Distributor Cap Resistance

[86 911 Targa]

^^^^^
Per the Bentley.


Measured value.
^^^^^
The cap is new.

So, what is the correct value?
Is there a resistor in the tower connection?

Thanks in advance,

Gerry

[DRACO A5OG]

I usually check the OHMs on the Rotor, if bad I replace as a pair. Nearly Zero, WTD??? If you are an optimist, 0.4999 would be nearly Zero right or would that be nearer to zero???

[86 911 Targa]

Don't know.

But, according to the Bentley, it sold be a short. 0 Ohms.

I am replacing both the cap and the rotor.

G.

[DRACO A5OG]

Hey Doc, check OHMs on ref & speed sensor.

If you like you can place your DME in my car to insure that is okay too.

Let me know,

J

[john walker's workshop]

Pull out the carbon and spring and check it.

[rick-l]

Well that was interesting.... I had an old cap sitting here

1. 5.8 k Ohms (variable reading)
2. 1.048 k Ohms
3. 1.026 k Ohms
4. 1.138 k Ohms
5. open
6. 1.58 k Ohms

Center was 5 meg

The numbers are just from a line on the side of the cap

[86 911 Targa]

Originally Posted by john walker's workshop

Pull out the carbon and spring and check it.

Why would there be a carbon resistance in the center coil tap?

RFI?

Back to my original question, is the Bentley wrong?

G.

[john walker's workshop]

Originally Posted by 86 911 Targa

Why would there be a carbon resistance in the center coil tap?
G.

Less than perfect contact between carbon, spring and terminal. Basically a non-problem.

[T77911S]

i just checked mine at it was 25 ohms

[bdonally]

Resurrecting this older thread - What should the cap resistance be?
Manuals say replace if the resistance is not near zero.
I have checked two Bosch 1235522368 caps and the resistance is 1025 ohms, +/-50.
That is consistent enough to make me wonder if the manual is a misprint.
I don't understand why there would be a resistor built into the cap as well as into the plug leads.
BTW, the plug leads are all 3K ohms, but the coil lead is zero. I can't find a spec for the coil lead.
Leads are all OEM Beru.

Any insight on this? I suspect I have change a couple of distributor caps unnecessarily.

[proporsche]

i think so too, no need to measure the cap ..i have never done ..never had a reason;-) put it on and drive.....specially new cap as said above

Ivan

[911pcars]

Yes. Throw $$ at it and build up a potential stockpile of parts, in this case distributor caps.

Multiple caps have measured 1K ohms. Some not. I suspect it could be the manufacturer's attempt at reducing RFI (in select markets?) that might interfere with the operation of electronic control units (and indirectly, sell more caps). Put it out there on the internet and see what they say. This bubble is perhaps not large enough to provide all pertinent data.

Sherwood

[T77911S]

does it matter if it is an HEI cap

[Superman]

Originally Posted by 911pcars

Multiple caps have measured 1K ohms. Some not. I suspect it could be the manufacturer's attempt at reducing RFI

My friend Sherwood threw out some stuff I'm not sure I agree with or understand but there is certainly some truth there. Beru spark plug ends have 1K resistance and the spark plug connectors have even more than that. From hazy recollection: 5K?

They do this to avoid radio interference. My car has no radio so I don't care, but I will tell you this: High voltage electricity will excitedly follow the path of least resistance. It will jump tens of centimeters. It will easily jump 1K Ohms. Unless it sees a quicker path.

bottom line: This cap will faithfully pass that signal to that spark plug. Unless it gets dirty inside.

[bdonally]

The caps I have are working; this is really just about clarifying what the Porsche and Bentley manuals say.
It seems that the manuals instructions to replace a cap if the resistance is not zero should be ignored and a spec of about 1K ohms should be used.

[mikedsilva]

What should the resistance be between the post in the centre of the cap (goes to coil) and the button on the inside?
I have 2 caps.. one is showing 1k ohm.. the other is showing 1 M ohm..

[proporsche]

mike.don`t worry about it;-)
Ivan

[mikedsilva]

Originally Posted by proporsche

mike.don`t worry about it;-)
Ivan

Seriously?

[proporsche]

yes..........;-) plus....as John said post #8.......
Ivan

is there a reason other than the book mentioned above???

[eastbay]

I don't get why anyone would use or pay attention to anything in a Bentley manual? It is the Readers Digest of car stuff.


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