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Luftweg

Testing the CPS (3x and 18x signals) with multimeter

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Posted (edited)

Hello, so I have a 1989 Reatta, with a 'crank but not start' situation.

 

I did the tests, but only with a multimeter (I didn't have the test light), with results as follows:

Spark ('NO'); 

ICM power ('YES'); 

CPS power ('YES'); 

3x signal ('YES'; the voltage reading alternated from 10v to zero, about every 120 degrees of rotation);

18x signal ('NO'; the voltage stayed at 10v and never went to zero -- and I turned as slowly as possible so as not to 'miss' a voltage change).

 

On the page with the tests, the descriptions for the CPS signals, only state that the test light should 'flash on and off' (which I extrapolated to mean that the voltage reading should alternate between 10v and zero).

 

My questions are:

1.)  Is there any reason (besides ease of visibility) that a voltmeter cannot be used in place of the 'test light' for the 3x and 18x tests?

2.) Because the 18x signal test on my '89 never goes to zero volts, is it correct to believe that indicates a malfunctioning CPS?

 

Interestingly, compared to my other '89 (now parts car), I noted that the bolt head for the harmonic balancer was not 1 & 1/8", but was 15/16", and that the metal shield for the CPS, and mount for that little damper piston were missing.   Obviously, in the past, 'someone' had removed the balancer and likely replaced the CPS, but did not remount the shield and damper piston (as well as used a different bolt for the balancer!).

 

Well, I appreciate any advice;  in lieu of such, I will be replacing the CPS (and moving the shield and

1 & 1/8" bolt over to the 'newer' Reatta)

 

Thanx,

K

Edited by Luftweg
typos

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I would agree the test light is simpler and perhaps easier than the voltmeter plus it is a simple on-off test that doesn’t require the nuance of the meter. I am guessing what you are calling a CPS shield is the bracket for the little damper shock on the engine? Early 88’s didn’t have that damper but was added as a running change so GM must have felt it was an improvement. Maybe removed to change the serpentine belt?
 

I think we have identified up to three different harmonic damper bolt configurations used over the years but not a definite progression on their use and appear to be interchangeable. Different head sizes and shaft configuration, some have a reduced diameter section and others are full size over their length?

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Most multimeters, digital or analog, can't react fast enough to the almost instantaneous rise and fall of the 18x signal. Nor can a 12 volt light bulb in a standard test light. That is the reason I used a LED to do the test in the tutorial. A LED can react almost instantly.

 

You might be able to set your meter on millivolts and see a blip but I couldn't with my meters. I have an analog meter with a needle, a cheap digital and a really good digital meter and none of them would detect the 18x signal. When I did the test on my car it was starting and running fine so I know the signal was there. I just couldn't see it with my meter.

 

Believe me... I like to do things the easiest way possible. If I could have done the tests reliably with a multimeter I wouldn't have recommended making a LED tester just to do the tests on the crank sensor.  I don't think I would dive in and replace the crank sensor based on the readings with a meter until I was certain it was giving me an accurate reading of the 18x signal. I recommend spending a few minutes and a couple of bucks to make the LED tester.

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BTW, Welcome to the forum Luftweg!

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Thanx Ronnie, I was afraid there was a special reason for the test light....    I'll have to find an equivalent at a different store (since RS is defunct)....

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Posted (edited)

Actually, I should have also asked, if a constant 10v from the 18x signal is even a possible mode of failure.....      

Anyway, I have an LED that I had gotten from Autozone a couple years ago for my flatbed truck (to use as a plate lamp)....  I'm hoping that this has sufficient 'flicker'.....

Edited by Luftweg

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Posted (edited)

So I made a test light...  I used a bright single LED that's normally used for a license plate lamp...   I ran both the 3x and the 18x tests, taking time to turn the crankshaft very slowly...

 

The 3x test passed, again (and the on and off was very distinct), but during the 18x test the light never went off...  I repeated it several times, going as slowly as possible to get a response -- but I never got a flicker...

 

At this point I think it's safe to think the CPS is malfunctioning, and I will buy one tomorrow....

IMG_3205.JPG

Edited by Luftweg

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I would assume the CPS is bad if it didn't test the same way mine did. But I've never tested a bad one so I couldn't say for sure.

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3 hours ago, Ronnie said:

I would assume the CPS is bad if it didn't test the same way mine did. But I've never tested a bad one so I couldn't say for sure.

 

I guess there would be at least 2 modes of failure:  either no signal at all, or a constant signal,....  I took a lot of care to turn that crankshaft extremely slow (like several seconds for each 10 degrees) , and had an assistant staring at LED with me....

 

Well, I guess I'll see soon if this is the reason for the car not starting....

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Posted (edited)

Here are the 2 different bolts from both of my 1989 Reattas....     I will be sure NOT to inadvertently 'swap' the harmonic balancers, or the bolts....  But, I will try to use the shield/piston-mount from the 'parts' Reatta,  on the 'good' Reatta....

IMG_3208.jpg

Edited by Luftweg
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Posted (edited)

Here is a couple of pictures of the CPS that I just removed (yes, I know, I'm slow, but I have other work to do outside)....

 

I think everyone would agree that this CPS is quite physically damaged, and likely to be the cause of the 'no start' (I hope)...

 

Actually, it's probably a miracle that it was testing okay on the 3x signal!

 

IMG_3211.JPG

IMG_3210.JPG

Edited by Luftweg
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I hope you will do the tests one more time when you get the new CPS installed and the engine running to confirm the instructions for testing the CPS are valid.

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Posted (edited)
2 hours ago, Ronnie said:

I hope you will do the tests one more time when you get the new CPS installed and the engine running to confirm the instructions for testing the CPS are valid.

Yes, that is certainly my intention -- if not just to satisfy my own curiosity.... and to see if my 'fancy' digital meter is capable of determining the 18x signal....

 

***  I've got another concern:  I'm trying to get the aluminum holder for the CPS off; I removed the 2 bolts, and can't seem to get it to slide over the pin ....  I may have leave the old holder on

 

thanx

Edited by Luftweg
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I have used a new sensor on the existing frame before myself. The casting skewered by a steel pin is a great candidate for corrosion. Is there something bent in the shutter wheels on the inside of the balancer? 

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Posted (edited)
15 hours ago, 2seater said:

I have used a new sensor on the existing frame before myself. The casting skewered by a steel pin is a great candidate for corrosion. Is there something bent in the shutter wheels on the inside of the balancer? 

  I have inspected the balancer, and there was one that was slightly out, and I carefully bent it back....

There appeared to be a 'scrape' along the side surface of one of the rings, where the sensor presumably touched it (see the sensor pics above, to see the obvious damage)...

 

* However, I'm strongly tending to believe that the CPS sensor had been replaced, and that the clearance was not carefully checked (in other words, it was mis-installed);

I only had the car for six to nine months, before the problem of stalling-after-it-warmed-up arose, which ultimately progressed to a no-start condition.

 

I had already done a Reatta CPS on my other 'older' 1989....  

During the current R&R job, I had removed the shield and brace from the 'older' one -- to use on the 'newer' Reatta (on which they were missing)...  

I also removed the balancer from the 'older' Reatta and inspected the CPS I had replaced (about 5 years ago), and there is no apparent damage...

I remember researching the 'job' at the time, and became keenly aware of the necessity of making sure the 'teeth' were not bent

(of course, they were, because the serpentine belt broke and wrapped around the crank, breaking CPS and bending the 'teeth' on the rings).

 

If I was industrious, I could cut a notch in the frame/holder, and remove it from the pin....  

I WAS trying to wrench it off a bit, so my worry was that I deformed/damaged it -- however I removed the CPS sensor seems to fit in okay, and I don't 'see' any damage.

 

THANX, for helping

Edited by Luftweg
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Mounting the new CPS into the old frame/holder revealed a crooked alignment with the balancer teeth....  

 

Well, I removed the balancer again, and there was a crack in the 'ear' of the CPS mount, because it broke off without much provocation....  

Thus, I needed to replace it, and in doing so, part of the pin broke as well (doh).

 

I'm of the impression that the pin isn't entirely necessary, if the new frame/holder can be installed in the correct location and secured with the bolts...

So I did that, and put the CPS on it....

When mounting the harmomic balancer again, it was not crooked, but it revealed several of the 'teeth' needed to be straightened, which I did...

 

Another cycle of balancer removal and mounting shows that there is no touching of the teeth to the CPS.

Unfortunately, I will have to finish the job Thursday, as I have work to do on Tues/Weds...

 

The saga continues....  

 

IMG_3221.JPG

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Well, I completed replacement of the CPS, connected the battery, cranked it, and it started immediately (and it hasn't been running for many months -- there is a story behind this delay).....

 

It was slightly rough-running, and there was a valve lifter 'tick', so I only initially ran it for 15 seconds and shut it down (there was a loose spark plug wire at the coils, so I secured that).

 

I let it sit for a minute, and re-started it, this time running for a minute...  I repeated a third time, and let it run until it warmed to 180 degrees...

The tick gradually went away, and the engine smoothed out nicely.

 

I guess this confirms the diagnosis results.

 

** I have not yet repeated the CPS tests, with my nice digital meter and LED test light -- however I plan to do that.

IMG_3226.JPG

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Glad to hear you got it running. It's good to know the test I did on my car helped you find your problem.  Will be interesting to see if your meter will perform the tests. At the time I wrote the testing  procedure my meter would not. I'm not sure if I had my newest meter at that time or not.

 

I have considered removing that test for the CPS from ROJ. I have some concerns that someone might get hurt by skipping some of the safety warnings that I wrote into the procedure.

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Posted (edited)
3 hours ago, Ronnie said:

Glad to hear you got it running. It's good to know the test I did on my car helped you find your problem.  Will be interesting to see if your meter will perform the tests. At the time I wrote the testing  procedure my meter would not. I'm not sure if I had my newest meter at that time or not.

 

I have considered removing that test for the CPS from ROJ. I have some concerns that someone might get hurt by skipping some of the safety warnings that I wrote into the procedure.

... Namely, for one, the need to 'kill the kickback' potential by removing spark plug wires?....     You could also put in a strong disclaimer, recommending that it 'only be performed by a trained mechanic'...

Edited by Luftweg
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Posted (edited)

*  Well, I've not done the CPS Tests yet (on a known good CPS) because, after the first night of the car starting (and apparently running smooth), the second day was very different. 

It then started a little hard, and ran rough, with some apparent skipping....

 

I took the spark plugs out and inspected, and they appeared pretty clean (except one was slightly dirtier -- so I cleaned it and replaced that wire).

 

The next day, I swapped the ICM from the other Reatta, and it started, seemingly running a bit better, but not perfect.

The following day, it would not start at all.

Checked spark: NO spark (yes, I know: how could it have started and run after the CPS job, if there was no spark then).

Checked ICM power: 12 volts

Checked power to CPS: only about 6 or 7 volts.

 

That's where I left off, and will address the ground to the ICM tomorrow...  (note: I don't have another ICM to swap... maybe they are both bad, or there is some serious grounding problem?)

 

Oh, just for shiggles, I did visually inspect the CPS, but didn't see any physical problems (of course, I can't see the whole thing with the balancer somewhat in the way).

Edited by Luftweg
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