new member greetings and ????s

greetings from TN!! now I need a little help please, a couple days ago I lost fire at the coil, the coil tested good, tested the control module and it tested bad, replaced it, no fix, my manual indicated it was either the module or the pick-up coil, so i replaced the pick-up, still no fix, and someone told me a faulty CPS would cause a loss of fire, can any-one cofirm this?? and where is the CPS?? while I was searching for it i broke the knock sensor, so now I get to replace it too. and if the CPS won't cause a loss of fire then where would you suggest looking for my loss of fire??
the rig is a pretty stock 90 with the 4.0
thanks in advance

A bad CPS will definitely cause no spark.

Not absolutely sure, but someone recently mentioned that to test for a good CPS on a RENIX, you should have about 200 Ohms between contacts A and B.

It is possible for the coil to be bad despite showing 'good' with the Ohmmeter test.

Here's this search. . .

http://www.naxja.org/forum/showthread.php?t=91075&highlight=Crank+Position+Sensor+Fire

good to know I am working towards a possible solution with the CPS, but where is it??
and which is more common, a dead coil or CPS?? it is my DD, I let it sit for a week while on vacation, and when i came back it started, but had a bad miss, but after a few minutes it disappeared and when i went to start it again about an hour later is when I lost fire

TN-XJ said:

good to know I am working towards a possible solution with the CPS, but where is it??
and which is more common, a dead coil or CPS?? it is my DD, I let it sit for a week while on vacation, and when i came back it started, but had a bad miss, but after a few minutes it disappeared and when i went to start it again about an hour later is when I lost fire

Click to expand...

Did you look at the thread I gave you? Everything you need to know about how to replace and find the CPS is all right there in those threads.

Does the Renix have a crank position sensor????? I don't think so. How do you know you don't have spark? What does it do when you try to start it?

Jess said:

Does the Renix have a crank position sensor????? I don't think so. How do you know you don't have spark? What does it do when you try to start it?

Click to expand...

A Renix does indeed have a CPS. Same location as the newer ones, different electronics.

SBrad001, sorry I glazed past it before I posted, but I went to it just now and it answered alot of ??, thanks for the thread,
Jess, it will turn over but not start, so I checked the obvious first,
1. I had fuel, (had pressure on the rail)
2. checked spark @ plugs, no fire
worked back from there and found the coil had no fire, and the rest is in my initial post.

This is also covered in the FAQ section

Matthew Currie said:

A Renix does indeed have a CPS. Same location as the newer ones, different electronics.

Click to expand...

The RENIX does NOT have a CPS( Crank Position Sensor) like they are referring to. It does have a Cam Position Sensor though and it would be located in the distributer. TN-XJ if you want, PM me your number and I can come take a look at it for you.

ok, a quick update
I replaced the CPS and still no go,
I think I might have a bad coil even though it tested good,
I checked the power to the control module and this is what I got, both while cranking and with the switch in the run position
plug 1, with one yellow wire ~4.6 to 5 volts
plug 2 yellow wire ~11.0
black wire nothin'
green/white wire nothin'

it seems right to me which means the coil is dead, any thoughts?

Check the sensor below the distributor cap. Camshaft position sensor is what the store had it listed as, although I was actually told it was the pickup coil......That was my problem when I had no spark.

Replaced the CPS just like you did and I still had no spark until I replaced the cam sensor.

Blaine B. said:

Check the sensor below the distributor cap. Camshaft position sensor is what the store had it listed as, although I was actually told it was the pickup coil......That was my problem when I had no spark.

Replaced the CPS just like you did and I still had no spark until I replaced the cam sensor.

Click to expand...

Do you people have a problem listening? How are you going to tell him that you replace the CPS and it made no difference when the RENIX system has no CPS. Maybe you should check the MAF sensor while you are at it.

rredalty said:

The RENIX does NOT have a CPS( Crank Position Sensor) like they are referring to. It does have a Cam Position Sensor though and it would be located in the distributer. TN-XJ if you want, PM me your number and I can come take a look at it for you.

Click to expand...

Apparently you dont know enough about a RENIX to know that they DO HAVE a Crank Position Sensor! Ive had to change mine twice since ive owned it. What makes you think it doesn't? Oh and your last post made me drop to the floor laughing.

The Renix has both a Crank sensor and a Cam sensor.

Cam sensor is in the Dist, and has nothing to do with spark, only timing during startup.
The crank sensor is on the bell housing 11 o'clock drivers side and It does fire the coil and injectors.

TN-XJ said:

ok, a quick update
I replaced the CPS and still no go,
I think I might have a bad coil even though it tested good,
I checked the power to the control module and this is what I got, both while cranking and with the switch in the run position
plug 1, with one yellow wire ~4.6 to 5 volts
plug 2 yellow wire ~11.0
black wire nothin'
green/white wire nothin'

it seems right to me which means the coil is dead, any thoughts?

Click to expand...

The small yellow wire is the pulse wire that comes from the ECU (computer), your tester seems better thn most, you got a reading (this takes a special tester to affectively test). The large yellow wire is power, when the key is turned on. Black is ground. Green is the tachometer wire. Might want to check the ground, just to eliminate that.

Crank position sensor, sometimes called the engine speed sensor among other things. Jeep has a habit of changing the name when they change the model run. I once ran my Renix for weeks with the cam position sensor disconnected, so I doubt it is essential. Though if it was shorted it may cause problems with the low voltage supply circuit from the ECU, which could affect the CPS (and other sensors).
A quick coil test, ohm between the plus and minus about 1 ohm, between the plus and the high voltage about 8-9 kilo ohms ( or 7-11 kilo ohms it's not exactly a percision item).
Coils don't often go bad. The ignition modules don't often go bad. the contacts between the igintion coil and the igniton module get kind of green, white and corroded on occasion and the high voltage wire from the coil to the distributor cap goes bad and shorts. Water gets into the distributor, high voltage wires, boots and causes ground paths.
The wires to the CPS often cook on the exhaust manifold and can short. Which rarley causes any lasting damage. The connectors between the CPS and the ECU (3 or 4 depending onthe year) get corroded. The CPS is a fairly low output component, it doesn't take much resisitance to cause a signal too weak to do any good.
Check the wires to the CPS (closely) and clean the connector, and then clean the next connector.
Make sure you tightened the CPS down completely and it is sitting in position correctly. The bolt heads are flush and you used the original bolts.
Possible a CPS wire *after* the first connector, right where it goes into the injector harness has been shaking up and down for years and finally fatigued all the way through the copper under the insulation. Squeeze the wire gently between your finger and thumb nail on the insulation and feel if you find a soft spot.

Have you checked all your grounds? Especially the ones bolted to the side of the block...When I put the engine back in from a rebuild, I forgot to hook those back up and got no spark at all, bolted them back on and it fired up right away.

first of all, thank to all those who have responded so far, it has really helped, because my Haynes manual is apparently useless because I didn't find any mention of the CPS when looking through it. and for those who have mentioned it, I have already replaced the cam position sensor, or pick-up coil or whatever you would like to term it as.
I only had a few minutes this afternoon when i installed the coil (which didn't help) so I didn't have enogh time to interrogate all the grounds well. When this issue first arose I checked the connections but apparently I need to go over them again because something is a-miss and it is starting to irritate me, hopefully thoroughly going through connections will reveal the culprit, but since it was a sudden evident I suspected it was an electrical component failure it appears I am wrong because I believe I have replaced everything that could be wrong, here's list and if I have missed anything let me know.
coi,
cam position sensor (pickup coil)
ignition module
crank position sensor (whether it's real or imaginary it's replaced)

THANK YOU again for ALL of the help

doin' some thinking (as dangerous as that is)

ok, is it logical to assume that if I am getting power to the control module then I should be getting fire to the coil?? especially since the ECU trigger has power? which would mean I should have fire at the distributor, correct? or would a lack of ground not allow the control module to work correctly even with power going to the module? just trying to figure out if I might have new defective control module

Re: doin' some thinking (as dangerous as that is)

TN-XJ said:

ok, is it logical to assume that if I am getting power to the control module then I should be getting fire to the coil?? especially since the ECU trigger has power? which would mean I should have fire at the distributor, correct? or would a lack of ground not allow the control module to work correctly even with power going to the module? just trying to figure out if I might have new defective control module

Click to expand...

The small yellow wire to the ignition control module (ICM/Renix) carries a pulsed signal *from* the ECU (engine contol unit/computer). The CPS (crank position sensor)(among other inputs for timing etc.) tells the ECU when to pulse/signal the ICM (ignition control module) which in turn pulses (builds and then collapses an electromagnetic field in the coil).
Building then collapsing (pulsing) the primary field in the ignition coil is what generates the high voltage. The coil is really nothing more than a transformer, 9-12 volts in and 35-50,000 volts out (approximate). But the primary part of the coil (12 V +/-)needs to pulse (or build and collapse), to generate the secondary voltage (high voltage).The coil is relatively high amperage, the ICM takes the small signal/pulse voltage from the ECU and then pulses the coil with a robust (fairly high amperage) pulse.
The pulsed square wave signal from the ECU to the ICM is hard to measure with an ordinary voltage tester, I've gotten mixed results (some movement/change in the readings but no real pulse) from both the DC scale and the AC scale on both a digital and analoge type meter. The ECU generates a square wave, the quicker the pulse or the quicker it builds a field and then collapses a field has input on the efficientcy of the coil and generated high voltage. A square waveform does this well, but is hard to measure with a common volt meter of any sort. It's likely a half wave form, not truly AC but not DC either.

Most times the input to the ECU from the CPS (fairly meager signal), is weak, either the CPS itself or the wiring and/or connections is the problem, when the signal (trigger) from the ECU to the ICM doesn't pulse (or the ECU doesn't generate the necessary square wave). Though I have heard but not seen myself, of other inputs failing and the ECU refusing to pulse the ICM. I've personnaly never experinced this.
Sometimes a very weak spark is confused with a no spark or when the high voltage grounds (or has a very high resistance) before it gets to the distributor cap. The only reliable way I've found to test spark, is to hook up a spark plug wire to the coil, put a plug in the end and ground it well. Look at the spark at the end of the plug. If the plug isn't grounded well it may ground through you, so caution is advised. I usually open up the plug electrode to around 60 thousandths. Do an ohm test on the coil to cap wire.

Clear as Mud