Please correct me if I am wrong:

I thougtht the CPS basically housed a Hall effect sensor that picks up the magnets embedded in the rotating gear of the engine. I see on other sites where someone is showing the magnetic strenght of a black CPS versus a gray CPS by picking up a washer. I know its not very scientific, but a crude start.

What is the name of the front gear with the slots?

Are there different slots to help determine cylinder order?

Are there magnets in the slots or does indeed the CPS have both a magnet and Hall effect to read the slot width?

The bracket that holds the CPS had a definite straight edge, is this for a strobe timing light to determine advance like on gas engines?

Has anyone ever read the output of the CPS via an oscilloscope to really see how the different CPSs behave?

Thanks

 

Yeah, tho cps has been a huge item of discussion on here and other sites. They used to say you want the black one, then the blue one, then the gray one, then .... I can't keep up with it anymore. Someone was doing more in-depth testing on them, can't find it now.

 

Yes the CPS is a hall effect sensor, but the magnet is inside the CPS. It reads slots or indentations in the cam gear as it spins. There is a wider groove and a narrow groove that represents TDC & BDC to let the PCM know which cylinder is doing what.

Here's what the cam gear looks like. You can see the top of the crank gear below.

 

Thanks for the info and picture Chris!

Is the timing basically fixed then, since there is no way to adjust the position of the CPS along the circular path of the slots? Does the CPS bracket provide some indication of timing to any marks on a pulley?

I thought I read somewhere that the various CPSs, blue, black, grey give different timings and therefore may result in different mileage and engine characteristics.

 

The CPS is the timing mark. Just like a slot on a crank used to be. The readings by the CPS is the same we used to get with a timing light. It's only used to read the position like the light was. Figuratively speaking, the PCM twists the distributor electronically to adjust the timing.

The reason you hear about the blue CPS adjusting the timing is the difference in size and the strength of the magnet. This changes the response time in how quickly of slowly the magnet reads the slots. Since the PCM was programmed based on a certain air gap and strength of magnet, adjusting these can cause the PCM to be a little off in the timing.

How the new CPS comes into play with timing, I do not know. It would make sense the new CPS also adjusts timing due to the difference size and strength, along with the fact it causes some trucks to idle rougher.

 

I actually have a Guassmeter at work and could test for the various magnetic field strengths of the different CPSs.

Is there some agreement that the original black CPS, prior to recall performed the best?

Is there any timing changes performed by the PCM?

Thanks!

 

The pcm changes timing ALL the time.
It uses the signal from the CPS and then adjusts the timing how ever it wants.

The best CPS would be one that simply gets a clean valid signal to the PCM.

 

So a clean, valid signal would result in what type of input to the PCM? And is there a measurable output that I can easily data log or see?

I guess my analogy would be on a gas engine: I would hook up my timing light to the #1 sparkplug and shoot the strobe at the pulley and see my timing. I could also see the advance at increasing rpm and adjust the distributor accordingly for the specified BTDC.

On our diesels, how do I know my CPS is telling the PCM to do something at a the correct time, not sure what this "something" is. Is this "something" a signal voltage to fire the injectors at a certain time?

If I can modify my CPS output via screeening of the different colored CPSs, how do I confirm this is what the engine likes?

Seems to me the PCM can only perform the timing changes within the parameters of the input of the CPS and a "bad" or "slow" CPS would slow down the true output of the PCM. Can the PCM "advance" the CPS signal?

 

If you want to adjust engine timing, buy a tuner.

If you are trying to find out if the CPS is working right, I'd simply assume it is if the engine is running nice.( I've never heard of an actual CPS test routine, but i suppose it would be possible)

 

Think of the CPS as your strobe. If you were to swap to some new fancy bulb that tiggered the light quicker when it read the #1 spark, or if the light took a half a second to light after it felt the spark, then you would not be able to twist the distributor to the correct degree because your strobe would be blinking just a hair off of when it was supposed to. Follow?

Now as Parkland pointed out, timing is no longer set and locked into place. The PCM adjusts timing as you drive. Give it more throttle under hard acceleration and the PCM will adjust timing. Set the cruise on a flat stretch of road, it tweaks the timing again, and so on.

Since the timing is always being adjusted, the light flashing a few milliseconds off is bound to affect something. A different air gap and different strength magnet is bound to adjust how the PCM reads TDC on #1 in my opinion. That and a few dollars will get you a cup of coffee.

 

Let's pretend this is the signal the pcm is getting from the CPS, and the dotted line is the threshold at which the PCM considers the signal worthy to trigger the next event.



As RPM's change, and conditions change, the computer is designed to factor in any changes. Including unwanted but natural limitations of the CPS. For example, the signal in real life would never be a digital spike, it would be a round waveform like in the picture.

You can see how a stronger signal might very well trigger the computer sooner, thus advancing timing. You can also see that as the signal gets weaker, eventually there would be no signal to trigger the computer, or during the vibrations of the engine it is fair to say it could run erratic.

I imagine the PCM also looks at the length of the signal to determine the actual peak, being 50% of the length of the wave. This is how lots of analog signals are used by a digital system. That said, the computer may or may not be capable of running proper with a CPS providing an "out of range" signal from the CPS.

A lot of this I'm guessing; thinking of other equipment and computer boards that I'm familiar with, so I hope i'm mostly accurate...but....

It comes back to that what you want is a good CPS. Once you have a good signal, everything else will be adjusted in the PCM properly.

 

Hey Guys, thanks for the fantastic information!

My motivation for trying to understand all this is my 2003 7.3 does have an occasional miss at idle and reading all the posts about CPSs never really have any conclusion to what works and why. Black, blue, gray, Ford, IH.....etc, etc

I have some extemely sharp Electrical engineering and software engineers sitting right next to me at work and they are willing to help me solve this.

I have worked with Hall effect sensors when my son and I built a data logging system for his racing karts. It was fairly straight forward and my simple mind tells me to get a reliable CPS to work, we first need to optimize what a Hall sensor requires in terms of magnetic field saturation. "Slow" CPSs are providing garbage input to the PCM and garbage in equals garbage out.

What was the driving factor of the Ford recall on these CPSs? I imagine the Hall outright failed. Anyone know what mfg and part number was used in the pre recall CPS. Of course, Ford probably has alternate sources of the Hall sensor and magnet. Throw in manufacturing variances and tolerances and its probably not to hard to have CPSs that output differently. To what the extent this output variability affect driveablilty and engine smoothness is hard to quantify.

I have a IH CPS on my desk right now. It is the 1876735c91. Yes, I know there are other IH CPS s that are supposedly "better?" and maybe Ford has a better one yet.

I think it is time for me to throw these on the Gauss meter at work and get a scope on the output on my CPSs so we can have some more data to discuss.

Thanks again, this forum has been a great resource!

 

please post here again when you learn something, we're always eager to learn anything we can.

I suppose you could create a mockup flywheel and measure the signal from several CPS's to see which are giving what type of signal.

There may even be a few guys around here that might donate a poor running CPS for the knowledge you'd bring back after testing!

 

Anybody know if the type of connector going to the CPS can be bought off the shelf or is it a special Ford only connector.

The reason I ask is I have a new oscilloscope ready to try and get the output signals from the various CPSs, just thought if these connectors can be bought somewhere I could make a nice adaptor to send to my scope.

Spent an hour at the local pick n pull to see if I could grab a harness of a trashed truck but no luck!