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BlueOvalKid 06-26-2013 05:42 PM

5.2L Crank Position Sensor Line Readings
I did try a search so if this exists my apologies and links to the right thread will be appreciated.

Vehicle: 93 Jeep GC 5.2L Auto

Issue: classic no start

I replaced the crank position with an aftermarket one and still having symptoms.

I then started measuring the voltages on the 3 lines to the sensor. Below is what I have and would like to verify. I've found information on the 4.0L sensor but nothing specific to the 5.2L.
- Power line: reading of 6.3v (seems high as I believe it should be 5.0v)
- Ground line: reading of battery voltage (believe ground is good)
- Signal line: reading of 9.54v constant (I believe this should fluctuate and should be either 0v or 5v depending on crank position)

Can anyone help me here with these readings? I think I have a DOA crank sensor.

dellis 06-26-2013 06:05 PM

I'm curious. What were the symptoms that led you to believe you had a failed crankshaft position sensor?

Some thoughts:
(a) Yes, it should be 5 volts ... but that comes from your PCM and not the CKPS. <--- Error (see post below)
(b) The signal line is not DC, but a square wave with irregular frequency, and it is generated as the crankcase turns.
(c) A ground line should be 0 volts.
(d) These electronics are flaky enough, and putting in generic sensors is asking for more trouble. Go with Mopar for these sensors.

What is the measurement between the ground pin and your 5V pin?

BlueOvalKid 06-26-2013 06:25 PM

Dellis, thanks for the reply.

You are correct that the signal voltage is a wave and should be 5v until it hits the magnet on the crank (every 45deg) which then causes it to break to 0v. So, with a digital voltmeter, and cranking the engine by hand with a socket, you should see the on/off voltage as you go around.

The ground line should show battery voltage if you hook the negative line to it and the positive to your battery. This will show that both the line is in fact grounded.

The power line should be 5v from the PCM. What's confusing me is that my power voltage is the 6.3v which is a bit high.

I'm convinced I have a DOA sensor and am going to go with OEM. I just didn't want to replace this again unless I have to, although it's really not that bad of a job.

dellis 06-27-2013 08:30 AM

OK ... but I'm still curious as to what diagnostics have led you to believe you had a crankshaft position sensor problem in the first place. The reason I write this is because without any other diagnostic information, then assuming two bad CKPS sensors in a row (original and replacement) is not as likely as assuming that your problem is elsewhere.

By the way, I looked up your Jeep and testing a CKPS operation would be done this way (please note that I had a voltage error in my original post):

(a) With the electrical connector disconnected and key in the "on" position, verify voltage to the CKPS from the PCM. It should be 8.0 volts for 1995 and earlier vehicles (I made an incorrect assumption earlier ... the 5 volt levels were introduced with the 1996 models). Test between the white/black (voltage) and the black/light blue (ground) wires. If it is not 8.0 volts, then you need to investigate the circuit and/or the PCM.

(b) Next check for damage to the CKPS ... place an ohmmeter across terminals B and C of the CKPS connector. The meter reading should be open (infinite resistance). If you notice measurable resistance, then the sensor is bad.

(c) Reconnect the sensor and put a scope or meter on the signal line. Remove the plugs and attach a breaker bar and socket to the crankshaft pulley center bolt. Turn the key to the "on" position and slowly rotate the engine a full rotation while watching the meter. On a 5.2, it should dip from 8.0 volts down to ground every 45 degrees as it hits the notch on the flywheel. If it is giving you other readings, then either (a) you have a bad CKPS or (b) the CKPS was installed with an improper distance from the flywheel (spacer not used, or not properly seated during installation).

If (a), (b), and (c) all check OK then your problem is elsewhere. In general, CKPS sensors do not erratically fail or degrade (that is, if they are bad then they are bad all the time), although I've read some cases where the CKPS works when cold but then fails as the engine temperature heats up the CKPS.

BlueOvalKid 06-27-2013 09:17 AM

Here are my no start symptoms:

- Get these lights on the dash (check engine, ABS, Seat Belt, etc.). Main one was Check Engine for me.

- Security light on dash is OFF. I believe this means the security is disabled.

- ASD relay appears to be working properly. I have also swapped it with the starter relay, as I'm able to crank the engine, and made no difference in either.

- I have tested every fuse, with a test light on both probes, in the fuse block under hood and passenger side and they are all good.

- No spark from the coil. I have hooked up a spark tester to the coil directly and am getting nothing out of the coil. The coil is getting 12v power to the connector but the signal line is getting nothing.

- Battery voltage is a good 13.1v.

- Fuel pressure is a constant 38lbs with my fuel pressure tester gauge hooked up.

At this point, I am down to the crank shaft sensor and reluctor in the distributor. I am working through the crank shaft sensor first.

If I'm missing something or overlooked anything please let me know.

dellis 06-27-2013 10:12 AM

I know this may sound elementary, but is the coil good?

I'm not sure what you mean by "the signal line is getting nothing" (in reference to the coil). The coil should have two wires, battery voltage and a connection to the PCM that is grounded through the PCM's Coil Driver. Are you measuring 12 Volts between these two wires, or 12 volts between the voltage line of the coil and a ground point?

If you have 12V across the two wires of the coil and no spark coming from the coil, then my first thought is that you have a bad coil and the coil needs to be tested / replaced.

Also, have you been able to read any PCM codes through your dash? If so, what are they?

BlueOvalKid 06-27-2013 10:21 AM

Coil is good and I have actually tested with a known good one and getting no spark out of the coil itself. The coil gets it's signal only if the crank sensor & reluctor are both working (at least that's my understanding).

The codes from the dash check engine light blinking are: 11, 12, 55.

dellis 06-27-2013 10:37 AM

Code 11: No distributor reference signal detected during engine cranking ...

This code is generated because the PCM is likely not getting a good camshaft or crankcase position signal. The code is not specific about which one, just that there's a problem with these signals.

If this were my car, since the CKPS was replaced with no effect, then I would be testing the camshaft position sensor (distributor pickup coil), the connector, and its wiring to the PCM. Do you have those test procedures?

BlueOvalKid 06-27-2013 11:06 AM

No, I don't have the reluctor/pickup coil tests.

If you can provide those it would be great.

I will continue to dig in and it appears we are on the same page. I am trying to eliminate the Crankshaft sensor before moving on so I have a systematic method and not jumping around.

Based on the line tests so far I still think the crankshaft sensor is DOA. I am going to Ohm across B&C lines to see what I get on both the old and replacement sensor and go from there.

dellis 06-27-2013 11:25 AM

The (a) and (b) procedures are the same as with the crankshaft position sensor. I am assuming that this sensor is also set up with an 8 volt supply.

But, it is a little easier to test for the signal. The signal produced from the camshaft position sensor is a regular square wave, so the RMS (AC) voltage on a digital meter that you should see would be half of the 8 V supply, or 4 volts. With everything connected, have your meter backprobed* into the connector's gray/black wire with the other end grounded. Then crank the engine to observe the RMS (AC) voltage. If you are using an analog meter, you should see the meter fluctuating between 0 and 8 volts.

*I usually put a sewing needle in though the back of the connector, and attach my multimeter lead to the needle.

Uniblurb 06-27-2013 12:57 PM

Dellis, some good info on checking the crank sensor and I've posted that same connector test before. I'll just add something in that it does matter which multimeter probes you put on pins B and C of the connector itself with the locking tab up. The black probe should go on pin B (ground cavity) and the red probe should go on pin C (power). While normally it doesn't matter which probes you use for checking resistance it does on the CKP and may have something to do with the magnet. Switching these probes (black to C and red to B) will give you a false reading. Meter should be set to the lowest ohm setting and as you said if there's any resistance at all you have a bad sensor.

BTW, I'm on my 4th crank sensor on my 96 4.0. Bad ground (rust/corrosion/oil) on the coil stud took out my PCM along with the CKP because all sensors are grounded through the PCM via this ground wire. Then put 2 junk aftermarket CKP's from Advance in it which drove me nuts and were DOA. Finally a Mopar CKP fixed my stalling/no-start problems.

BlueOvalKid 06-27-2013 04:22 PM

Could it be the PCM?

I have checked for the voltage at the Crankshaft position sensor and get nothing across the power & ground lines. I also get no voltage across the two lines at the coil.

I'm doubting the PCM though because the check engine light is on the dash for a couple of seconds when you turn the key on. Additionally, I can hear the ASD relay click (have even swapped it to confirm) and I have fuel pressure at the rail (38lbs constant).

Any thoughts on the PCM at this point?

dellis 06-27-2013 04:58 PM

Ummm ... didn't you say you had voltage earlier? Make sure your meter is set on DC, maybe you are probing the wrong wires, maybe the ignition key is not "on", or maybe you are probing the connector to the sensor rather than the harness to the PCM.

If you are still not seeing voltage coming from the PCM, let's consider that you have a short. That 8V signal powers not only the CamPS and the CrankPS, but also the Vehicle Speed Sensor. Disconnect all of those and then test for 8V from the PCM.

If, after disconnecting all three, you still do not see 8V, then I would probably see if the 5V signal from the PCM is being provided. It supplies other sensors such as the MAP, TPS, IAT, Temp Sensor, etc. If that voltage is ALSO gone, then I'm suspecting a problem with the PCM's voltage supply ... either that it is at fault, or it is entering a fail-safe mode due to a short.

You might also need to run through ZeeJay's dirty dozen before condemning your PCM ... and, in particular, the connector jiggle at the PCM.

But, yeah, voltage not coming from the PCM is not good at all.

BlueOvalKid 06-27-2013 06:32 PM

Ok, it would help if the idiot (aka me) controlling the voltmeter had it on the right setting. I rechecked and have voltage across the connectors for both crankshaft and reluctor.

What's interesting is that I have a 5v reference and not the 8v you mention on both.

I tested the resistance (ohm) and get infinity on both sensors so that tells me they should be ok. I had my meter set on 200ohm which is the smallest setting I have.

I then wanted to check the signal voltage on the distributor since it's easier to get to that connector. I back probed it and it reads 9.54v and never fluctates (digital or analog meter). This was with my meter set on dc volts.

I then borrowed a new distributor and hooked it up to the connector. I back probed the signal line and spun the distributor by hand, since I didn't install it yet, and get a constant 9.54v (digital & analog) reading.

Any thoughts?

BlueOvalKid 06-29-2013 03:25 PM


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