cps fix

I found a way to get a worn out Renix crank position sensor working. Wire a 0.01 uF capacitor across the sensor's wires.
uF stands for "microfarads".
0.01 microfarads can also be expressed as 10 nanofarads (nF), or 10,000 picofarads (pF).
Don't use an ordinary ceramic capacitor, heat affects them too much. The ceramic caps are the little orangey-looking discs.

This worked like a charm for me. The cherokee wouldn't start at all, no spark no matter how much I cranked it. I wired the capacitor up and it started right up. I'm an electronics hobbyist so I had bags of capacitors of different values. I tried 0.1 uF first; the jeep started but didn't run right. A 0.01 uF poly capacitor worked like a charm.

So guys, if you have an old jeep take along a .01 uF capacitor when you go trailing.

where would one obtain these 0.01 uF capacitors?

Michael Robinson said:

Wire a 0.01 uF capacitor across the sensor's wires.

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Thanks for sharing. Do you have a pic of how it looks like after wiring the capacitor, and would you say this to be a temp solution until a whole unit replacement?

Just for giggles, if is isn't too much trouble, disconnect the cap and try it again.
I don't understand how adding a capacitive load to an AC signal (albeit square wave) would do anything but round off, and/or load down the waveform.
To be fair, a certain capacitance coupled to the inductance of the pickup in the CPS would alter the resonance, changing the amplitude, but it seems too easy a fix, and so random.
It would be interesting to put a scope on the waveform coming from the CPS and see the difference.
You could have the classic "pinched and rubbed" wiring near the intake manifold. How long has this fix been working?
When my CPS quit, it was during my moving the wiring, and I discovered the outer tubing and one of the wires had been cut nearly off during an older unrelated repair, causing a stall and eventually no start.

"where would one obtain these 0.01 uF capacitors?"

I buy enough parts to justify ordering from suppliers,
but you could just go to Radio Shack. If the RS is big
enough to have the parts drawers, it will probably
have the caps. They'll charge you a buck for a ten cent part,
but there you go.

"Thanks for sharing. Do you have a pic of how it looks like
after wiring the capacitor, and would you say this to be
a temp solution until a whole unit replacement?"

No pic unfortunately. I kind of kludged it. I did use a pencil
torch to solder the cap to the wires, but you could just twist the
leads of the cap onto the wires. Yes, I consider it a temporary solution.
Once the magnet in the cps gets weak, it can only keep getting weaker.
Or it could have other problems. This solution will not work for a cps that's
completely shorted out.

"Just for giggles, if is isn't too much trouble, disconnect the cap and try it again.
I don't understand how adding a capacitive load to an AC signal (albeit square wave)
would do anything but round off, and/or load down the waveform. To be fair, a certain
capacitance coupled to the inductance of the pickup in the CPS would alter the resonance,
changing the amplitude, but it seems too easy a fix, and so random. It would be
interesting to put a scope on the waveform coming from the CPS and see the difference.
You could have the classic "pinched and rubbed" wiring near the intake manifold. How
long has this fix been working? When my CPS quit, it was during my moving the wiring,
and I discovered the outer tubing and one of the wires had been cut nearly off during
an older unrelated repair, causing a stall and eventually no start."

I learned about this trick from an electrical engineer. In industry, an engineer
will sometimes put a cap in parallel with a vrs to punch up a weak signal.
You need to get the cap's value right, but it works.
The signal from a variable reluctance sensor does not remotely resemble a square wave.
The vrs is a completely passive device. It has a coil and a magnet. The metal teeth
that pass the coil jerk the magnetic field, causing the coil to generate
pulses. You can easily see how adding some capacitance would have
a huge effect on what's happening here.
By rights such a circuit should have a capacitor in the first place, but that
would cost money, and since it works without one, well, you know the drill.
But with a cap in the circuit, it is more robust. Other variables, such as magnet strength,
would become less critical. The cap also makes the circuit less susceptible to noise.
Here's a link I googled to show you the shape of a vrs trace:
http://link-electro-usa.com/images/VariableReluctanceSensors1.pdf

Did you put that cap across the two wires or inline with one of them ? and if inline which lead ?

Across the wires. You could just cut and peel back the insulation to bare the wires and twist the capacitor leads on to them in an emergency.
Also, small caps like that don't have any polarity, no need to worry about getting it backwards.

Sounds like something to carry, might even have some in my old field service case from waaaaayyyyy back when we did components on the old Z80 controlled machines.

You can easily see how adding some capacitance would have
a huge effect on what's happening here.
By rights such a circuit should have a capacitor in the first place,

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Well I've been a EE for 35+ years and this is an old wives tale.

the link provided only mentions sensors mounted on distributors.
Maybe they are just that.
The FSM for Renix shows the waveform (I stand corrected) as a sawtooth.
Either way, put a cap across a variable AC signal, it will load it at these moderate frequencies.
This system and CPU were designed to work together the way they are, and the cost of an extra cap in the ECU on that data line would be minimal.
The fact that it works at all with a cap added just means the circuit has enough "tolerance" in it by design.
Just my opinion....

I dont understand a word you just said. Its like a dog with peanut butter on the roof of its mouth or something. I am a visual person, if you guys have any pics I would be extremely pleased. Thank you. And, keep up the good work. :thumbup:

The jeep book thingy says the electricity should look different than it does.
It's just one of those things.
I'm not book learned.

Was it green? :shhh:

Without the capacitor across the line, no start. With cap, starts. Reproducible, consistent.

People will stare a fact in the face and say, "But that can't be right" and go on to explain all the reasons why instead of trying to understand or just accepting it. Your cherished rationalizations may be dead wrong but you won't let go and change your way of thinking..
I want to toss my lunch just thinking about it.

Michael Robinson said:

Without the capacitor across the line, no start. With cap, starts. Reproducible, consistent.

People will stare a fact in the face and say, "But that can't be right" and go on to explain all the reasons why instead of trying to understand or just accepting it. Your cherished rationalizations may be dead wrong but you won't let go and change your way of thinking..
I want to toss my lunch just thinking about it.

Click to expand...

Not on the keyboard or monitor please...

Michael Robinson said:

Across the wires. You could just cut and peel back the insulation to bare the wires and twist the capacitor leads on to them in an emergency.
Also, small caps like that don't have any polarity, no need to worry about getting it backwards.

Click to expand...

Is Cap polarity an issue? OH, never mind, LOL.

On the why it can't possibly work topic, it has to do with morphidite electron theory. The electrons get confused on their path through life to a good ground (or in this case through the CPS to a good ground), and the Cap just helps them back on the right path!:banghead: :laugh3:

All kiding aside, nice post and one question, where exactly in the wiring harness did you install it, in other words near the computer, under the hood near???, or right at the CPS where it is a pain to reach it, what year wiring harness, wire numbers, colors??? OK, yes that was more than one question, but might help others down the road.

Now I have an idea, or suggestion. Some of us have been discussing the possibilty of using an OpAmp circuit to boost the voltage signal from the O2 sensor to tune in a leaner air/fuel ratio. Why wouldn't that also work on the CPS? In fact I don't see any reason it would not work. If it was a tunable OpAmp one could slowly boost the CPS signal as the magnetic strength of the CPS magnet disipates, possibly extending the CPS sensor life for years.

What a cool idea. :yelclap:

Ecomike said:

Is Cap polarity an issue? OH, never mind, LOL.

On the why it can't possibly work topic, it has to do with morphidite electron theory. The electrons get confused on their path through life to a good ground (or in this case through the CPS to a good ground), and the Cap just helps them back on the right path!:banghead: :laugh3:

All kiding aside, nice post and one question, where exactly in the wiring harness did you install it, in other words near the computer, under the hood near???, or right at the CPS where it is a pain to reach it, what year wiring harness, wire numbers, colors??? OK, yes that was more than one question, but might help others down the road.

Now I have an idea, or suggestion. Some of us have been discussing the possibilty of using an OpAmp circuit to boost the voltage signal from the O2 sensor to tune in a leaner air/fuel ratio. Why wouldn't that also work on the CPS? In fact I don't see any reason it would not work. If it was a tunable OpAmp one could slowly boost the CPS signal as the magnetic strength of the CPS magnet disipates, possibly extending the CPS sensor life for years.

What a cool idea. :yelclap:

Click to expand...

There's that "Morphodite electron theory" - we've talked about that before, haven't we?:read:

I did forget to mention a corollary to the Heisenberg Uncertainty Principle when we talked about that - experimentation has shown that a variation of the HUP can also apply to electrons flowing through a circuit - especially on automotive applications (where it seems to manifest first and most consistently.) This variation applies more directly to the particles than the observer - apparently, the particles (electrons) themselves become uncertain of where they should be going, and then end up going to the wrong places (or just "milling about smartly" and not getting anything done in the first place - kinda like boot privates and second lieutenants, in most cases. You Navy types would know the latter as "ensigns" - but the same principle applies...)

"There is no-one more dangerous than a second lieutenant with a map and a compass." Oddball faults like this are fuel for the proof of "commissioned electrons" who are expected to blaze the trail for the other electrons to follow (and end up doing so rather badly.):shhh:

Oh - before anyone else get to it, I'll go ahead and call :bs: on myself. I'm not an engineer - just a tech who has seen way too much weird stuff happening...

I can visualize how it may help the wave form and/or reduce static.

old_man said:

Well I've been a EE for 35+ years and this is an old wives tale.

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check out the big brain on Tom. :lecture:

Perhaps we just need a GUT (Grand Unification Theory) that unifies the MET & HUP theories? But before we did that we should probably consider the effects of gravity on the MAS of the electrons? (MAS= Milling About Smartly) since it might slow them down or redirect the poor misguided fellows. This is getting into some HEAVY theory now!


Any thoughts on using an OpAmp circuit to extend the life of these maginal CPSs?

5-90 said:

There's that "Morphodite Electron Theory" - we've talked about that before, haven't we?:read:

I did forget to mention a corollary to the Heisenberg Uncertainty Principle when we talked about that - experimentation has shown that a variation of the HUP can also apply to electrons flowing through a circuit - especially on automotive applications (where it seems to manifest first and most consistently.) This variation applies more directly to the particles than the observer - apparently, the particles (electrons) themselves become uncertain of where they should be going, and then end up going to the wrong places (or just "milling about smartly" and not getting anything done in the first place - kinda like boot privates and second lieutenants, in most cases. You Navy types would know the latter as "ensigns" - but the same principle applies...)

"There is no-one more dangerous than a second lieutenant with a map and a compass." Oddball faults like this are fuel for the proof of "commissioned electrons" who are expected to blaze the trail for the other electrons to follow (and end up doing so rather badly.):shhh:

Oh - before anyone else get to it, I'll go ahead and call :bs: on myself. I'm not an engineer - just a tech who has seen way too much weird stuff happening...

Click to expand...