[T3] weird idle dips

[Jim Adney]

On 24 Feb 2012 at 11:41, Chris Sheridan wrote:

> I always use Bosch Points, Condensor and Rotor, sometimes I can't find
> the rright Bosch Cap, but I make every effort to. I use the Bosch
> hi-speed service plugs as recommended in the owners manual. 

Ummm, where to start.... This is gonna be long, but I hope everyone 
will read this carefully, because there's LOTs of misunderstanding 
out there.

Let's go thru each of the ignition components, one by one:

Distributor Cap: Buy genuine Bosch. They will never wear out. The 
only ones I have EVER had to replace were ones that were actually 
cracked or had a broken center carbon contact. Keep in mind that the 
rotor doesn't actually touch the contacts inside the cap, other than 
the center contact. The outside contacts always have an air gap there 
that the spark must jump across. Since air is a MUCH better insulator 
than anything else you could have in there, a little corrosion on 
those contacts doesn't hurt anything. In fact, it probably helps, 
because it narrows the gap. I think it's been at least 35 years since 
I last replaced a Bosch distributor cap. If you want to be really 
nice to your cap, take it off, clean it inside and out, then oil it 
inside and out and wipe the excess oil off.

BTW, if you ever have a cracked Bosch cap, save the carbon brush. 
It's a replacable part that occasionally comes in handy.

Rotor: Buy genuine Bosch. They will last almost forever. In 40 years, 
I think I've replaced only 2, and only 1 on a VW. That one failed 
when the ~5 kOhm resistor opened up. It was 30-40 years old when it 
finally failed. Like the distributor caps, corrosion/burning on the 
tip is irrelevant.

Condensor: Buy genuine Bosch; use an old one in preference to a new 
one. I have never seen or heard of a bad Bosch condensor. Remember, 
Russ told us that Bosch offered a bounty to any mechanic who could 
come up with a failed Bosch condensor. None of the mechanics he 
worked with ever managed to find one. That translates into thousands 
of cars over dozens of years. I never replace them unless they are 
non-Bosch.

FI trigger points: The rubbing blocks on these will slowly wear, but 
if the cam is lubricated, they will last 100-200 kmiles before they 
start to give trouble. Sometimes they get a bit of dirt between the 
contacts, but the contacts themselves never burn or wear. To clean 
them, just slide a clean piece of paper in between them. NEVER use a 
points file on them.

A year or so ago, I finally came up with a way to re-set the FI 
trigger points to their original geometry, to compensate for worn 
rubbing blocks. I do this now to every distributor I rebuild. Once 
this is done, they should be good for another 100 kmiles, if they are 
installed with some lubrication. If you have old ones that you would 
like me to check and reset, I can do that very cheaply.  

Ignition points: I take them out and inspect them. If they are badly 
worn, I'll sometimes file them to get to fresh metal. This is a fair 
amount of work, so replacement is a reasonable option. Nevertheless, 
they should last 6-12 kmiles. If you have any kind of electronic 
ignition, they will last 50 kmiles or more, but the cam needs to be 
kept clean and lubricated.

If the cam has not been kept lubricated, the rubbing block will 
accumulate grit and grind a path into the cam. This path will be 
rough and will cause rapid wear on the rubbing block. Cleaning up 
worn cams is one of the more labor intensive things I do when 
rebuilding a distributor.

Spark Plug connectors: The standard SP connectors have a ~1 kOhm 
resistor built into them. Check these resistors occasionally, as they 
will sometimes open up when they get really old. If they are open, 
replace the connector. If you buy resistor plugs, I have non-resistor 
connectors that will permanently replace the resistor style 
connectors.   

Spark Plugs: Here's where I think we get to the root of your actual 
problem. You say you've been using the recommended high speed plugs, 
and that's probably your mistake. People tend to read that and think 
it will translate into better performance. What you need to know is 
that the SP insulator tip needs to run within a particular temp range 
in order to survive and keep itself clean. If it runs too hot it will 
not survive; if it runs too cool it will soot up and stop working 
right.

My guess is that you're using the high speed plugs and then doing 
rather normal driving. The high speed plugs won't get hot enough in 
normal driving to ever keep themselves clean. Switch back to the 
normal plugs and I suspect your problems will go away. I use Bosch 
W8AC or W8AP, but I hear good things about NGK, too.

I'm guessing that you're using W7ACs and this is your problem. They 
would be fine for racing, but bad for normal use. All my Type 3s have 
normal range plugs and they work just fine, even on our high speed 
highway runs to and from Type 3 Invasions!  They'll work fine for 
those occasional bursts to 100 mi/hr, too.   ;-)

If you spend lots of time at full throttle, and I mean hours, not 
seconds, then you should watch your plugs and change to cooler plugs 
if the insulators on your normal plugs start to look like they are 
starting to melt.

Finally, I'd like to make a plea to eveyone who still has the OG HV 
wire ends that go to the distributor. Those ends screw onto the wire 
and are nicer and better than anything else you can buy anywhere. 
They are NLA from VW and Bosch, so never throw them away. If your 
wires are cracked or so hard that they are about to crack, I sell SP 
wire by the foot, and it's cheap and easy to replace if you have the 
original style dist cap ends.

I have a very few of these OG ends available for sale, but expect to 
pay a premium for them.

> Sounds like I have to be totally diligent with coating the distributor
> shaft with grease - white lithium grease, correct?

Bosch makes a special grease for this. I have small, expensive tubes 
that should last multiple lifetimes, even for me. It's a rather 
sticky brownish grease. I suspect anything will do, but I try to use 
what Bosch recommends. Don't apply too much, you don't want it to fly 
off and get into the points.

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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