealer when you bought it, go online and investigate the wisdom of replacing it with a newer version. Ask me why later.

9) Fill the tank with gas. When the tank is full, there is no air space in the tank which can contain moisture. Put some Sta-Bil in the tank and one can of premium gas line treatment containing isopropyl alcohol.

10) If your car is due for an oil change, change it before you store it. If not, don’t worry about it.

11) Have you had your annual brake fluid flush? Better to do it more frequently than less. Brake fluid absorbs water from the air and letting it sit in the brake system all winter is not a good idea.

12) Purchase a carpet remnant for your garage’s cement floor. This will keep condensation down. –MC

Q–. I plan to have a direct oil feed installed in my Boxster, but I am confused.
Do I still need the LN Engineering bearing? Can I keep my existing bearing? Do you recommend a ceramic bearing? –Pete

A—With the direct oil feed, you may be able to use your existing bearing if it is in good condition. You can also purchase a new standard bearing if your original bearing feels rough or if you want to put a new one in for insurance. I would vote for the new one regardless since the cost is low and you cannot be sure of the lifespan of the original bearing. As far as the ceramic bearing, it is a fine idea and for even MORE insurance, go for it. Is the ceramic bearing actually necessary? I do not think so. The load factor on the original bearing is relatively light and simply supplying oil should make it last the life of the engine.

Q – The wipers on my 1990 C4 just stopped working. I have to drive the car so I am afraid to get stuck in the rain. I checked the fuse and it is fine. Gary

A – The most common problem that I have seen is dirty contacts in the switch itself. I have had some success by removing and cleaning the contacts but first things first. To make sure that the problem is not the motor, remove the intermittent wiper relay in the fuse box. If the wipers work, you can then drive the car until you can have the problem fixed. You will notice however, that they no longer park.

So assuming your wipers now work, you could have a bad switch or failed relay. My vote is to replace the relay first with a known good one and see if everything goes back to normal. The relay is located in the fuse box under the hood and identifying it is easy. The number is 928 615 101 01. If the wipers still don’t work with a good relay plugged in, you may need actual diagnosis and on your car, with the air bag and all, I would leave it to a professional.

On my car, (older Carrera) my intermittent wipers quit working and the park function failed at the same time. My cheesy solution is to park them wherever I want. For me, being vertically challenged, I like them to park on the right side of the windshield rather than the left anyway. On my personal to do list, intermittent wipers are a relatively low priority. – MC

Q – My 944 climate control doesn’t work and I am planning to drive it this winter so it has to keep me warm. When I rotate the fan control knob, nothing happens, it just spins. When I rotate the temperature control, I get no heat. Got any hints? This is going to be my daily driver and I’ve got plans for it but I need to keep the bill at a minimum right now. Calvin

A –       It is a rare individual who plans to drive a Porsche in the winter, and I salute you, sir.   I have driven my 944 in the winter too and it is an excellent car with all season tires and about 300 pounds of sand in the rear hatch area. No problem, except for the salt! Wash the underchassis regularly. But I digress…

The problems you are having could turn out to be quite expensive. For now, I will just focus on getting heat. First of all, the climate control should fail safe in defrost mode, full heat and yours does not. Have you had any cooling system work done on it? Sometimes an air bubble will keep the coolant from flowing through the heater core.  Assuming there are no bubbles and that warm coolant is reaching the valve, to see if the heater could work, disconnect the vacuum hose to the control valve, in the engine bay at the center of the firewall. You should now get heat. The heater control valve is the same part as used on older Audi 5000’s and when vacuum is absent, it goes full open, full heat. If you still get no heat, remove and inspect the valve.   I have seen some where the lever moves but it is not connected to the flap inside the valve.

As far as the fan, sometimes the knob simply breaks free from the shaft. Pull the knob off and see if you can rotate the inner part of the fan switch shaft. If you can turn the fan on…simple, a new knob fixes it. If you only get high speed, the fan resistor might have failed. The resistor fits onto the blower box, driver’s side top and it is one of the easiest fixes for missing fan speeds.

This should get you heat and hopefully by next spring, you can take the diagnosis to the next point and get the temperature control functioning again. – MC