Distributor cap. Time to replace?
 

Hi!

I have posted in another thread about my engine problem suddenly dying/hesitating, but the thread really is not getting much attention. So, while trying to figure out my problem and since I cannot simply buy a new set of plug wires due to job issues, I decided to pull the cap.

All six points(?) looked the same. Looks like carbon build up. I carefully took some fine sand paper and tried to clean each point. They are cleaner, but looks like they are pitted. The rotor arm had some build up as well that I cleaned up, but looks fine otherwise.

http://forums.pelicanparts.com/uploa...1172368351.jpg

Thanks for any input! :)

Dave


EDIT: I forgot to do a search first. SmileWavy And, I spelled Distributor wrong :rolleyes:

How many miles/years since you replaced the cap?

Looks like it was replaced 2/91 at 93493 miles. My dad kept all receipts and I have done the same. Car now has 224,500 miles.

Dave

Just looking at the pitting of the contacts and the apparent heat damage around the inside of the cap tells me it's time for a new one. The mileage confirms it. You can make the contacts look shiny again, but the gap between the rotor and distributor will increase possibly leading to poor spark and greater chance of arcing to ground inside the distributor.
I read your post about the engine cutting out intermittently and I don't know that this would be the cause, although it's possible. In my limited experience when I have had bad arcing wires or worn distributor cap the symptoms were misfiring under load and at higher rpms. My cars have not outright stalled though.
For what it's worth, the only time my 911 stalled I traced the problem down to a loose battery connection on the + terminal. Only clue I had to this was that one time it did it for long enough for me to notice that the starter didn't work and none of the accessories were on.
Intermittent failures are the mother of all automotive headaches ( that, and a lack of $$ ) Good luck!

You are way overdue for a cap and rotor replacement. The picture you posted looked pretty bad but I figured I'd ask since sometimes pictures can deceive if the the lighting and angle are wrong. I suspect that a set of wires would help but if you don't have the $ for them you still need a cap and rotor. Have you checked for arcing at night?

You might try using an old trick of spraying a mist of water (in a darkened garage) and see what sorts of ‘fire-works’ are creating havok...

That will tell you grossly something about the condition/location of the aging spark plug wires, distributor cap, etc…

Dave,

That isn't carbon build-up inside the cap at the contacts ... it is erosion, and from that receipt date, yes, the cap needs to be replaced!

Your spark plug wires can be rebuilt -- just replacing the cable with bulk wire from a parts store, hotrod shop, bike shop, etc.

All that is needed is 14 M3 crimp connectors,and aboout 25 feet of bulk 7 mm spark plug cable. The new M3 crimp ends are available at Porsche and Mercedes dealers, and can be crimped by them, sometimes as a courtesy.

Here is a document showing installation details:

http://www.beru.com/download/produkte/TI05_e.pdf

Just to update for any that plan this wire replacement ... the M3 crimp-on ends are pn 911.609.310.00 from the Dec. '95 edition of the Parts and Technical Reference Catalog!

911-609-310-00-OEM Cable Screw for Spark Plug Tube Connection, 911 (1990-98) $1.50

I've always had caps on my DME cars go a long time, and I think people generally replace them needlessly early . . . but 130,000 miles is a long time!

dentist90: Just trying to rule out the possibilities. When the old wires were arcing (and I have no idea for how long) I did not have my current problem. There really wasn't a problem, other than the wires were old, arcing and needed replacing. Positive cable is still taped up with duct tape from track day back in December. Negative is not. I can check tightness tomorrow.

Joe: No, not at night. Arcing makes a distinct sound and I have not heard it while poking around during the day. I will check tomorrow night though.

Jascha: I'll keep that as a last resort for now...

Warren: The current plug wires are Jacobs Energy Core. 8.5mm I replaced them long before joining here. Probably better to just replace them. Thanks for correcting me on the carbon v erosion.

BTW, The first time I started the car after taking the cap off, no problems, but I only let it run for a few seconds. Second time about an hour latter, the car started, but tach bounced about four times - engine idle followed, then went back to normal. Only other time that has happened, was at TRE, when they did the compression test. Then it bounced until they shut it off.

EDIT: I will order up a new cap ASAP, but the wires might have to wait a little longer. Sigh.... Thanks!!!

Dave

My dad never replaced things early. Slowly I am replacing most of the parts that are long time over do. I would replace everything at once, but don't have the means. So, if it ain't broke or life threatening, it will get a few move miles.

Dave: Change out the cap and rotor. Oil your distributor while they are off (do a search-its very easy). Start the car up at night and check for arcing with a fine mist of water (plant sprayer). If you have a bouncing tach, you may have a alternator/charging issue.

Will do. The engine and tach were reving/bouncing in sync. Both times this happened was after the plug wires were touched.

Dave,

When I serviced mine last summer, I changed the dist. cap and rotor among other things. They looked almost new, but I changed them regardless.

If not else, to be able to tell my tech imbecile academic doc colleagues that I have changed dist cap and rotor in my Porsche - all by myself.. ;)

I am still committed to make a silly impression on my Pelican fellow tech experts. :D

Yup...ready to be replaced...

Do you need the Beru tool or will a generic crimp tool work?

For the Pin I could see the generic working but what about the insulation crimp? Almost like a coax connector.

Pelican sells your distributor cap for $13.00. At the rate you're going, that's about 81 cents a year! Who says Porsche maintenance is expensive! :D

rick-l,

I believe you need that specialized crimping tool. They are available, though pricey. Certainly no Pelican without a shop would need one.

Many have said that Mercedes dealer service people will crimp for free after purchasing the M3 connectors. If you already had the bulk cable cut to lengths ...

The M3 screw part is 911.609.310.00 and is available at Mercedes or Porsche dealers, and the dealer can crimp the new one back on the wire! The Mercedes pn for the crimp on plug connector ends is 000.159.1438.

Early S Man: Any spec on that 7mm cable you refer to? Will most parts stores have it, is there a certain brand name to ask for, is there junk to avoid? Having priced the wire sets at a couple places, this looks cheap by comparison. Are the plug and dist ends available as a separate part no.? Thanks, Joe

Dave,

If you like, I will be glad to send you a used Bosch (~30K miles) distributor cap from my now gone (run over by an SUV) ’85 Targa.

I also keep a full set of back-up Beru wires that you can borrow to trouble shoot your electrical gremlins …

Update:

I drove the car Sunday, up on Mulholland and not one problem. I ordered an new Dist. cap and rotor from Pelican and it should be here tomorrow or the next day. Yeah, I really could route the $70.- elsewhere, but I really felt better replacing them with new.

As for the plug wires, I will see what happens with the new cap and rotor. I will replace the wires, but, not now.

Jascha: Thanks for the offer. We'll see how things go for now. I will keep your offer in mind. Sorry about your '85.

Dave

Joe,

The bulk ignition cable needs to be silicone rubber or Hypalon insulated, copper or stainless steel core. Belden, Packard 440, and Autolite SS 550 were good brands to get in the past.

I believe Accell, MSD, Magnecor all have good quality 7 mm cable available.

It has been suggested that a '60s vintage, solid wire core 'universal' $20 - $40 Accell set of wires for any V-8 Chevy or Mopar would serve as donor for a 911 set just by cutting off the V-8 spark plug connectors. By specifying a '60s wire set, the distributor connectors would fit the 911 cap directly. Then all that would be need after the donor wire is cut to proper length ... is to crimp on the six M3 connectors.

I have seen many use bigger wire between 8mm to 10mm for "stronger spark and more performance". Is it true? and is it posible?

While doing several things in my car this weekends, I opend up my cap and wipe them with sand paper since they look ok, yes they have some carbon burn at the tips. But $13 bucks for a set of cap and rotor are CHEAP to make the car run a little healthier. Too bad I need them quick, can't wait for shipping. Does anyone know if I can get them at local autopart stores. Are they ok to use?

Thanks.

As far as I have heard, thicker wires are just more insulation. Many folks change to "performance" wires for the cool colors only to find that they don't work (or last as long) as the standard factory wires. I replace my wires with Bosch and they work great.

Intermittent running can be many things on a DME car.

Did you replace or swap in your spare DME relay?

Check your voltage at idle and at 2500 rpms. It should not be above 15 v (IIRC).

I had an overvoltage that took out a resistor on my AFM and took out my radio. I had 17 volts at idle.

About a year later my DME intermittently died. This took a LOT of diagnostics.

Good luck.

My problem was solved months ago. Turns out it was one of three relays controlling my alarm. I forgot to number them before I switched their positions, but it fixed the stalling. I just need to replace all three relays.

rnln, I have a set of 8.5mm wires on my car. Really can't tell a performance difference.

Dave

slodave,
is it an after market alarm or factory one? Have you ever measure your current lost when key off, door closed? I asked this question because I have this problem and since you were working on your alarm, I hope you did.

It's a Clifford (older). I like it, as it is a keypad and other than the relays, quite reliable. No, there was no indication of a power drain. The car started to either lose power momentarily and then pick up again or it would quit and either turning the key would get it restarted (also had to punch in the alarm code) or worst case it was dead for about 20 minutes, then decided to start up again. It's been a couple of months now and the problem is gone.

Dave

IMHO, if you're asking the question, its time.

I personally believe that cap and rotor replacement should be done fairly frequently. Once those parts have been in service for 12K miles or so, the engine seems to respond favorably when they are replaced. I am nearly stunned that your cap and rotor have been in service well over 100K miles.

I replace my distributor cap and rotor at least once a year (3,000 miles) sometimes twice. I'm sure it's a sign that I could stand to get the distributor rebuilt, but that will have to wait. In the mean time Pelican Parts is making money off me.;)

Let me illustrate. When a 911 is cruising at 3000 rpm, there are one hundred fifty separate high voltage electrical signals going through that cap and rotor on their way to a spark plug. ONE HUNDRED FIFTY lightning bolts PER SECOND. At 6000 rpm there are THREE HUNDRED lightning bolts PER SECOND.

If the distributor cap were clear instead of opaque, it would look like a hellacious lightning storm is occurring in there.

High voltage signals are so excited, and so finicky, that if you take a graphite pencil and draw a line on the inside of the cap from the each electrode to the bottom of the cap, none of your spark plugs would fire.