Cdi tester

[dicklague]

I have read lots of posts here asking for trouble shooting help on older 911 CDI ignition systems.

One of the first troubleshooting steps is to see if you have a signal from your points, hall effect trigger or other source to the CDI. Basically the CDI is looking for a square wave signal from the trigger source.

I have a tester that I bought to do this. It is a tester made by MSD that puts out such a signal. It looks like this:



This tester works great to test Bosch, MSD, Permatune, any CDI.

I bought mine used on eBay, but it still was not cheap. New they cost $250 to $300. OK for a shop that is doing CDI work, but a little steep if you are using it to solve your CDI problem one time.

I have been looking at a BUILDING much cheaper device that will do the same thing. My theory is that if the price were in the $50 range, 911 owners who have some ignition knowledge would by one for that occasional testing.

What I have in mind is something simpler, maybe no digital readout. This would be a high quality rugged tester that will last for years, but more basic than the MSD.

My question is does this make sense to other Pelicans that have needed this type of tester. Would be pay $50 dollars or so for it?

Let me know. If I get some positive response I will release more details soon.

Thanks.

[boyt911sc]

I would buy a tester for $100 if it could diagnose a Bosch CDI condition. How would this tester evaluate a bad unit from a good one or vise versa? Just plug and read? Keep us posted.

Tony

[dicklague]

thanks for the feedback. It is not a diagnostic computer.


this tester substitutes for the points or depending on year of 911 other trigger systems.

If the CDI works with the tester installed you have a point or trigger problem. If it still does not work you have a CDI or Coil problem.

Coil can be tested with an ohm meter to eliminate if it is open or grounded.

[boyt911sc]

Dick,

The SC's have ignition rotors and no points. Would this tester of yours be able to distinguish a bad CDI from a good one? The two (2) most common CDI's used in 911 cars are the 3-pin (pre-'78) and 6-pin CDI ('78-'83). Aside from switching a good working unit in place of a 'suspect' CDI, a typical DIY'er won't have access to sophisticated electronic equipment to measure the square wave except for a few electronic guys.

I was thinking of something like they use to test electrical outlets. Plug the gizmo and it indicates by the light/s which wire is wrong or everything normal. Keep up the good work.

Tony

[patz]

Contact Ingo, "ischmitz" on the board, he's in Santa Barbara. He can diagnose and repair your box or exchange for a rebuilt with a warranty.

[T77911S]

it does sound like a good idea, cheap is the key. points guys dont need one.

its not really a square wave out of the dist.
the signal has a long slow ramp up then a very fast or sharp transition from + to - with a long slow ramp back to ground. here is something else that many dont know. the MSD needs the sharp transition to be from - to +. the bosch needs + to -
the sginal out of the dsit may depend on the rotation of the dist. (CW or CCW). i know on my 930 with CCW rotation the sginal i s upside down so i had to flip the wires to get the correct signal into the MSD.
one other thing about the MSD, it has an LED on it that shows the signal from the dist.

i would think a tester to check tha output o fthe dist would be easier and cheaper to make.

[boyt911sc]

Originally Posted by patz

Contact Ingo, "ischmitz" on the board, he's in Santa Barbara. He can diagnose and repair your box or exchange for a rebuilt with a warranty.

patz,

I know Ingo and spoke to him many times. He's very knowledgeable and very accommodating. But this post is all about a tool for DIY'ers application being proposed by another member. Not only is your post unnecessary, I find it 'rude' and offending to the OP.

Tony

[mysocal911]

Originally Posted by T77911S

it does sound like a good idea, cheap is the key. points guys dont need one.

its not really a square wave out of the dist.
the signal has a long slow ramp up then a very fast or sharp transition from + to - with a long slow ramp back to ground. here is something else that many dont know. the MSD needs the sharp transition to be from - to +. the bosch needs + to -
the sginal out of the dsit may depend on the rotation of the dist. (CW or CCW). i know on my 930 with CCW rotation the sginal i s upside down so i had to flip the wires to get the correct signal into the MSD.
one other thing about the MSD, it has an LED on it that shows the signal from the dist.

i would think a tester to check tha output o fthe dist would be easier and cheaper to make.

That's correct about the three pin CDI, i.e. a simple test with a test light can determine
whether the points signal is O.K. From the standpoint of testing the six pin CDI
signal, a simple ohms test (~600 ohms) and an A.C. voltage measurement
(~.50 - 1.0 A.C.) are all that's necessary. Let's not over-complicate the issue!

[dicklague]

What I am proposing is a cheaper version of the MSD tester. Something that will do the same job but for a much lower price. Hopefully at a price that would be attractive to the DIY Porsche guy who needs to trouble shoot a CDI system once or once in a while.

The testing could be on a workbench with a CDI unit, a coil, 12 VDC, and a test plug.

The test plug could be one like this:



Or and adjustable one:


You would attach this test plug to the output of the coil. The proposed signal generator would provide the "points" or ignition signal.You can visually see the spark that the system is putting out.

Of course this could be done with the components in the vehicle and the engine not running. If it operates properly, you know your CDI and coil are operating.

As mentioned the points or trigger input can be measured with an AC volt meter.

I am not proposing a one shot tester that will light up status lights. that would be nice, but you would never recoup you development costs due to a limited market.

[dicklague]

An update on the CDI tester idea.

I have been working on a unit that basically is a square wave generator. Same concept as the MSD unit but at a fraction of the price.

The idea is to have a square wave to trigger the CDI so that you can see if the CDI and coil system is working.

This can be done in the car or on the workbench. The tester could be used to troubleshoot other items that use a square wave input like a tachometer for example.

Currently I am working on a unit that can put out a single frequency and another unite that has 2 fixed frequencies. These frequencies would correspond to idle and high RPM like 10K.

The single frequency could be 2000 RPM.

Packaging would be a small case with 3 wires coming out of it with alligator clips on the end. Red and black for power and ground, and third white wire for square wave signal output.



I am shooting for a less than $50 retail price on these simple, but I feel very handy testers.

[dicklague]

This is a prototype unit that is single frequency. It has a red LED pilot light to tell you it is working. Wires have alligator clips for power, ground and output.





Here is the generator in operation with the output going to an automotive tester that is showing RPM output. Multiply this X 10 for actual RPM.....so this would be 1870 RPM. In the production unit we would adjust this to 2000 RPM before shipping.

I would love some feedback on what I have come up with so far.

THANKS.

[boyt911sc]

I have six (6) Bosch CDI in my inventory and they were all tested good but I don't have a bad unit. If your device could differentiate a bad one from a good one or vise versa, I'll be happy to get one. But it is not clear at this stage what set-up or accessories would be needed to make the test using your device. Keep us posted.

Tony

[dicklague]

Originally Posted by boyt911sc

I have six (6) Bosch CDI in my inventory and they were all tested good but I don't have a bad unit. If your device could differentiate a bad one from a good one or vise versa, I'll be happy to get one. But it is not clear at this stage what set-up or accessories would be needed to make the test using your device. Keep us posted.

Tony

Tony

I will post a photo of the set up.

What you need is:

1. a 12 volt power supply that puts out 5 amps or more.....could even be a jumper from a car battery.
2. CDI
3. Coil
4. plug wire from coil to spark plug or tester.

and of course this square wave generator.

I will do a photo in today of the bench set up.

Thanks for your interest. Maybe I should make you part of my testing program. You sound like a prime candidate.

Dick

[dicklague]

Here are a few photos of the bench test set up.
This shot shows the overall set up. I have a 12vdc bench power supply and the leads for this are at the top right. Black leads are -12vdc, red are +12vdc. Large red is the high voltage wire from the coil to the plug gap.

The coil used here is a NOLOGY transformer type coil of course any coil that works with the CDI can be used.

The white wire goes from the square wave generator to the point/trigger input on the Bosch 3 pin CDI.

This test can also be done with the CDI and coil in the 911 with the engine not running. Just disconnect the center wire on the rotor and hook that to the spark gap.




This is a little closer. Of course the black box with the red LED is the prototype basic square wave generator. This one is set for 2000 RPM on a 6 cylinder engine.




In this shot you can actually see a nice fat spark from the CDI which indicates the the CDI and coil are working well.

[boyt911sc]

Dick,

Could you show similar demo for a 6-pin CDI? My interest and curiosity is in 6-pin CDI diagnostic test. Thanks.

Tony

[ischmitz]

This is what I use, a simple signal generator around an NE555 and some parts I had floating around. It can do 3-pin, 6-pin, and 8-pin and can simulate 2 different RPMs.



I always wanted to make something nicer and one day I will. I have tons of ICL8083 and am thinking of a sweeping generator that runs the RPM between 600 and 6000.

ingo

[dicklague]

Originally Posted by boyt911sc

Dick,

Could you show similar demo for a 6-pin CDI? My interest and curiosity is in 6-pin CDI diagnostic test. Thanks.

Tony

I don't have a 6 pin around right now, but the connections are similar



With the CDI on its back on the bench, left to right:
1.brown & brown/white (Coil - and ground), 2. purple/black (tach), 3. black (green wire coax shield in heat shrink)

Bottom row Left to right:
1. White to coil +, 2. Red (power from white T connector), 3. Green (green wire coax core)

so the bottom row on the 6 pin is the same as the demo.

Only difference is the BROWN & BROWN/WHITE is ground. In my demo it is clipped to the case lug. For the 6 pin you would connect ground at the upper left connector.

[dicklague]

We are working on a multiple RPM model and have a prototype at the present time.

[dicklague]

Originally Posted by dicklague

I don't have a 6 pin around right now, but the connections are similar



With the CDI on its back on the bench, left to right:
1.brown & brown/white (Coil - and ground), 2. purple/black (tach), 3. black (green wire coax shield in heat shrink)

Bottom row Left to right:
1. White to coil +, 2. Red (power from white T connector), 3. Green (green wire coax core)

so the bottom row on the 6 pin is the same as the demo.

Only difference is the BROWN & BROWN/WHITE is ground. In my demo it is clipped to the case lug. For the 6 pin you would connect ground at the upper left connector.

maybe this is more clear from and Early S Man post:

Here is the pinout looking into the connector with the mounting flange sitting on the hand or table ...

. 31/1 ... TD ... 31d

. A . . . . 15 . . . 7

==============

31/1 -- Power ground
31d -- Signal ground [green coax shield] for trigger signal

15 -- +14 Volt power lead

7 -- Trigger signal from distributor magnetic pickup coil

TD -- Tachometer Drive signal

A -- +460 Volt pulse output to coil
__________________
Warren Hall, Jr.

[timmy2]

Just received a tester from Dick to try out for him.
I need to find a spare coil as my old one has mysteriously vanished....?
On first glance the unit is nicely constructed and looks better than the prototype.
I will get set up and test it out on a spare 6 pin cdi I have and report back.
(Once I find my coil.. GRRR)