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Old 05-11-2010, 03:17 PM   #1
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Default What are the symptoms of a bad crank sensor

I have an 89 cherokke with a 4.o that i have a bad issue with. It bogs out and spits/sputters and pops in the exhaust when giving it gas. I thought it was a bad stator in the dist. but wrong , no change. Any ideas on a bad crank sensor or map sensor?
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Old 05-11-2010, 08:41 PM   #2
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My friend had a 2000 and when he would drive it would sputter and stall and it got worse and worse until it just would start anymore. Sure enough it was the Crank Shaft Position Sensor and he was good to go.

I yanked on the wire on mine on accident while swapping in a header. When i put it all back together to start it up. No spark. replaced the CPS and it was golden.

A lot of times with the cherokee and no spark its more than likely the CPS but with anything else like MAP sensors im not to sure but here is a link that may help you out.

http://www.lunghd.com/Tech_Articles/...iagnostics.htm
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Old 05-12-2010, 03:51 AM   #3
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The CKP is used to generate timing data for spark and fuel injection - so the usual Sx of a failed CKP is "crank, no start." And, generally, they either work or they don't.

Here's a funny little thing that most people don't catch - follow the vacuum line from the MAP sensor on your firewall to the throttle body (pax side.) That little rubber bung often pops loose, and you end up with no MAP signal (which screws seriously with fuel metering) and a vacuum leak (with generally screws with running.)

If the bung feels loose going back in, you can stick it in place a bit better - put some RTV (not much!) on the part that goes into the "blind" hole. If you put it on the hole that the vacuum line goes into, you could end up clogging the line if you're not careful - easier to just avoid the trouble from the off.

Are you able to keep it running long enough for parts to get warm - two to three minutes? If you can, see if the problem goes away. If it does, retorque the manifold screws and check again - the problem should lessen, if not go away (if the problem has gone on long enough, the gasket will have burned through and want replacing. I've covered tips and tricks for how to do that elsewhere on several boards - including this one.)

If you check those and the problem persists, check for further Sx and report.

(Sx = Symptoms. I spend far and away too much time talking to doctors...)
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Old 05-12-2010, 05:10 AM   #4
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The CPS is a Hall effect transducer that varies its output voltage in response to changes to magnetic field. Inside the sensor there is a little magnet that lies along a piece of wire.
When the magnetic field is disturbed by the passing of the reluctor ring teeth it generates an inductive current in the piece of wire attached to the magnet.
The signal produced by the CPS is an analogic square waveform that varies in frequency in response to the overcoming speed (RPM) of the reluctor ring teeth and grooves. This tells the ECU at what speed the crankshaft is turning.
Another information provided by the CPS is piston top dead center (TDC). On the flywheel there are three big holes that produce a long "zero" signal. The holes are only three because in a six cylinder the pistons move in pairs, therefore you have two pistons at TDC at a time. Now, how does the ECU know which of the two TDC is fireing and which is exhausting?
That's the work of the sync pulse stator (camshaft position sensor) in the distributor. According to the position of the rotor the sync pulse stator recognizes which of the two is fireing and tells the ECU "hey, give fuel to cylinder number X!" and magically the engine turns over and runs all by itself...
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Old 05-12-2010, 05:55 AM   #5
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Quote:
Originally Posted by fantic238 View Post
The CPS is a Hall effect transducer that varies its output voltage in response to changes to magnetic field. Inside the sensor there is a little magnet that lies along a piece of wire.
When the magnetic field is disturbed by the passing of the reluctor ring teeth it generates an inductive current in the piece of wire attached to the magnet.
The signal produced by the CPS is an analogic square waveform that varies in frequency in response to the overcoming speed (RPM) of the reluctor ring teeth and grooves. This tells the ECU at what speed the crankshaft is turning.
Another information provided by the CPS is piston top dead center (TDC). On the flywheel there are three big holes that produce a long "zero" signal. The holes are only three because in a six cylinder the pistons move in pairs, therefore you have two pistons at TDC at a time. Now, how does the ECU know which of the two TDC is fireing and which is exhausting?
That's the work of the sync pulse stator (camshaft position sensor) in the distributor. According to the position of the rotor the sync pulse stator recognizes which of the two is fireing and tells the ECU "hey, give fuel to cylinder number X!" and magically the engine turns over and runs all by itself...
I was trying to figure out how the CPS knew what position the flywheel was in, thanks. After I had my flywheel turned and I was installing it and I could not find anything in the manuals that stated a correct position on the flywheel to crank, so I just mounted it, after I was done I curios on how it knew where it was at (CPS to Flywheel) this explains it.
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Old 05-12-2010, 06:44 AM   #6
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This has been one hell of an educational thread! Thanks 19cherokee89 for asking the question. What I am taking away from this is that a CPS does not just slowly go bad and cause things like poor idle or poor starting. When it goes bad there is little or no warning. It just stops working all together... would that be a correct statement? I have had some tell me to check the CPS for my low idle issue but is not likely the problem what I am reading here.
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Old 05-12-2010, 07:17 AM   #7
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Originally Posted by ken72 View Post
This has been one hell of an educational thread! Thanks 19cherokee89 for asking the question. What I am taking away from this is that a CPS does not just slowly go bad and cause things like poor idle or poor starting. When it goes bad there is little or no warning. It just stops working all together... would that be a correct statement? I have had some tell me to check the CPS for my low idle issue but is not likely the problem what I am reading here.
There are some cases when the CPS works intermittently. Sometimes the wire is broken or the connector contacts are oxidated. Another rare case is whan you have dirt with high content of iron (red sands) in the bellhousing. The dirt goes to fill some of the grooves of the reluctor ring and the readings are staggered.
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Old 05-12-2010, 04:22 PM   #8
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At first I thought my stator was bad in the dist. It could be wiggled around inside the dist. and the used on i got was solid. I also got the coil and module and installed them. with no help. It is getting harder to start if at all. I am going to try a crank positioning sensor I will post the results when i do it this weekend.
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Old 11-21-2011, 12:17 AM   #9
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I think i have a bad one also, Mine now gets horrible gas milage, it lost power, and throws the CEL for cylinder 2 misfire intermittently. I blew the head gasket a while back and hasnt been the same, so ive been thinkin the timing was messed up or something the in top end didnt go back together right but it souinds like i probably messed mine up while takin off/ puting back on the exhaust manifold.

What do yall think?
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Old 11-21-2011, 05:17 AM   #10
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If you want to test your CPS for voltage, here's how to do it. The resistance test sometimes recommended is not always accurate.

Renix CPS Testing and Adjusting
 
 
Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.
Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.
The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.
Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected.
You should get a reading of .5 AC volts.
If you are down in the 3.5 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer.
Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.
A little trick for increasing the output of your CPS is to drill out it’s mounting holes with the first drill bit that just won’t fit through the original holes. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.
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Old 11-22-2011, 01:35 AM   #11
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Quote:
Originally Posted by ken72 View Post
This has been one hell of an educational thread! Thanks 19cherokee89 for asking the question. What I am taking away from this is that a CPS does not just slowly go bad and cause things like poor idle or poor starting. When it goes bad there is little or no warning. It just stops working all together... would that be a correct statement? I have had some tell me to check the CPS for my low idle issue but is not likely the problem what I am reading here.
when the crank sensor went out on a car i had it was all at once as well drove to nashville 3 hrs away and when I started home it totally crapped it pants and stopped running there was no getting it to start without a new sensor
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Old 11-22-2011, 05:26 AM   #12
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Pretty much how they work. One day they just die. Cool thing on a Renix is that by doing the AC voltage test at the first sign of trouble you can see it's getting weaker before it gives up the ghost..
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Old 12-01-2011, 09:04 AM   #13
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Would the crankshaft position sensor cause the jeep to backfire while trying to start up??
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Old 12-01-2011, 10:03 AM   #14
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My CPS went bad last year. Would turn over but not start. Gauge cluster lights were all screwy. Pulled the dash apart, it was not the problem. Narrowed it down to CPS with NAXJA and Haynes. Pretty easy to replace if that's what it is.
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Old 12-01-2011, 11:50 AM   #15
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To clarify and stop the rumor:
The CPS is NOT a Hall Effect Device. There is no semi-conductor materiel in it. And it does not require a separate Voltage to power it.
It's simply a magnet with a very fine wire wrapped around it.

The wire breaks inside, or the pigtails attached to the fine wire breaks. Often it's the connector that gets corroded. Unplug, plug back in - fixed!

It provides the pulse to tell the PCM when to fire the injectors and when to make the spark.
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