Diagnose this blip under acceleration please Options

[s13u74cr4]

Sometimes under acceleration I get this slight hiccup. As if for a moment it stalls. Quickly recovers, and only under acceleration. And it seems only when not fully warm. Almost like for a moment it’s fuel starved. I have replaced ALL all the fuel lines, SS lines, so I think the issue is elsewhere just don’t know where.

Link to a video. I don’t think embedding the video in a post works.
Video

[porschetub]

Sometimes under acceleration I get this slight hiccup. As if for a moment it stalls. Quickly recovers, and only under acceleration. And it seems only when not fully warm. Almost like for a moment it’s fuel starved. I have replaced ALL all the fuel lines, SS lines, so I think the issue is elsewhere just don’t know where.

Link to a video. I don’t think embedding the video in a post works.
Video

Check your dizzy isn't gummed up on the top advance plate, after cleaning vacuum check the advance is @ full advance and not leaking ,it should hold vacuum for a reasonable amount of time can't remember off hand but 12 inHg will be enough ,the" suck on the hose trick " isn't enough for a real test, (IMG:style_emoticons/default/beer.gif) .

[mark04usa]

The reaction from your tachometer would indicate ignition fault.

[emerygt350]

The reaction from your tachometer would indicate ignition fault.

Yep, what Mark said.

I would check ALL of your connections to the coil, maybe it has a bad connector that loses it when the motor torques.

Definitely electrical though.

[s13u74cr4]

Check your dizzy isn't gummed up on the top advance plate, after cleaning vacuum check the advance is @ full advance and not leaking ,it should hold vacuum for a reasonable amount of time can't remember off hand but 12 inHg will be enough ,the" suck on the hose trick " isn't enough for a real test, :beer1: .

I did the “trick” which I remember from my VW days and that does work. Got a vacuum gauge thing to see what the pressure is, just need to figure out how to measure it correctly. If I use a bulb to produce the suction it will hold.

When I replaced the vacuum hoses I found that the place the hoses connect was actually loose on the distributor body. I tightened that up but if does not move smooth or easy really like I think it would.

The PO installed a Petronix. I notice the little ground wire is essentially gone. Does it not use one?

[emerygt350]

It could be the pertronix unit, as that is sending the 'ground' to the coil. However, those symptoms are not what you would get from mechanical issues from the distributor like a gummy advance.

[gereed75]

Looks like a Petronius fault to me. They can be glitchy and typically effect the tach signal as you are seeing.

They are great when working but

[FlacaProductions]

That pertronix looks like it's worth a little double-checking of the set up gap. I'd also peel that sticker off the top of it - don't need that floating around in there.

[s13u74cr4]

That pertronix looks like it's worth a little double-checking of the set up gap. I'd also peel that sticker off the top of it - don't need that floating around in there.

Good call on the sticker, didn't even think of that.

Looking at the install manual from the Petronix site, it states the air gap: 0.010” to 0.050”.

That a pretty big variance. Anyone have a more precise one they used?

[L-Jet914]

In the Petronix unit I have in my 74 1.8L, I used the plastic feeler gauge it came with to set the air gap.

[FlacaProductions]

Yes - the pertronix came/come with a small plastic feeler used to set the gap - but i'm guessing it's not THAT critical as long as it's in the range you listed. I'd split the diff and just use a 0.020" feeler.

[s13u74cr4]

No plastic gauge and must not be precise with a range like that. Good call on the median.

Yes - the pertronix came/come with a small plastic feeler used to set the gap - but i'm guessing it's not THAT critical as long as it's in the range you listed. I'd split the diff and just use a 0.020" feeler.

[Superhawk996]

. I notice the little ground wire is essentially gone. Does it not use one?

Yes you need the braided ground strap between the sliding points / Pertronix plate and the fixed portion below it that physically connects to the distributor body which then connects to the engine case.

Your ground path is now dependent on an intermittent ground between moving plates.

[s13u74cr4]

Took out the Petronix and the ground is gone. I read a few threads where it was said you didn’t need it with the ignition. Their manual says you do.

[Superhawk996]

I read a few threads where it was said you didn’t need it with the ignition.

Unless those threads explain where the ground is supposed to come from you can pretty much rest assured they are (IMG:style_emoticons/default/bs.gif)

Every wiring diagram I’ve seen for a Pertronix needs a ground.

Boggles my mind how many people won’t follow the manufacturer directions. (Not referring to OP - mean bogus information all over the internet)

I’ve soldered a few of these in the past.

Desoldering braid (without flux embedded in it) works well for the ground strap.

The biggest problem is getting enough heat into the plates to flow solder. A high watt soldering gun is what I’ve had luck with.

[emerygt350]

Why on earth would you remove it to begin with?

[Superhawk996]

Why on earth would you remove it to begin with?

Just extra parts. Every good Murican’ shade tree mechanic knows the Germans just put extra stuff on these cars that isn’t needed. (IMG:style_emoticons/default/av-943.gif) (IMG:style_emoticons/default/happy11.gif)

[s13u74cr4]

I read a few threads where it was said you didn’t need it with the ignition.

Unless those threads explain where the ground is supposed to come from you can pretty much rest assured they are :bullshit:

Every wiring diagram I’ve seen for a Pertronix needs a ground.

Boggles my mind how many people won’t follow the manufacturer directions. (Not referring to OP - mean bogus information all over the internet)

I’ve soldered a few of these in the past.

Desoldering braid (without flux embedded in it) works well for the ground strap.

The biggest problem is getting enough heat into the plates to flow solder. A high watt soldering gun is what I’ve had luck with.

Couple different threads where I got it wasn’t needed from. In case it confuses others.

www.914world.com/bbs2/index.php?showtopic=305819

www.914world.com/bbs2/index.php?showtopic=322066

[emerygt350]

So you are saying this isn't what is causing your hiccup? Have you checked out the connections at the coil and on the way there? Is there some way to test the pertronix unit?

[Superhawk996]

I read a few threads where it was said you didn’t need it with the ignition.

Unless those threads explain where the ground is supposed to come from you can pretty much rest assured they are (IMG:style_emoticons/default/bs.gif)

Every wiring diagram I’ve seen for a Pertronix needs a ground.

Boggles my mind how many people won’t follow the manufacturer directions. (Not referring to OP - mean bogus information all over the internet)

I’ve soldered a few of these in the past.

Desoldering braid (without flux embedded in it) works well for the ground strap.

The biggest problem is getting enough heat into the plates to flow solder. A high watt soldering gun is what I’ve had luck with.

Couple different threads where I got it wasn’t needed from. In case it confuses others.

www.914world.com/bbs2/index.php?showtopic=305819

www.914world.com/bbs2/index.php?showtopic=322066

Let’s close this out with the “why” and review how it works.

Here’s the overview of the wiring for a Pertronix:


The red wire is +12v power into the Pertronix

The black wire coming out of the Pertronix is what controls the coil - it goes to the coil (-) terminal just like the points used to. This black wire is a switched ground that performs the same switching function as the points. This black wire is not a chassis ground.

So where does the Pertronix get the chassis ground to switch to control the coil or to power the Pertronix?

That chassis ground is coming from the engine case up through the distributor body, then crosses over the braided ground wire between the fixed distributor body and the moving points plate that the Pertronix is mounted to.

Without this chassis ground from the engine case, there is no ground for the Pertronix to switch. The reality is that you will get a partial ground without the braided ground strap but it isn’t a solid, reliable ground. It depends on incidental contact between the distributor fixed plate and the moving plate. This isn’t an acceptable ground path for anything electronic.

Here are the Pertronix instructions (see #10) that reference the need for the original ground to be retained and that the distributor body is the chassis ground.



Now let’s modify the original picture to capture the whole circuit including the implied chassis ground that is the distributor body.