Electrical theory help

[8Mud]

I´ve got a Renix CPS, that tests good, 210 ohms of resistance out of the vehicle cold.
Thinking what could be wrong with this bugger. Seems like with the resistance, it has a winding of some type in there. Actually with the core magnet in it, it appears to be a small generator.
Magnets get tired and old trick to get tractor generators (like alternators but older) going again was to flash the field with 24 volts, to remagnatize the field magnets.
If I figure out if it´s possible or not, I have a flexplate out of an XJ, to set up a test with, on the bench and see if the generated voltage changes with a flashed magnet. More, less or none.
Next question, it´s been so long since I flashed a generator magnet I can´t remember if polarity was important or not.
A hint at the amount of voltage that may be tolerable and still do something would also be helpfull. Also the voltage that would just turn it into a fuse or a one time lightbulb.
The worst that could happen is I turn my questionable CPS, the old one from a recent replacement, into total junk.
It´s possible, I think to flash the magnet and put some new life into a CPS, while probably not a fix, something to get you home in a pinch.
We may stumble onto something, that may be a boon to XJ kind.

 

[old_man]

You are totally on the wrong course. Hitting it with a voltage will toast it. The pickup is a variable reluctance type pickup. The most common problem that will effect them is spacing from the pickup wheel. It should be only about .005" away from the flywheel/flex plate, or in other words the thickness of a sheet of paper.

You don't give much info. Have you tried another CPS? What was the symptom? Corrosion on the contacts is the most common failure mechanism. Electrical interference can also cause problems. I've even seen a fried spark plug wire cause the CPS to generate false pulses.

Give us a history, along with year model and engine size.

 

[Lou]

I don't know about the Renix stuff, but with the '91-('96?) ECU the CPS uses a Hall-effect sensor. There is also a magnet in there. The Hall-effect sensor will have a resistance, but it is not a coil.

With the CPS connected(polarity may matter) to a meter as if to measure resistance, try passing something magnetic(e.g. bolt--not a magnet) in front of it. The resistance should change.

Note: (it is possible that the voltage supplied by the meter during this test may not be enough to power the Hall-effect sensor in order for it to function properly)

To remagnetise the magnet, pole orientation(and polarity) probably matters. You would need an external coil to do that--if at all possibly effective.

You may have a point about the magnet dying out over time.
Try using a hand compass to see if there is any magnetic 'UMPH' left in there.

If you have a good CPS, you might be able to compare the magnets in the two CPSs by check how far away the magnets in the respective CPSs are still able to affect the compass.

 

[8Mud]

I already replaced the CPS sensor, the no starts were getting closer together, on a hunch I changed the CPS, seems to have worked out. Did have some ignition problems going on, washed my motor, but cleaned dried and blew out everything most everywhere. The contacts in the CPS plug, are a little discolored, but the new CPS sure seemed to help. It will start reliably now, for the last few days anyway. I´m wondering about my plug wires also, ohm test good, but who knows, I´m not going hunting the hard way, I´ve got a weak bladder. Seems logical random high voltage would mess with it.
I tried moving metal closer and farther away from the CPS, ohms change. I have a third CPS on a tranny with no flex plate and did an ohm test on it, it had 35 fewer ohms than the "bad" one, both cold, no metal near.
I´ll look at it a little closer and see if I can devize a test, with a dial gauge or something. Just curious.
I often like to find out what made a part fail. Think I´m gonna clean the CPS plug a little better, just for the heck of it.
I´ll try the compass test, I have two CPS's but both old, but with different ohm values. I´m sure not pulling the new one back out, was a pain to get in there.

 

[carnuck]

I've had luck with just cleaning crud off the CPS and readjusting height from the flexplate (sometimes crank thrust bearing wear allows the crank to mave slightly away from the CPS forwards or backwards and cut the signal)

 

[8Mud]

I´ve got to weld up my exhaust manifold, soon, I´ll have a closer look. I´m gonna jump the CPS wires at the C-101 connector for sure. I know Chev, are sensitive to wire length, was wondering if it´s the same for the Renix CPS. Logic tells me to make the wires as short as possible, but that may be a mistake.
Crazy Renix are tempermental, after I put the new CPS in idle, Idle RPM´s dropped a hundred or two and it idles rough, but sure starts a lot better. I´m going to have to change my spark plug cables first though, I suspect a high voltage leak someplace, though I haven´t found it yet, maybe I´ll have my son look for it, when he yells, we´ll know where it´s at :laugh3: .
By the way, I tested the CPS harness plug for voltage and had something like 3 and a fraction DC, on both wires to chassis ground. I don´t have another Renix around to compare to. It was a quick test, more out of curiosity, than actually testing for anything, I´ll have another look see, things were kind of hectic at the moment.
Nothing seriously wrong with my old Renix, but my mileage did go south, just before the CPS crapped out. Gas here is like $1.30 a quart or so, I keep track of my mileage pretty closs. My plugs look really good, even though I do idle alot. Lite tan, to very lite grey (almost white) on a cold plug, burn looks good, definetly not running rich.

 

[carnuck]

If the only thing you did was swap out your CPA, then it may be sitting slightly retarded from the original one. File the holes where it mounts to the trans so you can slide it over a bit and you will see the RPM go back up. (or down if you move it the wrong way) This is how the stroker list guys help adjust timing a bit to compensate for the higher compression.

 

[8Mud]

If the only thing you did was swap out your CPA, then it may be sitting slightly retarded from the original one. File the holes where it mounts to the trans so you can slide it over a bit and you will see the RPM go back up. (or down if you move it the wrong way) This is how the stroker list guys help adjust timing a bit to compensate for the higher compression.

Thanx :thumbup: I´ll give it shot, when I have my intake off. Ì'm not gonna try it from the bottom. It runs OK now, just not right.
I also moved my TPS settings back to OEM, while I was trying to figure out what was wrong, but my idle didn´t change much, till after the CPS. I also did a tune up (it was past due).
I´m gonna take the heat shields of the intake and reroute a couple of things, so maybe I´ll be able to access the CPS, from the top after the manifold work. Maybe I´m just kidding myself though, I've got big hands. :laugh3: