Checking the CAS Voltage.

[Cougar]

There has been a lot of posts here dealing with the Loyale model crank angle sensor (CAS) and trying to determine if there is trouble with it. I have been curious to know if by using a digital voltmeter, in the AC volts mode, if it will show the pulses from the CAS. Since I don't have a Loyale model anymore to check this out myself others have offered to check this out so it may help others later on. My hope is that just using a common digital voltmeter it will be sufficient to make the test with. I know a scope will work but since not many folks own one of them I wanted to try the test this way so more folks would be able to use the test.

 

There are four wires going between the CAS and the ECU. The color of the wires will vary depending on which model you have so just keep that in mind. Checking the DC voltage on the wires, I believe one will have 12 volts on it, another will be ground, and two of the wires will have about 5 volts DC on them. These are the wires of interest for the test. I think one of the 5 volt wires is a reference and may not change at all. The other wire will carry the pulses from the opto-coupler in the disty and this is what I am trying to measure. Here is what I suggest for the test procedure:

 

First find out what two wires have the 5 volts DC on them by checking the voltage on each one with reference to ground.

 

Set the meter to read AC volts. Whatever meter is used it needs to be able to block and DC voltage in the AC mode. Most digitals will do this.

 

Next, place the probes across both of the wires that had the 5 volts DC on them and while cranking the engine take the meter reading and see what it is.

 

Another check would be to measure one of wires at a time and use ground as a reference for each one. Again, while cranking the engine.

 

The results may vary between meters that can read true RMS and those that can't.

 

If someone could post the results of this test from a working engine it would be great.

[Cougar]

Paging Skip or Daeron.... can either of you help out with this?

[Gloyale]

Paging Skip or Daeron.... can either of you help out with this?

 

I'll do it today on my GL Turbo. Still having coffee.

 

 

 

 

BTW, you are the ignition and charging man. Nice project. Good for the USRM

[Cougar]

Thanks Gloyale, I appreciate the help on this. If this works as I think it should it will help others later on.

 

You always post great advice and help for members here.

[hooziewhatsit]

The disk inside the disty has two different sets of slots; one with 360 slots, for each degree, and 4 very large slots for each cylinder, I believe.

 

So, I think the two remaining wires will have those two signals on them.

 

Putting a meter in AC mode should read those signals just fine.

 

-Dave

[discopotato03]

This form of CAS is pretty simple and reliable . All that generally goes wrong with them is the LED device can lemon out . Once your sure that the cap/rottor button/leads are ok there isn't much else in them . I guess you could check the optical disk to make sure it hasn't rubbed and damaged the slots and thats about it .

 

My Australian Factory 87 WSM shows 4 wires that run between the dizzy/CAS and the computer as follows in the round black plug .

 

1) BR Control unit ground .

2) B Control unit (position signal) .

3) W Control unit (reference signal) .

4) R Control unit power supply .

 

I take 1) and 4) to be power and earth from the computer and can't see why you couldn't run external wires for test purposes . The position signal tells the computer in crank degrees where the crank (pistons really) are in the four stroke cycle . The reference pulse tells the computer when its coming up to no 1 cylinder in the start up phase . Until it gets that reference pulse innitially it doesnt have a clue where the engine is as it first cranks over .

 

If I was having problems I'd try another diode pack that was known to be good and if no good go looking for wiring issues .

 

My 2c spent , cheers Adrian in Aust .

[Skip]

Cougar, please let me apologize

We are having our version of winter

and I didn't want/need to brave the snow and cold.

Suffice it to say "I whimped out."

So

I went out to the shed and dug out a CAS dist

from an EA82

 

Armed with it, a cordless drill, my trusty Fluke 77

and some power supplies.

I set up the test shown below.

 

For the pure 5 volt DC supply I rewired some

RC NiCads, for the 12V DC I used a jump box.

Voltages on these were monitored by the

small multimeter shown in the background.

 

I choose to disassemble the dist for clarity.

The slots Dave mentioned can be seen as

can the evil rotor screw.

Cover was replaced for the test.

 

This distributor model number

22100 AA400 D4P86-03 7103

came from a running engine

 

The wire colors are:

red, black - assumed battery voltage

(Note: black showed continuity to dist body)

green, white - assumed test for AC wires

 

Test results below show various

application of the voltages involved

Drill speed was set at approx 300 RPM

 

5 Vdc + on green

5 Vdc - on white

12 Vdc + on red

12 Vdc - on black

 

Fluke - set on auto range AC Volts --> 0 Vac

_________________________________

5 Vdc + on white

5 Vdc - on green

12 Vdc + on red

12 Vdc - on black

 

Fluke - set on auto range AC Volts --> 0 Vac

 

____________________________________

0 Vdc + on white

0 Vdc - on green

12 Vdc + on red

12 Vdc - on black

 

 

Fluke - set on auto range AC Volts --> 0.084 Vac

This voltage varied as a direct function of RPM

 

______________________________________

0 Vdc + on white

0 Vdc - on green

0 Vdc + on red

0 Vdc - on black

 

Fluke - set on auto range AC Volts --> 0 Vac

 

 

It shows the test worked only

when no reference voltage was

applied -- > very odd

or

my entire test procedure is up for question.

Which I will say looks like a bit of a Rube Golberg.

(please excuse the unprofessional appearance)

 

I am sorry for the delay and the whimping out

Let hope Daeron or Gloyal

have better results.

 

[Cougar]

Thank you very much for doing that Skip. I don't blame you one bit for "whimping out" on this. Your test setup is the next best thing to the real thing I would say. I was hoping to see a better AC signal reading on this. My idea may not be of any help here.

[Gloyale]

IIRC,,,,I'm not sure, but I think the Green is the 12v wire. Red and white are Sig and Ref? I'll check.

 

I dropped the ball and didn;t get to the test today. I've got a Festiva that distracted me all day. Not the type of festiva you'd want distracting you though:rolleyes:

 

BTW, does anyone know the test procedure for the pickup/ignition module inside the disty of an 89 Ford Festiva, 2bbl carb?

[Cougar]

To Gloyale,

 

I wish I could help you with that but I don't know.

 

 

To Skip,

 

After looking at your pictures again I noticed something about the slots on the CAS wheel I didn't realize before. It looks to me there may be two seperate opto sensors involved with this which I wasn't aware of. Is this correct? If that is so then I would think that the AC voltage reading should be done with the common probe to ground and the other to each one of the signal lines, one at a time. You may have done that already but I couldn't tell from what you stated on your test.

 

Also it may help to slow the RPM down on the drill. I don't know how fast the rotor normally spins while the engine is cranking but it may be more like around 30 RPM as a guess.

[Gloyale]

Well, it' odd because the Wiring diagrams show the wire colors and position at the end of the body harness. Not the colors on the pigtail on the disty. Only the ground wire remains the same, black.

 

But if you have the car handy for reference here's the corresponding colors on the body side

 

G/B = 12v

 

G/Y = reference

 

B/W + position

 

I do know that power is diagonal to the ground wire on the connector.

 

 

There was also a thread that seemed to discover that some models of dity have the green and white wires switched, and need to be repinned for use in other models(MPFI to SPFI or ice versa) It may have been his own wiring problems though.