Which one, rebuilt Bosch or Perma Tune CD ignition
 

I won't bore everyone with details, but it was told to me after a flat out coil failure, that the original Bosch CDI box is "sending" to much resistence to the coil, shortening it's life. BTW the entire ignition system on my car is original, except for the sparkplugs. I know I should replace the wires, but for now I need to deal with this CD box issue. A new Perma-Tune box is $534, from our hosts here. At the same time, a rebuilt Bosch unit is $369. What is the recommendation on this? Is the Perma tune that much better to warrant 200 extra. Also, what is the reliability of these rebuilt units? The coil that is in the car now is from another SC, who's owner had recently switched to MFI. Any thoughts would be appreciated.

Whoever 'told' you that preposterous story ... was blowing smoke, pure and simple! It simply makes no sense at all in the context of electronics and the operation of a CDI system! Coils in a CDI system typically die because of 'Flashover' ... when the normal load [spark gap] presented by the spark plugs is removed because of failures associated with the distributor cap or rotor, or the spark plug wires. When given too large a spark gap ... the coil shorts internally.

Was the car in normal operation when the coil failed, or was the 'genius' that told you a tall tale doing some troubleshooting by malpractice???

The following thread gives some basic cautions while doing troubleshooting a CDI system:

http://forums.pelicanparts.com/showthread.php?s=&threadid=203100&highlight=cdi+do cumentation

ps,

I doubt you would bore anyone here with 'details' ... more detail is always better!

Get a rebuilt Bosch CD unit (if you need one, after thorough troubleshooting). I have purchased several on this board for about $150 each. Take Warren's advice, he's the "man" here!

i second that.

Ok here are the details. Shortly after I had bought the car in Oct of '05, the car died on me at a light. It was idling fine, then jusr cut out. I rolled (was on a slight hill) off to a side street. The car cranked, but didn't fire over. I pulled the coil wir off the dist. placed it near a bolt, I had my daughter crank the engine, no spark. Got car towed to my house, pulled the coil off my Mercedes SL, wired it up to the leads in the 911, and it started right up. Bought a Bosch coil through Autozone, put it in, good to go for almost exactly 1 year and approx. 10,000 miles. Did I mentione I like to drive this car? Anyhow, the scenerio for the second coil failure, I was participating in a "run" with other Porsche owners through NY. At a point we pulled into a resturant parking lot to regroup. I was out of the car speaking with other owners, with the car idling. My kids were sitting in the car, when the car stopped running. The person in question that ultimately suggested a faulty ignition box, first ruled out an overheated ignition box by having me retrieve some ice from the forementioned resturant. To shorten this up a bit. We left the car at the resturant and continued the "run", by me and my kids getting a lift from someone who brought his Audi wagon. 3 hours later we returned to the car, tried starting it, nothing. I had the car towed to this gentleman's garage in NY, where he looked at it for me. He suggested that one, the Bosch coil I got from Autozone was a knock-off. Two, that the CD box is causing/sending too much resistance in the system. He gave me a used coil from acustomer's SC that had just been swapped to MFI. Now, as I mentioned before, the car still has it's original sparkplug wires. I know I should replace the wires just due to the fact that they are going on 25 yrs old. However I would really like to know that the coil problem is going to go away, if I replace the wires.

Don't even consider Permacrap.....get the rebuilt Bosch unit from Pelican. Very rarely fails.....I know the rebuilder. Send in your unit as a core.

Well with that said, I would still rather have the problem fixed with a new set of wires, if that indeed could cause the coil to work harder/short out internally. If I understand Warren's comments correctly.

Better yet, get two Bosch units and keep one as a spare. Stay away from the PermaDoom!

"A new Perma-Tune box is $534, from our hosts here. At the same time, a rebuilt Bosch unit is $369. What is the recommendation on this?"

There are those on the forum who cite the mantra, "you get what you pay for". In this case, most folks disagree.

As for the CD unit sending too much resistance - not possible. Resistance can be created to resist current flow, but you can't send it anywhere else, although the thought of connecting the car battery to an IPOD could be considered sending resistance, or creating one. A melted circuit board pretty much guarantees an open circuit (infinite resistance). :)

Sherwood

I have purchased several Bosch CD units from fellow Pelicans for approx. $150 and they are fine. I like to have spares...

Ok, so is there a set value of resistance I should be getting? In other words, how do I check this out for myself. I have a basic voltmeter. I also know that something cannot "send" resistance, possibly he meant there was too much resistance in the CD box. Eitherway, before I buy an electronic part that cannot be returned, I want to know what the problem is. Could the old sparkplug wires be causing this?

I suggest looking at the wires while the engine is running in a darkened garage or moonless night. If you see any arcing or blue 'glow' around thew wires ... then they are leaking energy that should be going to the spark plugs.

The wires should be replaced or rebuilt if you have any visible leakage. Many Pelicans have successfully rebuilt their own wire sets and had good results!

The ends of the OEM Beru wire set unscrew from the black copper-cored wire.

The Beru connector at the spark plug has a built-in resistor of nominal 3000 or 4000 Ohms resistance. That resistance element can fracture and go 'open' so there is no continuity from the wire end to the spark plug end. They can also be intermittent, so that is why I have recommended a 'shake' test where the ends and held tightly to test leads and the connector is shaken strongly.

The distributor end of the wire may or may not have a 1000 Ohm resistance element. Same tests as above.

Replacement screw-on ends are available.

The wire/cable portion can be replaced with bulk cable from many sources.

New wire must have Beru M3 screw terminations crimped onto the end to mate with the factory connectors. The M3 screw ends are available from Porsche or Mercedes dealers, and can be crimped on by them.

Here is a Beru document that illustrates the M3 connector installation.

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

friends don't let friends permatune...

I've pushed my car thru a busy intersection after my brand new, professionally installed Permatune started failing when it got hot under 3,000 miles. I was forced to use the Permatune when my Bosch finally died after 200K miles..

About the only thing I noticed about the Permatune is that the car in fact started quicker, and seemed to have better overall response using that thing. But, what good is any of that if you're pushing the car after it gets hot? I replaced it with a used Bosch unit and it runs like it should.

Moral of the story: Permatune is a false savings, buy the Bosch.

sorry, my permatune has served my 73 well since 1981 when it cost around $75.00. I had to have it overnighted to Watkins Glen when my original Bosch died.
Bill K

I don't believe the "newer" Permatunes are built to the same specs/quality that the older ones were. I bought a new Permatune in 2002 and it failed the next summer (heat-related?) and I replaced it with a used Bosch unit. Lonnie Lenarduzzi (sp?) from PermaTune was very helpful, but the PermaTune CD unit I bought failed several times and didn't work until the temps dropped. No "heat-related" issues from the Bosch unit...

I would replace the wires simply because of age and use a rebuild CDI unit. Come on! 24 years of good service! Give that car some love/TLC...

If you want to go with a different unit get the MSD.

art may be right..could explain the differences in history bewteen older and contemporary permatunes. where does permatune build theirs now? are they made out of the country or are the components bought from out of the country..?

It sounds to me like you just need to replace your coil and be on your merry way. There is nothing in here to indicate a problem with your CDI. I agree you should probably check or replace your spark plug wires.

-Andy

I've had a Permatune in my SC for about 10 yrs with no problems.