Jiggling distributor cap affects engine RPMs

[PPPP]

I've been trying to troubleshoot the backfire issue with my new 911. After poking around the distributor I found this. Please see attached video.

https://m.youtube.com/watch?v=mk95fcGsrzA&feature=youtube_gdata_player

[Jonny H]

A couple of thoughts:

The trigger wire at the back of the distributor is very close to a metal oil line. Make sure that it is not touching it and is properly insulated.

Your HT leads are very close to the left hand cooling tin which also is rubbed away to bare metal. I would guess that the spark has a much easier job jumping to the metalwork rather than going all the way to the spark plug.

Look at the engine running in the dark. You will see stray sparks if you have a problem.

[DRACO A5OG]

How does the cap look underneath and are the retainer springs worn/loose?

Post some pics, because vid of dizzy does not look correct at all.

[PPPP]

I have looked for arcing in the dark and have even used a grounded screwdriver to poke around the spark plug wires without finding any issues.The retaining clips seem slightly loose.



...

[Jonny H]

Run!! It's a Marrelli!!

[PPPP]

Originally Posted by Jonny H

Run!! It's a Marrelli!!

That's bad I'm guessing. Auto parts store says they have a cap for $10. Worth a shot?

[gptom]

If the clips are loose, try bending them to tighten

tom

[DRACO A5OG]

Isn't the dust cover underneath missing, it could account the the slop too???

Check parts pdf.

[PPPP]

Originally Posted by DRACO A5OG

Isn't the dust cover underneath missing, it could account the the slop too???

Check parts pdf.

Thanks, I can see on google images for "911 distributor dust cover". Maybe the previous owner overlooked it? What does it look like installed?

[timmy2]

Here is a photo of my dust cover on my '78.

[Jonny H]

Originally Posted by PPPP

That's bad I'm guessing. Auto parts store says they have a cap for $10. Worth a shot?

I refer to the actual distributor, which looks to be a Marelli. The design has the weights up top, just under the rotor. These distributors aren't the best, they have very 'bouncy' points. Several engine builders I know would discard in favour of a Bosch unit. Having said that, this isn't causing your actual problem right now.

If you take the two rotor screws out and remove it, you can see the weights/springs. Might be worth having a look and cleaning them up. There is no dust cap.

[T77911S]

the CD uses ground as a trigger to fire the plugs.
the ground path is thru the plate of the points, dist, eng and back to the CD. i cleaned all this up on my 77 and it helped. my problem was more i noticed the engine would "drop out" if i moved the dist.
i cleaned the mouting place for the points, where the plate contacts the dist housing, the shaft where it contacts the block. it helped a lot.
its just a matter of cleaning the tarnish off all the contact points.

not sure how lose your cap is, but that may be an issue itself.

[PPPP]

Thanks for the picture. Does the dust cover effect the distributor cap in its position when clamped down?

[DRACO A5OG]

I think it does, because it acts as a spacer, without it you may have just too much slop. Verify with your year free pdf file PAG Parts Katalog

[Jonny H]

Sorry, I wasn't clear in my previous post. I meant that the Marelli distributor design doesn't have a dust cap.

[PPPP]

Originally Posted by DRACO A5OG

Verify with your year free pdf file PAG Parts Katalog

Not quite sure what you mean (Pretty new here). Where can I find this part?

Thanks everyone, you guys rock!

[PPPP]

Originally Posted by Jonny H

Sorry, I wasn't clear in my previous post. I meant that the Marelli distributor design doesn't have a dust cap.

Ok, Thanks for that info. It's not supposed to have a dust cap. Maybe the slop is from worn out spring hooks. I'll try a new cap and tweak the spring clips to hold it down tighter.

T77911S: Thanks, I'll trace the ground path from the points plate and clean that up too!

[DRACO A5OG]

^^^ well it appears you do not have a dust cover per design.

Okay well here is the link to your year's PAG Katalog: Porsche Genuine Parts Catalogue - Porsche Cars North America

GO to the bottom and find your year.

[patz]

I doubt that you will get a cap for a Marelli for ten bucks. I doubt that you will FIND a cap.

Run the engine at night, turn the lights off, look for arcing.