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Luftweg

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

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Posted (edited)

Today, I went out to check the grounding of the ICM...  I had left the pin through the CPS supply wire, the night before, so I thought I might check the voltage again.....  

Voila!  It now measured 10 volts...

So, then I thought I might check to see if it turned over...   I had not changed anything in regards to grounds, or anything else...

Yes, it started and ran -- a touch rough, but it ran and didn't stall out (I let it run until warm, then shut it down)....

Puzzling...

I think I'll replace the ICM and Coils with new ones, and see what happens then (I'll still check/clean  the grounds).....  

In any case, I don't think the CPS can be defective (or, maybe it still could be?)...

 

 

Edited by Luftweg
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I've heard of people accidentally getting two of the seals between the ICM and the connector preventing the connector from pulling up far enough to make good connection on the pins. Might want to check that if you have been swapping ICMs.

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Ah, yes... good call... I check

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Posted (edited)

Update:

 

I still have not gotten the car to run smoothly, or consistently.....  and it's getting frustrating...  I've had to move this to somewhat of a side project.

 

I got 2 used ICM/coil packs (from 97 and 07 series II 3800);  one gave no 'kick' at all, and the other one kind of started but then sputtered out.

 

The original Magnavox ICM/coil pack would start -- sometimes -- and even run for up to a half-hour or so, but fairly roughly, and on several of these trials it would suddenly and instantly stall out.

 

ICM tests for the CPS supply voltage, gave erratic results:  sometimes it would be 10 volts; other times (for instance after stalling), it would bounce around, 3v, 6v, etc.

Shaking the wires, seemed to cause jumps in the voltage.

I'm currently suspecting the harness around the ICM connector has some continuity issues in the wires, and I'm in the process of splicing-in the end section from the parts car.

 

If this proves to be fruitless, I'm starting to wonder if the new CPS is indeed defective.

 

Fuel pressure at the rail is 42 psi, although I've only currently tested that while it was cranking (not running).

 

** There's a backstory: last year (since I didn't have time) I made the mistake of taking the car to a local mechanic, who became lost with it... failed to identify the failure of the chewed-up CPS, and was pushing for the ECM..  I balked and towed car back home...  The car was actually running when I brought it to him, but was stalling once it warmed up (and wouldn't restart until it cooled for 10-15 minutes).

Edited by Luftweg

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Back story tells me it is either a failing Ignition Control Module or crank sensor.

 Not directed at you, but I wish everyone would go out and buy and extra coil pack/ICM, try it and put it on the shelf. Then when something like this happens one can try the back stock ICM/Coil Pack and isolate the issue to the crank sensor.

 The problem you now have is that you are buying used ICM/Coil Packs and are unsure if they are any good which complicates your testing.

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6 hours ago, DAVES89 said:

Back story tells me it is either a failing Ignition Control Module or crank sensor.

 Not directed at you, but I wish everyone would go out and buy and extra coil pack/ICM, try it and put it on the shelf. Then when something like this happens one can try the back stock ICM/Coil Pack and isolate the issue to the crank sensor.

 The problem you now have is that you are buying used ICM/Coil Packs and are unsure if they are any good which complicates your testing.

 

The wires leading up to the ICM connector look like they've been skewered dozens of times, and shaking them seemed to change the reading of the voltage to the CPS (but of course -- because sticking a pin through a wire is not the best methodology...  it might be better to check at the CPS connector itself)...  This is why I'm splicing-in the connector and some length of wire harness -- attempting to rule out wire damage, which could also give intermittent symptoms and test results....

 

Since I didn't put on the 'shield'/vibration-mount-bracket, the harmonic balancer can be taken off fairly easy, and I can inspect, (visually) the CPS.

I guess I could run the CPS electrical tests as well (as long as I know the ICM is putting out the 10 volt supply).

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1 hour ago, Luftweg said:

he wires leading up to the ICM connector look like they've been skewered dozens of times, and shaking them seemed to change the reading of the voltage to the CPS (but of course -- because sticking a pin through a wire is not the best methodology...

It seems the write-up on how to test the CPS might have been more harmful than helpful if it has damaged your wiring harness.

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Posted (edited)
16 hours ago, Ronnie said:

It seems the write-up on how to test the CPS might have been more harmful than helpful if it has damaged your wiring harness.

 

Well, the mechanic I had brought it too (and maybe work by previous owner?) seemed to have made a bit of 'swiss cheese' out of some of the wires (I don't think he used a tiny needle/pin)...

This is the guy who told me first the ICM was bad (and I gave him the one from the other Reatta (which was starting) to swap) then the car wouldn't start at all -- even after he swapped back the original ICM... Then he jumped right to ripping the ECM out (but I stopped him), yet he totally missed the chewed-up CPS.... (The car was running when I brought it to him, but stalled after warming, and restarted again after 10-15 min).

I suppose it's also possible that he left other wires and/or hoses loose or disconnected(?)

 ( I might post pictures of the condition of the wires)

 

As far as the probing is concerned, I think perhaps pulling the rubber grommets out from around the wires in the connector (which I was subsequently able to do carefully with a tiny screwdriver) to allow a skinny probe right on the terminals at the ICM, is safer for the wires -- but more time-consuming....

 

The junkyard ICMs are a wild card....  which is why I might simply buy that new Herko, Magnavox-style ICM/coil pack combo (around 65 bucks)...  I could be the guinea pig for that...

I'd leave the Delco upgrade for another time -- once the car is running good.

 

Heat wave outside; not sure how much I'll get to do...

 

The saga continues...

Edited by Luftweg

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I had taken off the harmonic balancer, and visually inspected the CPS, and it appears to be completley unscathed.

 

I have also finished splicing in the harness section before the ICM (I spliced the newest '07 harness section, which uses 14 wires, so I just capped-off the end of the 2 unused wires). 

 

The 'Herko' ICM and coil-pack arrived today; here are some pictures:

IMG_1601.JPG

IMG_1602.JPG

IMG_1603.JPG

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* CPS Testing With Multimeter, And Inconsistent 18x Signal *

 

Well, after I put the harmonic balancer back on, I ran the CPS tests again, partly to make sure the new CPS was functioning properly, and partly to see if my digital multimeter would 'catch' the 18x signal.  I also used the LED test light on both the 3x and 18x signals....

 

First, my Klein digital multimeter was able to catch the 18x signal.

However I was only catching 17 pulses per rotation.

Then, testing with LED test light, I AGAIN only got 17 pulses.

 

So I decided to mark the harmonic balancer with a red Sharpie, at every exact moment that the LED light turned on.

I did a few rotations and refined the marks, then counted them.

 

YES, indeed, there were only 17 pulses.

Not only that, but a few to several of the pulses were not at constant degree intervals.    One interval was about double the degrees of rotation (possibly the 'missing' pulse?)

 

I rotated the crankshaft another time -- very slowly -- and again the LED went on, exactly at  the marks I had made -- only 17 of them.....

 

I think I may possibly have narrowed down the rough running/skipping, to either the new CPS, or the teeth on the back of the harmonic balancer...

It's strange because I inspected the teeth when I had the harmonic balancer off, and they appeared to not be bent or distorted (I had the balancer off to visually inspect CPS, which looked fine)....  

 

Could it be that the new CPS is 'weak' or not robust enough to properly catch all the teeth intervals (in other words, even the slightest variation in tooth alignment is enough to cause a failure in triggering)?  Or perhaps they've been magnetized?...  

 

On the old 89 Reatta (which is now parts car), I had changed the CPS not too many miles ago (maybe 10k?), so I could swap that one in and see what happens... and run the LED tests again.

In any case, when I re-remove the harmonic balancer, I'll take some pictures  and post here.

 

... The pictures below show the readings on the Klein meter, when voltage changes.

 

 

 

 

 

IMG_1620.JPG

IMG_1619.JPG

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I guess that is odd but I've never counted the pulses. I just checked to see if they were there. You have a good meter. My old one I had at the time I wrote the tutorial wouldn't work for testing the CPS. I have since bought a new meter that might work but I've not tried it on the CPS tests. I don't believe it's as good as the meter you have.

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This youtube channel guy shows how to test the CPS when the engine is running, with an oscilloscope analyzer.

 

** This should be recommended as an educational video, to understand the 3800 CPS

 

The 18x pulses are regularly spaced.

Of course, we know the 3x signals are not quite even (because the teeth have different size gaps).

It's apparently the interplay between overlap of the 18x and 3x gaps that indicates to the ICM when and which spark plug fires.

And of course, there are only 3 firings, since this is a 'waste spark' ignition.

 

https://youtu.be/jACyNHl_L1g

Screen Shot 2020-08-01 at 2.48.40 PM.png

Edited by Luftweg
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Condition of teeth on harmonic balancer....   Nothing noticibly misaligned....

 

Below are links to 2 videos.  

One shows condition of teeth, and the other shows locations of pulses (when LED test light came on).

 

 

https://youtu.be/khfjP-BKcpg

 

https://youtu.be/-qJOGWdjLfU

IMG_1622.JPG

IMG_1621.JPG

Edited by Luftweg
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I want to add separately, that I replaced the CPS with the one from the parts car (that CPS only has about 10k miles on it).

 

The engine started almost instantly, and ran smooth (although the valve lifters had drained down, so it was clacking a bit).

 

I will start it again tomorrow to check again....  

*** I should probably not get too ahead of myself trusting that the situation is fixed ***

However, at this point, it appears that the 'NEW' CPS I had bought from Autozone, was probably defective

(the old CPS had been replaced, because it was clearly chewed up by the signal teeth, probably due to poor installation, under a prior owner).  

When I first installed it, the engine started, though it ran just a bit rough. Then over the course of a couple days, starting and running became worse.  

Sometimes it started, sometimes not.  It would skip every few seconds or so, and almost backfire.  

Since it was a new part, AND since it did start initially, and later (half the time), I didn't fully suspect a defective CPS (though I did think about the possibility).

Suspecting a bad ICM, I had tested the voltage feeding the CPS, and sometimes the reading would be low, other times normal.

I went through a series of used ICM/coilpacks:  One was off the parts car, two were off '97 and '07 3800s, and another is a brand new one (the Herko). 

The engine would not start at all with these, but ironically replacing the original ICM seemed to allow the engine to start again -- though roughly.

Finally, I decided for shiggles to check the CPS signals, and that's when I found the irregularity with them (and only 17 pulses for the 18x signal!).

When I put the CPS from the parts car on, I rechecked the 18x and 3x signals;  the 18x signal intervals where seemingly regular now -- and there were actually 18 of them.

 

I should note that I could see absolutely no physical damage to the new, Autozone CPS, upon a visual bench inspection. 

 

 

Edited by Luftweg

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This is the most thorough investigation of the CPS I have seen and am impressed. Is it possible the 18x are the non-pulses, the in betweens?

 

Conventional wisdom says the CPS either works or not, but it appears that over time, we are finding that it is not true. There can be partial failures, or intermittent failures too, making diagnosis much more difficult.

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I admire your dedication to find the source of your problem. Most people would have given up and took the car to a garage or would have sold he car. Your testing went way beyond with I did in the tutorial I wrote. I learned a lot from what you have done. My tutorial was intended to be a basic test to determine why an engine wouldn't start if you had no spark. Your testing covered that and much more. Good job!

 

I've not had time to watch all the videos but I will soon.

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3 hours ago, Ronnie said:

I admire your dedication to find the source of your problem. Most people would have given up and took the car to a garage or would have sold he car. Your testing went way beyond with I did in the tutorial I wrote. I learned a lot from what you have done. My tutorial was intended to be a basic test to determine why an engine wouldn't start if you had no spark. Your testing covered that and much more. Good job!

 

I've not had time to watch all the videos but I will soon.

 * Words cannot express my appreciation of that!....  Although, most people call me persistently annoying...  

 

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