1973 Caddy eldorado ignition sores

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1973 Caddy eldorado ignition sores

Postby HC_CDC » Fri May 09, 2014 12:00 am

I could really use some help from people who have scoped older cars with contact points and single coil engines, having problems, this is a 1973 Cadillac Eldorado 500 CID which came in with a bad oil pump and damaged distributor rotor gear according to my client (another workshop). They repaired all the mechanical damage, renewed the distributor and sparkplugs and tested the engine. Car misfired badly. Cables looked and resistance tested OK and water spray test and grounded screwdriver proximity test did not show any problems. They found carburettor had a lot of issues and ordered a new one. After it was installed they asked me to check why there were still a lot of misfires. Scoped it and found that they mounted the condenser for the coil entry on the coil discharge because the points sparked excessively. (They know because they specialize in restoring old Minis). As they know practically nothing about 4 barrel carbs they also needed me, having tuned many old V8s on the dyno.
I never scoped doubtful coils or iffy point distributors yet, was lucky I suppose, they were either good or really bad.
This one runs, could even say very usable, after setting mixtures and correcting the issue with the condenser on the coil feed. Still has slight random misfires though.
Off idle under load road testing car almost seems perfect but then big V8s always seem to be smooth with a bit of load even if they misfire a bit.
I attach primary waveform current and voltage, have really weird behaviour on and before the spark line, and high oscillations after the points open on the coil current line. Parts here not available and thus everything to be ordered in the US but want to be sure, is this bad coil, bad points, bad distributor cap/rotor (new but origin unknown), both or what?
Thanks for your help.
Henk
Attachments
1511 with snap throttle higher idle.psdata
1973 Eldorado V8 primary ignition current and voltage
(4.65 MiB) Downloaded 176 times
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Re: 1973 Caddy eldorado ignition sores

Postby Steve Smith » Fri May 09, 2014 2:58 pm

Hello and thank you for the post. I have attached a waveform from a E-Type Jaguar with traditional points and condenser ignition demonstrating contact breaker arcing (Sorry I do not have a good example). We also have a case study that may be of interest at https://www.picoauto.com/tutorials/jaguarIdleSpeed.html
with poor grounding at the distributor base plate.
I have downloaded your waveform and will take a look over the next few days.
These may help or I am sure there are more out there.......Take care.....Steve
Attachments
20131107-0002.psdata
(3.07 MiB) Downloaded 133 times
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Re: 1973 Caddy eldorado ignition sores

Postby Robski » Fri May 09, 2014 3:23 pm

is the charger on the laptop/PC/battery ?
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Re: 1973 Caddy eldorado ignition sores

Postby HC_CDC » Fri May 09, 2014 9:01 pm

Robski wrote:is the charger on the laptop/PC/battery ?


Thanks for replying. Laptop on battery with extra ground clamp from shell waveform generator connector to car chassis.
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Re: 1973 Caddy eldorado ignition sores

Postby HC_CDC » Fri May 09, 2014 9:57 pm

steve smith wrote:... We also have a case study that may be of interest at https://www.picoauto.com/tutorials/jaguarIdleSpeed.html with poor grounding at the distributor base plate.
I have downloaded your waveform and will take a look over the next few days.
These may help or I am sure there are more out there.......Take care.....Steve


Thanks Steve, yes thinking about it you would expect arcing to give about that picture. Certainly voltage wave looks a lot like the Caddy. The current wave on the caddy is a lot more stable though, although you can see variations of up to a ms in dwell time when you look at individual combustion events. Let`s see what other suggestions and maybe even exactly the same pattern solved by somebody already. Since the distributor is supposedly new (contact area of points did not look like it though) did not consider bad ground there but will certainly double check that soon. Meanwhile decided to order new coil, cap and rotor, contact points and capacitator from the US of A not to delay things too much. Surprised this worked so well back then considering that at 45 degrees dwell you only have 1.5 ms charge time avaialble on the coil at 4000 rpm with single point v8 distributors! No wonder MSD and ACCELL like stuff is so popular in the US, any improvement must be very notable above 4000 rpm.

Thanks again for your time..
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Re: 1973 Caddy eldorado ignition sores

Postby Fat Freddy » Sat May 10, 2014 11:13 am

Steve

Would the 8 and 10 bit resolution settings alter these captures? I have seen injector captures displayed incorrectly using incorrect settings?

FF
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Re: 1973 Caddy eldorado ignition sores

Postby HC_CDC » Sat May 10, 2014 10:32 pm

Fat Freddy wrote:Steve

Would the 8 and 10 bit resolution settings alter these captures? I have seen injector captures displayed incorrectly using incorrect settings?

FF


http://www.picotech.com/education/oscil ... ement.html
“Resolution enhancement is a technique for increasing the effective vertical resolution of the scope at the expense of high–frequency detail. Selecting resolution enhancement does not change the scope’s sampling rate or the amount of data available.”
I assume Steve can explain this better but here is my understanding of the topic.

I found a very good explanation of vertical resolution enhancement in a Picoscope manual I downloaded some time ago just to see what info a more expensive scope manual would give….
Picoscope4262Manual. Don’t remember why I picked that one but anyway, para 5.13 in that manual gives all the details. It is probably also mentioned in other manuals- I recommend you have a look at it.
Basically I sample at spec. resolution and then, when I look at static/saved data and the signal looks very dirty/noisy, I apply the enhancement by means of the probe selector (Channel Options Button) Often it helps to get a better idea of what’s happening using this adjustable filter and I find it very useful that it`s built-in. I find the Pico software incredibly good and I am sure I will find it better the more I discover what I can do with it, and I am not even talking about automotive.
I regret that PICO decided not to give that free for the 2204 as well, missed that when I bought it and now cannot even use it as an expansion unit to a real automotive one I think, still have to dig in to that. Back to the enhancement topic; from what I read it doesn’t really matter how your enhancement is set during capturing because the original samples in un-enhanced resolution remain in the data file and are always retrievable.. Thus this can be applied to an existing file, not so clear from the manual!
Quite often I look at the waveforms taken during a session a lot later and discover info that I had not even given a thought in the heat of trying to solve a problem quickly, this is how I found that you could apply the enhancement on an existing file. Just click on you’re A,B,C,D channel option button and change the resolution as you please, as long as you realize how you are looking at the data. If you applied enhancement it will be mentioned in the info panel on the side. Hope this took away your doubt.
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Re: 1973 Caddy eldorado ignition sores

Postby Fat Freddy » Sun May 11, 2014 9:54 am

Hi Henk.

Thanks for the reply. I ask only too learn so don't take my questioning as criticism. :wink:

Hope this took away your doubt.

Not really. As mentioned earlier I have seen totally incorrect displays of injector captures when it has been displayed (if I recall correctly, it displayed current flow after the circuit had been switched off).

Basically I sample at spec. resolution and then, when I look at static/saved data and the signal looks very dirty/noisy, I apply the enhancement by means of the probe selector (Channel Options Button) Often it helps to get a better idea of what’s happening using this adjustable filter and I find it very useful that it`s built-in. I find the Pico software incredibly good and I am sure I will find it better the more I discover what I can do with it, and I am not even talking about automotive.

Why don't you use the filter? After all that is what it is their for.

http://www.picotech.com/education/oscil ... ement.html
“Resolution enhancement is a technique for increasing the effective vertical resolution of the scope at the expense of high–frequency detail. Selecting resolution enhancement does not change the scope’s sampling rate or the amount of data available.”

It does but if followed up with -
For example, it can boost the effective resolution of a PicoScope 6000 Series scope from 8 bits to 12 bits, and the 12–bit PicoScope 4000 Series high–resolution scopes can deliver up to 16 effective bits. The resolution enhancement is selectable in increments of 0.5 bit.

Your capture is reduced from 12 to 8 and 10 bit.

Last of all is this warning in the software -
Some side-effects will be observed when using resolution enhancement. These are normal and can be counteracted by reducing the amount of enhancement used, increasing the number of samples captured or changing the timebase. Trial and error is usually the best way to find the optimum resolution enhancement for your application. The side-effects include:

Widened and flattened impulses (spikes)

Vertical edges (such as those of square waves) turned into straight-line slopes

Inversion of the signal (sometimes making it look as if the trigger point is on the wrong edge)

A flat line (when there are not enough samples in the waveform)



I understand your theory but just need some input from the Pico guys.

Thanks
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Re: 1973 Caddy eldorado ignition sores

Postby HC_CDC » Sun May 11, 2014 11:50 pm

Fat Freddy wrote:Hi Henk.

Thanks for the reply. I ask only too learn so don't take my questioning as criticism. :wink:

No problem, not offended easily :) ...


Why don't you use the filter? After all that is what it is their for.

I think the filter ads capacitance to the circuit, thus data arrives changed as compared to unfiltered. That would also explain why I can`t find where to set the filtered view on an existing file except by changing the bits. If that with applying the filter is the case you can't remove the filter from the captured data, the question is, does it really matter in this case?

Your capture is reduced from 12 to 8 and 10 bit.


The 2204 is an 8 bit scope, 20V, Freddy. I think I could reduce the voltage range to say 0 to 60 to get more real resolution of the firing line, only not sure if the 200V plus peak (20 after the 10:1 probe really) would not fry the scope which than would be set to receive 0-4 volts. Steve??

Last of all is this warning in the software -
Some side-effects will be observed when using resolution enhancement. These are normal and can be counteracted by reducing the amount of enhancement used, increasing the number of samples captured or changing the timebase. Trial and error is usually the best way to find the optimum resolution enhancement for your application. The side-effects include:

Widened and flattened impulses (spikes)

Vertical edges (such as those of square waves) turned into straight-line slopes

Inversion of the signal (sometimes making it look as if the trigger point is on the wrong edge)

A flat line (when there are not enough samples in the waveform)



That more or less speaks for itself, that's exactly why I use the enhanced view on and off, more or less, on the existing file.

Let`s see what Steve comes up with, I am inclined to take the route of solving the likely problem of the arcing, maybe combined with a small internal issue with the coil. Ordering an electronic conversion kit for the distributor and a coil and just to be sure a cap and rotor again. The cost of all those parts except for the conversion kit, is negligible, the transport charged is what makes it often so complicated, for instance points cost around $5 but transport €30, if its 200 gram or 2 kilos that transport cost stays about the same, so you might as well order whatever you (think you) need for maintenance of that system in one go, sooner or later you're gonna need it anyway-

Once I got the ignition sorted (looking normal) and there is still rough running I can focus on the mechanics.

I see on the forum that you are digging into most of the cases with zest Freddy, learned a few new things looking at it, thanks!

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Re: 1973 Caddy eldorado ignition sores

Postby Steve Smith » Thu May 22, 2014 9:56 am

Hello again and first of all an apology to all. The last line in my post reads “I have downloaded your waveform and will take a look over the next few days” which was 2 weeks ago! No excuses but I have been away training with our new NVH kit which I have to say has been a real revelation.

The burning question I have is, “Have the Cadillac parts arrived and if so how is the engine running?” (Do you any waveforms after fix?)

Thank you so much for all the posts here too as it really has set me off on a quest for answers.

Looking at the waveform from the Cadillac I can see the area of concern surround the “points open” and why the oscillations? This event is also mirrored in the coil primary voltage suggesting current continues to flow (in some form) pointing towards condenser or condenser ground error.

Reading your notes attached to the waveform you have mentioned cleaning the points and installing donor points, and an issue in your post regarding an error in dwell of around 1ms.

This leads me onto distributer shaft bushing wear and “drive error” with “backlash” which are all relevant around the big events that take place at “points open” Whilst the dizzy is new/repaired why the 1 ms variation in dwell? (Food for thought as ever)

Interesting point you raised regarding the dwell period V charge time; I can imagine the issues that unfold at 4000rpm + with the errors above.
In your waveform notes you mentioned “resistance coil wire feed on coil”, this had me thinking about ballast ignition, is this relevant to this vehicle i.e. is it installed?

Looking at comparisons between the Cadillac and the Jaguar, burn times are similar but the formation and quality of the burn on the Cadillac is very poor compared to the Jaguar. Voltage drop across the contacts/points during the dwell period of the Cadillac is good along with the induced voltage, however the max current is down 0.3 amp! I will be intrigued to see the waveform after fix as you have suggested electronic ignition modification.

I do have a question about your current value/shape as it never appears to “Zero” and remains around 140 mA with an uneven current ramp, how is your clamp on other switching circuits?

I will definitely follow up the questions on resolution etc. Still catching up at present.

Thanks gain for the posts to date, take care……Steve
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