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-   Porsche 911 Technical Forum (http://forums.pelicanparts.com/porsche-911-technical-forum/)
-   -   Bouncing Tach when Cold, and Zap Noises (http://forums.pelicanparts.com/porsche-911-technical-forum/856863-bouncing-tach-when-cold-zap-noises.html)

wwest 04-03-2015 07:22 PM
Quote:
Originally Posted by tirwin (Post 8560961)
OsoMoore,

EMI is not directly the issue (EMI may not even be an issue). Let's break this down.

If we slowed down time and watched the moment the CDI fires the coil, the rotor will (normally) be at the optimum point in it's travel to create a complete path: coil->coil wire->dizzy cap->rotor->plug wire X->plug X.

This is the normal case. There is some resistance along this path. We'll call it resistance A.

The we have the abnormal case, where the current is arcing along some abnormal path. We'll call that path B and resistance B.

In your case, when you first discovered the problem the resistance along path B was lower than path A.

Normally path A should have much lower resistance and always "win" given any other available choice of path.

So the question there is why is your normal resistance path "losing" given that you have an abnormal path that includes air?

You can temporarily fix the problem through insulation and increasing the air gap by moving wires around but that is not a long term fix.

Address that first. It's time for new plug wires. You will have done some regular maintenance you're due for and eliminated a variable.
From looking at the carbon paths/traces on the inside of the distributor between the contact points we must assume the CDI is being fired while the rotor tip is NOT aligned with the contact point. If we look upstream from the "open" circuit (the large distance between the rotor tip and the contact point) we also see arcing. No surprise.

The distributor should NOT vibrate!

wwest 04-03-2015 07:36 PM
Look at the pictures inside the cap in post #1 (if you can avoid the optical illusion).

Not only are there carbon traces between the contact point but it appears the tip of the rotor is scratching the side of the distributor cap.... the source of the virbration?

OsoMoore 04-03-2015 08:00 PM
Quote:
Originally Posted by wwest (Post 8561111)
From looking at the carbon paths/traces on the inside of the distributor between the contact points we must assume the CDI is being fired while the rotor tip is NOT aligned with the contact point. If we look upstream from the "open" circuit (the large distance between the rotor tip and the contact point) we also see arcing. No surprise.

The distributor should NOT vibrate!
The vibration feels like it is happening because of arcing inside or near the distributor. It only happens during the little arcing episodes.

The scratches on the tip of the old rotor were from me sanding it to try to remove corrosion. I haven't seen any marks on the new rotor. I'll look carefully tomorrow.

I'm also going to grab my timing light and verify that the dizzy-coil wire is or isn't firing properly.

Presumably I should see 3 positions of the crankshaft wheel, because it is firing 3 times per two rotations, right?

wwest 04-03-2015 08:13 PM
Quote:
Originally Posted by OsoMoore (Post 8561140)
The vibration feels like it is happening because of arcing inside or near the distributor. It only happens during the little arcing episodes.

The scratches on the tip of the old rotor were from me sanding it to try to remove corrosion. I haven't seen any marks on the new rotor. I'll look carefully tomorrow.

I'm also going to grab my timing light and verify that the dizzy-coil wire is or isn't firing properly.

Presumably I should see 3 positions of the crankshaft wheel, because it is firing 3 times per two rotations, right?
I was referring to the scratches and carbon traces on the inside of the distributor cap in line with the rotor tip travel

tirwin 04-03-2015 08:24 PM
Quote:
Originally Posted by wwest (Post 8561111)
From looking at the carbon paths/traces on the inside of the distributor between the contact points we must assume the CDI is being fired while the rotor tip is NOT aligned with the contact point. If we look upstream from the "open" circuit (the large distance between the rotor tip and the contact point) we also see arcing. No surprise.
That is a possibility and why I suggested that the rotor may be misaligned -- maybe the distributor is off by one or more teeth. Should be easy to verify.

Quote:
Originally Posted by wwest (Post 8561111)
The distributor should NOT vibrate!
Of course it shouldn't. It may be necessary to disassemble and inspect the dizzy but I would try to verify a few simple things first.

wwest 04-03-2015 08:36 PM
Quote:
Originally Posted by tirwin (Post 8561159)
That is a possibility and why I suggested that the rotor may be misaligned -- maybe the distributor is off by one or more teeth. Should be easy to verify.



Of course it shouldn't. It may be necessary to disassemble and inspect the dizzy but I would try to verify a few simple things first.
End play, vertical travel of the distributor shaft..

SmileWavySmileWavySmileWavy Op could not initially seat the new cap, new rotor appeared to be not fully seated, down...

Distributor shaft was for some reason in the "up" end play position?

Pictorially Ops distributor is rotationally very close to the one in my '78.

If you look closely at the rotor tip and the copper "contact" points on the cap it seems obvious that the clear majority of sparks are occurring with the tip properly aligned.

Once it warms up, probably.

tirwin 04-04-2015 04:07 AM
OsoMoore,

Here are the things I would consider looking into further as next steps.

- Failing coil. The coil could be struggling to fire.

- Bad grounds. Check and clean. The spark plug grounds itself by being screwed into the case.

- Bad plug(s). Plug gap too large?

- Failing plug wires.

- Distributor. Verify that the rotor is properly aligned. This is a 5 minute job. Check for vertical and lateral play. I believe you proved the rotor is seated properly the other day.

Worst case, you replace the coil, plugs and wires and it doesn't fix the problem and you have done regular maintenance. But you have also eliminated possible contributing factors so you're closer to narrowing down the problem.

The best path for the electrons is not happening. Don't lose sight of that. It is trying to tell you something.

I'm going to re-read your last post about possible vacuum leaks and respond shortly.

tirwin 04-04-2015 04:37 AM
Quote:
Originally Posted by OsoMoore (Post 8560690)
As an exercise in determining the green wire's damage, I wrapped it in electrical tape and reinstalled the distributor. The spark plug wires are shielded by their braided covers in the area where they run near it, and that combined with the electrical tape and a bit of distance makes it seem likely that it is not receiving any interfering signals.

There was no change - there are still occasional spurts of arcing I can hear, and the distributor vibrates during these episodes.

However I have some more information that may be relevant. After the engine has been running and dropped down to normal operating RPM, a low 'whoooo' noise begins. It sounds sort of like someone blowing across the top of a beer bottle. If I remove the oil refill cap, the noise goes away immediately (and the engine begins to run choppy). I had previously assumed this was unrelated, but after noting the vacuum hose to the dizzy, I'm not so sure.

Is this the noise of a vacuum leak? Perhaps this is confusing the distributor, and thus the ignition system?
The feeling of mechanical vibration should be distinctive.

The low noise does sound like a possible vacuum leak. By taking the oil fill cap off you're making it worse. The engine running more choppy when you do that is consistent with that. The combination of vac leak and poor spark is not good.

Now is the vac leak related to the spark and distributor? It sounds to me like they are separate issues. Does your dizzy have the advance/retard vac ports or just advance? Retard is an emissions thing that affects idle. If you have it, just disconnect it and plug it with a golf tee. The advance vac should not be an issue. The dizzy uses mechanical advance as the primary mechanism and vac is additional assistance. It should not be affecting anything at idle.

So I would focus on addressing the spark issue first and then chase down a possible vac leak next.

That green dizzy wire is starting to look ratty. It is not a question of IF it will need to be replaced, just WHEN.

Sorry if you mentioned this already, but I don't recall. What CDI are you running?

timmy2 04-04-2015 07:00 AM
http://forums.pelicanparts.com/porsche-911-technical-forum/795232-distributor-green-wire-loose-frayed.html
Post 19 for photos.

OsoMoore 04-04-2015 07:48 AM
CDI is a Bosch 0 227 300 004.

I hooked up a timing light and see lots of interesting things. I'll post details when I understand it further, but essentially some cylinders are firing when it is not their turn. And the main coil wire sometimes isn't firing when it should.

The timing light is very awesome!

The rotor seems solidly in place. You can pull it outward a little, but it springs right back down. The markings on the new rotor seem to fall within it's contact point.

OsoMoore 04-04-2015 08:39 AM
Spark plug is showing the dry sooty deposit - not surprising considering the weak ignition or occasionally missing spark.

timmy2 04-04-2015 09:15 AM
Firing when not their turn indicates you may have the plug wires in the wrong spot.
Firing order is counter clockwise from cylinder 1 where the notch in the dizzy body is.
The sticker shows position of cylinders as viewed from above. The arrow points to the front of the car.

http://forums.pelicanparts.com/uploa...1428167552.jpg

OsoMoore 04-04-2015 09:20 AM
I checked the firing order carefully, and they are correctly positioned. Maybe it is arcing over from another's firing time? Or maybe the arc, occurring near my timing light pickup, is causing a strobe at the wrong time?

I got out my big Bentley book and started working through the section. Discovered all my spark plug wires run between 4.01 and 4.09 Kilo-Ohms. They should be 3K! Definitely getting those replaced as soon as they can arrive from PP.

Now that I have a real day with real sunlight and time to think, I suspect this problem will be solved soon! I also looked inside the old cap and can see arc trails in various spots.

wwest 04-04-2015 10:09 AM
Quote:
Originally Posted by OsoMoore (Post 8561578)
CDI is a Bosch 0 227 300 004.

I hooked up a timing light and see lots of interesting things. I'll post details when I understand it further, but essentially some cylinders are firing when it is not their turn. And the main coil wire sometimes isn't firing when it should.

The timing light is very awesome!

The rotor seems solidly in place. You can pull it outward a little, but it springs right back down. The markings on the new rotor seem to fall within it's contact point.
How long does it take for things to warm up enough that the engine runs normal?

Once it warms up, runs normal, have you tried CHILLING the CDI to see if the problem returns?

I don't think that there should be any significant end play, vertical travel, in the distributor shaft. With end play the driven gear tooth angle against the engine's drive gear, would tend to force the shaft upward or downward depending...

Still don't like the rotor tip carbon arc being so near the bottom of the cap contact.

"springs right back down.." with the engine "cold" how much rotor rotation as it moves from the "up" back to the down position.?

Vibrating of the cap may be due to the vertical shaft travel which might also make/break the magnetic field thereby causing extra sparks..

tirwin 04-04-2015 10:37 AM
OsoMoore,

I was working on my car earlier and a thought occurred to me.

An original symptom was bouncing tach. The 6-pin CDI connector has a wire going to the tach in it.

If the CDI and coil are stepping up the voltage, then a change in input voltage will result in a change in output voltage. Maybe this is what is common to the two symptoms.

OsoMoore 04-07-2015 05:10 AM
@wwest - When the engine is cold and idling high, I think it is still doing it's spark thing but I can't hear over the higher idle noise or see any tach activity over the already increased tach from the cold idle. It is when the engine is warm and quiets down to ~900 idle that I can really see the effects. The vertical travel is less than 1 mm - extremely small.

@tirwin - I've re-plugged the 6 pin connector at the CDI. This seems possibly how they are related. I am hoping it will all be clear when these new 3K resistance wires arrive on Wednesday.

The worst part of working on your own car is waiting for parts. But I couldn't stomach the extra $50 to get parts two days earlier.

tirwin 04-07-2015 05:36 AM
OsoMoore,

I can completely relate on waiting on parts! I'm in the same boat waiting on a stupid pin to finish the transmission.

Looking forward to hearing your results after changing the wires. Did you go with OEM Berus?

OsoMoore 04-07-2015 07:25 AM
Quote:
Originally Posted by tirwin (Post 8565525)
OsoMoore,

I can completely relate on waiting on parts! I'm in the same boat waiting on a stupid pin to finish the transmission.

Looking forward to hearing your results after changing the wires. Did you go with OEM Berus?
I actually found a shop that makes wire sets for about 1/3 the normal prices. Apparently they buy the connectors and wire in bulk. I read some reviews and they seemed legit, so I went for it.

OsoMoore 04-09-2015 05:19 AM
Got the new wires in, and that didn't solve the problem.

It will run fine sometimes, and then go on its little arcing spree. I'll be watching the wires with my timing light. The spark will be happening at the right position. Then suddenly it starts happening at the intervals when other cylinders should be firing, accompanied by the arcing noise.

When watching the coil to dizzy wire with the timing light, it appears to only be firing at one of the six proper positions. I will examine it more carefully tonight. I think it may be time to take apart the distributor, or possibly the CDI box. If I can steal an oscilloscope I can watch the green signal wire, right?

Here's what I am thinking with the oscilloscope.
If I can confirm the dizzy is sending the correct regular signal to the CDI (green wire), then the dizzy signal circuit is OK and I can blame the CDI or the coil. If the CDI is sending the correctly timed wire to the coil, then the CDI and dizzy signal circuit are OK.
And so on down the signal path. Is that right?

tirwin 04-09-2015 05:42 AM
OsoMoore,

You're getting closer. So we know it is inconsistent. Let's talk through other possible causes.

Failing CDI: usually gets worse with heat. try getting a can of freeze spray and see if the condition improves when it cools down. That could be why it seems inconsistent. Do you notice that the coil fires properly at cold start and symptoms worsen as the engine warms up? As we discussed the other day this could be the common element to the bouncing tach wire too.

Green wire: The green wire is the trigger for the CDI to fire the coil. If it is damaged it could be causing the coil to fire before or after it should.

Coil: I don't remember if you had tried a new coil yet. You might want to think about getting one. Worst case you have a spare handy.

Distributor: Internals could be in need of refresh. I would try to rule out a couple more things that are simple first. Dizzy rebuilds are not cheap.

Any chance a local Pelican could lend you a known good CDI/coil to try?


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